Abstract:
A method and apparatus for depositing metals and metal-like substances in two and three dimensional form without a substrate in a safe, rapid and economical fashion using gas shielded arc welding equipment and programmable robotic motion. The method and apparatus includes the use and application of robotic controls, temperature and position feedback, single and multiple material feeds, and semi liquid deposition thereby creating near net shape parts particularly well suited to rapid prototyping and lower volume production.

Description:
RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Patent Application Ser. No. 61/892,526 entitled “Method and Apparatus for Fabrication of Articles by Molten and Semi-molten Deposition”, filed Oct. 18, 2013, the disclosure of which is herein incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to equipment and processes used for the fabrication of parts by depositing layers of metallic material, commonly referred to as additive manufacturing, and more particularly to equipment and processes which fabricate metallic items formerly made by processes such as casting, welding, subtractive machining, and forging, and generally does so without the need for specialized tooling and long lead times associated with these manufacturing processes. 
       BACKGROUND OF THE INVENTION 
       [0003]    Fabrication of three-dimensional metal articles by deposition of successive layers of metallic powder or weld beads, where the layers are heat bonded together to build the object, is well known in the field. 
         [0004]    Processes using plasma or laser fused deposited metals have been used for many years to produce a layered structure on a substrate, but are typically very energy intensive and extremely slow. The required equipment is expensive to purchase and operate as a high energy plasma generator is needed to vaporize the powder stream or high energy laser beam is needed to generate the melt-pool on the growth surface. 
         [0005]    Similarly, processes using energetic wire deposition enable the rapid prototyping and manufacture of fully dense, near-net shape components on a substrate. However, the deposition must be done slowly to allow each layer to cool prior to the next layer being added. In addition, the resulting items produced by these deposition methods often require the removal of the substrate as a secondary operation, which can increase the cost, destroys the substrate when being removed, can damage the object from which the substrate is being removed, or require careful engineering to incorporate the substrate into the structure of the item being manufactured, thereby limiting the configurations that can be produced. 
         [0006]    The bonded layers from these current processes are sometimes milled to a final shape either after each layer is formed, or after all layers have been made. Those knowledgeable in the art accept that parts fabricated using this welding method, are either small—due to the large amount of heat inputted through the welding process- or extremely expensive due to the long time needed to fabricate them. 
         [0007]    Sintered metal processes use powdered materials and a high power laser beam to selectively melt the powdered material, layer upon layer. Although relatively accurate, these processes are also slow and require a high temperature post processing operation to obtain a usable part. Even after post processing, the resulting part has the physical properties of a sintered metal part rather than being homogeneous. Furthermore, post processing can result in significant distortion and the required equipment is expensive. Laser melting of powered materials can be used and thus eliminate the need for oven post heating, but are even slower due to the increased heat. 
         [0008]    These processes used to fabricate three dimensional metallic items by adding layers of material have many disadvantages. Similarly, processes such as casting and forging require large investments in tooling and equipment and thus fundamentally suited only for large volume production Processes such as welding are generally labor intensive, require highly skilled personnel and require a great deal of pre-assembly preparation and post assembly finishing. In addition, these processes typically require long periods of time to complete the production of a single part due to all the drawings and preparation required for the individual components. What is needed, therefore, is a method and apparatus to reduce the amount of capital equipment investment, process expense, and time needed to fabricate a 3 dimensional part, including the amount of time needed to form the part and the amount of time to finish the part for final use. 
       SUMMARY OF THE INVENTION 
       [0009]    A method of and apparatus for depositing metals and metal-like substances in three dimensional form in a rapid and economical fashion is herein disclosed, such that the new process satisfies an unmet need of single and smaller volume production in creating near-net shape parts, and providing an avenue to limited production heretofore unavailable, while not precluding its use in large volume production as well. As described herein, the new process of the present invention can form a metal part or a metal-like part comprising a composite including a metallic material, a combination of different metallic materials, a ceramic material, and components of various other materials. 
         [0010]    The present invention uses modified gas shielded arc welding equipment referred to as GMAW (Gaseous Metallic Arc Welding) and also known as MIG (Metallic Inert Gas). It can also use TIG (Tungsten Inert Gas) processes and apparatus in the same embodiment. The MIG or TIG welding torch is mounted onto a multiple axis robotic mechanism to automatically deposit one or more metals in layers according to the part design while simultaneously heating or cooling the resulting built-up structure to achieve a faster deposition of material and to maintain and improve dimensional accuracy. 
         [0011]    The metal-like part exhibits some metallic properties while not being entirely made of a metal. In one embodiment, the metal-like material is provided as a feedstock by enclosing the non-metallic components within a tube of metal. While some currently known MIG welding wire uses a tube of metal surrounding a flux core, a metal-like feedstock as used herein, in one embodiment, includes a tube of metal having a core other than a flux core. 
         [0012]    In addition, a method is disclosed whereby a metallic three dimensional item is produced without the need of being permanently attached to a preform or substrate during the manufacturing process. The resulting part does not require removal of a difficult to remove substrate, to provide a near-net-shape part requiring no further removal of structure. 
