Abstract:
A method of controlling operation of an electron beam gun and wire feeder during deposition of pools of molten matter onto a substrate to form beads upon solidification of the molten matter. The method includes providing a substrate and a wire source. A molten pool of liquid phase metal is formed on the substrate by melting the wire utilizing an electron beam generated by an electron beam gun. The liquid metal solidifies into a solid phase. A controller utilizes data from a sensor to adjust a process perimeter based, at least in part, on data generated by the sensor.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
       [0001]    This patent application claims the benefit of and priority to U.S. Provisional Application No. 62/323,355, filed on Apr. 15, 2016, titled “APPARATUS AND METHOD FOR DETECTING FLAWS AND FEATURES FOR PROCESS CONTROL OF ELECTRON BEAM WIRE ADDITIVE MANUFACTURING,” the entire contents of which is hereby incorporated by reference in its entirety. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    The invention described herein was made in the performance of work under a NASA contract and by employees of the United States Government and is subject to the provisions of the National Aeronautics and Space Act, Public Law 111-314, §3 (124 Stat. 3330, 51 U.S.C. Chapter 201), and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefore. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    Various additive manufacturing technologies have been developed. One such technology is Electron Beam Freeform Fabrication (EBF 3 ). The EBF 3  process can be utilized to build complex, near-net-shape parts requiring substantially less raw material and finish machining than traditional manufacturing methods. It is envisioned that EBF 3  may be utilized to manufacture a wide range of components such as metallic aerostructures and spare parts, tools, or structural elements. These parts span a wide range of scale and material choices ranging from small, detailed aluminum parts to large, near-net-shape superalloy components for rocket motors. 
         [0004]    EBF 3  devices and processes are described in U.S. Pat. Nos. 8,452,073 and 8,344,281, and U.S. Patent Publication Nos. 2015/0258626, 2010/0270274, and 2010/0260410. However, known additive manufacturing processes may suffer from various drawbacks. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    One aspect of the present disclosure is a method of controlling operation of an electron beam gun and wire feeder during a deposition process in which pools of molten matter (e.g. metal) are deposited onto a substrate. Beads upon solidification of the molten matter. The method includes providing a substrate and a wire source. A molten pool of liquid phase metal is formed on the substrate by melting wire utilizing an electron beam generated by an electron beam gun. The liquid metal solidifies into a solid phase. A sensor is utilized to generate data related to at least one of a thermal transient, one or more alloy physical properties and/or melting range, a width and/or shape of the molten pool, tracking of the wire and/or the molten pool and flaws in the solidified metal. A process parameter is adjusted based, at least in part, on the data generated by the sensor. The sensor data may be generated at speeds of about 1 Hz or more or about 5 Hz or more and the process may be adjusted at speeds of about 10 Hz or more or about 20 Hz or more. 
         [0006]    The method may include changing a raster pattern of the wire source and/or electron beam to deflect ahead, back, or to the side to spread heat. The raster pattern may be adjusted at speeds of about 10 Hz or more or about 20 Hz or more. 
         [0007]    The method may also include detecting/tracking molten pool size and shape to detect increases and/or decreases in molten pool size, wherein the molten pool size comprises one or more of pool width, length, aspect ratio, area, centroid and reducing power of the electron beam gun to reduce molten pool size, or to detect decreases in molten pool size, and increasing power of the electron beam gun to increase molten pool size. 
         [0008]    The process may include detecting changing thermal patterns that result in different bead geometries and/or microstructures and increasing or reducing power of the electron beam gun to increase or reduce molten pool size to correct bead geometries and/or microstructures. 
         [0009]    The method may also include detecting a melting temperature of the molten matter (e.g. metal), and providing sufficient power, travel speed, and/or feed rate to melt the wire. 
         [0010]    The method may include detecting dealloying in molten matter (e.g. metal), and reducing a power of the electron beam and/or increasing travel speed of the electron beam and/or changing beam focus to reduce the temperature of the molten matter (e.g. metal). 
         [0011]    The method may include detecting viscosity of the molten matter (e.g. metal) and changing beam angle relative to the molten pool and/or wire entry angle relative to the molten pool. 
         [0012]    The method may also include detecting a surface tension of the molten pool, and changing beam angle relative to the molten pool and/or wire entry angle relative to the molten pool to reduce surface tension. 
         [0013]    The method may also include detecting excessive or deficient height and/or width of a molten pool at a start, and adjusting timing of one or more of a starting beam power, a travel speed, and a wire feed rate to reduce or increase height and/or width of the molten pool. 
         [0014]    The method may also include detecting narrowing or widening of a solidified deposit, and adjusting one or more of a beam power, a beam raster, a travel speed, and a wire feed rate to increase or decrease the width of the solidified deposit. 
         [0015]    The process may also include detecting variations in one or more of a deposit height, a width, and a shape at a stop location, and adjusting one more of a beam power, a travel speed and a wire feed rate to provide uniform height and/or width and/or shape. 
         [0016]    The method may also include detecting variations in one or more of solidified deposit width and height due to abrupt changes in build direction, and adjusting one or more of a beam power, a beam raster, a travel speed, and a wire feed rate to reduce variations in at least one of a deposit width and a height. 
         [0017]    The process may also include detecting incomplete wire melting, and providing beam focus and deflection up the wire to preheat the wire and/or preheating the wire via a separate heater, and/or reducing a wire feed rate and/or switching to a smaller diameter wire. 
         [0018]    The process may also include detecting dripping of melted wire, and increasing a wire feed rate and/or decreasing a beam power and/or increasing a travel speed of the wire source and/or changing (e.g. decreasing) a wire feed height distance. 
         [0019]    The process may also include detecting stabbing and/or wire dragging, and decreasing a wire feed rate and/or increasing a beam power and/or decreasing a travel speed of the wire feeder and/or changing (e.g. increasing) a wire feed height distance. 
         [0020]    The process may include detecting one or more of residual stress, curvature, or twist in the wire as it is fed into the molten pool, and providing beam deflection up the wire to redirect the wire into the molten pool. 
         [0021]    The process may also include detecting if the wire does not enter the molten pool at a desired (correct) location, and adjusting a position of the wire feeder relative to the molten pool and/or halting the process if wire is detected outside the molten pool. 
         [0022]    These and other features, advantages, and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims, and appended drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0023]    The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. 
           [0024]      FIG. 1A  is a partially fragmentary perspective view of a large EBF 3  system that includes a Sciaky electron beam welder; 
           [0025]      FIG. 1B  is a partially fragmentary perspective view of a first portable EBF 3  system; 
           [0026]      FIG. 1C  is a partially fragmentary perspective view of a second portable EBF 3  system; 
           [0027]      FIG. 2A  is an NIR image from a side-mounted orientation; 
           [0028]      FIG. 2B  is an NIR image from a downward angle-mounted orientation; 
           [0029]      FIG. 2C  is a chart of thermal molten pool data from 5 sequential layers showing thermal transients; 
           [0030]      FIG. 3A  is a schematic of a camera installation in an EBF 3  system; 
           [0031]      FIG. 3B  is a perspective view of a bench set-up with Schott fiber optics and Hamamatsu camera; 
           [0032]      FIG. 3C  is an NIR image from a downward angle-mounted orientation; 
           [0033]      FIG. 4A  is a schematic diagram of a CCD camera mounting ring and optical path in an EBF 3  system; 
           [0034]      FIG. 4B  is a partially fragmentary perspective view of an NIR camera and gas shield installation in an EBF 3  system; 
           [0035]      FIG. 5A  is a thermal image of 316 stainless steel with line plots showing deposition temperature variation; 
           [0036]      FIG. 5B  is a thermal image of Ti-6A1-4V with line plots showing deposition temperature variation; 
           [0037]      FIG. 5C  is a thermal image of Inconel® 625 with line plots showing the deposition temperature variation; 
           [0038]      FIG. 6  is a schematic diagram of a SWIR camera mounting and optical path in a portable EBF 3  chamber; 
           [0039]      FIG. 7A  is a SWIR temperature image during EBF 3  deposition of aluminum 2219; 
           [0040]      FIG. 7B  is a line plot corresponding to the SWIR image of  FIG. 7A ; 
           [0041]      FIG. 8  is a partially schematic fragmentary cross-sectional view showing EBF 3  operation; and 
           [0042]      FIG. 9  is a partially schematic fragmentary top plan view showing EBF 3  operation. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0043]    For purposes of description herein, the terms “upper,” “lower,” “right,” “left,” “rear,” “front,” “vertical,” “horizontal,” and derivatives thereof shall relate to the invention as oriented in  FIGS. 1A, 1B, and 1C . However, it is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification, are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise. 
         [0044]    A first EBF 3  machine  1 A is shown in  FIG. 1A , a second EBF 3  machine  1 B is shown in  FIG. 1B , and a third EBF 3  machine  1 C is shown in  FIG. 1C . Machine  1 A is based upon a commercially available 42 kW Sciaky electron beam welder, and machines  1 B and  1 C comprise “portable” systems designed for EBF 3  flight experiments.  FIGS. 1A-1C  show the interiors of the processing chambers of the three EBF 3  machines  1 A,  1 B, and  1 C, respectively. For relative size comparison, the working volume (i.e., volume accessible by both the electron beam and wire feeder) of the large Sciaky machine  1 A is approximately 0.75 meters×1 meters×2 meters, while the two portable machines  1 B,  1 C each have working volumes of about 0.3 cubic meters. The large machine  1 A accepts wire spools containing up to about 15 kg of material, while the smaller machines  1 B and  1 C use standard 0.5 kg wire spools. The large system  1 A weighs approximately 50,000 kg, while the portable systems  1 B and  1 C each weigh about 900 kg ready to operate. 
         [0045]    The operational concept of the EBF 3  process is to build a near-net-shape metal part directly from a CAD file in a layer-additive manner without the need for molds or tooling dies. In this process, an electron gun  5 A,  5 B,  5 C generates an electron beam  6 A,  6 B,  6 C, respectively that is used as a heat source to create a small molten pool on a substrate (e.g. baseplates  8 A,  8 B,  8 C, respectively) into which wire  10 A,  10 B,  10 C from a wire feeder  12 A,  12 B,  12 C, respectively is fed. The substrate (baseplate) can be composed of identical or different material than the deposited metal depending upon the application. The electron beam  6 A,  6 B,  6 C and wire feed assembly  12 A,  12 B,  12 C, respectively are translated with respect to the baseplate  8 A,  8 B,  8 C, respectively to follow a predetermined tool path, similar to conventional computer-aided machining practice. The deposited material solidifies immediately after the electron beam  6 A,  6 B,  6 C has passed, having sufficient structural strength to support itself. This process is repeated in a layer-wise fashion, resulting in a near-net-shape part requiring minimal finish machining. Careful attention to process control minimizes transient thermal effects, such as distortion, until the part cools and the part can be removed from the vacuum chamber  4 A,  4 B, or  4 C. 
         [0046]    EBF 3  offers several unique attributes among the competing metallic additive manufacturing approaches. First, it is scalable in size and deposition rate, allowing fabrication of parts measuring a few cubic centimeters up to parts 1 cubic meter or larger, restricted only by the size of the vacuum chamber. High deposition rates with larger bead sizes enable near-net-shape construction of large structures using established aerospace alloys such as aluminum 2219 and 6061, stainless steel 304 and 316, Inconel® 625 and 718, and titanium Ti-6A1-4V. Second, EBF 3  uses wire feedstock as opposed to metal powder for high feedstock usage efficiencies and safe operability in reduced gravity environments such as low-Earth orbit. Third, the electron beam used to melt the metal wire requires that the process be conducted in a vacuum chamber; vacuum enables processing of traditional aerospace alloys, most of which cannot be melted in air without oxidation degrading their metallurgical properties. Finally, EBF 3  offers the promise of fabrication of structures with functionally graded metallurgy. By selectively introducing wires of different compositions during the deposition process, the chemistry and resulting physical properties of the metal structure can be varied continuously throughout the part and tailored to its exact service requirements. 
         [0047]    While the basic operational concept of EBF 3  is simple, a closer look reveals dozens of variables, each affecting the outcome and many of which are interdependent. As discussed in more detail below, there are several major challenges to the acquisition and use of real-time sensor data to monitor and control the process. One aspect of the present disclosure is the use of imaging techniques and data analyses to detect anomalies and refine the EBF3 process through real-time monitoring and control to mitigate these challenges. 
