Patent Publication Number: US-11034094-B2

Title: Welding machine for controlling direction and magnitude of weld force vector during a plastic welding operation

Description:
REFERENCE TO RELATED APPLICATIONS AND PRIORITY CLAIMS 
     This application claims the priority of application Ser. No. 15/668,104, filed Aug. 3, 2017, which claims priority of Application No. 62/371,701, filed 5 Aug. 2016, the entire contents of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to hot plate welding for joining one plastic part to another plastic part. 
     BACKGROUND 
     Plastic parts are commonly manufactured by a molding process, such as blow molding or injection molding, and then further processed by one or more operations such as boring, drilling, and/or welding. 
     Welding is a process for joining plastic parts together by melting plastic at a location in each part where a weld joint is to be created, then placing the parts together so that their melt pools merge together, and finally allowing the melt pools to solidify into the finished weld joint. 
     One type of plastic welding is referred to as contact welding. Contact welding comprises placing parts which are to be joined together in direct contact with a heating element, such as a hot plate, at locations on the parts where a weld joint is to be created, and then after sufficient melting of plastic, placing the parts together at the melt pools and allowing the melts to solidify. 
     Another type of plastic welding is non-contact welding which comprises placing a heating element a short distance from a part and using radiated heat, instead of direct contact, to melt plastic. 
     SUMMARY OF THE DISCLOSURE 
     A weld joint at which parts are to be joined has a shape which is a function of the geometries of the parts. Some parts may have shapes which allow the weld joint to lie in a two-dimensional flat plane. After melting of plastic at locations on the parts where a weld joint is to be created, the parts can be joined together by moving them together in a direction perpendicular to the two-dimensional flat plane and applying a controlled force in that same direction until the melts solidify. The direction in which the holding force is applied is called the weld force vector and the two-dimensional plane of the weld joint is called the weld plane. 
     Other plastic parts may have shapes which require the weld joint to be three-dimensional rather than flat. A three-dimensional weld joint can range from being relatively simple to relatively complex. An example of a relatively simple three-dimensional weld joint is one which has slight three-dimensional curvature. A relatively complex three-dimensional weld joint is one which is more extremely curved and/or irregular. An example of such a weld joint is one which joins housing parts of a housing of an exterior lamp assembly which is used in certain automotive vehicles. Such housings are styled by automotive designers to wrap around a corner of a vehicle. For example, a tail lamp assembly primarily faces rearward but also wraps around a side of a vehicle. The weld joint of such an assembly must be leak-proof, and if it is not, the assembly is scrapped. 
     When plastic welding is being considered for joining the housing parts of some proposed lamp assembly designs, analysis of the designs by plastic welding engineers and technicians may conclude that no weld joint geometries exist which would reliably assure manufacture of leak-proof assemblies in a mass-production operation. 
     The present invention provides a solution for such situations and can be applied to both contact welding and non-contact welding. 
     Briefly, the present invention comprises a hot plate welding machine which has two or more movements for varying direction and/or magnitude of the weld force vector when joining a first part to a second part after respective weld joint locations on both parts have been melted and the parts are placed together. One movement is that of one or both platens of a welding machine which are relatively moveable toward and away from each other along a first linear axis, which may be referred to as a z-axis. The present invention provides for moving at least one of the two plastic parts along at least one axis other than the z-axis, such as an x-axis, a y-axis, or both an x-axis and a y-axis. 
     One general aspect of the invention relates to a plastic welding machine for welding plastic parts together which comprises an upper platen and a lower platen which are relatively moveable on a frame toward and away from each other in a direction parallel with a z-axis. 
     A slide assembly comprises a base plate which is disposed against a surface of one of the upper and lower platens opposite the other of the upper and lower platens and which is fastened to the one of the upper and lower platens. 
     A first tooling half which is mounted on the other of the upper and lower platens comprises a fixture in which a first plastic part can be fixtured for welding. 
     The slide assembly comprises a tooling plate which faces the other of the upper and lower platens and which is movable relative to the base plate in a direction lying in a plane which is transverse to the z-axis. 
