Abstract:
An electron beam welding apparatus includes an electron beam generator for selectively emitting an electron beam into a weld chamber. The electron beam welding apparatus further includes a measuring device for detecting an intensity of the electron beam and a slit plate disposed between the electron beam generator and the measuring device. The slit plate permits passage of the electron beam through a slit formed in the slit plate, and the measuring device determines a location of the electron beam in dependence upon the detected intensity of the electron beam passing through the slit. The electron beam welding device further includes thermally non-conductive and/or absorbing materials strategically placed between parts to be welded and all components of mechanical assemblies requiring precision location.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application Ser. No. 60/652,465, filed on Feb. 11, 2005, and herein incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates in general to a method and apparatus for improved electron beam welding, and deals more particularly with a method and apparatus for improved electron beam welding that substantially eliminates the temperature distortion of tooling within the welding chamber while providing precise confirmation of the electron beam position.  
       BACKGROUND OF THE INVENTION  
       [0003]     Electron beam welding (EBW) is a fusion joining process that produces a weld by impinging a beam of high energy electrons upon a weld joint. The high energy electrons provide the necessary heat to fuse, or weld, two or more workpiece articles together along the weld joint.  
         [0004]     Known EBW assemblies typically utilize measurement devices, like optical viewing systems, to determine the approximate location of the electron beam. Typically, Faraday Cups are known to be used for precisely measuring the electrical quality of the electron beam, but is not known to be used to identify the location of the generated electron beam.  
         [0005]     Many high precision electron beam welds are performed in a weld chamber that enjoys some measure of a vacuum, most often a high vacuum. In practice, the workpiece to be welded is held (by means of, e.g., a collet or other fixing means) opposite the emission end of the electron beam generating device while the workpiece is mechanically moved beneath the beam, or the electron beam generator is moved above the workpiece, or the electron beam is deflected by electromagnetic means, or the like, or by some combination of the foregoing.  
         [0006]     As is also known, one of the advantages of the electron beam welding process compared to any other fusion welding process is its flexibility, which is due to all welding parameters being electrical in nature, including the electron beam itself. Without any change of hardware, process parameters can be varied in a wide range simply by changing control settings. For instance, the process allows for dynamically deflecting and moving the electron beam in order to join two stationary pieces together. The electromagnetically deflected beam can be positioned on the joint with very high accuracies of less than 0.001 inches, which is comparable to the precision of mechanical means, but avoids any wear over time that is known to alter the precision of such mechanics.  
         [0007]     EBW assemblies are therefore utilized in the manufacture of many high precision components. Economic and other production concerns have increased pressure to manufacture such components in a mass production environment, to which the EBW assemblies are initially well suited.  
         [0008]     There are, however, several concerns related with the mass production of components via an EBW assembly that can potentially affect the accuracy of the EBW assembly as a whole. Chief amongst these concerns is the problem of thermal drift, or distortion, of those tooling surfaces exposed to the thermal radiation effects of the electron beam impingement device.  
         [0009]     In particular, the heat generated by the electron beam conducts through the workpiece and thereby over time heats up all tooling within the weld chamber. The heat radiation coming from the hot weld also heats up all surrounding areas of the EBW assembly. Thus, the heat that is inherently generated via the operation of the EBW assembly during the mass production of components very often causes a displacement, drift or distortion of all tooling within the weld chamber. That is, the heat generated as a by-product of the EBW process can cause the movement of the collet or fixing method with respect to the emission end of the electron beam generator or affect the relative positioning of other tooling within the weld chamber. Over time, the amount of thermal displacement of the tooling can exceed that of the accuracy of the electromagnetic deflection system resulting in the beam to workpiece positioning accuracy being determined by the tooling.  
         [0010]     As will be appreciated, the mass production of components, if done over and over again within the same weld chamber, and utilizing the same tooling, exacerbates the difficulties of thermal distortion or drift. Thus, there exists a need to address the thermal concerns of known EBW assemblies while providing positive measurement of the electron beam position relative to the tooling even though the tooling is drifting or distorting due to heat.  