         [0048]    The first major challenge to sensor integration into the EBF 3  process is the deposition environment itself. Efficient generation and transmission of the electron beam requires high vacuum (10 −5  Torr or lower), meaning that sensor electronics in the chamber must (preferably) be vacuum-rated. This implies little or no permissible outgassing from electronics or packaging and the ability to run uncooled or with conductive and radiative cooling only. Unlike vacuum processes such as electron microscopy, EBF 3  is a relatively “dirty” process that results in metal vapor contamination of line-of-sight surfaces inside the vacuum chamber. Unprotected optical surfaces such as lenses or mirrors will become coated with metal vapor that will periodically need to be removed. Translation of the part and/or electron beam gun during part fabrication results in a moving molten pool that is difficult to track unless sensors are incorporated into the electron beam gun carriage. The size of the electron beam gun and the gun-to-work distance also place practical limits on the size and placement of cameras or other sensors. 
         [0049]    Second, EBF 3  is an inherently thermally transient process. Several factors contribute to this, beginning with its layer-additive nature. The continuously moving molten pool over a relatively cold baseplate or previous layer encounters a different cooling path and thermal mass with each successive layer. Variations in the geometry of the part such as section thickness changes, ends or corners also contribute to these changes. Thermal transients need to be better managed to enable repeatability necessary for certification of additive manufacturing processes for use in many applications. Therefore, sensors capable of measuring thermal distributions are important for tracking changes in the molten pool (by detecting the thermal gradients between liquid and solid phases) over time. 
         [0050]    Third, the physical properties of each metal alloy (e.g., specific heat, melting temperature, thermal conductivity, vapor pressure) necessitate different process parameters such as beam power, beam raster, wire feed rate and translation speed. Factors of 2×-10× difference depending upon the material and part geometry are not uncommon, often requiring equally wideband sensors. Less obvious are process accommodations arising from material properties such as molten pool surface tension and liquid metal viscosity, which affect the shape and behavior of the molten pool during deposition. Differing vapor pressures of various alloying additions can result in selective de-alloying (constituent loss) in the deposited material. Controlling the temperature of the EBF 3  process has been shown to impact alloy compositional losses. The temperature-dependent variation of emissivity also affects thermal imaging, requiring unique sensor calibrations and camera settings to optimize the imaging. While emissivity is well documented for many pure metals and common engineering alloys, it is not generally known for functionally graded materials deposited with EBF 3 . Since it is of interest to use EBF 3  to deposit materials with widely varying physical properties, wideband sensors capable of detecting the thermal environment for low melting temperature alloys like aluminum up to high melting temperature alloys like nickel are more versatile. 
         [0051]    The fourth challenge involves geometric variations in the deposit that result from imperfect coordination of heat and mass flow (electron beam power and wire feed) during starts, stops and abrupt changes in build direction. These variations include bulbs (build-up of excess material at starts), necking (narrowing of the deposit) or tailing-off (deficit in deposit height approaching a stop). Although bead widths are affected with each of these variations, the more significant impact is on the height of the deposited material. Since the EBF 3  process is a layer-additive process, even minute perturbations in height accumulate and cause large errors over time as the build progresses. Even parts measuring as small as 10 cm in height can represent over 100 layers. Therefore, the sensor type and its location in the build chamber preferably provide precise measurement of the bead height. 
         [0052]    The closely related fifth challenge involves the relative direction of wire in-feed and deposit direction to the geometric variations in the deposit. Changes in the wire orientation with respect to the translation direction (e.g., wire lagging or pushing the molten pool, or entering from the side) and wire elevation (e.g., entry angle relative to the horizontal) can subtly change the geometry of the deposit. Equally important, fabrication of some parts may require multiple side-by-side beads to develop the required section width, and the shape of the molten pool depends upon the presence and relative location of adjacent beads. For example, for multi-bead deposits it is often easier to “push into” adjacent beads than to reach over them but this is not always possible due to other constraints. If the width of the bead and the influence of the wire on the molten pool can be measured in real-time, minor adjustments to processing parameters such as wire feed rate and translation speed can be implemented to improve part precision. 
         [0053]    Sixth, random process errors result from variability in the wire feed. The wire is primarily at room temperature until it crosses into the electron beam path, at which point it is subjected to an abrupt thermal gradient, melting over a very short distance as it enters the molten pool. Larger diameter wire, therefore, retains substantial stiffness as it enters the molten pool, potentially resulting in several errors. In the event of excess heat, insufficient wire feed, or wire feeding above the electron beam/substrate intersection point, dripping may occur. Conversely, insufficient heat, excess wire feed, or wire feeding below the electron beam/substrate intersection point may result in “wire stabbing” which can cause the wire to oscillate back and forth in the molten pool; skip, causing fluctuations in the deposit height; or deflect off the bottom of the molten pool and divert out of the beam altogether. Improper wire location or poor timing of the start/stop sequence will often result in wire sticking through the welds. Some errors of this nature have also been observed due to cast (residual curvature or twist in the wire not removed by the wire straightener) or simple mechanical misalignment of the wire feed apparatus that was not immediately apparent. To measure wire feed anomalies, it may be beneficial to track wire position relative to the molten pool. This may require a sensor with a wider field of view and the ability to measure geometric features that have widely different temperatures. 
         [0054]    A seventh major challenge is encapsulation of flaws within the EBF 3  deposits. Voids and porosity have been observed due to contamination (cleanliness) of the wire, wire variability, or programming errors in the steps between side-by-side beads and layers. Inclusions can occur when the molten pool picks up a contaminant from contaminated wire or from metal vapor condensate flaking off and falling into the deposit. Lack of fusion between layers can occur due to insufficient heating before or during the deposition steps, improper programming of the layer height, or oxidized surfaces when the part has been exposed to air prior to initiating or resuming interrupted EBF 3  deposition. Similar to welding operations, hot cracking or quench cracking can occur due to high thermal gradients, insufficient preheat or microsegregation that occurs with rapid cooling. Material property variations can also occur due to microstructural or chemical variations. For example some alloys will form strong textural orientation due to preferential crystallographic freezing that follows the cooling path. Finally, large thermal gradients and thermal contraction can result in residual stresses that will manifest as distortion, or in the extreme case, cracking. These defects and the mechanisms to control and avoid their formation are somewhat understood. 
         [0055]    The ability to detect, quantify and repair flaws that occur during the EBF 3  deposition process is beneficial. Evaluating thermal diffusivity using thermal imaging cameras is one way to detect embedded flaws during deposition. 
         [0056]    The solution to these challenges resides in integration of imaging systems into the EBF 3  systems to monitor the process. Image analyses to identify the anomalies and control logic to implement corrective action are then required to fully close the processing control loop. 
       Internal Mount CMOS Camera 
       [0057]    Initial NIR imaging approaches to monitoring the molten pool during the EBF 3  process were investigated from 2003 to 2005. The first camera selected was from Silicon Imaging, model SI-1280. This is a 12-bit, digital Complementary Metal-Oxide Semiconductor (CMOS) camera, which has particular advantages for the EBF 3  process environment. Data is digitized in the camera reducing the susceptibility of signals to noise in transmission lines. CMOS cameras directly measure the current in the detector so there is no charge build-up in the pixel wells as in a Charged Coupled Device (CCD). Therefore CMOS cameras will not bloom or streak when overexposed. For example, if the electron beam energy density is too high, the resulting plasma would “wash out” a normal CCD camera, preventing viewing of the molten pool. A CMOS sensor will simply “peg out” a pixel at its maximum value, leaving adjacent pixels unaffected. The exposure was controlled through a LabView Camera Link interface. This camera has a 1.28 megapixel chip, but can be operated with a smaller region of interest at very high speeds. At 100×100 pixels, frame rates of 3000 fps can be achieved. 
         [0058]    The CMOS camera consumes very low power, producing less heat and reducing the need for cooling in the vacuum environment. A water-cooled coldplate was installed against the camera body for precautionary measures, but the camera also operated for short periods of time without overheating in the vacuum environment without the coldplate. The compact design of this camera (45×52×50 mm) enabled installation on a bracket directly on the electron beam gun. Pinhole and secondary optics were installed with a flow controller to meter argon into the camera/pinhole system to protect the optics from being occluded by metal vapor. This optical camera was bandpass filtered down to the NIR range and calibrated to provide thermal information. 
         [0059]      FIGS. 2A and 2B  show data from the Silicon Imaging camera on Ti-6A1-4V. The color scale in  FIGS. 2A and 2B  was calibrated to show the Ti-6A1-4V liquidus temperature as light orange, and the solidus temperature as blue. The camera was installed in two different locations attached to the electron beam gun: orthogonal to the wire feeder with a wider field of view to capture height and cooling path data ( FIG. 2A ), and opposite the wire feeder focused down on the molten pool to capture molten pool shape and size ( FIG. 2B ). A series of experiments on Ti-6A1-4V was performed, depositing five successive layers on a deposit 25 cm in length, and a single bead width. The solidus temperature was outlined based on analysis of the thermal images. After five layers, the length of the molten zone doubled at constant power and travel speed, illustrating the dependence of the process on geometry and thermal history ( FIG. 2C ). The goal in using these data is to adjust process parameters to maintain a constant tail length and thus cooling rate. 
       Fiber Optic+External Mount CCD Camera 
       [0060]    Although the CMOS camera has high speed data acquisition, good compatibility with the vacuum environment, and resistance to blooming of oversaturated pixels to adjacent pixels, the resolution and low light capabilities were inferior to CCD cameras in the 2003 to 2005 time period. For comparison, the second camera evaluated at that time was a Hamamatsu C8484-05 12-bit CCD  14  ( FIGS. 3A, 3B ) with a 1.37 megapixel chip. The CCD camera  14  has excellent NIR characteristics and operates at low light levels. The camera  14  was also programmed through the LabView Camera Link interface. 
         [0061]    The Hamamatsu camera  14  was too large to mount on the electron beam gun and was not well adapted to the vacuum environment. With reference to  FIG. 3A , this set-up relied on fiber optic transmission of images from a pinhole and imaging optics  26  via a Schott wound image bundle. The fiber bundle  16  passes out of vacuum chamber  18  to a relay lens  20  and beam splitter  22 , and the image was monitored by two cameras, a Silicon Imaging SI-1280 24 and a Hamamatsu C8484-05 14. Each camera has its own relay lens, so magnifications could be independently adjusted. The optical/NIR filters  28 ,  30  are accessible without opening the vacuum chamber  18 . The coherent fiber bundle  16  from Schott has transmission out to 1.2 microns (the IR limit of the imaging sensors) and about 800,000 fibers (or pixels). This configuration offers flexibility for process diagnostics. For example, the SI-1280 camera  24  may be run at very high frame rate for real-time process sensing, and the Hamamatsu camera  14  may be run at a slower frame rate with a larger field of view for spatial resolution in the process area and detection of the wire feed position. Filters may be used to monitor in the NIR range with the CCD camera  14 , and very short shutter speeds may be used to control high intensity light emanating from the molten pool. This provides thermal details in the molten pool ( FIG. 3C ), but due to the short shutter speed and losses from the fiber optic bundle  16 , thermal data in the surrounding areas were lost. The camera was not permanently integrated due to damage sustained to the Schott fiber optic bundle  16 , as a result of fibers shifting with the moving electron beam gun and vacuum. The ends of the fiber optic bundle  16  could be redressed, but was not pursued. 
       Backscattered Electron (BSE) Detector 
       [0062]    From mid-2008 to mid-2009 an effort was made to develop an electron imaging system that could be used to actively monitor and measure the EBF 3  deposit height and wire position relative to the beam. Additional objectives of this work were to explore the capabilities of the electron beam gun system to raster the beam at relatively high frequency in specific patterns to preferentially direct energy to the wire or the molten pool, and to detect the onset of process errors due to wire feed errors or misalignment. 
         [0063]    Normal operation of the EBF 3  electron beam generates large quantities of primary electrons, secondary electrons, x-rays, neutral particles, ions and backscattered electrons, all with a wide range of energies. Of these possible signal sources, backscattered electrons (BSEs) were chosen because of their directionality and high retained energy fraction. A custom-built BSE detector  34  ( FIG. 1A ) was purchased from ETP-Semra in Australia and installed in the large EBF 3  vacuum chamber  4 A ( FIG. 1A ). In order to improve the signal-to-noise ratio (i.e., to capture only those scattered from the molten pool), a series of negatively-biased screening electrodes were placed at the entrance to the detector. BSEs of sufficient energy to transit the screening stages enter the detector and strike a phosphor screen, generating photons which travel through a light pipe to a photomultiplier tube. Output from the photomultiplier tube is then used to construct an image of the target area. 