     A second tooling half is mounted on the tooling plate for movement with the tooling plate and comprises a fixture in which a second plastic part can be fixtured for welding to the first plastic part. 
     The slide assembly comprises a drive which is operable to move the tooling plate relative to the base plate in the direction lying in the plane which is transverse to the z-axis. 
     Another general aspect of the invention relates to a plastic welding machine for welding plastic parts together comprising an upper platen and a lower platen, which are relatively moveable on a frame toward and away from each other in a direction parallel with a z-axis, and a first slide assembly and a second slide assembly. 
     Each slide assembly comprises a base plate and a tooling plate which is movable relative to the respective base plate in a respective direction lying in a plane which is perpendicular to the z-axis. 
     The base plate of the first slide assembly is disposed against a surface of one of the upper and lower platens opposite the other of the upper and lower platens and is fastened to the one of the upper and lower platens, and the base plate of the second slide assembly is disposed against and fastened to the tooling plate of the first slide assembly. 
     A first tooling half is mounted on the other of the upper and lower platens and comprises a fixture in which a first plastic part can be fixtured for welding. 
     A second tooling half is mounted on the tooling plate of the second slide assembly for movement with the tooling plate of the second slide assembly relative to the base plate of the second slide assembly. 
     The second tooling half comprises a fixture in which a second plastic part can be fixtured for welding to the first plastic part. 
     The first slide assembly comprises a first drive which is operable to move the tooling plate of the first slide assembly relative to the base plate of the first slide assembly in a first direction which is perpendicular to the z-axis, and the second slide assembly comprises a second drive which is operable to move the tooling plate of the second slide assembly relative to the base plate of the second slide assembly in a second direction which is perpendicular to both the z-axis and the first direction. Another general aspect of the invention relates to the methods performed by the plastic welding machine, as claimed in application Ser. No. 15/668,104, now U.S. Pat. No. 10,562,232. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a portion of a plastic welding machine. 
         FIG. 2  is a perspective view of a portion of  FIG. 1  on a larger scale. 
         FIG. 3  is an enlarged elevation view of a portion of the plastic welding machine in the direction of arrow  3  in  FIG. 2 . 
         FIG. 4  is an end view in the direction of arrows  4 - 4  in  FIG. 3 . 
         FIG. 5  is an end view in the direction of arrows  5 - 5  in  FIG. 3 . 
         FIG. 6  is an enlarged perspective view of a portion of  FIG. 3  turned upside down and with some parts removed for clarity of illustration. 
         FIG. 7  is a view of  FIG. 6  rotated 180°. 
         FIG. 8  is an enlarged view, partly in cross section, of a portion of  FIG. 6  as viewed from a different direction. 
         FIG. 9  is an enlarged top plan view of a portion of  FIG. 6 . 
         FIG. 10  is an enlarged view in circle  10  of  FIG. 3 . 
         FIG. 11  is an enlarged view in circle  11  of  FIG. 6  showing detail which cannot be seen in  FIG. 7 . 
         FIG. 12  is an enlarged view in circle  12  of  FIG. 6 . 
         FIG. 13  is a perspective view of two plastic parts which are to be welded together. 
         FIG. 14  is an enlarged view of a portion of  FIG. 13 . 
         FIG. 15  is a perspective view of the two plastic parts of  FIG. 13  turned counterclockwise. 
         FIG. 16  is an enlarged view of a portion of  FIG. 15 . 
         FIGS. 17 and 18  are vector diagrams for explaining certain principles of the present invention. 
         FIGS. 19 and 20  are vector diagrams for explaining certain additional principles of the present invention. 
         FIGS. 21-22  are cross section views illustrating two other plastic parts which are being welded together. 
         FIG. 23  is a perspective view of a portion of another plastic welding machine, looking from the right front toward the left rear of the machine. 
         FIG. 24  is a perspective view of a portion of  FIG. 23  on a larger scale, looking from the left front toward the right rear of the machine. 
         FIG. 25  is a perspective view of  FIG. 24  looking from the left rear toward the right front of the machine. 
         FIG. 26  is an enlarged perspective view of a portion of  FIG. 25  shown by itself apart from the welding machine, looking from the left rear toward the right front. 