         [0011]     Over time, the amount of thermal displacement (e.g. within one production shift) of conventional tooling (stationary or moving) can be larger than the achievable accuracy of the beam positioning, meaning that the limiting factor for overall beam-to-joint accuracy lays within the mechanical design of the tooling. In such an environment where highest accuracies are required to satisfy the demanded specification, the tooling design has to consider heat sources and related thermal growth over time.  
         [0012]     The demand for minimal thermal growth of the tooling over time (e.g. one shift) can be solved with a combination of active cooling and the use of materials with low thermal conductivity, which restricts the thermal flow coming from the part while welding. The present design allows the temperature to be balanced in the tooling assembly thus minimizing thermal growth over time and thereby maintaining the workpieces&#39; positioning accuracy within allowable technical limits. In addition, a measuring tool has been designed and integrated into the system for the use as a control feature. It allows the machine operator to automatically determine the accuracy and stableness of beam deflection and tooling thermal displacement in production before each assembly gets welded.  
         [0013]     With the forgoing problems and concerns in mind, it is the general objective of the present invention to provide a method and apparatus for improved electron beam welding that substantially reduces or eliminates the temperature distortion of tooling within the welding chamber and provides an accurate method of determining the position of the electron beam relative to the tooling.  
       SUMMARY OF THE INVENTION  
       [0014]     It is an object of the present invention to provide an improved electron beam welding assembly.  
         [0015]     It is another aspect of the present invention to provide an improved electron beam welding assembly that has an increased ability to ameliorate the effects of thermal distortion or displacement of the tooling inside the weld chamber.  
         [0016]     It is another aspect of the present invention to provide an improved electron beam welding assembly that includes a plurality of various insulating elements to protect differing areas from thermal radiation within the weld chamber.  
         [0017]     It is another aspect of the present invention to provide an improved electron beam welding assembly that positions an insulating element between the beam generating device and the measuring tool.  
         [0018]     It is another aspect of the present invention to provide an improved electron beam welding assembly that positions a plurality of insulating elements about the detection chamber and Faraday Cup assembly, thereby isolating the tooling and measuring device from thermal radiation from the Faraday Cup assembly within the weld chamber.  
         [0019]     It is another aspect of the present invention to provide an improved electron beam welding assembly that provides cooling channels through the insulating plates in order to protect the tooling of the electron beam welding apparatus from thermal radiation.  
         [0020]     It is another aspect of the present invention to provide an improved electron beam welding assembly that is capable of precisely, and repeatedly, detecting and adjusting the position of the electron beam.  
         [0021]     It is another aspect of the present invention to provide an improved electron beam welding assembly that utilizes a slit plate in conjunction with a Faraday Cup assembly and control system to precisely, and repeatedly, detect and adjust the position of the electron beam.  
         [0022]     It is another aspect of the present invention to provide an improved electron beam welding assembly that utilizes thermally non-conductive pins, or other contacts, in the workpiece holding fixture, thus protecting the workpiece holding fixture from the distorting effects of thermal conduction and radiation.  
         [0023]     These and other objectives of the present invention, and their preferred embodiments, shall become clear by consideration of the specification, claims and drawings taken as a whole. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]      FIG. 1  is a schematic illustration of an improved electron beam welding (EBW) assembly, in accordance with one embodiment of the present invention.  
         [0025]      FIG. 2  illustrates a top plan view of the beam position measuring tool of the improved EBW assembly.  
         [0026]      FIG. 3  illustrate section A-A, taken through the beam position measuring tool shown in  FIG. 2 .  
         [0027]      FIG. 4  illustrate section B-B, taken through the beam position measuring tool shown in  FIG. 2 .  
         [0028]      FIG. 5  illustrates a top plan view of the protective platen of the improved EBW assembly.  