         [0013]    The present invention provides, in different embodiments, an object, part or item which does not include a permanently attached base or substrate. As discussed herein, the build table upon which the object is formed is removably adhered to the object, such that the object remains fixed to the build table during forming of the part, but is removable from the build table without significantly altering the form of either the part or the build table. Consequently, the build table is reusable to form additional objects of the same or different sizes or different designs. 
         [0014]    In one or more embodiments of the present invention, there is provided a method and apparatus to rapidly produce one or more parts to be used in place of castings, weldments, and forgings, while eliminating the need for tooling or molds to produce the part. 
         [0015]    In one or more embodiments of the present invention, there is provided a method and apparatus to provide a near net shape part with optimum dimensional accuracy. As used herein, a near net part is a part produced by a manufacturing process which is close to a finished part. The near net shape part requires a minimal amount of after-part finishing processing typically a limited and controlled material removal process and polishing, if necessary. 
         [0016]    In one or more embodiments of the present invention, there is provided a method and apparatus configured to control the built in stresses in the part, so that the desired physical material properties of the part are obtained. 
         [0017]    In one or more embodiments of the present invention, there is provided a method and apparatus configured to control the grain structure of the material in the part, so that the desired physical material properties of the part are obtained. In one or more embodiments, a submerged deposition process takes place below the top surface of the quenchant which provides properly controlled parameters, wherein the quenchant fluid and decomposition byproducts are excluded from the hot zone primarily by the action of mechanical shielding, shield gas, and deposition byproduct outflow. An inverted process allows gravity to assist in shielding the hot zone. 
         [0018]    In one or more embodiments, a means of determining the temperature of the quenchant at a predetermined distance from the part as a means of temperature direction and control is provided. Such means of monitoring temperature includes optical monitoring or sensor based monitoring. 
         [0019]    In one or more embodiments of the present invention, there is provided a method and apparatus configured to control and prevent an outflow of molten material from a hot zone wherein material is being deposited in a deposition, or hot zone, where the material is still molten or semi-molten. 
         [0020]    In one or more embodiments of the present invention, there is provided a method and apparatus configured to control and prevent a plastic flow or sag of deposited material in and adjacent to the hot zone. 
         [0021]    In one embodiment, the part is deposited layer by layer on a build table of copper, copper clad, or other suitable metallic material to provide the electrically conductive surface. In a second embodiment, the deposition is made using at least two wires of differing polarities to allow for the initial layer to be deposited on either a platen of metallic surface or a non-metallic surface such as a ceramic table. The use of the two wire approach also minimizes the heat input to the structure being fabricated and the energy needed to produce it. This reduced energy input allows the part to be fabricated more quickly. In this two wire embodiment, the material is deposited in a range of temperatures that include the material&#39;s temperature in plasma, molten and semi-molten states. 
         [0022]    Generally, the semi-molten state is used during a first pass in order to produce a continuous initial deposition surface or trace partially adhering to the surface of the platen, such adhesion being sufficient to prevent lifting of said trace during subsequent passes, but insufficient to preclude easy removal of the completed item or part, said adhesion being achieved by adjustment of deposition parameters and selection of suitable platen materials for the type materials being deposited. Suitable platen materials include heat resistant conductive and non-conductive materials and are capable of being temperature controlled by the quenchant fluid. 
         [0023]    In different embodiments, the deposition process benefits from a light dusting of a metallic powder on the surface of the platen to ensure electrical conduction. 
         [0024]    In one or more embodiments of the present invention, there is provided a method and apparatus configured to provide a safe environment for an operator and to control the unrestricted discharge of process byproducts. Byproducts are removed and processed by conventional means if desired, as is well known in the field of welding and other manufacturing processes. 
         [0025]    In one or more embodiments, a gas sensor is provided to monitor the presence of undesired atmospheric or by product gasses, as well as a means for controlling the influx of additional shield gasses to exclude the atmospheric or by product gasses from the deposition zone. 
         [0026]    In different embodiments, computer controls are integrated into the other process controls, as is known in the art. 
         [0027]    According to one embodiment of the present invention, there is provided an apparatus configured to fabricate a metal or metal-like object including a deposition head configured to deposit a metal or a metal-like material and a multi-axis robotic system. The multi axis robotic system is configured to support the deposition head and is further configured for movement in a first plane. A build table is disposed beneath the deposition head. The build table defines a support surface parallel to a first plane, wherein the build table is configured for independent movement in a first axis substantially perpendicular to the first plane. 
         [0028]    According to another aspect of the present invention, there is provided an apparatus configured to fabricate at least one of a metal or metal-like object including a plurality of deposition heads, wherein each of the deposition heads is configured to deposit a metal or metal-like material of a different type and each includes a tool bracket. A multi-axis robotic positioning system includes a head support including a master bracket configured to support the tool bracket of one of the plurality of deposition heads wherein the multi-axis robotic positioning system is further configured for movement in a first plane. A build table is disposed beneath the multi-axis robotic positioning system and defines a support plane, wherein the build table is configured for movement in the first axis independently of movement of the head support in the first axis. 