         [0064]    Several different mounting arrangements for the detector  34  were tried with varying degrees of success for producing an unobstructed view of the EBF 3  process zone without exposing the sensor to metal vapor. The best viewing angle was ultimately obtained with the detector mounted directly in line with the wire feed nozzle  32  ( FIG. 1A ) at an elevation angle of about 15° above the workpiece (baseplate  8 A). As with the optical/NIR cameras, the sensor  34  was also susceptible to metal vapor contamination. 
         [0065]    Some high quality images were obtained with the BSE detector  34 ; however, these images were obtained with very low beam current (1-5 mA) and a raster scan pattern specifically designed for imaging, not deposition. In other words, images of this type could not be obtained using the beam parameters in real time during an actual build; imaging scans would have to be conducted separate from the build process. Also, during the build process the beam path is confined to the molten pool and not rastered outside a very small target area. It was possible to infer, but not directly measure, the deposit height with a single BSE detector. The efforts to monitor wire position and preferentially direct beam energy into the wire or the molten pool with the BSE detector were quite successful, and revealed that some information as to geometric error conditions (dripping, wire feeding off-center to the molten pool) could easily be detected. 
         [0066]    Despite these promising results, BSE imaging was ultimately abandoned as a means to provide information to the closed-loop control system. This was mainly due to its relatively high cost and the bulkiness of the detector system. In addition, the BSE detector required modification of the electron beam rastering and focusing coils to coordinate the beam location with the sensors in the detector. As a research and development tool, the BSE detector was useful, but challenges with obtaining images during beam power and raster patterns typical for deposition, and the ability to image but not measure temperatures led to the decision to explore other sensors. 
       Internal Mount CCD Camera 
       [0067]    It was learned from the experiences described above that camera location may be important for observation of the molten pool sufficient to provide data usable for closed-loop control of the process. 
         [0068]    With reference to  FIG. 4A , a miniature CCD camera  36  (a Prosilica GC1380H) may be utilized in an EBF 3  system  10 . In order to optimize the image and provide future additional capabilities, an instrumentation ring  38  may be attached to the electron beam gun  5 D. The instrumentation ring  38  provides the ability to position cameras and other hardware in nearly any location around the gun  5 D. The instrumentation ring  38  includes upper and lower rings  38 A,  38 B with diagonal struts  40  connecting the upper and lower rings  38 A,  38 B. The cameras (or other instrumentation) may be adjustably attached to the diagonal struts  40  with sliding brackets  42 . The diagonal struts  40  allow the cameras to be moved to any position around the electron beam gun  5 D. The slide brackets  42  allow the pitch angle of the camera to be modified/adjusted. Two cameras may be utilized to image the melt pool at 180° and 90° from wire feeder  12 D. 
         [0069]    The NIR band was selected to image metals of higher melting temperatures such as 316 stainless steel, Ti-6A1-4V, and Inconel® 625. The Prosilica GC1380H camera  42  is a non-cooled CCD camera with a frame rate of 30 Hz at full resolution through a GigE interface. A water-cooled coldplate  44  was installed against the camera body  36 A to provide cooling in the vacuum environment of vacuum chamber  4 D. The camera pixel array size is 1360×1024 (pixel pitch size of 6.45 μm×6.45 μm). The dynamic range of camera  42  is 12 bits. The imaging spectral band may be set at 0.875 to 1.05 μm using a long pass filter to allow imaging temperatures from 700 to approximately 2,200° C. An NIR neutral density filter may be used to reduce the transmission by a factor of 10. The C-mount optical package contains a 150-mm relay lens pair, a protective window (B270 material), and an extension tube with a gas fitting  46  ( FIG. 4B ). The gas fitting  46  allows for a small amount of inert gas to flow out of the 3 mm diameter aperture  48  and thus prevent window clouding due to residual metallic particles dispersed during the electron beam excitation. The resolution of camera  42  is approximately 0.006 cm/pixel. 
         [0070]    A radiometric calibration may be utilized to convert the pixel values (intensity counts) to temperature, define the temperature imaging limits of the system, determine the optimal threshold values for closed loop control metrics (based on the wire melting temperature), correct for material dependent emissivity, and selection of the optimal integration time. A radiometric characterization was performed on the NIR camera/optic  42  using a calibrated blackbody radiation source set at various temperatures. The process involves the calibration of the radiance counts to actual temperature values. The temperature values used were 700, 800, 900, 1,000 and 1,100° C. at specified sensor integration times ranging from 10 to 50,000 μs. Using a given emissivity value, the radiance is then converted to temperature using a linear interpolation of the system&#39;s radiance response. 
         [0071]      FIGS. 5A-5C  are NIR temperature images and line plots along the deposition of 316 stainless steel ( FIG. 5A ), Ti-6A1-4V ( FIG. 5B ), and Inconel® 625 ( FIG. 5C ). The 316 stainless steel temperature image was obtained using an integration time of 1500 μs and emissivity literature value of 0.66. The Ti-6A1-4V temperature image was obtained using an integration time of 1000 μs and emissivity of 0.48, and the Inconel® 625 temperature images were obtained using an integration time of 1500 μs and emissivity of 0.77. The measured temperature values agree with literature values for 316 stainless steel, Ti-6A1-4V, and Inconel® 625 at the transition point for the respective melting point ranges of 1370 to 1400° C., 1604 to 1660° C., and 1290 to 1350° C. respectively. This permits measurement of the molten pool shape and area, the semi-solid area and length, and transient cool down regions. These metrics may be used for adjusting process parameters such as beam power, beam raster, wire feed rate and traverse speed during closed loop control. 
       Internal Mount Short-Wave IR (SWIR) Camera 
       [0072]    Longer wavelength cameras may be utilized for imaging lower melting temperature alloys (e.g. aluminum). With reference to  FIG. 6 , a Short-Wave Infrared (SWIR) camera  50  may be installed in a portable EBF 3  system  1 E. Due to the space limitations, a periscope-style camera assembly  52  was developed in order to image the molten pool. The electron beam gun  5 E has a robotic arm  54  with four degrees of freedom. The camera  50  is attached to the front side  56  of the robotic arm  54  in a vertical position which does not limit the system&#39;s range of motion. Mirrors  58 A and  58 B direct the image to the camera  50 . The SWIR camera  50  may be actively cooled by a coldplate  60  which is operably connected to an external water chiller by water lines (not shown). The SWIR camera  50  is positioned approximately 45° off the forward deposition direction (the direction to the left in  FIG. 6 ). Due to the space limitations in this EBF 3  system, the system&#39;s wire feeder  12 D is positioned approximately 45° off the opposite side of the robotic arm  56  (immediately behind the camera  50  in  FIG. 6 ). 
         [0073]    The SWIR band may be utilized to image metals of lower melting temperatures such as aluminum. The digital SWIR camera  50  may comprise an Allied Goldeye G-032. This camera requires temperature stabilization using an internal thermoelectric cooler. The camera pixel array size is 636×508 (pixel pitch size of 25 μm×25 μm). The camera&#39;s dynamic range is 14 bits with a maximum frame rate of 100 Hz at full resolution through a GigE interface. The spectral response of the camera&#39;s detector is approximately 0.950-1.7 μm and this allowed measurement of temperatures from about 300° C. to about a 1000° C. The camera  50  may be protected within an aluminum enclosure that is liquid cooled. The camera&#39;s optic is a C-mount 50 mm lens with 75% or better transmission between 0.700 μm to 1.9 μm. A protective window comprising a Mylar® polyester film  62  may be used to protect the optical system from metal vapor resulting from the electron beam deposition process. Camera resolution is approximately 0.015 cm/pixel. With a molten pool size of 0.2 cm to 0.6 cm, this camera resolution results in the regions of interest being captured by 10&#39;s of pixels across. 
         [0074]    A radiometric characterization may be performed using a calibrated blackbody radiation source set at various temperatures for the SWIR camera  50 . The process involves the calibration of the radiance counts to actual temperature values. The temperature values used were 300, 400, 500, 550, and 600° C. at specified sensor integration times ranging from 120 to 15,000 μs. 
         [0075]    A SWIR temperature image and line plot collected during the deposition of aluminum 2219 are shown in  FIGS. 7A and 7B , respectively. The aluminum 2219 temperature image was obtained using an integration time of 200 μs and an emissivity value of 0.2. As shown on the line plot, the measured temperature values agree with aluminum 2219 literature values at the transition point for the melting point range of 543 to 643° C. This permits measurement of the molten pool shape and area, but the semi-solid and transient cool down regions were not detected for the integration time and frame rate (20 Hz) used in this example. 
         [0076]    The vacuum, thermal, metal vapor environment and limited space in the EBF 3  process pose challenges for sensor selection and integration into the system for real-time process monitoring and feedback. Since EBF 3  is inherently a thermally transient process, thermal data are of interest to correlate with microstructural and non-destructive evaluations to identify metallurgical features and flaws that drive the mechanical properties of the deposited materials. Due to space constraints, multiple sensors may not be feasible, so sensors that can capture all of the suitable data are sought. Suitability of a particular imaging technology for use in the EBF 3  process is also a concern. Suitability may be determined by consideration of the available frame rate, resolution, signal-to-noise ratio, spectral response, vacuum compatibility, ruggedness, size, and cost. 
         [0077]      FIGS. 8 and 9  generally illustrate an EBF 3  system  1  and provide an overview of the process. More detailed descriptions of process and controls are provided below in connection with Tables 2-8. EBF 3  system  1 , ( FIGS. 8 and 9 ) includes a wire feeder  12  that feeds wire  13  in the direction of the arrow A, and wire  13  is melted by a beam  6  produced by electron gun  5 . The wire  13  melts as it intersects the beam  6  to form a molten pool  64  that cools and hardens to form a solid deposit  66  of solidified metal on substrate or base plate  8 . Molten pool  64  and solid deposit  66  together form a bead  63 . As discussed in more detail below, the process may result in a vapor or plasma plume  74 . The wire feeder  12  may be positioned to feed wire  13  at an angle α 1 , and electron gun  5  may be positioned at an angle α 2  relative to the base plate  8 . The solid deposit  66  generally has a height “H” ( FIG. 8 ) and a width “W” ( FIG. 9 ). However, various defects in the process can lead to raised areas  66 A ( FIG. 8 ) having an increased height, and/or regions  66 B or  66 C having increased width ( FIG. 9 ). It will be understood that regions (defects) having reduced height and/or width may also be formed. During the process, drops of molten material  68  and/or unmelted pieces or portions of wire  70  may be formed. 
         [0078]    If these various defects are detected by sensors such as cameras  14  and/or  24 , the wire feed rate, angle α 1  and/or θ 1  or θ 2  ( FIG. 9 ) may be adjusted to reduce or eliminate the development of these defects. Similarly, the angle α 2  of electron beam  6  produced by electron gun  5  may be changed/adjusted. Also, the position of the electron beam may be changed as shown by the dashed line  6 A ( FIG. 8 ) to change the point at which the electron beam  6 A is incident on the wire  13  and/or molten pool  64 . The sensors (e.g. cameras  14  and/or  24 ) may be operably connected to a controller  72  that controls electron gun  5  and wire feeder  12 . As shown in Tables 2-8 below, the images and other data from the sensors may be utilized by the controller  72  to continuously adjust the electron gun  5  and wire feeder  12  during operation to correct defects detected by the sensors in a closed loop control. In general, the adjustment parameters may be developed analytically and/or by testing. 
         [0079]    During operation, the wire feeder moves in the direction X which is generally parallel to the base plate  8  at a height “HW” ( FIG. 8 ). The electron gun  5  generally travels at the same velocity in the direction X. The height HW of the wire feeder  12  can be adjusted, and the velocity of the wire feeder  12  and/or electron gun  5  in the direction X can also be adjusted during operation. It will be understood that translation of the electron gun  5  and the wire feeder  12  is not limited to the X direction, and these components may be translated along any vector in the X-Y plan relative to the base plate  8 . 
         [0080]    In general, defects caused by excessive heat can be corrected by reducing the energy of electron gun  5 /electron beam  6  and/or by raising the rate of movement of wire feeder  12  in the direction X and/or by increasing the wire feed rate. Conversely, defects resulting from insufficient heat can be corrected by reducing the power of electron gun  5 /electron beam  6  and/or reducing the movement of the wire feeder  12  in the direction X and/or reducing the wire feed rate. 
         [0081]    Table 1 (below) summarizes qualitatively how well the five sensors capture data to address the EBF 3  process challenges. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Summary of sensor suitability to measure features associated with EBF 3  process challenges. 
               