         [0029]      FIG. 6  illustrates a side plan view of the protective platen of  FIG. 5 .  
         [0030]      FIG. 7  illustrates a top plan view of an alignment cover for use with the protective platen of  FIGS. 5 and 6 .  
         [0031]      FIG. 8  illustrates a side plan view of an alignment cover for use with the protective platen of  FIGS. 5 and 6 .  
         [0032]      FIG. 9  illustrates a front plan view of an alignment cover for use with the protective platen of  FIGS. 5 and 6 .  
         [0033]      FIG. 10  illustrates a top plan view of a collet and insulating pins for use in holding the workpiece that is to be welded, in accordance with one embodiment of the present invention.  
         [0034]      FIG. 10A  illustrates a side plan view of a collet, as shown in  FIG. 10 .  
         [0035]      FIG. 10B  illustrates a section through the collet, shown in  FIG. 10 .  
         [0036]      FIG. 11  illustrates a top plan view of a collet and insulating pins for use in holding the workpiece that is to be welded, in accordance with another embodiment of the present invention.  
         [0037]      FIG. 11A  illustrates a side plan view of a collet, as shown in  FIG. 11 .  
         [0038]      FIG. 11B  illustrates a section through the collet, shown in  FIG. 11 .  
         [0039]      FIG. 12  illustrates a top plan view of a rotary assembly for moving the collet used with the present EBW assembly.  
         [0040]      FIG. 13  illustrates a side plan view of the rotary assembly shown in  FIG. 12 .  
         [0041]      FIG. 14  illustrates a section (A-A) through the rotary assembly shown in  FIG. 13 .  
         [0042]      FIG. 15  illustrates another section (B-B) through the rotary assembly shown in  FIG. 13 .  
         [0043]      FIG. 16  illustrates a precision locating assembly for use with the EBW assembly, in accordance with one embodiment of the present invention.  
         [0044]      FIG. 17  shows a section taken through the precision locating assembly of  FIG. 16 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0045]      FIG. 1  is a schematic illustration of an EBW assembly  100 , in accordance with one embodiment of the present invention. As shown in  FIG. 1 , a weld chamber  102  encloses a workpiece and fixturing assembly  106 , a beam position measuring tool  108  and a protective platen  110 . As will be appreciated, operation of the various components noted may be directed via an integrated control system  112 . It will be readily appreciated that  FIG. 1  is a schematic representation only, and as such, does not represent specific structure or specific structural orientation with respect to the EBW assembly  100 .  
         [0046]     In contrast with known EBW assemblies, the beam position measuring tool  108  operates in conjunction with the control system  112  to not only initialize the EBW assembly  100  prior to its first use, but is also employed to help monitor and control the movement of the electron beam produced by the electron beam generator device  104 . In this regard, the beam position measuring tool  108  provides feedback signals to the control system  112  so as to continually take into account the measured or detected position of the electron beam, thereby enabling precise control over the movement of the electron beam.  
         [0047]      FIG. 2  illustrates a top plan view of the beam position measuring tool  108 , while  FIGS. 3 and 4  illustrate sections A-A and B-B respectively, taken through the beam position measuring tool  108  shown in  FIG. 2 . It will be readily appreciate that, as illustrated in  FIGS. 3 and 4 , a known Faraday Cup assembly  115  (shown schematically) is housed within a detection chamber  113  created by a frame and top plate  114  and defined within the beam position measuring tool  108 .  
         [0048]     Referring to  FIGS. 2-4  in combination, it will be seen that the beam position measuring tool  108  consists, in substantial part, of an overall frame having a top plate  114 , a slit plate  120  and a plurality of insulating elements, or plates,  116 . As best shown in  FIG. 2 , an internal enclosure of ceramic plates  116  (shown in phantom), or other thermally insulating material, are disposed within the tool  108  so as to provide the frame and slit plate  120  some measure of thermal protection from the Faraday Cup assembly  115  housed within the detection chamber  113 .  