         [0029]    According to still another aspect of the present invention, there is provided a method of fabricating an object formed from a metal or metal-like material on a platen. The method includes depositing a plurality of spots of material on the substrate, wherein each of the plurality of spots is separated from an adjacent one of the plurality of spots of material; depositing a bead of material between each of the adjacent ones of the plurality of spots of material to connect adjacent spots with the deposited bead of material; depositing a continuous bead of material on top of the plurality of spots of material and the beads of material between adjacent ones of the plurality of spots; and successively depositing a continuous bead of material on a previously deposited continuous bead of material to complete the fabrication of the object. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]      FIG. 1  is a block diagram of the major components and subassemblies of a fabrication system. 
           [0031]      FIG. 2 . illustrates a deposition nozzle module of the present invention. 
           [0032]      FIG. 3 . illustrates a prototype part made by an embodiment of the present invention. 
           [0033]      FIG. 4 . illustrates a two wire deposition device of the present invention. 
           [0034]      FIG. 5 . illustrates an alternative two wire deposition device of the present invention. 
           [0035]      FIG. 6  illustrates another embodiment of a portion of a fabrication system. 
           [0036]      FIG. 7  illustrates an underneath perspective view of a platen assembly. 
           [0037]      FIG. 8  illustrates a top perspective view of a platen assembly including deposition of material. 
           [0038]      FIG. 9  illustrates a side view of a nozzle head fixture and a nozzle assembly. 
           [0039]      FIG. 10  illustrates a back view of a nozzle head fixture and a docked nozzle assembly. 
           [0040]      FIG. 11  illustrates a front perspective view of a nozzle head fixture and a docked nozzle assembly. 
           [0041]      FIG. 12  illustrates a perspective view of a part being formed with a part fixture. 
       
    
    
     DESCRIPTION 
       [0042]    The present invention is directed to the fabrication of an object using three-dimensional computer models and computer numerical control (CNC) robotics to control the position of the application of a metal or metal-like deposit. The present invention is directed to form a metal-based or metallic two or three dimensional object, as contrasted with known three dimensional plastic printing technologies in use today for providing objects made of plastic. The fabrication of these objects formed of metal does not require the use expensive tooling or molds. Additionally, the present invention is particularly well suited to rapid prototyping and lower volume production of metallic parts. 
         [0043]    In one or more embodiments, the apparatus includes an inert gas arc nozzle fed with wire and gas, a non-stick build surface mounted to a moving table, a multi-axis robotic actuators, a master controller, sensors, a tank full of quenchant, an enclosure, and an air filtering system. 
         [0044]    At least one distance sensor, or alternatively, electronic arc length sensing, as currently employed by welding manufacturers such as Lincoln, Fronius, Miller, ESAB etc, continuously monitors the height of the previously deposited metallic layer and compares the actual height of the pervious layer to the specified height. If any section of the layer is lower than specified, the system can go back and fill it prior to starting the new layer, or the speed of deposition can be modified to deposit additional material at the low section. 
         [0045]    A temperature monitoring means and simultaneous partial submersion of the part in a bath of quenchant fluid while building layers is used to heat or cool the part as each new layer is deposited in the one or more embodiments. This feature allows control of built in stresses as well as manipulation of the final grain structure and material properties. The supplemental control of part temperature, near but not coincident with the hot zone of the deposition, provides fine control of item characteristics including the ability to prevent outflow of deposited material from the vicinity of the hot zone and to preclude plastic flow or sag adjacent to the hot zone. In some embodiments, submersion in a bath of quenchant fluid as a means of heat control is advantageous over a spray or a quenchant cascade, as liquid does not remain on the surface to which material is being deposited during the next pass nor is liquid introduced into the hot zone. Consequently, the risk of steam, hydrogen and oxygen production which can cause embrittlement or porosity is thereby reduced or eliminated. 
         [0046]    The present invention provides a safe environment for the operator and controls the unrestricted discharge of process byproducts by providing an enclosure to trap toxic fumes generated during the deposition process. The enclosure also retains the inert gas used to shield the welding arc from undesired atmospheric gases, so that less inert gas is needed. In addition, the inert gas within the enclosure, in different embodiments, is purged and reused for the next part. 
         [0047]    As depicted in  FIG. 1 , a fabrication system  1  includes a Build Table  5  acting as a support for the part being fabricated. The Build Table  5  is supported by Build Table Supports  6  and is raised or lowered by way of Build Table Height Actuators  7  into a bath of quenchant Fluid  10 , which is contained in a tank  11 . As illustrated, the actuators  7  are located outside the quenchant fluid  10  and the tank  11  such that the actuator and the support are not immersed in the fluid. In this embodiment, the actuators  7  are located within an enclosure  40 . The temperature of the quenchant Fluid  10  is maintained by a Temperature Control Unit  12 . A quenchant Level  15  is maintained at a monitored, fixed position so that the Build Table  5  and a portion of the fabricated part are cooled or heated, as discussed herein. As used herein, the term “build” is used to refer to a part being produced or “built”. In one or more embodiments, the quenchant fluid  10  includes a quenchant configured to cool the object being formed on the build table  5 . 
         [0048]    A multi-axis Robotic Actuator System  20  is positioned above the Build Table  5 . The Robotic Actuator System  20  includes at least one Z Axis Actuator  21  which moves a Z Axis Rod  25  vertically, as illustrated, relative to the Build Table  5 . A Deposition Nozzle Module  30  is attached to the end of the Z Axis Rod  25  and is connected to a Deposition Power Supply  35  and a supply of Inert Gas  36  by way of a Welding Tether  37 . The described welding and deposition equipment is familiar to those knowledgeable in MIG or TIG welding processes, but modified to deliver much lower power and very different waveforms than typically used for welding applications. The inert gas  36  is also known as a shield gas. 