         FIG. 27  is an enlarged rear elevation view in the direction of arrow  27  in  FIG. 26 . 
         FIG. 28  is an enlarged front elevation view in the direction of arrow  28  in  FIG. 26 . 
         FIG. 29  is an enlarged end view in the direction of arrows  29 - 29  in  FIG. 28 . 
         FIG. 30  is an enlarged end view in the direction of arrows  30 - 30  in  FIG. 28 . 
         FIG. 31  is a perspective view of a portion of  FIG. 26  which has been removed from  FIG. 26  and turned upside down, some parts having been removed for clarity of illustration. 
         FIG. 32  is a view of  FIG. 31  looking from a different direction. 
         FIG. 33  is a schematic front view of another welding machine. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an example of a plastic welding machine  33  comprising an upper platen  34  and a lower platen  35  each of which is independently movable on a frame  37  toward and away from the other in a direction parallel with a main vertical z-axis as suggested by arrow  36 . Frame  37  comprises vertical uprights  37 A,  37 B which are horizontally spaced apart. Parallel rails  39 A,  39 B of a first rail pair are respectively fastened to uprights  37 A,  37 B at a higher elevation than are parallel rails  39 C,  39 D of a second rail pair. A servo motor controlled ball screw actuator  41 A moves upper platen  34  vertically up and down on rails  37 A,  37 B, and a servo motor controlled ball screw actuator  41 B moves lower platen  35  vertically up and down on rails  39 C,  39 D. A slide assembly  38  is fastened to a lower face of upper platen  34 .  FIG. 2  is an enlarged view of upper platen  34  by itself. 
     Detail of slide assembly  38  is shown in  FIGS. 3-12 . Slide assembly  38  comprises a base plate  40  which is disposed against the lower face of upper platen  34  and fastened to upper platen  34 . Slide assembly  38  also comprises a tooling plate  42 . A tooling half (not shown) is fastened to tooling plate  42  and has a fixture for holding one of two plastic parts which are to be welded together. The plastic parts are also not shown. Another tooling half (also not shown) is fastened to the upper face of lower platen  35  and has a fixture for holding the other of the two plastic parts which are to be welded together. 
     While tooling plate  42  is removed from  FIGS. 6 and 7  for clarity of illustration, tooling plate  42  appears in other Figs. Tooling plate  42  is movable relative to base plate  40  in a direction parallel with an x-axis and perpendicular to the z-axis as suggested by arrow  44  in  FIG. 2 . Two parallel rails  46 ,  48  extend lengthwise parallel with the x-axis and are disposed against a lower face of, and fastened to, base plate  40 . Three bearing assemblies  50  can slide along each rail  46 ,  48  in directions parallel with the x-axis. The bearing assemblies  50  which can slide along rail  46  are separated from tooling plate  42  by a spacer bar  52  which is also removed from  FIGS. 6 and 7  for clarity of illustration. The bearing assemblies  50  which can slide along rail  48  are separated from tooling plate  42  by a spacer bar  54 . Fasteners (not shown) pass through clearance holes  56  in spacer bars  52 ,  54  to fasten bearing assemblies  50  associated with each rail to tooling plate  42 . Because bearing assemblies  50  are constrained by their engagements with rails  46 ,  48  to move in a direction along each rail  46 ,  48  parallel with the x-axis, tooling plate  42  is constrained to move relative to base plate  40  also in a direction parallel with the x-axis. 
     Also mounted on base plate  40  is a servo driven actuator  58  for moving tooling plate  42  along rails  46 ,  48 . Servo driven actuator  58  is shown in greater detail in  FIGS. 8, 9, and 12  to comprise a servo motor  60  whose output shaft is parallel the x-axis and is coaxially coupled with one end of a ball screw  62  whose axis is coaxial with that of servo motor  60  so that the axis of ball screw  62  is also parallel with the x-axis. 