         [0049]     That is, during operation of the EBW assembly  100  the Faraday Cup assembly  115  will absorb and radiate increasing amounts of thermal radiation due to the incident electron beam B. It is therefore one important aspect of the present invention that the thermally insulating elements  116  are disposed adjacent to the Faraday Cup assembly  115  such that the elements  116  will protect the frame and slit plate  120 , as well as the other components within the weld chamber  102 , from the effects of thermal radiation emanating from the Faraday Cup assembly  115 .  
         [0050]     Also illustrated in  FIG. 2  are two alignment slits  118  (although it will be readily appreciated that at least one, but any number, of alignment slits may alternatively be present) which are formed in the slit plate  120 . The slit plate  120  is preferably formed as a tungsten plate (or the like), and the two alignment slits  118  are opened to the path of the electron beam, so as to assist in the calibration of the position of the electron beam.  
         [0051]     The frame with top plate  114  is thermally and electrically connected to the same support structure as the fixturing assembly  106  to ensure thermal stability between these two devices, thereby minimizing any relative movement between them and ensuring a conductive path to ground for any electrons contacting the slit plate  120 . Alternately, or in addition to, the frame with top plate  114  could include conduits or channels for active cooling.  
         [0052]     As is typical of Faraday Cup installations, the Faraday Cup  115  is electrically isolated from the machine and an insulated wire is passed through the wall of the vacuum chamber  102  and connected to the machine control system  112 . Any electrons from the electron beam B that impinge on an alignment slit  118  will pass through the slit and be captured by the Faraday Cup  115 , with the results passed through to the control system  112  for analysis.  
         [0053]     Unique to this application, the positioning of the slit  118  provides a precise reference of the location of the beam relative to the fixturing assembly  106 , as follows: If the electron beam B is programmed to pass through slit  118 , and it does as confirmed by the Faraday Cup  115  housed in chamber  113  and related electronics, the position of the electron beam B is precisely known and confirmed. If a significant number, or a predetermined percentage, of electrons are not detected by the Faraday Cup  115  as passing through the slit  118 , the position of the programmed beam path is thereby known to be astray. Once detected as being astray, the altering of the beam path can be accomplished automatically or manually by the control system  112 .  
         [0054]     It is therefore an important aspect of the present invention that the beam position measuring tool  108  which incorporates a Faraday Cup assembly  115  is utilized to detect the position of the electron beam B. That is, as opposed to known electron beam welding devices which may utilize a Faraday Cup to determine the electrical quality of the emitted electron beam, the present invention advantageously makes use of the Faraday Cup assembly  115  integrated into the beam position measuring tool  108  to determine the quality, as well as the location/position, of the electron beam B, via the integrated use of the slit plate  120  in conjunction with the control system  112 .  
         [0055]     Thus, the present invention utilizes the detected intensity of the generated electron beam to actively monitor, and automatically or manually compensate for, any deviation of the position of the electron beam B, as caused by the thermal displacement of the tooling within the weld chamber  102 .  
         [0056]     Additionally, the slit plate  120  and its supporting frame with top plate  114  are thermally isolated from the Faraday Cup  115  as to minimize heat transfer from the Faraday Cup  115  to the support frame which would cause undesired thermal distortion of same resulting in a displacement of slit  118 .  
         [0057]     It is therefore another important aspect of the present invention to substantially reduce or eliminate the detrimental effects of thermal distortion/displacement of the frame and slit plate  120  and resulting distortion/displacement of the slit  118  by surrounding the detection chamber  113  (and Faraday Cup) with an enclosure of thermally insulating plates  116 , which may be ceramic, or other insulating materials. These insulting elements  116 , effectively isolate the frame and slit plate  120  from thermal radiation emitted by the Faraday Cup that may, over time, affect the precision of slit  118  position.  