         [0049]    The Build Table  5 , bath of quenchant Fluid  10 , Robotic Actuator System  20 , and Deposition Nozzle Module  30  are all contained within an Enclosure  40 . In one or more embodiments, the Enclosure  40  creates a controlled Enclosed Space  45  for the process which is isolated from outside temperature variations and air currents. The inert gas is contained within the Enclosed Space  45  and maintained at a desired Inert Gas Level  46 , thus minimizing the chance of contamination of the material being deposited to form the part. While the inert gas level  46  is shown as a clearly defined gas level, this level is for illustrative purposes only. During operation of the system  1 , the gases present in the enclosure  40  intermix, with the level of shield gas being determined by the concentration of the mixture rather than a physical level as shown. 
         [0050]    The byproducts generated by the process are also contained in the Enclosed Space  45  and in or more embodiments the byproducts are vented by way of a Vent Fan  47  to appropriate filters, scrubbers or environmental controls in order to ensure operator safety. An oxygen sensor  48  is operatively connected to the controller  50  to monitor and control the level of oxygen gas within the chamber. If the chamber is determined to have too much oxygen gas, or not enough inert gas, the controller  50  delays the start of the deposition process or turns off the system, so that repairs or adjustments can be made. 
         [0051]    In another embodiment, the sensor  48  is used to provide for a reduction of shield gas during material deposition. The higher the concentration of shield gas in the chamber, the lower the requirement for shield gas input at the nozzle. Initially the chamber contains normal air, with that air being excluded from the deposition zone by the shield gas being input present at the nozzle. In other optional operating settings, normal air is completely removed from the chamber and the chamber is filled with a shield gas before beginning the formation of the part. 
         [0052]    In one or more embodiments, the enclosure  40  is a sealed container in which an inert gas, such as carbon dioxide, or argon, or a selected mix of inert gases is used in the part forming process. The enclosure  40  is coupled to a gas circulation system (not shown) as would be understood by those skilled in the art. The inert gas, such as carbon dioxide and argon are removed and trapped from the air and reused in the enclosure  40 . 
         [0053]    A central Computer Controller  50  is connected to all subassemblies of the apparatus by means of a Temperature Control Cable  53 , a Robotic Control Cable  54 , and a Deposition Power Supply Control Cable  55 . The Computer Controller  50  has master control over each of the subsystems along with control over the entire process, as described below. 
         [0054]    As depicted in  FIG. 2 , the Deposition Nozzle Module  30  incorporates a Holding Device  61  for securing a Deposition Nozzle Assembly  63  as well as the Welding Tether  37 . A Part Temperature Sensor  66 , an Electronic Height Gauge  67 , and a Gas Monitoring Probe  68  are also mounted to the Deposition Nozzle Module  30  so that all supported components remain in the same relational position as they move together. These sensors are connected to the Computer Controller  50  by way of a Nozzle Module cable  69 . It is important to note that the Part Temperature Sensor  66  is positioned and oriented so that it can accurately measure the temperature of the part at some preset distance between the top of the part, where the new materials layer is being deposited, and the build table or quenchant Level  15 . 
         [0055]    The Electronic height gauge  67  determines if any areas of the part are lower than desired. Optionally, in one or more embodiments, additional height sensors are mounted to ensure that the top of the part is in the correct position as determined by the height of the build table  5  with respect to the nozzle module  30 . It is known in the art that the Robotic Actuator System  20 , in different embodiments, include multiple axes and thus allow manipulation of more than one Deposition Nozzle Module  30 . Multiple Deposition Nozzle Modules  30  allow for faster deposition rates or deposition of two materials at the same time. In one or more embodiments where the nozzle assembly  63  incorporates a MIG welding head, the welding head is inputting heat during formation of the part with up to 7,000 watts of power. 
         [0056]    The typical Direction of Travel  70  for the Deposition Nozzle Module  30  is depicted. An angular orientation  71  of the nozzle relative to the part is employed for the purposes of maximizing deposition rate and minimizing heat buildup while narrowing the spread of the deposited material. This angular orientation  71  is not an essential element of the invention, but is shown for clarity and as an illustration of established practice. In this case, an additional rotational element would be added to the nozzle as is already common in the art to enable omnidirectional movement. In one or more embodiments, feed wire is used to provide material for the build-up of the item being produced, and the wire discharge means can be a MIG nozzle, TIG feed wire dispenser, or any similar means available to the art. Feed wire provides advantages over powdered metal for cost, environmental, and safety reasons. 
         [0057]    The sample part  80  depicted in  FIG. 3  was made without use of the quenchant Fluid  10 . The uneven Top Surface  81  of this sample part, which includes sag  82 , illustrates how improper cooling results in a part which lacks dimensional stability during fabrication and which includes unwanted defects. The teachings of the present disclosure, in contrast however, provide a dimensional stability of the part which, in some cases, reduces the amount of after-processing needed finish a part or the number of dimensionally inaccurate parts. 
