Abstract:
A method and apparatus for forming shaped articles such as heat exchanger plates and fuel cell plates from a strip of material. The apparatus includes a feed mechanism for feeding the strip; one or more forming devices which form peripheral features and/or discontinuities in the strip; and an alignment device which maintains constant spacing between the discontinuities and thereby avoids accumulation of incremental feeding errors. Preferably, the strip is re-aligned once for each plate produced. The alignment device comprises a pilot pin and a pilot hole punch for forming index holes in the strip, and can be integral with or separate from the forming devices. One preferred apparatus utilizes a forming device comprising a plurality of punches mounted on a reciprocating frame or gantry structure.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to apparatus and methods for production of shaped articles, more particularly to apparatus and methods for performing a number of stamping and/or punching operations on a strip of material.  
       BACKGROUND OF THE INVENTION  
       [0002]     Heat exchangers are commonly formed from stacks of flat plates. In such heat exchangers, spaces between adjacent plates define internal flow passages. Heat exchangers of this type are described in U.S. Pat. No. 5,794,691 (Evans et al.) and U.S. Pat. No. 6,244,334 (Wu et al.). This type of stacked plate construction is also used in fuel cells and electrolyzers. In these applications, individual plates (bipolar plates) may be bonded together in pairs containing spaced apart passages for coolant flow between them, and outer facing passages for reactant fluid flow. The bipolar plate pairs are then assembled into a stack comprising catalyst-coated membranes and gas diffusion layers sandwiched between each of the bipolar plate pairs. The plates described herein are typically metal, although other materials such as conductive composite polymer materials may also be used.  
         [0003]     For metallic constructions, each individual plate in a stacked plate heat exchanger or fuel cell may be formed by a plurality of separate punching and/or stamping operations performed by one or more different devices. For example, the plates can be formed from a strip by punching apertures, bosses and/or other discontinuities in a central portion of the plate and then passing the strip through a progressive stamping die to form the periphery of the plate and to separate it from the strip. The strip may be unwound from a coil and incrementally fed to the punching apparatus by a feed mechanism having one or more feed rollers.  
         [0004]     In such operations it is difficult to ensure that the discontinuities formed by the various punching operations are properly spaced from each other and from the periphery of the plate. In particular, small errors in feeding the strip are repeated for each incremental advance of the strip. These errors are compounded during the course of a production cycle and may result in parts which do not meet specifications and must be scrapped or may contribute to small incremental assembly errors that are initially undetected but can result in decreased product yield in the downstream assembly process, resulting in even greater losses.  
         [0005]     Moreover, traditional progressive dies can be extremely expensive for plates that require forming sections to produce the intricate patterns of formed channels and bosses typically required for fluid passages in the intended product applications. Finally, in some heat exchanger constructions and most fuel cell constructions, optimum functional design requires dissimilar plates to be joined alternately in the assembled stack. Such dissimilar plates often have common peripheral features for bonding but have different form sections (different channel patterns or channel heights), or different manifold boss or other internal feature locations or heights. In the case of fuel cell constructions for instance, separate anode and cathode plates are required, which may require substantially different geometric features and channel heights. To produce products of this type by conventional means, two different progressive dies must be purchased at a substantial cost increment. Moreover to maintain balanced production flow in a continuous production setting, the two dies would need to be run in parallel on two presses, further compounding the cost and complexity of operation. To date, it has not been possible to produce different types of plates from a single strip of material, in a mass production environment, without using complex and expensive manufacturing equipment as described above.  
         [0006]     The need exists for apparatus and methods which are able to accurately perform a plurality of punching and/or stamping operations and which permit efficient production of different types of plates from a single strip of material, preferably using low cost tooling equipment which allows the production of different or alternating types of parts in a balanced production flow process.  
       SUMMARY OF THE INVENTION  
       [0007]     In one aspect, the present invention provides an apparatus for forming a plurality of shaped articles from a strip of material, the apparatus comprising: a feed mechanism for incrementally feeding the strip of material in a forward direction along a strip feed axis; a forming device which receives the strip of material from the feed mechanism and which forms discontinuities in the strip of material at axially-spaced intervals; an alignment device for maintaining constant axial spacing between the discontinuities, the alignment device being located in fixed axial relation to both the forming device and the feed mechanism, the alignment device comprising a frame structure having a first portion and a second portion between which the strip is fed, the first and second portions being movable toward and away from one another, a pilot hole punch for forming pilot holes in the strip and a pilot pin rigidly mounted in axially-spaced relation to one another on the first portion of the frame structure, the pilot pin being spaced forward of the pilot hole punch so that the pilot pin is insertable into a pilot hole previously formed by the punch; wherein the pilot pin and the pilot hole punch each have a length such that when the first and second portions of the frame structure are moved toward one another, the pilot pin passes through a pilot hole before the punch contacts the strip and aligns the strip relative to the pilot hole punch and the forming device.  