         [0058]     Returning now to  FIG. 1 , in operation the electron beam generator device  104  emits a high energy electron beam B which is incident upon the workpiece. The heat radiation stemming from the welding process can often cause thermal distortion of the conductive portions of the EBW assembly  100 , inclusive of the frame that connects all of the components within the EBW assembly  100  (i.e.,  106 ,  108  and  110 ).  
         [0059]     It is therefore an important aspect of the present invention that the EBW assembly  100  include devices that protect the frame, and the associated tooling, from such undesirable thermal radiation. These devices and methods include: 1) the protective platen  110  in the area between the workpiece and fixture assembly  106  and the beam position measuring tool  108  (shown in  FIG. 5 , and to be discussed later); 2) thermal barriers between the Faraday Cup and the beam position measuring tool  108  (e.g., plates  116 ; described previously); 3) providing thermally conductive connections between the beam position measuring tool  108  and the system frame which also mounts the fixture assembly (as described previously); 4) an alignment cover  130  to protect the beam position measuring tool  108  from thermal radiation from the heated workpiece being welded; and 5) thermal barriers incorporated into the precision locating assembly (shown in  FIGS. 16-17 , and to be discussed later).  
         [0060]     Turning now to  FIGS. 5 and 6  which more dearly illustrate the protective platen  110 . The protective platen  110  is envisioned to be formed from thermally non-conductive materials, such as but not limited to ceramics or the like. Moreover, the protective platen  110  may also be fashioned from a thermally conductive material, such as copper, provided that a cooling channel and/or conduit is formed therein to provide a cooling effect to the protective platen  110 . It will be readily appreciated that the protective platen  110  may also be formed from a thermally non-conductive material equipped with cooling channels and/or conduits.  
         [0061]      FIG. 5  illustrates a top plan view of the protective platen  110 . As discussed previously, the protective platen  110  includes one or more cooling channels and/or conduits  122  formed, molded or otherwise disposed therein. The cooling conduits  122  include an inlet aperture  124  and an outlet aperture  126  through which a supply of cooling fluid is passed. The cooling fluid may be any fluid capable of absorbing thermal energy, including but not limited to water, oil, liquefied nitrogen or the like.  FIG. 6  illustrates a side view of the protective platen  110 .  
         [0062]     It is therefore another important aspect of the present invention that by placing the thermally non-conductive protective platen  110  above the beam position measuring tool  108 , the beam position measuring tool  108  is thereby protected from the most damaging effects of the thermal radiation produced during electron beam welding. Moreover, by optionally and selectively cooling the protective platen  110  with the cooling channels/conduits  122 , the thermally insulating effects of the protective platen  110  may be further increased.  
         [0063]     Returning to  FIG. 5 , two alignment apertures  128  are formed in the protective platen  110  so as to selectively expose the alignment slits  118  in the beam position measuring tool  108  below. That is, an automated alignment cover  130  (shown in plan and side views, respectively, in  FIGS. 7-9 ) is controlled via the control system  112  (or manually) to uncover the alignment apertures  128 , thus permitting the electron beam to selectively enter through the alignment slits  118  and be detected by the beam position measuring tool  108 , as discussed previously.  
         [0064]      FIGS. 10 and 11  illustrate yet another important aspect of the present invention. As shown in  FIG. 10 , a collet  132  is designed to selectively close about, and hold, the workpiece to be welded. A collet is shown by way of example, but it will be readily appreciated that any workpiece holding fixture would also be applicable to the concept of the present invention.  
         [0065]     In order to assist in the thermal protection of the collet  132  itself, the present invention contemplates disposing a plurality of ceramic pins  134  (or other thermally isolating material appropriate for the workpiece holding function) about the inner periphery of the collet  132 , thereby providing a thermally non-conductive interface between the heated workpiece and the body of the collet  132 . The ceramic pieces can be loosely connected to the collet and provide high accuracy, or alternatively, they may be permanently bonded to the collet and grounded in place for the highest possible accuracy of the system.  FIG. 11  is much the same as  FIG. 10 , however the collet  132   a  enjoys an array of six ceramic pins  134   a  disposed about the inner periphery of the collet  132   a.    