         [0058]    Prior to operating the apparatus, a 3D solid computer model of the desired part is sliced into virtual layers and saved into an electronic file (not shown). This electronic file is then entered into the Computer Controller  50  of the apparatus. At the start of operation of the apparatus, a set of commands from the Computer Controller  50  causes the Build Table  5  to be initially positioned in or above the quenchant Level  15  and the Robotic Actuator System  20  and the Z Axis Actuator  21  to position the Deposition Nozzle Module  30  at a starting point and a predetermined optimum distance above the Build Table  5 . The Enclosure  40  is optionally filled at this time with the Inert Gas  36 , by turning on the flow or re-introducing gas which was saved from previous runs. 
         [0059]    After checking and confirming that the environment within the Enclosure  40  is being maintained at proper operating conditions by way of the oxygen sensor  48 , the Computer Controller  50  turns on the Deposition Power Supply  35  and the flow of the Inert Gas  36 . Feed wire is delivered to the nozzle and an arc is struck. The first layer of the part is deposited onto the Build Table  5  according to the profile in the sectioned 3D model file. Subsequent layers, as determined by the 3D solid computer model and the virtual layers thereof, are deposited to form a complete part. 
         [0060]    The speed, power settings, and direction of the material deposition are determined by preloaded parameters within the Computer Controller  50 . Since the temperature sensor  66  is mounted as part of the nozzle module  30 , the temperature sensor  66  is adjacent to the location of the deposition of material, i.e. the deposition or hot zone, and records the instantaneous temperature at a set distance from the deposition or hot zone. This data is received by the controller  50  and used in a computer modeling of an overall part temperature. For example, upon completion of a layer, the average temperature of an aluminum part is read using readings from the temperature sensor  66  and the Build Table  5  is lowered or raised to cool or heat the part to a desired temperature prior to moving on to deposition of the next layer. The build can be delayed or slowed down if the part is not within an acceptable temperature range, and thus ensure one or more of: 1) proper bonding between layers, 2) prevention or reduction of part sagging from addition heat input, 3) obtaining the desired material grain structure, and 4) achieving desired physical properties. Also, under the right conditions, the build is continuous and includes one, homogeneous material including the transition from layer to layer. Travel speed control is, therefore, an additional parameter which, can be used to control part temperatures. As is known in the art, distortion control in forgings, castings and thin sheet metal parts as well as minimal residual stresses in forgings and castings can be achieved by hot water quenching using hot water or water/polyalkalene glycol mixtures. 
         [0061]    Movement of the build table  5  is combined with movement in the Z axis of the Z Axis Rod  25  and is controlled by the controller  50  to vary the distance between the quenchant and the hot zone of the part while keeping the deposition parameters constant. Therefore, the distance between the hot zone and the quenchant level  15  and the portion of the part submerged, is continuously varied based on instantaneous temperature readings, or is varied based on a model of overall part temperature and varied in discrete steps as desired. 
         [0062]    The temperature of the part as measured by the small single point temperature sensor  66  is received by the controller  50  and is used to determine an average temperature over time, as the nozzle assembly  63  moves along the path to deposit the material. In this embodiment, a line can also be used for the temperature sensor, to achieve some mechanical averaging of the signal sent to the controller. In either case, the controller  50  is configured to use the received temperature values to average the temperature over time as would be understood by those skilled in the art. 
         [0063]    During the deposition of each subsequent layer, the Z Axis Actuator  21  positions the Deposition Nozzle Module  30  at a predetermined height from the top of the part, as predetermined by previous experimental testing of the apparatus. The Electronic height gauge  67  determines if any areas of the part are lower than desired. In another mode of operation, the arc provided by the nozzle assembly  63  is used to obtain a localized visual reference point corresponding to the height of the part being formed. 
         [0064]    The build is correctable by going back over the low sections, changing speed and deposition parameters, or aborting the process if the part height or position is found to be out of an acceptable tolerance. 
         [0065]    Note that it is envisioned that the X-Y starting point for each layer, is moved slightly relative to a previous starting point of the previous layer, so that there is minimal effect from the transient deposition during arc start up. Furthermore, material deposition proceeds along a continuous path without interruption to minimize the number of starting points. 
         [0066]    In an alternate operating mode, the use of an analysis of deposition voltages, currents, and other deposition supply characteristics which are affected by the deposition process, are used to monitor height. Common in the welding industry is the use of voltage monitoring to determine arc length and “stick out” which is the length of wire protruding from a MIG nozzle during a welding operation. With a known distance for arc length, a known Deposition Nozzle Z axis position, and a known “stick-out”, dynamic determination of material height in the deposition zone is a simple subtraction operation. This result is then be used to control the deposition rate, robotic motion speed, and maintain optimal build height either in conjunction with height sensor  66  and other sensors or as a standalone control. 
         [0067]    In one or more embodiments of the present invention, the wire used in forming the part is a standard MIG welding wire but having a reduced amount of silicon. A typical silicon concentration for a currently available E70 MIG wire is in the range of 0.5-0.9% SI. In one or more embodiments for use herein, the feedstock wire includes a silicon level of approximately 0.2% or below SI. 