         [0008]     In another aspect, the present invention provides a method for forming a plurality of shaped articles from a strip of material, comprising the following steps: incrementally feeding the strip of material in a forward direction along a strip feed axis; forming discontinuities in the strip of material at axially-spaced intervals; periodically aligning the strip to maintain constant axial spacing between the discontinuities by use of an alignment device comprising a frame structure having a first portion and a second portion between which the strip is fed, the first and second portions being movable toward and away from one another, the alignment device including a pilot hole punch and a pilot pin rigidly mounted in axially-spaced relation to one another on the first portion of the frame structure; after each said incremental feeding step, moving the first and second portions of the frame structure toward one another, thereby causing the pilot hole punch to punch a pilot hole in the strip and to simultaneously cause the pilot pin to pass through a pilot hole previously formed by the pilot hole punch; wherein the pilot pin and the pilot hole punch each have a length such that, during movement of the first and second portions of the frame structure toward one another, the pilot pin passes through a pilot hole before the punch contacts the strip, and the pilot pin thereby aligns the strip relative to the pilot hole punch. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The invention will now be described, by way of example only, with reference to the accompanying drawings in which:  
         [0010]      FIG. 1  is a perspective view of an apparatus according to a first preferred embodiment of the invention;  
         [0011]      FIG. 2  is a side elevation view of the apparatus of  FIG. 1 ;  
         [0012]     FIGS.  3  to  10  are schematic side elevations showing a preferred alignment device according to the invention; and  
         [0013]      FIG. 11  is a perspective view of stamped strip stock produced using a preferred method and apparatus according to the invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0014]      FIGS. 1 and 2  illustrate a preferred apparatus according to the present invention. Apparatus  10  unwinds a flat strip  12  of a material such as sheet metal from a coil  14  and converts it through a plurality of punching and stamping operations to a shaped article which, in the drawings, comprises a dished plate  16  for a heat exchanger. Examples of patents describing dished plate heat exchangers include U.S. Pat. No. 5,291,945 (Blomgren et al.) and U.S. Pat. No. 6,182,746 (Wiese et al.).  
         [0015]     As shown in  FIG. 11 , the plate  16  has a periphery  18  provided with a side wall  20  and a central portion  22 . The central portion  22  is provided with one or more discontinuities which, in the context of dished plate production, are typically selected from one or more members of the group comprising ribs, dimples, holes and raised apertured bosses. These discontinuities are typically formed by punching, stamping or drawing the sheet metal strip  12  using one or more punches and/or dies. It will, however, be appreciated that other types of discontinuities can be formed in the strip  12 . For example, discontinuities can be formed by welding other components onto the strip or by cutting or bending the strip.  
         [0016]     In the preferred embodiment shown in the drawings, the central portion  22  of plate  16  is provided with two holes  24  and two raised apertured bosses  26 . A heat exchanger (not shown) can be formed by stacking plates  16  one on top of each other in a conventional manner, as described in the Blomgren et al. and Wiese et al. patents mentioned above.  
         [0017]     The apparatus  10  further comprises a feed mechanism  28  for incrementally feeding the strip  12  of material in a forward direction (as shown by arrows A and B) along a strip feed axis S. The feed mechanism  28  is schematically illustrated in the drawings as comprising an upper feed roller  30  and a lower feed roller  32  between which the strip  12  passes. The feed rollers  30 ,  32  are mounted in a frame member  33  which is provided with an engagement mechanism  34  for moving the rollers  30  and  32  toward and away from one another in the directions indicated by double-ended arrow C.  
         [0018]     As would be apparent to one skilled in the art, the strip  12  is incrementally advanced in the forward direction (arrow B) when engaged along its top and bottom surfaces by the upper and lower rollers  30 ,  32  and with rollers  30 , 32  rotating as indicated in  FIGS. 3, 5  and  10 . Similarly, the strip  12  is released from engagement with feed mechanism  28  when rollers  30 ,  32  are moved away from one another.  