     Ball screw  62  is supported at two different locations along its length by two bearing assemblies  64 ,  66  which are mounted on base plate  40 . Between its two points of support by bearing assemblies  64 ,  66 , ball screw  62  is engaged with a nut  68 . Nut  68  is non-rotatably mounted within a housing  70  which is fastened to tooling plate  42 . Consequently when servo motor  60  turns ball screw  62 , ball screw  62  imparts x-axis motion to tooling plate  42  through mechanical interaction with nut  68  because nut  68  cannot rotate within housing  70  and housing  70  is fastened to tooling plate  42 . Because servo motor  60  is bi-directional, it is capable of moving tooling plate  42  in either of two opposite directions parallel with the x-axis. 
     How the axis of ball screw  62  is made parallel with the x-axis will be explained with reference to  FIG. 11 .  FIG. 11  shows a part  75  having a circular cylindrical head  75 H and a circular cylindrical shank  75 S which is fit to a circular hole in base plate  40  to one side of ball screw  62  so that the outer margin of head  75 H is disposed flat against the lower surface of base plate  40 . A part identical to part  75  is fit to another hole in base plate  40  to the opposite side of ball screw  62  in the same way.  FIG. 11  also shows one of two slots  77  which have been machined in the bottom surface of the housing of bearing assembly  64  to either side of ball screw  62 . Each slot  77  has a length parallel with the x-axis and opposite side surfaces which face each other and lie in parallel planes which are parallel with the axis of ball screw  62 . The width of each slot  77  is just large enough to allow the head  75 H of the respective part  75  to fit to the respective slot. Heads  75 H are spaced a distance apart from each other which allows each head to precisely fit between opposite sides of the respective slot when servo driven actuator  58  is being assembled to base plate  40  thereby assuring that the axis of ball screw  62  is parallel with the x-axis. 
       FIG. 10  shows detail of a dowel  71  which is used for setting slide assembly  38  to upper platen  34 . It is also used to set tooling plate  42  to base plate  40  during assembly of tooling plate  42  to base plate  40  by properly locating tooling plate  42  to base plate  40  at an initial phase of assembly before bearing assemblies  50  are fastened to tooling plate  42 . Dowel  71  fits with precision to bushings  71 A,  71 B which are precisely located in the respective plates  40 ,  42 , and when placed in the bushing of one plate, dowel  71  will fit to the bushing of the other plate only when the bushings are in precise coaxial alignment in a direction along the z-axis. Proper alignment of the two plates in a circumferential direction around dowel  71  will result in proper location of bearing assemblies  50  to tooling plate  42  to allow bearing assemblies  50  to be fastened to tooling plate  42 . 
     For welding two plastic parts together, one part is fixtured in a tooling half mounted on one platen and the other part is fixtured in a tooling half mounted on the other platen. Placement of the parts in their tooling half fixtures may be performed manually by a person operating welding machine  33  or by an industrial robot (not shown) whose operation is controlled in coordination with that of welding machine  33 . 
     An initial step in plastic welding comprises heating surfaces of the plastic parts at locations where a weld joint is to be created. That step can be performed by moving platens  34 ,  35  to positions which place the surfaces to be heated sufficiently far enough apart to allow a heat source tool  72  ( FIG. 1 ), such as a hot plate having three-dimensional heating surfaces, to be placed between the plastic parts. The plastic parts are aligned in the x-axis direction and in a y-axis direction which is perpendicular to both x-axis and z-axis directions so that the weld joint locations on both fixture plastic parts mutually align in an x,y plane. One or both platens  34 ,  35  is or are then moved other to place the fixtured plastic parts in contact with, or sufficiently close to, the heat source tool to melt the plastic of each part along the weld joint location. After sufficient melting of the plastic of both parts, one or both platens  34 ,  35  move away from each other to locations which allow the heat source tool to be removed from between the parts. Movement of the heat source tool may be performed by an industrial robot in coordination with operation of welding machine  33 . 
     With melting of plastic along the weld joint locations on the parts having been completed, one or both platens is or are then moved in the z-axis direction to place the plastic parts together and force their melt pools to merge by applying force in a direction parallel with the z-axis (i.e. a z-axis weld force vector). With the melt pools beginning to merge, servo-driven actuator  58  then operates to cause force to be applied to the weld joint in a direction parallel with the x-axis (i.e. an x-axis weld force vector). By controlling the magnitudes of the weld forces being applied by the z-axis and x-axis weld force vectors, direction and magnitude of the resultant weld force vector can be controlled. 