             
          
           
               
                   
                 Sensor Technology 
               
             
          
           
               
                   
                 Section 4.1: 
                 Section 4.2: 
                 Section 4.3: 
                 Section 4.4: 
                 Section 4.5: 
               
               
                   
                 Internal 
                 Fiber Optic + 
                 Internal Mount 
                 Internal 
                 Internal 
               
               
                 EBF 3   
                 Mount  
                 External 
                 Backscattered 
                 Mount 
                 Mount 
               
               
                 Process 
                 CMOS 
                 Mount CCD 
                 Electron (BSE) 
                 CCD 
                 SWIR 
               
               
                 Challenges 
                 Camera 
                 Camera 
                 Detector 
                 Camera 
                 Camera 
               
               
                   
               
               
                 1) Deposition 
                 Pinhole optics; 
                 Pinhole w/  
                 Vapor shield; 
                 Pinhole 
                 Pinhole  
               
               
                 environment 
                 Cold plate 
                 fiber optics; 
                 Fully vacuum 
                 optics; Cold 
                 optics; Cold 
               
               
                 (vapor contamination; 
                 for camera  
                 Externally 
                 compatible 
                 plate for 
                 plate for 
               
               
                 vacuum compatibility) 
                 cooling 
                 mounted 
                   
                 camera 
                 camera  
               
               
                   
                   
                   
                   
                 cooling 
                 cooling 
               
               
                 2) Thermal transients 
                 Yes 
                 Limited 
                 No 
                 Yes 
                 Yes 
               
               
                 3) Alloy physical 
                 NIR 
                 NIR 
                 n/a 
                 NIR  
                 SWIR  
               
               
                 properties/melting 
                 signature 
                 signature 
                   
                 signature 
                 signature 
               
               
                 range 
                   
                   
                   
                   
                   
               
               
                 4) Height measurement 
                 Limited 
                 Limited 
                 Not 
                 Limited 
                 Limited 
               
               
                 (with one camera) 
                   
                   
                 demonstrated 
                   
                   
               
               
                 5) Width measurement 
                 Yes 
                 Limited 
                 Yes, but not 
                 Yes 
                 Limited 
               
               
                   
                   
                   
                 demonstrated in 
                   
                   
               
               
                   
                   
                   
                 real time 
                   
                   
               
               
                 6) Wire/molten pool 
                 Yes 
                 Limited 
                 Not 
                 Yes 
                 Limited 
               
               
                 tracking 
                   
                   
                 demonstrated 
                   
                   
               
               
                 7) Real-time flaw 
                 Yes 
                 Limited 
                 Limited 
                 Yes 
                 Yes 
               
               
                 detection 
               
               
                   
               
             
          
         
       
     
         [0082]    Various issues associated with the deposition environment can be corrected as shown in Table 2. 
         [0000]    
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Deposition Environment 
               
             
          
           
               
                 # 
                 EBF3 Process Challenge 
                 Manifestation in Deposit 
                 Corrective Action Required 
               
               
                   
               
               
                 1 
                 Deposition Environment 
                   
                   
               
               
                 1a 
                 vacuum 
                 not an impact to deposit; 
                 install cooling jacket; sensor 
               