         [0019]     As it is unwound from roller  14  by the feed mechanism  28 , the strip  12  is fed axially along a feed table  36  to a first forming device  38  which forms discontinuities in the strip  12  of material at axially-spaced intervals. Preferably, the first forming device comprises a frame structure  40  having an upper arm  41  and a lower arm  42  which are substantially parallel to one another and are connected together at their ends by a pair of side members  47 ,  49 . The frame structure  40  is supported to reciprocate laterally of the strip feed axis S (in the directions indicated by arrows D and E). As shown in  FIG. 1 , the lower arm  42  of frame structure  40  may preferably be supported by a stationary beam  43  along which it can be moved laterally. A reciprocating drive (not shown) is provided for reciprocating the frame structure  40  laterally of the strip feed axis S along beam  43 .  
         [0020]     A plurality of tools for forming discontinuities in the strip  12  are supported on the upper arm  41  of the frame structure  40 . In the preferred embodiment shown in the drawings, in which the discontinuities comprise holes  24  and bosses  26 , the tools comprise punches  44 . A total of four punches  44  are illustrated in the drawings. However, it will be appreciated that more or fewer punches  44  may be required, depending on the form and orientation of the discontinuities in the article  16 . In the embodiment shown in the drawings, one of the punches  44  is for forming the holes  24  while the other three punches  44  are for forming and shaping the bosses  26 .  
         [0021]     Each of the punches  44  is actuated by a punch actuator mechanism  45  which, in the preferred embodiment shown in the drawings, comprises a pneumatic cylinder  46  having a piston  48  pivotably connected to a bell crank  50 . As shown in  FIG. 2 , each bell crank  50  is pivotable about a fixed point  51  and is connected to its associated punch  44  through a pivoting connecting arm  52 .  
         [0022]     Located directly under the frame structure  40  and under strip  12  is a lower die block  53  which is provided with a plurality of die buttons  54 , each of which mates with one of the punches  44 .  
         [0023]     As will be appreciated, the provision of multiple punches  44  on the transversely reciprocating frame structure  40  provides great flexibility and enables the formation of various configurations of discontinuities in the central portions  22  of plates  16 . For example, a controller (not shown) may be programmed so that the punches  44  form different configurations of discontinuities in alternating plates  16 . Therefore, the apparatus of the present invention conveniently permits the production of two or more different plates from a single strip  12  of material.  
         [0024]     In addition to forming different configurations of discontinuities on alternating plates, the apparatus according to the invention also has the ability to produce discontinuities of different heights on alternating plates. This is advantageous, for example, in the manufacture of anode and cathode plates for use in fuel cells. Typically, the anode and cathode plates are provided with different rib patterns and channels of different height. The provision of different channel heights in alternating plates can be accomplished by several methods, including the use of a programmable, variable stroke press or by using an additional die on alternating plates to provide greater channel height.  
         [0025]     The apparatus according to the invention may also include one or more additional forming devices. In the preferred embodiment shown in the drawings, a second forming device  56  is provided. Forming device  56  preferably comprises a stamping apparatus and, as shown in the drawings, more preferably comprises a progressive stamping die for forming the peripheries  18  of plates  16  and for separating the plates  16  from the strip  12 . The second forming device  56  includes an upper stamping die  58  and a lower stamping die  60 . Where the second forming device  56  comprises a progressive stamping apparatus, the dies  58 ,  60  preferably comprise a plurality of stamping stations  62 ,  64 ,  66  and  68  in which features of the periphery  18  and/or central portion  22  of plate  16  are progressively stamped. It will be appreciated that the number of stamping stations in the progressive stamping apparatus may vary from that shown in the drawings.  
         [0026]     The second forming device includes a mechanism  78  for opening and closing the dies  58 ,  60  in the directions indicated by double-ended arrow F ( FIG. 1 ). As shown in the drawings, the mechanism  78  may comprise hydraulic cylinders  80  having pistons  82  which act on a block  84  carrying the upper stamping die  58 .  
         [0027]     The apparatus according to the invention also comprises an alignment device  85  for maintaining constant axial spacing between the discontinuities formed in strip  12 . In order to maintain constant spacing, the alignment device  85  is located in fixed axial relation to the first and second forming devices  38 ,  56  and to the feed mechanism  28 .  
         [0028]     The alignment device  85  is schematically illustrated in the drawings as comprising an upper die  86  and a lower die  88  between which the strip  12  is fed. The dies  86  and  88  are mounted in a frame member  118  which is provided with a hydraulic cylinder  120  or similar means to open and close the dies.  86  and  88 . As shown in FIGS.  3  to  10 , the upper and lower dies are movable toward and away from one another.  