     This is diagrammatically illustrated in  FIGS. 17 and 18  where z-axis force being applied by platens  34 ,  35  to force the melt pools together is represented by vector VZ, x-axis force being applied by tooling plate  42  is represented by vector VX, and the resultant weld force vector is represented by the vector VR. Because the magnitude and/or direction of vector VR is a function of the magnitude of the z-axis force and the magnitude of the x-axis force, changing the magnitude of the z-axis force and that of the x-axis force changes magnitude and direction of resultant vector VR. A controller coordinates x-axis force and z-axis force being applied to the weld joint by coordinating control of servo-driven actuator  58  with control of servo drives  41 A,  41 B to create a desired direction and magnitude for resultant weld force vector VR. 
     The ability to control the direction and magnitude of a weld force vector in a plastic welding operation is advantageous when the plastic parts have complex three-dimensional weld joint shapes.  FIGS. 13 and 14  illustrate parts  80 ,  82  which have been placed in a position which provides a slightly concave/convex three-dimensional weld joint for welding the parts together using only a z-axis force. However, the designs of those particular parts have features  84 ,  86  which preclude welding because those features would interfere with each other if the parts were to be moved toward each other only in the z-axis direction. 
     Reorienting the parts as shown in  FIGS. 15 and 16  removes the interference, but has the undesired consequence of converting the three-dimensional weld joint in  FIGS. 13 and 14  into a shape which is not conducive for reliable mass production in a welding machine that can apply only a z-axis weld force vector. Reliable mass-production is compromised because in the position of  FIGS. 15 and 16 , the weld joint assumes a much more vertical orientation at the left end portions of the parts than in the position of  FIGS. 13 and 14 . That more vertical orientation causes the component of z-axis force which is normal to the surfaces at those left end portions to be much smaller than the component at the right end portions. 
     By operating slide assembly  38  to impart an x-axis force component in coordination with a z-axis force component being applied by platens  34 ,  35 , the resultant weld force vector which is being applied to the entire weld joint can be made sufficiently large in a suitable direction to achieve desired quality for mass-produced welded parts. A resultant weld force vector being applied to the plastic parts can remain constant in both magnitude and direction during the entire time that the parts are being forced together, or its magnitude and/or direction may change while the parts are being forced together. 
       FIGS. 21-22  illustrate an example of the latter for two parts  90  and  92  being welded together. The right side of part  90  is being forced against a flange of part  92  by only a z-axis force vector Z 0  to create a proper weld joint at that location. Because the wall of part  90  on the left side is inclined to the direction of force vector Z 0 , it may not be properly welded to part  90  using only z-axis force. At some point during the time before the melt pools of the weld joint of the respective parts at the right and left solidify, the direction of the resultant weld force vector is changed from Z 0  to Z 1  by using slide assembly  38  to apply force in a direction parallel with the x-axis The resultant force Z 1  better aligns with the wall of part  90  on the left side as suggested by  FIG. 22 , allowing that wall of part  90  to become properly joined with part  92 . Force Z 1  may cause the melts on the right side to smear slightly but that won&#39;t affect integrity of the finished weld joint. 
       FIG. 23  shows another plastic welding machine  133  having an upper platen  134  and a lower platen  135  which are relatively movable along a vertical z-axis as suggested by arrow  36 . Like machine  33 , machine  133  comprises servo motor controlled ball screw drives  41 A,  41   b  and a slide assembly  38  which in all material respects is like the one described above, but unlike machine  33 , machine  133  has a second slide assembly  180  fastened to upper platen  134 , and slide assembly  38  is fastened to slide assembly  180 . 
     As shown by  FIGS. 24-32  slide assembly  180  comprises a base plate  182  which is disposed against, and fastened to, upper platen  134  and a tooling plate  184  against which base plate  40  of slide assembly  38  is disposed and fastened to. A tooling half (not shown) for fixturing one of two plastic parts which are to be welded together remains mounted on tooling plate  42  of slide assembly  38 . Another tooling half (also not shown) for fixturing the other of the two plastic parts is mounted on lower platen  135 . 