               
                   
                   
                 affects ability to measure key 
                 selection with low heat 
               
               
                   
                   
                 features-sensor electronics 
                 generating electronics/vacuum 
               
               
                   
                   
                 overheat 
                 compatibility 
               
               
                 1b 
                 vacuum 
                 not an impact to deposit; 
                 use vacuum compatible 
               
               
                   
                   
                 affects ability to measure key 
                 materials for sensors, 
               
               
                   
                   
                 features-sensor outgassing 
                 packaging, wires; vacuum- 
               
               
                   
                   
                   
                 compatible lubricants if 
               
               
                   
                   
                   
                 needed 
               
               
                 1c 
                 metal vapor 
                 not an impact to deposit; 
                 pinhole optics with or without 
               
               
                   
                   
                 affects ability to measure key 
                 argon (inert gas) back 
               
               
                   
                   
                 features-sensor optics 
                 pressure; scrolling mylar film 
               
               
                   
                   
                 occluded/changes over time as 
                 over windows/optics; mirrors; 
               
               
                   
                   
                 vapor builds up 
                 ion shield; select sensors not 
               
               
                   
                   
                   
                 sensitive to metal vapor 
               
               
                   
                   
                   
                 deposition 
               
               
                 1d 
                 constrained gun-to-work 
                 not an impact to deposit; 
                 mirrors &amp; small sensors 
               
               
                   
                 distance &amp; moving gun 
                 affects ability to measure key 
                 installed on moving gun and 
               
               
                   
                   
                 features-tight space to install 
                 fit within gun-to-work 
               
               
                   
                   
                 sensors; sensor location and 
                 distance; remote sensors may 
               
               
                   
                   
                 angle to adequately view 
                 be usable for wider field views 
               
               
                   
                   
                 and track molten pool 
                   
               
               
                   
                   
                 as it traverses across 
                   
               
               
                   
                   
                 the parts 
                   
               
               
                 1e 
                 radiation (from 
                 not an impact to 
                 use IR transparent 
               
               
                   
                 electron beam) 
                 deposit; affects ability 
                 windows with radiation 
               
               
                   
                   
                 to measure key features- 
                 protection shroud 
               
               
                   
                   
                 leaded glass windows 
                 around externally- 
               
               
                   
                   
                 not IR transparent 
                 mounted sensors; 
               
               
                   
                   
                   
                 install sensors 
               
               
                   
                   
                   
                 or transmission 
               
               
                   
                   
                   
                 lines (such as fiber optic 
               
               
                   
                   
                   
                 cables) inside chamber 
               
               
                   
               
             
          
         
       
     
         [0083]    The Process Challenges and Corrective Actions of Table 2 are believed to be straightforward, such that a detailed description is not necessary. 
         [0084]    With reference to Table 3, various issues related to thermal transients can be detected/measured and corrected as shown. 
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Thermal Transients/Control 
               
             
          
           
               
                   
                 EBF 3  Process Challenge 
                 Manifestation in Deposit 
                 Corrective Action Required 
               
               
                   
               
             
          
           
               
                 3a 
                 Instantaneous transients 
                 Fluxuations in molten 
                 Rapid monitoring of molten 
               
               
                   
                 (molten pool traversing 
                 pool and bead width 
                 pool, change raster pattern to 
               
               
                   
                 over cold baseplate) 
                 along length 
                 correct (deflect back or to 
               
               
                   
                   
                   
                 sides to spread heat more 
               
               
                   
                   
                   
                 evenly); high speed detection 
               
               
                   
                   
                   
                 and corrective action 
               
               
                 3b 
                 Build-up of background 
                 Gradual increase in 
                 Long-term tracking of 
               
               
                   
                 heat (due to multiple layers) 
                 molten pool size (length 
                 molten pool size &amp; shape; 
               
               
                   
                   
                 width, aspect ratio, area, 
                 reduce power to correct; low 
               
               
                   
                   
                 centroid) resulting in 
                 speed detection and 
               
               
                   
                   
                 mushrooming of bead 
                 corrective action 
               
               
                   
                   
                 width (first layer 
                   
               
               
                   
                   
                 narrower than subsequent 
                   
               
               
                   
                   
                 layers due to changing 
                   
               
               
                   
                   
                 cooling path) 
                   
               
               
                 3c 
                 Changing cooling path  
                 Changing thermal 
                 Long-term tracking of 
               
               
                   
                 (as build up part, due to 
                 patterns results in 
                 molten pool size &amp; shape; 
               
               
                   
                 conductive-only cooling 
                 different bead geometries 
                 reduce power to correct; low 
               
               
                   
                 path) 
                 &amp; microstructures 
                 speed detection and 
               
               
                   
                   
                   
                 corrective action 
               
               
                   
               
             
          
         
       
     
         [0085]    In an Electron Beam Freeform Fabrication (EBF 3 ) process according to one aspect of the present disclosure, an electron beam  6  ( FIG. 8 ) is used as a heat source to create a small molten pool  64  on a substrate  8  into which wire  13  is fed. The electron beam  6  and wire feed assembly  12  are translated with respect to the substrate  8  to follow a predetermined tool path. This process is repeated in a layer-wise fashion to fabricate metal structural components. 
         [0086]    EBF 3  is an inherently thermally transient process. Several factors contribute to this, beginning with its layer-additive nature. The continuously moving molten pool  64  over a relatively cold baseplate  8  or previous layer encounters a different cooling path and thermal mass with each successive layer. Variations in the geometry of the part such as section thickness changes, ends or corners also contribute to these changes. Thermal transients can be taken into account by controller  72  to enable repeatability necessary for certification of additive manufacturing processes for use in many applications. Sensors (e.g. cameras  14 ,  24 ) capable of detecting/measuring thermal distributions may be utilized to detect/track changes in the molten pool  64  by detecting the thermal gradients between liquid and solid phases over time. 
         [0087]    Thermal gradients from deposition onto a cold substrate  8  can cause rapid fluxuations in the molten pool  64 , resulting in changing width W ( FIG. 8 ) at bead  63  along the length of the bead  63 . Over time, the background heat and changing cooling path tends to result in a gradual increase in the molten pool size (length, width, area, aspect ratio, or centroid) causing an increase in the bead widths W. High speed imaging (&gt;10 frames per second) of the molten pool  64 , using optical, near infrared, infrared, or band-passed filtered optical cameras  14 ,  24  or pyrometers may be implemented to measure the molten pool size, shape and/or temperature. Controller  72  may be configured (e.g. programmed) to monitor these measurements and compare the measured values to baseline values. When the measurements are within a predefined threshold set by the user, no modifications to the deposition parameters are made by controller  72 . When the measurements are outside (above or below) the threshold, the frequency and amplitude of the fluxuations are measured. For high frequency fluxuations, the electron beam focus and raster pattern can be adjusted to match the frequency of the fluxuation, increasing or decreasing the size of the beam and raster or deflecting the electron beam  6  ahead, to the sides, or behind the molten pool  64  to smooth the shape of the bead  63 . For gradual changes in the molten pool size (length, width, area, aspect ratio, or centroid) or increase or decrease in the length of the cooling path behind the molten pool  64 , the beam power (current and/or accelerating voltage) is increased (when the molten pool  64  is shrinking) or decreased (when the molten pool  64  is growing) by a small increment (1-2 milliamps or 1-2 kilovolts). Since the response time of the gradual thermal gradients is slow, a change is made in the beam power, then the molten pool  64  and/or cooling tail sizes are monitored for one or more seconds before another change is made. 
         [0088]    Table 4 is a summary of various issues related to thermal properties and associated corrective actions. 
         [0000]    
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Alloy Thermal Properties 
               
             
          
           
               
                   
                 EBF 3  Process Challenge 
                 Manifestation in Deposit 
                 Corrective Action Required 
               
               
                   
               
               
                 4a 
                 Melting temperature 
                 Lower melting 
                 Selection of appropriate sensors 
               
               
                   
                 detectable with imaging 
                 temperature alloys not 
                 to detect lower temperatures; 
               
               
                   
                 sensors (to detect edges  
                 visible with same sensor 
                 calibration of sensors to lower 
               
               
                   
                 of molten pool) 
                 as higher melting 
                 melting temperatures; use of 
               
               
                   
                   
                 temperature alloys 
                 reflectance changes from molten 
               
               
                   
                   
                   
                 to solid to detect molten pool 
               
               
                   
                   
                   
                 boundaries; low speed detection 
               
               
                   
                   
                   
                 and corrective action; does not 
               
               
                   
                   
                   
                 require continuous monitoring or 
               
               
                   
                   
                   
                 adjustments once set 
               
               
                 4b 
                 Liquidus/solidus range 
                 Affects precision of 
                 Selection of appropriate sensors 
               
               
                   
                 detectable with imaging 
                 deposit and control 
                 to detect lower temperatures; 
               
               
                   
                 sensors (to detect edges of  
                 possible 
                 calibration of sensors to lower 
               
               
                   
                 molten pool and trace 
                   
                 melting temperatures; use of 
               
               
                   
                 cooling path in tail area) 
                   
                 reflectance changes from molten 
               
               
                   
                   
                   
                 to solid to detect molten pool 
               
               
                   
                   
                   
                 boundaries; low speed detection 
               
               
                   
                   
                   
                 and corrective action; does not 
               
               
                   
                   
                   
                 require continuous monitoring or 
               
               
                   
                   
                   
                 adjustments once set 
               
               
                 4c 
                 Specific heat 
                 Affects selection of 
                 Power increased, travel speed 
               
               
                   
                   
                 power, travel speed 
                 decreased, and/or wire feed rate 
               
               
                   
                   
                   
                 decreased simultaneously to 
               
               
                   
                   
                   
                 increase power to melt (converse 
               
               
                   
                   
                   
                 is also true to decreased power to 
               
               
                   
                   
                   
                 melt); low speed detection and 
               
               
                   
                   
                   
                 corrective action; does not 
               
               
                   
                   
                   
                 require continuous monitoring or 
               
               
                   
                   
                   
                 adjustments once set 
               
               
                 4d 
                 Thermal conductivity 
                 Affects selection of 
                 Power increased, travel speed 
               
               
                   