         [0029]     As shown in  FIG. 3 , the upper die  86  of the alignment device  85  may preferably comprise a pair of die plates, including a first die plate  90  and a second die plate  92  biased apart by a coil spring  94  or other suitable biasing means. The first die plate  90  carries a pilot hole punch  96  and a pilot pin  98  and the second die plate  92  is provided with apertures  100  and  102  through which the pilot hole punch  96  and pilot pin  98  can move reciprocally as described below.  
         [0030]      FIG. 3  illustrates the first step of a production cycle, in which an end of the strip- 12  is fed by rollers  30 ,  32  to the first forming device  38 . As illustrated in  FIG. 3 , when the rollers  30 ,  32  of feed mechanism  28  engage the strip  12  and are rotated as indicated by arrows H and  1 , the strip  12  is advanced by an incremental amount in the direction shown by arrow G. The forward end of the strip becomes received between the upper and lower dies  86 ,  88  of the alignment device  85 . The upper and lower dies  86 ,  88  are open to permit feeding of the strip.  
         [0031]     As shown in  FIG. 4 , rotation of the rollers  30 ,  32  is discontinued in order to stop incremental feeding of the strip  12 , but the rollers  30 ,  32  remain in engagement with the strip  12 . The upper die  86  of the alignment device  85  is then brought down to punch a pilot hole  104  in the strip  12 . The plug  106  removed by the punch  96  is preferably ejected from the apparatus  85 . As shown in  FIG. 4 , the pilot hole punch  96  preferably extends into an aperture  108  in the lower die  88  when the upper and lower dies  86  and  88  are closed.  
         [0032]     Following formation of the pilot hole  104 , the dies  86  and  88  are opened and rollers  30  and  32  are again actuated to cause forward feeding of the strip by an incremental amount as shown in  FIG. 5 . Feeding of the strip  12  is discontinued once the strip reaches the position shown in  FIG. 6 .  
         [0033]     As can be seen from  FIG. 6 , the incremental amount by which strip  12  is fed corresponds to a distance between the pilot hole punch and the pilot pin, causing the pilot hole  104  to become aligned with the pilot pin  98 . However, due to feeding errors, the pilot hole  104  may not be precisely aligned with the pilot pin  98 . The magnitude of the misalignment shown in  FIG. 6  may be exaggerated. In  FIG. 6 , the rollers  30 , 32  have advanced the strip  12  slightly too far forward. If left uncorrected, these feeding errors would lead to inaccuracies in the locations of the discontinuities which would be compounded over the course of a production cycle.  
         [0034]     The strip  12  is brought back into alignment as shown in  FIGS. 7 and 8 . First, rollers  30 ,  32  are disengaged from the strip  12 , for example by withdrawing one or both rollers  30 , 32  away from the strip  12 .  FIG. 7  shows roller  30  being withdrawn in an upward direction in order to disengage the strip  12 . During or after disengagement of the strip from rollers  30 ,  32 , the upper and lower dies  86  and  88  of the alignment device are again closed. As can be seen in  FIG. 7 , the relative lengths of the pilot pin  98  and the pilot hole punch  96  are such that when the upper and lower dies  86 ,  88  of the alignment device are moved toward one another, the pilot pin contacts the strip  12  first and passes though the previously formed pilot hole  104  before the punch  96  contacts the strip  12 . The pilot pin  98  has a rounded tip  99  which contacts the edge of the pilot hole  104 , causing movement of the strip until it is precisely aligned with the pin  98 . The pin  98  then passes through the pilot hole  104  to be closely received inside an aperture  110  in the lower die  88  of alignment device  85 . As will be appreciated, the disengagement of feed mechanism  28  permits the strip to be moved by a small distance either backward as shown in  FIG. 7 , forward or laterally. In order to provide effective alignment, the pilot hole punch  96  and pilot pin  98  are preferably of substantially the same diameter.  
         [0035]     After the strip  12  is aligned as shown in  FIG. 8 , the upper and lower dies  86  and  88  continue to close and the pilot hole punch  96  is then brought into contact with the strip  12  so that a second pilot hole  104 ′ is formed in the strip  12  and a second plug  106 ′ is ejected from the device  85 . It will be appreciated that the distance between pilot holes  104  and  104 ′ corresponds exactly to the distance between the pilot hole punch  96  and the pilot pin  98 . Following formation of the second pilot hole  104 ′, the upper and lower dies  86 ,  88  of device  85  are open and the rollers  30 ,  32  of feed mechanism  28  are again brought into engagement with the strip for further incremental movement. It will also be appreciated that the rollers  30 ,  32  may be brought into engagement with the strip  12  before opening of the dies  86  and  88 . For example, the rollers  30 ,  32  can be brought into engagement with strip  12  during or immediately after formation of pilot hole  104 ′, and immediately after alignment of the strip  12  by the pilot pin  98 .  