         [0066]     While  FIGS. 10 and 11  illustrate a plurality of ceramic pins  134 , the present invention is not so limited in this regard as the thermal barrier may alternatively be of any appropriate size or configuration.  FIGS. 10A and 10B  illustrate a side view and a section A-A, respectively, of the collet  132 , while  FIGS. 11A and 11B  illustrate a side view and a section B-B, respectively, of the collet  132   a.    
         [0067]     As discussed previously, the electron beam may be electromagnetically deflected (by a known process and apparatus) during the welding process. The electron beam generator  104  and/or the collet  132  (or other fixture) may also be rotated or otherwise shifted during welding so as to impart a spiral or curved weld to the workpiece. In this regard,  FIG. 12  illustrates a top plan view of a rotary assembly  140  for moving the collet  132 .  FIG. 13  illustrates a front plan view of the rotary assembly  140 , while  FIGS. 14 and 15  shown sections A-A and B-B respectively of the rotary assembly shown in  FIG. 13 .  
         [0068]     As best seen in  FIGS. 13-15 , the rotary assembly  140  includes one or more cooling channels/conduits  142  formed therein for providing the rotary assembly  140  with some measure of thermal stabilization during the welding process. Inlet and outlet distal ends,  144 , are provided to supply the cooling channels/conduits  142  with a suitable cooling fluid, as discussed previously.  
         [0069]      FIG. 16  illustrates a precision locating assembly  150  for use with the EBW assembly  100 , in accordance with one embodiment of the present invention.  FIG. 17  shows a section A-A taken through the precision locating assembly  150 . As shown in  FIGS. 16 and 17 , the precision locating assembly  150  includes a ceramic plate or housing  152  within which is supported a spring biased pin  156 . As will be appreciated, the spring biased pin includes a distal end which contacts the workpiece that is to be welded in the EBW  100 . In this manner, the spring biased pin  156  provides the necessary electrical connection of the workpiece, upon which the electron beam B is incident, to ground.  
         [0070]     In operation, the precision locating assembly  150  is pressed to the workpiece against the force of a biasing spring  153 , whereby the pin  156  is caused to retract into the housing  152  until the workpiece substantially contacts an insulating collar or tube  154  disposed about the pin  156 . While the pin  156  is preferably made from a conductive material so as to provide an exit path to ground for the electrons striking the workpiece, the housing  152  and the tube  154  are themselves formed from ceramic or other thermally insulating materials so as to isolate the precision locating assembly  150  from the thermal conduction of heat passing from the workpieces and through the pin  156 .  
         [0071]     It is therefore another important aspect of the present invention that the precision locating assembly  150  is also isolated and protected from undesirable thermal drift of its components, via the application of ceramic (or other materials having low thermal coefficients) thermal barriers, such as those that form the housing  152  and the tube  154 . By ensuring that the components of the precision locating assembly  150  do not experience thermal drift during operation of the EBW assembly  100 , the present invention substantially eliminates the erroneous positioning of the workpiece as it relates to the electron beam B.  
         [0072]     As will be appreciated by consideration of the embodiments illustrated in  FIGS. 1-17  that the present invention provides for the substantial elimination of thermal drift or distortion within the vital components of the EBW assembly  100  while repeatedly providing precise positioning of the joint to the electron beam. Moreover, by thermally insulating those vital components, the present invention enables the accurate and repeated mass production of workpieces welded in the weld chamber  102 .  
         [0073]     While the invention has been described with reference to the preferred embodiments, it will be understood by those skilled in the art that various obvious changes may be made, and equivalents may be substituted for elements thereof, without departing from the essential scope of the present invention. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention includes all equivalent embodiments.