     Tooling plate  42  continues to be movable relative to base plate  40  in a direction parallel with the x-axis and perpendicular to the z-axis as suggested by arrow  44 . Slide assembly  180  functions to move slide assembly  38  in a direction parallel with the y-axis as suggested by arrow  186  and perpendicular to both the x-axis and the z-axis. 
     Slide assembly  180  further comprises two parallel rails  188 ,  189  which extend lengthwise parallel with the y-axis and are fastened to base plate  182 . Two bearing assemblies  190  can slide along each rail  188 ,  189  parallel with the y-axis. The bearing assemblies  190  which can slide along rail  188  are separated from tooling plate  184  by a spacer bar  192  which removed from  FIGS. 31 and 32  for clarity of illustration. The bearing assemblies  190  which can slide along rail  189  are separated from tooling plate  184  by a spacer bar  194 . Fasteners fasten the bearing assemblies  190  associated each rail to base plate  182  by passing through clearance holes  196  in spacer bars  192 ,  194 . With bearing assemblies  190  secured to tooling plate  184 , tooling plate  184  can move relative to base plate  182  along a direction parallel with the y-axis. 
     Also mounted on base plate  182  is a servo driven actuator  198  for moving tooling plate  184  on base plate  182 . Servo driven actuator  198  is shown in greater detail in  FIGS. 31 and 32  to comprise a servo motor  200  whose output shaft is parallel with the y-axis and is coaxially coupled with one end of a ball screw  202 . Ball screw  202  is supported at two different locations along its length by two bearing assemblies  204 ,  206  which are mounted on base plate  182 . Between its two points of support by bearing assemblies  204 ,  206 , ball screw  202  is engaged with a nut  208 . Nut  208  is non-rotatably mounted within a housing  210  (like nut  68  in housing  70  of servo driven actuator  58 ). Housing  210  is disposed on, and fastened to, tooling plate  184  to align the axis of ball screw  202  parallel with the y-axis, in the same way as housing  70  aligns ball screw  62  parallel with the x-axis. Consequently when servo motor  200  turns ball screw  202 , ball screw  202  impart motion to tooling plate  184  through nut  208  and housing  210  in a direction parallel with the y-axis. Because servo motor  200  is bi-directional, it is capable of moving tooling plate  184  in either of two opposite directions parallel with the y-axis. 
     With base plate  40  of slide assembly  38  fastened to upper platen  34  and base plate of slide assembly  180  fastened to tooling plate  42  of slide assembly  38 , welding machine  133  is able to control direction and magnitude of the weld force vector when joining a first plastic part to a second plastic part after respective weld joint locations on both plastic parts have been melted and the parts are placed together. In machine  133 , the weld force vector is a function of z-axis force being applied to the plastic parts by platens  134 ,  135 , x-axis force being applied to the parts by tooling plate  42  acting through slide assembly  180 , and y-axis force being applied to the parts by tooling plate  184  of slide assembly  180 . This is diagrammatically illustrated in  FIGS. 19 and 20  where z-axis force being applied by the platens is represented by vector VZ, the x-axis force being applied by tooling plate  42  is represented by vector VX, the y-axis force being applied by tooling plate  184  is represented by vector VY, and the resultant weld force vector is represented by the resultant vector VR. Because the magnitude and direction of vector VR is a function of the magnitude of the z-axis force, the magnitude of the x-axis force, and the magnitude of the y-axis force, changing the magnitudes of z-axis, x-axis, and y-axis forces changes magnitude of vector VR and direction of resultant vector VR in three dimensions. A controller coordinates operation of drives  41 A,  41 B, servo driven actuator  58 , and servo driven actuator  198 . 
     Rather than mounting one slide assembly on another slide assembly, one slide assembly may be mounted on one platen and the other slide assembly on the opposite platen, as shown schematically in  FIG. 35  where slide assembly  38  is fastened to upper platen  34  and slide assembly  180  is fastened to lower platen  35 . A slide assembly may also be used during movement of one part toward another to avoid potential obstructions in a path of movement in a direction parallel with the z-axis.