         [0036]     The steps illustrated in FIGS.  6  to  10  are then repeated for each incremental movement of the strip  12 , such that a series of precisely aligned pilot holes  104  are formed along the length of the strip  12 . The pilot holes  104  can be seen in the strip  12  shown in  FIG. 11 . As illustrated, pairs of pilot holes  104  are preferably formed at regularly spaced intervals along opposite edges of the strip  12 .  
         [0037]     The alignment device  85  may be located at any one of a number of different locations along the strip feed axis S. In the preferred embodiment shown in  FIGS. 1 and 2 , the alignment device  85  is located between the feed mechanism  28  and the first forming device  38  and is mounted on the same base  112  as the first forming device  38 . In the alternative, the alignment device  85  may preferably be located between the first and second forming devices  38 ,  56  or it may be incorporated into either the first or second forming device  56 . For example, where the second forming device is a progressive stamping apparatus, the alignment device  85  may preferably be located at a first stamping station of the apparatus. The alignment device  85  may also comprise a self-contained unit which may be movable relative to the other components of the apparatus.  
         [0038]      FIG. 11  illustrates the appearance of strip  12  as it is conveyed through an apparatus  10  such as that illustrated by  FIGS. 1 and 2 , comprising a first forming apparatus  38 , a progressive stamping die  56  and an alignment device  85 . The portion of strip  12  shown in  FIG. 11  is divided into segments A to G in order to identify the various forming operations according to the invention.  
         [0039]     Since the alignment device  85  is located ahead of both the first and second forming apparatus  38 ,  56  in  FIG. 1 , the first feature formed in strip  12  is the pilot hole  104 . This is illustrated at segment A of the strip  12  shown in  FIG. 11 . The pilot hole  104  is formed as shown in  FIGS. 4 and 8  by the pilot hole punch  96  of the alignment device  85 . In order to permit alignment of the strip  12 , it is preferred that the progressive stamping die  56  be open during alignment of the strip  12  and formation of pilot holes  104 .  
         [0040]     Next, at segment B of the strip  12 , discontinuities are formed in the central portion of the strip  12  by the first forming device  38 . In the preferred embodiment of the invention, the discontinuities comprise a pair of laterally spaced holes  24  and a pair of laterally spaced bosses  26 , the center-to-center distance between the holes  24  and the bosses  26  corresponding to a distance L 1  and the center-to-center distance between the holes of one plate and the bosses of an adjacent plate corresponding to distance L 2 .  
         [0041]     Following formation of a pilot hole  104  by the pilot hole punch  96 , the strip  12  is fed forwardly along the axis S by an incremental amount L 2 , following which the holes  24  are formed by one of the punches  44  of the first forming device. It is to be noted that the holes  24  are formed with the rollers  30 ,  32  of the feed mechanism  28  engaging the strip  12 . Following formation of holes  24 , the strip  12  is advanced by amount L 1  and the bosses are formed by one or more of the other punches  44  of the first forming device  38 . The bosses  26  are preferably formed in three steps; pre-piercing, forming and final piercing. During formation of the bosses  26 , another pilot hole  104  is punched by the alignment device  85 . Thus, the strip  12  is advanced by an amount L 1 +L 2  for each alignment operation, so that only one set of pilot holes is punched for each plate.  
         [0042]     After formation of the holes  24  and bosses  26 , the remaining forming operations, shown at segments C to G of  FIG. 11 , are performed by the progressive stamping apparatus  56 . Preferably, the closing of the progressive stamping die  56  is synchronized with the operation of the alignment device  85  such that the dies of the progressive stamping apparatus  56  close immediately after alignment of the strip  12  by the pilot pin  98 . As with the alignment device  85 , the strip  12  is advanced by an amount L 1 +L 2  for each progressive stamping operation. The progressive stamping apparatus  56  is preferably provided with index pins  70  which engage the pilot holes  104  and maintain proper alignment of the strip as it passes through the progressive stamping apparatus.  
         [0043]     Although the invention has been described in connection with certain preferred embodiments, it is not limited thereto. Rather, the invention includes all embodiments which may fall within the scope of the following claims.