         [0068]    Given that the Inert Gas  36  is typically heavier than air, the inert gas  36  tends to sink to the bottom of the Enclosure  40 . The Inert Gas Level  46  is continuously monitored so that the deposition process is always performed in an inert gas environment. Furthermore, monitoring of other, undesirable gases, such as hydrogen near the deposition site, is performed to help ensure optimum conditions for the metal deposition process. In this way, porosity, material embrittlement, and other deposition flaws are reduced or avoided resulting in a part that has the desired mechanical properties. 
         [0069]    Once the last layer is deposited and the part is therefore completed, the inert gas is purged from the enclosed space with the Vent Fan  47  and through a filter to clean the air of undesirable fumes. The Deposition Nozzle Module  30  is moved out of the way by the Robotic Actuator System  20  and the build table  5  is raised out of the quenchant  10  to allow the part to be unloaded from the apparatus. At least one door in the enclosure  40  provides access to remove the completed part. 
         [0070]      FIG. 4  illustrates the optional use of two MIG Welding Nozzles  91  to rapidly deposit metal without the need for a conductive Build Table  5 . Either an AC waveform or DC− polarity is provided by one Large Feed Wire  92  and DC+ polarity is provided by another Small Feed Wire  93 . In one or more embodiments, other combinations of waveforms optimized to achieve, in one or more embodiments the semi-molten state of the Large Feed Wire  92  are provided. The size of the wires and the relative speed of the wire feeds are set in conjunction with the waveforms, voltages, currents and polarities so that the Small Feed Wire  93  softens the Large Feed Wire  92  but does not completely melt it to the “droplet” stage. Thus, the Large Feed Wire  92  is then able to be laid down in a semi-molten state to make the first pass, with no need for conduction through the Build Table  5 . After the first layer is deposited, the waveforms are switched so that one or both of the wires produces fully molten droplets on the subsequent passes in order to help minimize the heat input to the part and to optimize bonding and other deposition qualities. 
         [0071]    Varying the heat input and the quenching affects the material properties in the deposited material, as well as providing control over warpage tendencies. As depicted, the deposition nozzles are angled towards each other so that the Large Feed Wire  92  and Small Feed Wire  93  intersect at a convenient distance above the build table  5 . Practitioners in the art will readily recognize that the relationship between an included angle between the deposition nozzles and the height above the build table  5  allows for variations in order to achieve optimum results and either or both angles are varied as needed. 
         [0072]      FIG. 5  illustrates an alternate embodiment which substitutes a non-consumable TIG Electrode  100  for the Small Feed Wire  93  in the above embodiment, such as is commonly used in Tungsten Inert Gas (TIG) welding. In this embodiment, the TIG Electrode  100  is used to soften the Large Feed Wire  92  to allow deposition of the material, allowing switching of current between the TIG Electrode  100 , the MIG Large Feed Wire  92 , and the Build Table  5  if a metallic build table surface is used. This allows controlling the initial deposition as well as subsequent passes by using suitable configurations of currents for each purpose. 
         [0073]    It should be understood that a combination of a Large Feed Wire  92 , a smaller wire and a TIG electrode, or more than one wire of equal or different diameters might be used to practice the invention, or that a single wire with a TIG Electrode  100  might be used to deposit material onto the Build Table  5  as initially described herein in lieu of feeding current through the feed wire and using a typical MIG process. 
         [0074]    In the one or more embodiments, regardless of the type of nozzle or nozzles installed, the size of the feedstock wire and the relative speed of the wire feeds are determined in conjunction with the waveforms, voltages, polarity, and currents to be used by the deposition nozzles. It should be noted that the first pass requires different settings than subsequent passes and on subsequent passes after the first pass, the configuration and parameters are such as to create some localized heating of the formerly deposited layer in the deposition zone, either by current flow or by proximity such that acceptable bonding is achieved. 
         [0075]      FIG. 6  illustrates an embodiment of the fabrication system  1  including a build table  102  disposed within a tank  104 . The tank  104  is filled with a quenchant and the build table  102  is lowered into the tank  104  by supports  106 , as previously described. In this embodiment, the build table  102  includes a frame  108  which defines a planar support plane. The frame  108  includes a plurality of cutouts  110 , each of which is configured to accommodate a removable platen  112  having a build surface  114 . The build surface  114  includes non-stick deposition surface including a high-temperature-resistant flat plate  116  which provides a smooth flat plane for the molten and semi molten material being deposited. The flat plate  116  includes a sufficient thickness configured to provide the necessary strength to support the part being fabricated. The shape and size thereof is sufficient to avoid warping when subjected to the heat of deposition. In one or more embodiments, the flat plate  116  includes a copper or a copper alloy. 
         [0076]    As can be seen in  FIG. 6 , each of the cutouts  110  is formed in the frame  108  with crosspieces  118  of appropriate shape to receive one of the platens  112 , wherein one or more edges  120  abut an edge  120  of an adjacently located platen  112 . In an embodiment, the adjacent edges  120  form a seam that is sufficiently narrow to substantially prevent the heated material from entering the gap between the adjoining platens  112 . While a table  102  having twelve cutouts  110  is illustrated, the present disclosure is not limited to a table  102  having twelve cutouts, and more or less cutouts of varying sizes are possible. 