                   
                 power, travel speed 
                 decreased, and/or wire feed rate 
               
               
                   
                   
                   
                 decreased to increase power to 
               
               
                   
                   
                   
                 melt (converse is also true to 
               
               
                   
                   
                   
                 decreased power to melt); low 
               
               
                   
                   
                   
                 speed detection and corrective 
               
               
                   
                   
                   
                 action; does not require 
               
               
                   
                   
                   
                 continuous monitoring or 
               
               
                   
                   
                   
                 adjustments once set 
               
               
                 4e 
                 Vapor pressure (function 
                 Dealloying in molten 
                 Reduce power (accelerating 
               
               
                   
                 of temperature &amp; 
                 pool (&amp; resulting 
                 voltage and/or beam current) 
               
               
                   
                 pressure) 
                 deposit); causes build-up 
                 increase travel speed and/or wire 
               
               
                   
                   
                 on inside of system &amp; on 
                 feed rate to reduce temperature, 
               
               
                   
                   
                 sensor optics 
                 reduce molten pool size &amp; 
               
               
                   
                   
                   
                 duration of exposure of molten 
               
               
                   
                   
                   
                 pool surface to vacuum; change 
               
               
                   
                   
                   
                 beam focus to switch between 
               
               
                   
                   
                   
                 keyhole vs. conduction mode; 
               
               
                   
                   
                   
                 low speed detection and 
               
               
                   
                   
                   
                 corrective action; does not 
               
               
                   
                   
                   
                 require continuous monitoring  
               
               
                   
                   
                   
                 or adjustments once set 
               
               
                 4f 
                 Emissivity 
                 Different alloys not 
                 Use independent sensor 
               
               
                   
                   
                 visible with same sensor 
                 calibration (with black body 
               
               
                   
                   
                 settings 
                 radiation source); use handbook 
               
               
                   
                   
                   
                 values to adjust empirically;  
               
               
                   
                   
                   
                 may be able to approximate 
               
               
                   
                   
                   
                 liquidus/solidus range based on 
               
               
                   
                   
                   
                 change in reflectivity; low speed 
               
               
                   
                   
                   
                 detection and corrective action; 
               
               
                   
                   
                   
                 does not require continuous 
               
               
                   
                   
                   
                 monitoring or adjustments  
               
               
                   
                   
                   
                 once set 
               
               
                 4g 
                 Molten viscosity 
                 Affects wire feed 
                 Change deposition angle of 
               
               
                   
                   
                 direction, ability to build  
                 beam and wire entry angle into 
               
               
                   
                   
                 unsupported overhangs 
                 molten pool with respect to 
               
               
                   
                   
                   
                 deposit and/or changing a raster 
               
               
                   
                   
                   
                 pattern of the wire source and/or 
               
               
                   
                   
                   
                 the electron beam; low speed 
               
               
                   
                   
                   
                 detection and corrective action 
               
               
                 4h 
                 Surface tension 
                 Affects wire feed 
                 Change deposition angles of 
               
               
                   
                   
                 direction, ability to build 
                 beam and wire entry angle into 
               
               
                   
                   
                 unsupported overhangs 
                 molten pool with respect to 
               
               
                   
                   
                   
                 deposit and/or changing a raster 
               
               
                   
                   
                   
                 pattern of the wire source and/or 
               
               
                   
                   
                   
                 the electron beam; low speed 
               
               
                   
                   
                   
                 detection and corrective action 
               
               
                 4i 
                 Brightness/high intensity 
                 Not an impact to deposit; 
                 Band pass filtering to reduce 
               
               
                   
                 of molten pool and 
                 affects ability to measure 
                 intensity; shorter shutter 
               
               
                   
                 surrounding plasma 
                 key features-washes out 
                 speeds/integration times to 
               
               
                   
                 plume 
                 or saturates sensors, 
                 prevent sensor saturation; 
               
               
                   
                   
                 reducing detectability of 
                 electronic selection of different 
               
               
                   
                   
                 lower melting 
                 regions of interest and setting 
               
               
                   
                   
                 temperature regions of 
                 different integration times for 
               
               
                   
                   
                 interest 
                 different regions; sensor 
               
               
                   
                   
                   
                 selection to reduce or eliminate 
               
               
                   
                   
                   
                 pixel saturation and bloom; low 
               
               
                   
                   
                   
                 speed detection and corrective 
               
               
                   
                   
                   
                 action; does not require 
               
               
                   
                   
                   
                 continuous monitoring or 
               
               
                   
                   
                   
                 adjustments once set 
               
               
                   
               
             
          
         
       
     
         [0089]    Differing vapor pressures of the alloying additions can result in selective de-alloying (constituent loss) in the deposited material (e.g. deposit  66 ,  FIGS. 8 and 9 ). Controlling the temperature of the EBF 3  process impacts alloy compositional losses. Sensors  14  or  24  ( FIGS. 4 and 9 ) may comprise a spectrometer that is configured to measure the energy or wavelength of the ion species in the vapor plume  74  and/or or the x-rays produced from the electron beam  6  interacting with the molten pool  64 . This data can be utilized by controller  72  to identify the chemical species in the vapor or plasma plume  64  created by the electron beam  6 . Specifically of interest is quantifying the amount of different alloying addition species in the vapor/plasma plume  74 . If the ratio of species in the vapor plume  74  are similar to the ratio of these elements in the target alloy chemistry, no action is required. However, if the ratio of the species in the vapor plume  74  differs by more than a predefined maximum allowable amount (e.g. about 10%, about 15%, about 20%) some corrective action may be desired to maintain a more uniform alloy chemistry. To reduce the size of the vapor plume  74 , several corrective actions may be taken. For example, softening the beam focus (moving to a wider beam) to switch between keyhole vs. conduction mode mitigates (reduces) the degree of vaporization. Reducing the power (reducing accelerating voltage and/or beam current) and/or increasing the translation speed and wire feed rate reduces the temperature of the material in the molten pool  64 , and also reduces the size of molten pool  64 . Reducing the size of molten pool  64  (width, length, area, aspect ratio, or centroid) mitigates the size of the vapor plume by reducing the duration of exposure of the molten pool surface to vacuum. Selective vaporization cannot be entirely eliminated because this is a physical property of elements, but it can be mitigated by reducing the amount of overheating, size of the molten pool  64 , and duration of exposure of the molten pool surface to vacuum. 
         [0090]    Tables 5, 6, and 7 summarize issues associated with height/width measurement, wire entry, and wire anomalies, respectively. 
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Height/Width Measurement 
               
             
          
           
               
                   
                 EBF 3  Process Challenge 
                 Manifestation in Deposit 
                 Corrective Action Required 
               
               
                   
               
             
          
           
               
                 5a 
                 Starts 
                 Build up bulbs (extra 
                 Adjust timing of starting 
               
               
                   
                   
                 height and width at start,  
                 beam power, beam raster, 
               
               
                   
                   
                 due to incorrect timing 
                 travel speed, wire feed rate; 
               
               
                   
                   
                 between beam on, wire 
                 high speed detection and 
               
               
                   
                   
                 feed entering molten 
                 corrective action, short 
               
               
                   
                   
                 pool, and travel speed- 
                 duration 
               
               
                   
                   
                 controlling inertias) 
                   
               
               
                 5b 
                 Necking-narrowing of 
                 Narrowing of deposit, 
                 Can control if eliminate 
               
               
                   
                 deposit within layer being 
                 often just behind a bulb 
                 bulbs at starts &amp; abrupt 
               
               
                   
                 deposited (along length of 
                 at start or at abrupt 
                 changes in geometry; high 
               
               
                   
                 deposition direction) or at 
                 change in build direction 
                 speed detection and 
               
               
                   
                 base of deposit (first layer 
                   
                 corrective action, short 
               
               
                   
                 narrower than subsequent 
                   
                 duration 
               
               
                   
                 layers due to changing 
                   
                   
               
               
                   
                 cooling path) 
                   
                   
               
               
                 5c 
                 Stops 
                 Depression of height, 
                 Adjust timing of ending 
               
               
                   
                   
                 cratering of molten pool, 
                 beam power, beam raster, 
               
               
                   
                   
                 tailing off (height drops 
                 travel speed, wire feed rate; 
               
               
                   
                   
                 due to thinner layer 
                 high speed detection and 
               
               
                   
                   
                 deposited) 
                 corrective action, short 
               
               
                   
                   
                   
                 duration 
               
               
                 5d 
                 Abrupt changes  
                 Narrowing/widening  
                 Adjust timing of beam power, 
               
               
                   
                 in build direction 
                 of deposit and 
                 beam raster, travel speed,  
               
               
                   
                   
                 increase/decrease in 
                 wire feed rate-possible feed- 
               
               
                   
                   
                 height before during and 
                 forward option to program 
               
               
                   
                   
                 after abrupt changes in 
                 known geometric effects  
               
               
                   
                   
                 build direction 
                 with programmed changed  
               
               
                   
                   
                   
                 as approach changes in  
               
               
                   
                   
                   
                 direction; high speed  
               
               
                   
                   
                   
                 detection and corrective  
               
               
                   
                   
                   
                 action, short duration 
               
               
                   
               
             
          
         
       
     
         [0091]    As shown in Table 6, various issues associated with the wire entry direction can be corrected as shown. 
         [0000]    
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                 Wire Entry Direction 
               
             
          
           
               
                   
                 EBF 3  Process Challenge 
                 Manifestation in Deposit 
                 Corrective Action Required 
               
               
                   
               
               
                 6a 
                 wire enters leading edge  
                 narrower deposit 
                 no correction required 
               
               
                   
                 of molten pool 
                   
                   
               
               
                 6b 
                 wire enters trailing edge  
                 easily freezes wire in 
                 slight increase in wire feed 
               
               
                   
                 of molten pool 
                 molten pool (wire stick 
                 height distance to avoid wire 
               
               
                   
                   
                 or stabbing/wire 
                 sticks, raster beam across wire 
               
               
                   
                   
                 dragging) 
                 to preheat/melt, decrease wire 
               
               
                   
                   
                   
                 feed rate, increase wire 
               
               
                   
                   
                   
                 elevation angle into molten 
               
               
                   
                   
                   
                 pool; high speed detection 
               
               
                   
                   
                   
                 and corrective action 
               
               
                 6c 
                 wire enters side of  
                 wider molten pool due to 
                 slight increase in wire feed 
               
               
                   
                 molten pool 
                 wire pushing molten 
                 height distance to avoid wire 
               
               
                   
                   
                 pool over 
                 sticks, raster beam up wire to 
               
               
                   
                   
                   
                 preheat/melt, decrease wire 
               
               
                   
                   
                   
                 feed rate, increase wire 
               
               
                   
                   
                   
                 elevation angle into molten 
               
               
                   
                   
                   
                 pool; high speed detection 
               
               
                   
                   
                   
                 and corrective action 
               
               
                 6d 
                 wire enters at an angle into  
                 wider molten pool due to 
                 depends on whether angle is 
               
               
                   
                 molten pool (relative to 
                 wire pushing molten 
                 closer to entering leading 
               
               
                   
                 travel direction) 
                 pool over 
                 edge vs. side or trailing edge 
               
               
                   
                   
                   
                 of molten pool-vary wire 
               
               
                   
                   
                   
                 feed height distance, raster 
               
               
                   
                   
                   
                 beam up wire to preheat/melt, 
               
               
                   
                   
                   
                 wire feed rate, and wire 
               
               
                   
                   
                   
                 elevation angle into molten 
               
               
                   
                   
                   
                 pool as a function of the 
               
               
                   
                   
                   
                 direction of wire feed with 
               
               
                   
                   
                   
                 respect to translation 
               
               
                   
                   
                   
                 direction; high speed 
               
               
                   
                   
                   
                 detection and corrective 
               
               
                   
                   
                   
                 action 
               
               
                 6e 
                 side-by-side fills 
                 overlaps/gaps critical in 
                 programmed path planning to 
               
               
                   
                   
                 controlling heat build-up 
                 push into side vs. reaching 
               
               
                   
                   
                 and geometry of built 
                 over previously deposited 
               
               
                   
                   
                 parts 
                 bead; low speed detection and 
               
               
                   
                   
                   
                 corrective action 
               
               
                 6f 
                 wire elevation (entry angle 
                 angle too low limits 
                 45 degrees is ideal; lower 
               
               
                   
                 relative to horizontal) 
                 build shapes due to 
                 angle gives shorter wire time 
               
               
                   
                   
                 hardware crashes, 
                 in beam before entering 
               
               
                   
                   
                 incorrect angle can 
                 molten pool &amp; pushes molten 
               
               
                   
                   
                 contribute in wire 
                 pool when fed to side; higher  
               
               
                   
                   
                 anomalies (detailed 
                 angle difficult to achieve with 
               
               
                   
                   
                 below) 
                 size of gun but directs wire 
               
               
                   
                   
                   
                 into molten pool (better for 
               
               
                   
                   
                   
                 wire entering side or trailing 
               
               
                   
                   
                   
                 edge of molten pool); high 
               
               
                   
                   
                   
                 speed detection and corrective 
               
               
                   
                   
                   
                 action, does not require 
               
               
                   
                   
                   
                 continuous monitoring or 
               
               
                   
                   
                   
                 adjustments once set 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 7 
               
             
             
               
                   
               
               
                 Wire Anomalies 
               
             
          
           
               
                   
                 EBF 3  Process Challenge 
                 Manifestation in Deposit 
                 Corrective Action Required 
               
               
                   
               
               
                 7a 
                 Lack of wire cleanliness 
                 May be difficult to detect in 
                 If detected, insert note into data 
               
               
                   
                 (from dust due to poor 
                 process-sparking or ejecta 
                 set; if greater than set threshold 
               
               
                   
                 storage conditions, 
                 during deposition, brighter 
                 value, halt deposition and 
               
               
                   
                 oxidation due to age and 
                 or different plasma vapor 
                 inspect/clean or replace wire 
               
               
                   
                 poor storage conditions, 
                 plume; manifests as small 
                 spool; high speed detection and 
               
               
                   
                 residual lubricants from 
                 porosity, inclusions or 
                 corrective action, short duration 
               
               
                   
                 wire drawing) 
                 minor localized chemistry 
                   
               
               
                   
                   
                 variations in deposit 
                   
               
               
                 7b 
                 Abrupt thermal gradients  
                 At higher wire feed rates, 
                 Beam focus and deflection up 
               
               
                   
                 in wire due to feeding into 
                 can result in incomplete 
                 wire to preheat wire; use of 
               
               
                   
                 molten pool (lack of wire 
                 wire melting or “chopped” 
                 external wire preheating 
               
               
                   
                 preheat) 
                 wire bits transmitted into 
                 (resistance, inductance, radiant- 
               
               
                   
                   
                 molten pool; reduced 
                 careful not to induce EMI  
               
               
                   
                   
                 diameter wire sticks out of 
                 that will interfere with electron 
               
               
                   
                   
                 side of deposit 
                 beam); reduce wire feed rate; 
               
               
                   
                   
                   
                 switch to smaller diameter 
               
               
                   
                   
                   
                 wire; high speed detection and 
               
               
                   
                   
                   
                 corrective action, short duration 
               
               
                 7c 
                 Dripping (due to excess 
                 Irregular height, 
                 Increase wire feed rate; 
               
               
                   
                 heat, insufficient wire feed 
                 compounds with multiple 
                 decrease beam power (current); 
               
               
                   
                 or wire feed height distance 
                 layers 
                 increase travel speed; adjust 
               
               
                   
                 too high) 
                   
                 wire feed height distance; high 
               
               
                   
                   
                   
                 speed detection and corrective 
               
               
                   
                   
                   
                 action 
               
               
                 7d 
                 Stabbing/wire dragging 
                 Wire oscillates back and 
                 Decrease wire feed rate; 
               
               
                   
                 (due to insufficient heat, 
                 forth, traces grooves in 
                 increase beam power (current); 
               
               
                   
                 excess wire feed, or wire 
                 deposit, deflects off bottom 
                 decrease travel speed; adjust 
               
               
                   
                 feed height distance too 
                 of molten pool and diverts 
                 wire feed height distance; high 
               
               
                   
                 low) 
                 out of beam/molten pool 
                 speed detection and corrective 
               
               
                   
                   
                   
                 action 
               
               
                 7e 
                 Wire cast (residual stress, 
                 Wire sticks out of side of 
                 Improved wire straighteners in 
               
               
                   
                 curvature or twist in wire) 
                 deposit, wire misses 
                 system; beam deflection across 
               
               
                   
                 curls wire away from 
                 beam/molten pool 
                 wire to redirect into molten 
               
               
                   
                 molten pool 
                 altogether, wire oscillates 
                 pool; high speed detection and 
               
               
                   
                   
                 back and forth, wire 
                 corrective action 
               
               
                   
                   
                 position is biased to one 
                   
               
               
                   
                   
                 side of the molten pool 
                   
               
               
                 7f 
                 Poor timing of wire/beam 
                 Wire stick/freezes in 
                 Feed-forward approach (pre- 
               
               
                   
                 starts &amp; stops 
                 molten pool (resulting in 
                 program starts and stops based 
               
               
                   
                   
                 pulling gun/wire feeder out 
                 on empirical or theoretical 
               
               
                   
                   
                 of alignment, can leave 
                 timing); monitor for anomalies 
               
               
                   
                   
                 cracks or unmelted wire in 
                 and set threshold to interrupt 
               
               
                   
                   
                 deposit), wire retracts too 
                 build if anomalies detected are 
               
               
                   
                   
                 early results in excess heat 
                 above threshold; increase 
               
               
                   
                   
                 buildup, reducing deposit 
                 preheat; detect quickly-stop, 
               
               
                   
                   
                 height and increasing width 
                 back up translation, turn on 
               
               
                   
                   
                 locally 
                 beam to cut wire, then adjust 
               
               
                   
                   
                   
                 wire feed height distance; high 
               
               
                   
                   
                   
                 speed detection and corrective 
               
               
                   
                   
                   
                 action, short duration 
               
               
                 7g 
                 Wire position too high/low 
                 Too high-dripping; too 
                 Alignment check before 
               
               
                   
                 or wire feeder rotated, so 
                 low-stabbing or dragging; 
                 initiating deposition; adjust 
               
               
                   
                 wire does not enter molten 
                 rotated-wire sticks out 
                 position of wire feeder with 
               
               
                   
                 pool at correct location 
                 side of deposit or misses 
                 respect to molten 
               
               
                   
                   
                 beam/molten pool 
                 pool/deposition surface; 
               
               
                   
                   
                 altogether or wire position 
                 interrupt build if wire detected 
               
               
                   
                   
                 is biased to one side of the 
                 outside molten pool; high speed 
               
               
                   
                   
                 molten pool 
                 detection and corrective action, 
               
               
                   
                   
                   
                 short duration 
               
               
                   
               
             
          
         
       
     