         [0077]    As seen in  FIG. 6  and  FIG. 7 , platens  112  include a flat plate  116 . Fixedly attached to the underside surface of the flat plate  116  is a plurality of heat dissipating fins  122 . Each of the fins includes a length sufficient be in contact with the quenchant  10  and in sufficient quantity to draw the heat from the flat plate  116  and to dissipate the heat into the quenchant  10 . The length of the fins  122 , extending from the underside surface of the flat plate  116 , is such that when the build table  102  is in the uppermost position, the ends of the fins  124  are immersed in the quenchant  10 . In this manner, the quenchant  10  is below the surface  114  of each of the flat plates  116  and does not interfere with the deposition. The number and length of the fins  124  can vary and still achieve the desired heat transfer. 
         [0078]    As further illustrated in  FIG. 7 , the plate includes an engaging portion  126 , which in the disclosed embodiment, is formed as part of the fin structure. Different engaging structures are possible. The engaging portion defines a channel  128 , between the flat plate  116  and the engaging portion  126 , and is configured to receive a portion of the frame  108 , which in the embodiment of  FIG. 6  is a portion of one of the crosspieces  118 . In this way, each of the platens  112  is forced into maintaining good electrical contact with the table  102  during the formation of a part to provide the electrical connection to strike and maintain a consistent arc. 
         [0079]    Referring again to  FIG. 6 , the tank  104  includes a back wall  130  having a horizontally located rectangular aperture  132 , also known as a weir, which provides for the overflow of quenchant through the aperture  132  and into an overflow reservoir  134 . The overflow reservoir  134  includes a capacity sufficient to collect overflow of quenchant as the table  102  and the part being formed are lowered into the tank  104 . The aperture  132 , therefore, provides precise fluid level control of the quenchant remaining in the tank  104 . The quenchant in the overflow reservoir  134  is cycled back into the tank for circulation and then pumped back into the tank  104  when the build is complete. 
         [0080]    A heat exchanger  135  includes a radiator  136 , located at the back wall  130 , and a fluid exchange device  138 , fluidically coupled to the radiator  136 . The fluid exchange device  138  includes a pump which circulates a temperature controlled fluid, such as a refrigerant, through the radiator  136  thus cooling the quenchant located in the tank  104 . In one or more embodiments, a sensing device is immersed in the quenchant to determine the temperature of the quenchant. Eliminating the heat exchanger  135  and circulating the quenchant through the fluid exchange device is equivalent. 
         [0081]    The fluid exchange device  138  is configured to adjust the temperature of the temperature controlled fluid moving through the radiator  136 . The temperature of the quenchant  10  located in the tank  104  is thereby raised or lowered to provide a temperature for controlling the temperature of the part being formed. In this way, the build process is optimized for providing usable parts having the desired properties. 
         [0082]      FIG. 8  illustrates a portion of the platen  108  including the flat plate  116  defining the surface  114 . As described above, the surface  114  includes a non-stick deposition surface which provides a smooth flat plane for the molten and semi molten material being deposited. Using the deposition nozzle module  30  of  FIG. 1  including the deposition nozzle assembly  63 , a part is formed through the deposition of molten or semi-molten metal or metal-like material at the surface  114 . To begin the formation of the part, a plurality of spots  140  of the material are deposited at spaced locations on the surface  114 . To deposit the spots  140 , the power supply  35  is adjusted to deliver a current to the nozzle assembly  63  which is sufficient to adhere the spots  140  to the surface  114 , in a relatively secure fashion, such that a metal bond is formed between the surface material and the deposited spot material. If the plate  116  is formed of copper, for instance, the power is adjusted sufficiently to break through the oxidation at the surface to provide good, consistent, electrical contact. 
         [0083]    Each of the spots  140  includes a mound of material, which provides a stable structure electrically connected to the plate  116  upon which the remainder of the part is formed. Once the spots  140  are deposited, a bead of molten or semi-molten metal or metal like material  142  is deposited between each of the spots  140  to connect one spot  140  to the next spot  140  or alternatively over or next to the spots  140 . In forming the beads  142 , the power of the power supply is adjusted to provide a current typically lower than the current used to form the spots  140 . In this fashion, the beads  142  do not form a metal bond with the surface  114 , but do form a bond with the spots  140 . Once a first layer  144  of the part, including spots  140  and beads  142  are formed, additional layers  146  formed of continuous beads of material are deposited on previously formed layers, as described above. As a result, the deposition nozzle assembly  63  does not act as a welder, but instead is used to merely melt the metal wire fed through the nozzle. The power does not bond the metallic beads  142  to the no stick plate  116 . The application of the beads  142  are either continuous or segmented as illustrated and is varied depending on the spacing of the spots  140  and other parameters including sensed temperatures, material types, and speed of deposition. 
         [0084]    The part is easily removed from the build surface  114  by tapping the part or the build surface or by the application of a minor impact force to the part or build surface. 
         [0085]    The power setting of the power supply  35  during the deposition of the beads  142  and subsequent layers  146  is not at a level typically used in a metal to metal welding process, but is reduced from that level and is generally a fraction of that used in a typical welding process. In one embodiment, the power level being used is approximately twenty five percent or less than the power typically required in a welding operation for the same metal. The power supply setting can also be adjusted to vary the current or voltage used to form the layers in response to the temperature being sensed by the temperature sensor  66 . For instance, as additional layers are formed, the temperature being sensed changes due to part geometry and the power supply setting is adjusted accordingly. In the one or more embodiments, the polarity of the electrode of the nozzle assembly  63  is alternated from positive to negative depending on the layer and material of deposition. To facilitate the change in polarity, a silicon controlled rectifier (SCR) is used within the wire feed circuit of the nozzle assembly and build table to change polarity as necessary. 