         [0092]    Geometric variations in the deposit  66  ( FIGS. 8 and 9 ) that result from imperfect coordination of heat and mass flow (electron beam power and wire feed) during starts, stops and abrupt changes in build direction to follow a desired part feature (such as taking a 90-degree turn, changing from deposition in the “X” direction to deposition in the “Y” direction in a rectilinear translation configuration). These variations include bulbs (build-up of excess material at starts), necking (narrowing of the deposit) or tailing-off (deficit in deposit height approaching a stop), and build-up followed by necking around corners. Both bead widths W ( FIG. 9 ) and height H ( FIG. 8 ) of the deposited material  66  are affected by these changes in translation speed and geometry. The height H is typically a more critical variable because it has an accumulative effect if uncorrected. Since the EBF 3  process is a layer-additive process, even minute perturbations in height H will accumulate into large errors over time as the build progresses (for example, parts measuring as small as 10 cm in height can represent over 100 layers). Therefore, the sensor type and its location in the build chamber preferably enable precise measurement of the bead height H in addition to bead width W. High speed imaging (&gt;10 frames per second) may be utilized to capture these events, since they involve a complex timing of translation speed and direction, wire feed, and beam start/stop that occurs very quickly. 
         [0093]    Imaging may be accomplished with one or more near-infrared, infrared, or band-pass filtered optical cameras ( 14 ,  24 ) positioned at an angle with respect to the molten pool  64  to allow observation of bead height H. Most angles will work, as long as the camera ( 14 ,  24 ) is not oriented straight down on the molten pool  64  (looking along the axis of the electron beam  6 ). The geometry of the location of the camera is typically fixed, so the vertical and horizontal location of the molten pool  64  relative to the wire feeder  12  and substrate  8  can be determined with simple trigonometry. Identification of the location of the molten pool  64  may be determined by calculating the centroid and comparing it to the wire location. As the centroid moves closer to the wire location, the height H is increasing, and as the centroid moves farther away from the wire location, the height H is decreasing. This height measurement can then be used by controller  72  to increase or decrease the wire feed rate to raise (increased wire feed rate) or lower (decreased wire feed rate) the height H of the deposited bead  63 . Furthermore, the wire feed rate can be synchronized with the translation speed, using the X and Y speeds from feedback on the X and Y translation stage motors, to automatically correct the wire feed rate for speed changes at starts, stops, and changes in translation direction. The measured height H would further increase or decrease the wire feed rate to maintain a constant height H across the entire layer on the part. If the wire feed rate cannot be synchronized to the translation speed, corrections based solely on height H will also work (i.e. the wire feed rate does not necessarily need to be synchronized with the translation speed). 
         [0094]    Control of the EBF 3  process also includes consideration of the relative direction of wire in-feed and deposit direction to the geometric variations in the deposit  66 . Changes in the orientation of wire  13  with respect to the translation direction (e.g., wire lagging or pushing the molten pool  64 , or entering from the side) and wire elevation (e.g., entry angle α, relative to the horizontal) can subtly change the geometry of the deposit. Also, parts may require multiple side-by-side beads  63  to develop the required section width, and the shape of the molten pool  64  depends upon the presence and relative location of adjacent beads  63 . For example, for multi-bead deposits it is often easier to “push into” adjacent beads than to reach over them but this is not always possible due to other constraints. Use of cameras (such as optical, band-pass filtered optical, near-infrared, infrared) to measure the width W of the bead  63  and the direction of travel can be used to monitor the effects of relative direction of wire in-feed into the molten pool  64 . The control system  72  is programmed to make minor adjustments based on the direction of the wire feed into the molten pool  64  as follows: If the wire  13  is feeding into the trailing edge of the molten pool  64  or into the side of the molten pool  64 , the beam power may be increased slightly (1 milliamp or 1 kilovolt), the electron beam deflection may be changed to deflect the beam  6 A onto the wire  13  to preheat the wire  13  before it enters the molten pool  64 , the translation speed may be decreased by 1-2 inches per minute, the wire feed rate can be decreased by 5-10 inches per minute, or the wire feed height distance HW ( FIG. 8 ) can be increased by 0.001 to 0.002 inches to reduce the potential for wire sticks. The amount of change may be maximum when the wire  13  is feeding into the trailing edge of the molten pool  64 , and proportionally less as the translation direction approaches the wire feeding into the leading edge of the molten pool. If the wire  13  is entering into the leading edge of the molten pool  64 , corrections are typically not required. For side-by-side beads for a fill pattern, the electron beam power may be increased slightly and/or may be deflected slightly such that the beam  6  impinges on the side of the neighboring bead to facilitate edge bonding. 
         [0095]    Random process errors result from variability in the wire feed. The wire  13  is generally at or near room temperature until it crosses into the electron beam path, at which point it is subjected to an abrupt thermal gradient, melting over a very short distance as it enters the molten pool  64 . Larger diameter wire, therefore, retains substantial stiffness as it enters the molten pool  64 , which may, result in various errors or defects. In the event of excess heat, insufficient wire feed, or wire feeding above the electron beam/substrate intersection point, dripping may occur. Conversely, insufficient heat, excess wire feed, or wire feeding below the electron beam/substrate intersection point may result in wire stabbing which can cause the wire  13  to oscillate back and forth in the molten pool  64 ; skip, causing fluctuations in the deposit height H; or deflect off the bottom of the molten pool  64  and divert out of the beam  6  altogether. 
         [0096]    Improper wire location or poor timing of the start/stop sequence may result in wire sticks. Some errors of this nature may occur due to cast (residual curvature or twist in the wire  13  not removed by the wire straightener) or simple mechanical misalignment of the wire feed apparatus  12  that may not be immediately apparent. To measure wire feed anomalies, an important feature to track is the position of wire  13  relative to the molten pool  64 . This may be accomplished with optical, near infrared, infrared, or band-pass filtered optical cameras ( 14 ,  24 ), where the camera is focused on the molten pool  64  and wire entry into the molten pool  64 . Because the wire  13  is entering the electron beam  6  above the surface of the molten pool  64 , it appears as a step feature in the molten pool images, when viewed from most angles (except for within about 15 degrees of straight down on the molten pool  64 ). The wire location (either the edges of the wire or the calculated centroid) may be tracked relative to the molten pool  64  (again, using either the edges of the molten pool  64  or the calculated centroid). The wire location preferably remains in a constant relationship to the molten pool  64  (i.e. they line up on the same centerline at a constant distance apart). Corrective actions may be implemented by controller  72  if the wire location changes with respect to the molten pool location by more than a preset threshold amount. 
         [0097]    At higher wire feed rates, incomplete wire melting or “chopped” wire bits transmitted into molten pool  64  or bits of wire  70  ( FIG. 9 ) may exit the molten pool  64  and stick out of side of deposit  66 . This may be corrected by defocusing the electron beam  6  and/or by deflecting the electron beam  6 A towards the wire  13  to preheat the wire  13 , increasing the electron beam power, or reducing the wire feed rate. Dripping occurs when the height H of the deposit  66  is too low and the distance between the wire  13  and the molten pool  64  increases to the point that the wire  13  melts in the beam  6  above the molten pool  64 . Drips  68  ( FIGS. 8 and 9 ) begin with an instability in the molten pool  64  and an increase in the distance between the wire location and the molten pool  64 . Correction action may include increasing the wire feed rate, and/or by decreasing the power and/or by increasing the translation speed. Corrective action is preferably taken early when the wire location increases the distance from the molten pool  64 , thereby eliminating most occurrences of dripping. In the event that the wire location is too close to the molten pool  64  (height H of the deposit  66  is too high), the wire  13  may start stabbing, oscillating back and forth, and/or dragging. This may be detected by a decrease in the distance between the wire location and the molten pool  64 , and may be corrected by decreasing wire feed rate, increasing beam power, or decreasing translation speed. If residual curvature is present in the wire, the wire  13  may not enter the molten pool  64  from a consistent location. The corrective action when the wire location is changing, particularly on a low frequency (&lt;3 to 5 Hz) basis, may be to either automatically jog the wire (if the wire feeder  12  is equipped with a translation motor) or to deflect the electron beam  6 A up the sides of the wire  13  to direct the wire  13  into the molten pool  64  (deflection of a beam up the sides of wire is disclosed in U.S. Pat. No. 8,344,281). 
         [0098]    As shown in Table 8 below, various issues associated with miscellaneous factors can be corrected as shown. 
         [0000]    
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 8 
               
             
             
               
                   
               
               
                 Miscellaneous Factors 
               
             
          
           
               
                   
                 EBF 3  Process Challenge 
                 Manifestation in Deposit 
                 Corrective Action Required 
               
               
                   
               
               
                 8a 
                 Vapor condensate flakes off 
                 Produces voids and 
                 Clean facing surfaces between 
               
               
                   
                 wire feeder nozzle, electron 
                 porosity or inclusions in 
                 deposition runs; monitor 
               
               
                   
                 beam gun, or other facing 
                 final deposit; if condensate 
                 condensate build-up and 
               
               
                   
                 surfaces and lands in molten 
                 buildup is large enough 
                 identify threshold to interrupt 
               
               
                   
                 pool 
                 (such as bead forming at 
                 for cleaning surfaces; design 
               
               
                   
                   
                 end of wire tip) can freeze 
                 gun and wire feeder shielding 
               
               
                   
                   
                 out molten pool and cause 
                 to minimize surface area facing 
               
               
                   
                   
                 wire stick or large 
                 molten pool; apply line-of-sight 
               
               
                   
                   
                 geometric discontinuity in 
                 shielding that can be 
               
               
                   
                   
                 local bead height/width 
                 removed/replaced (such as  
               
               
                   
                   
                   
                 Al foil wrap); high speed  
               
               
                   
                   
                   
                 detection and corrective  
               
               
                   
                   
                   
                 action, short duration 
               
               
                 8b 
                 No wire feed (due to wire 
                 Molten pool increases in 
                 Adjust wire feed rate; adjust 
               
               
                   
                 jams, birds nest, empty wire 
                 size rapidly, height drops 
                 tension on wire feeder; 
               
               
                   
                 spool) or low wire feed 
                 (due to overheating with no 
                 interrupt build to manually 
               
               
                   
                 (wire drive rollers slipping, 
                 wire feed) 
                 correct wire feed issues 
               
               
                   
                 friction in wire guide tubes) 
                   
                 (replace wire spool, cut out 
               
               
                   
                   
                   
                 wire birds nests, fix wire jams, 
               
               
                   
                   
                   
                 etc.); high speed detection and 
               
               
                   
                   
                   
                 corrective action, short 
               
               
                   
                   
                   
                 duration 
               
               
                   
               
             
          
         
       
     
         [0099]    The preceding description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the following claims and the principles and novel features disclosed herein. 
         [0100]    All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if a term in the present application contradicts or conflicts with a term in the incorporated reference, the term from the present application takes precedence over the conflicting term from the incorporated reference. 
         [0101]    All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. Each range disclosed herein constitutes a disclosure of any point or sub-range lying within the disclosed range. 
         [0102]    The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. “Or” means “and/or.” As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. As also used herein, the term “combinations thereof” includes combinations having at least one of the associated listed items, wherein the combination can further include additional, like non-listed items. Further, the terms “first,” “second,” and the like herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the particular quantity). 
         [0103]    Reference throughout the specification to “another embodiment”, “an embodiment”, “exemplary embodiments”, and so forth, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and can or cannot be present in other embodiments. In addition, it is to be understood that the described elements can be combined in any suitable manner in the various embodiments and are not limited to the specific combination in which they are discussed.