         [0086]    The controller  50  is configured to control the application of the material being deposited by the nozzle module  30  during formation of a part. The controller includes one or more computer processors configured to operate according to software based routines which are written to implement the embodiments of the invention. Whether implemented as part of an operating system or a specific application, component, program, object, module or sequence of instructions the software routines are hereafter referred to herein as “computer program code”, or simply “program code”. The computer program code typically comprises one or more instructions that are resident at various times in various memory and storage devices in the controller, and that, when read and executed by one or more processors in the controller, causes the robotic actuators, welding power supply, and chilling device to perform the steps necessary to execute formation of the object or parts. 
         [0087]    In addition, it should be appreciated that the method or methods described herein are implementable in various program code and should not be limited to specific types of program code or specific organizations of such program code. Additionally, in view of the typically endless number of manners in which computer programs may be organized into routines, procedures, methods, modules, objects, and the like, as well as the various manners in which program functionality may be allocated among various software layers that are resident within a controller or computer if used, (e.g., operating systems, libraries, APIs, applications, applets, etc.), it should be appreciated that the invention is not limited to a specific organization. 
         [0088]    The controller  50  and resident program code is configured to form a 3 dimensional metallic part of any shape through the control of a number of parameters and conditions including material temperatures, hold times, deposition speed, tool identification, and power settings of the power supply to optimize deposition rates for a given layer of the part. In addition, as described herein different materials and different wire sizes can be used, either in a single nozzle assembly or in multiple nozzle assemblies which are changed by hand or automatically in the system  1 . Weld parameters and temperature sensor emissivity is also controllable for different materials. 
         [0089]      FIG. 9  illustrates a side view of an embodiment of a nozzle head fixture  150  and a nozzle assembly  152 . The nozzle head fixture  150  is configured to engage a plurality of different nozzle assemblies  152 , each of which is directed to forming a bead of material of a different type. For instance, a plurality of nozzle assemblies  152  are parked at a docking station (not shown) for intermittent use during the formation of a part. One of the nozzle assemblies  152  is selected by the controller  50 , based on the type of material to be deposited, and that nozzle assembly  152  is picked by the nozzle head fixture  150  from the appropriate location of the docking station where the pick is made. The nozzle head fixture  150  is coupled to the Z axis actuator  21  Z-rod  50  of  FIG. 1  which in turn is coupled to wrist actuator  156 . The wrist actuator  156  is configured to rotate the head fixture  150  about the z-axis defined by the z-rod  50 . A temperature probe  160 , such as that previously described, is coupled to the nozzle head fixture  150  and is configured to sense the temperature of the product being formed. In another embodiment, each of the nozzle assemblies includes a temperature probe. A tool bracket  164  which is coupled to a torch portion  166  of the nozzle assembly  152 . A nozzle head  167  extends below the tool bracket  164 . A flexible conduit  168  coupled to the torch portion  166  supplies the predetermined type of wire and gas. The master bracket  158  includes an aperture  170  configured to receive a portion of the tool bracket  164 . As seen in  FIG. 9 , the tool bracket  164  includes a channel  172  configured to hang the tool from the docking station or other storage rack when not in use. In one or more embodiments, the storage rack is located within the enclosure  40 . 
         [0090]      FIG. 10  illustrates a back view of the nozzle head fixture  150  and the nozzle assembly  152 . The nozzle head fixture  150  is configured to support a position sensor  176 . 
         [0091]      FIG. 11  illustrates a front perspective view of the nozzle head fixture  150  and the docked nozzle assembly  152 . As can be seen, the beam of the temperature sensor extends below the bottom edge of the tool bracket  164 . 
         [0092]      FIG. 12  illustrates a perspective view of a part  180  being formed with a part build fixture  182 . The part build fixture  182  is located adjacently to a side  184  of the part  180  and includes a non-stick surface  186  upon which a shelf  188  is formed by the deposition process. The part fixture  182  provides support for the shelf  188  such that the shelf  188  extends from the wall  184  in a cantilever and accurate fashion. Removal of the part fixture  182 , after completion of the part  180  leaves a space or void below the shelf  188 . Additionally, a specially made form  190  of non stick material is added to during formation, as needed, to provide a desired geometry to the finished part  180 . Alternatively, cavities, elevated surfaces and smooth surfaces are similarly formed. The use of such fixtures and forms provides for a more accurate control of the geometric shapes, dimensional sizes and finishes of the objects being formed. In the one or more embodiments, however, the formation of overhangs, arches and similar structures are formed without the use of supplemental supports. The formation of these types of structures are provided with the addition of one additional axes of movement which enables the nozzle to be angled upwards through an selectable and controlled angle of 90 degrees or more to enable the deposition of material in a horizontal direction, a direction angled from horizontal, or upwards from horizontal. 
         [0093]    While exemplary embodiments incorporating the principles of the present invention have been disclosed herein, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.