Abstract:
A progressive die for shaping a consecutive series of discs from a strip of relatively stiff material, comprising a series of adjacent die stations including a slot cutting station, a plurality of intermediate stations, and a cut off station, the slot cutting station including cutting means for forming at least one laterally extending slot between adjacent discs while leaving at least one narrow deformable bridge connecting the adjacent discs, the intermediate stations including cutting means for shaping the discs, and the cut off station including cutting means for severing the bridge. A strip of relatively stiff material includes a series of consecutive discs formed along the length thereof, at least two adjacent discs having at least one laterally extending slot therebetween and at least one narrow deformable bridge connecting the adjacent discs. A process for die punching a series of shaped discs from a strip of relatively stiff material comprises the steps of cutting at least one slot through the strip between each pair of adjacent sections and forming at least one narrow deformable bridge connecting each pair of adjacent discs, shaping the discs between the bridges, and severing the bridges.

Description:
FIELD AND BACKGROUND OF THE INVENTION 
   This invention relates to a process for die punching (stamping) a strip of material such as metal, to a machine for performing the process, and to a product produced by the process. While the process and apparatus described and claimed herein have utility in other fields, the specific example described and claimed herein relates to the production of steel laminations for an electromotive device such as a motor. 
   The conventional manner of producing laminations is by feeding a long strip of lamination steel through a progressive die. The die has a series of stations and at each station a cut is made in the steel strip, thereby progressing from strip material to finished laminations. 
   In one process, a strip of straight slit steel is fed into a progressive die which progressively shapes the straight strip into finished laminations. In another process, a wide sheet of metal is cut by a scroll die into a plurality of scroll or zigzag strips, each scroll strip including a series of connected precut sections or discs. Each disc is then shaped by a progressive die into a finished lamination. Further, the discs have pilot holes in them, and each station of the progressive die has pilot pins which engage the pilot holes of the discs for the purpose of orienting the discs properly in the die stations during the punching operations. 
   There has been a problem with the foregoing prior art procedure which has resulted in a substantial downtime and loss of lamination steel. The problem arises because the between-center spacing between the successive die stations of the progressive die is fixed but the between-center spacing, or distance, between lamination discs may vary. As a specific example, a progressive die may have a feed length of 5.787″; a spacing of 5.787″±0.0002″ between stations one and two; and, because the tolerance is nonaccumulative, a spacing of 17.361″±0.0002″ between stations one and four. The center-to-center distance between lamination discs, on the other hand, are variable and the variations are accumulative. 
   An attempt to solve the foregoing problem has been to make the between-center spacing of successive lamination discs slightly longer than the theoretical feed length. For example, the between-center dimension between the discs has been made up to 0.0020″ longer than the feed length. This extra length can cause the metal strip to bow or buckle as it moves through the die; on the other hand, if the between-center spacing of the discs is not long enough, the discs cannot be fed through the die because the pilot pins of the dies cannot match the pilot holes of the discs. The result has been a disruption of the punching operation and a loss of strip metal. 
   It is a general object of this invention to provide improved process and apparatus for avoiding the aforementioned problems. 
   SUMMARY OF THE INVENTION 
   Apparatus in accordance with this invention comprises die means for shaping a consecutive series of discs from a strip of relatively stiff material, said die means comprising a slot cutting station, said slot cutting station including cutting means for forming at least one laterally extending slot between adjacent discs while leaving at least one narrow deformable bridge connecting said adjacent discs. 
   Apparatus in accordance with this invention further comprises a strip of relatively stiff material including a series of consecutive discs formed along the length thereof, at least two adjacent discs having at least one laterally extending slot therebetween and at least one narrow deformable bridge connecting said adjacent discs. 
   A process in accordance with this invention is for die punching a series of shaped discs from a strip of relatively stiff material, said process comprising the steps of cutting at least one slot through said strip between each pair of adjacent sections and forming at least one narrow deformable bridge connecting each pair of adjacent discs, shaping said discs between said bridges, and severing said bridges. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood from the following detailed description taken in conjunction with the accompanying figures of the drawings, wherein: 
       FIG. 1  illustrates a prior art apparatus and method for die forming metal laminations; 
       FIG. 2  illustrates apparatus and method for die forming metal laminations in accordance with this invention; 
       FIG. 3  is a schematic illustration of dies in accordance with this invention; 
       FIG. 4  is an enlarged view of fragments of laminations and illustrates this invention; 
       FIG. 5  is a view similar to  FIG. 4 ; and 
       FIGS. 6 and 7  illustrate alternative embodiments of the invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1  illustrates a prior art process for producing laminations for an electromotive machine such as an electric motor. The laminations are punched from a strip  10  of lamination steel which is fed through a conventional progressive die (not illustrated in  FIG. 1 ). The progressive die includes a plurality of punching stations A through I (station G being omitted because it is repetitious), and at each station a portion of the strip is removed to produce a finished rotor lamination disc at station D and a finished stator lamination disc at the final station I. A plurality of such discs are assembled in a stack to form stator and rotor cores. 
   The strip  10  ( FIG. 1 ), in the received form which is fed into the die at station A, includes a series of sequential discs or sections, and in this example, discs  10   a  to  10   f ,  10   h  and  10   i  are illustrated and associated, respectively, with the die stations A through F, H and I. In the received form, each disc has four angled outer sides  11  to  14  (see disc  10   a ), two connecting sides  15  and  16 , and a centrally located pilot hole  18 . 
   At station A, the die includes a pilot pin  19  which extends into the pilot hole  18  and centers the disc  10   a  in this die station. This station also includes four punches  21  which form four round pilot holes  22 . At each of the subsequent stations, four pilot pins  23  extend into the holes  22  in order to orient the discs at the stations. 
   At die station C, a banding slot  26  and two trim slots  27  are formed along the connecting sides of the two discs  10   c  and  10   d . As shown by the enlargement of the slot  26 , the ends  28  of the slot are angled; the ends of the slots  27  are semicircular. At station D, the rotor lamination  33  is removed from the strip. 
   At station E, the die includes punches which trim the outer sides of the disc  10   e  removing fragments  31  and a thin ring of material  35  is removed from the center of disc  10   e  to assure ID/OD concentricity and provide for rotor OD to stator ID clearance (air gap). It should be noted that the outer ends of the slots  27  are cut away so that the discs are thereafter attached by two relatively wide connecting sections  32  at the ends of the banding slot  26 . 
   At the subsequent stations, the stator winding slots  34  are cut. At the final station I, a cut is formed through the connecting side along the center of the connecting sections  32  and the banding slot  26 , thereby severing the finished forwardmost disc from the strip  10 . The angled sides of the slot  26  result in a dovetail-shape opening which may be used to receive a banding strip that secures a stack of laminations together, in a conventional manner. 
   The die stations are at fixed distances apart and the tolerances are nonaccumulative, as previously explained. On the other hand, the center-to-center distances between the discs making up the strip  10  are not uniform. Consequently, the variations in the disc distances may result in a situation where the pilot pins cannot enter the pilot holes  22 , resulting in disruption of the punching operation and loss of lamination metal. 
     FIGS. 2 and 3  illustrate apparatus in accordance with this invention, which avoids the foregoing problem. In this specific example of the invention, a strip  40  having the same initial shape as the strip  10  shown in  FIG. 1  is fed into a progressive punch and die assembly  41  shown schematically in  FIG. 3 . Again the progressive die set  41  may include nine stations and only stations A, B, C, H and I are illustrated in  FIG. 3 , and lamination discs  40   a ,  40   b ,  40   c ,  40   h  and  40   i  are illustrated in  FIG. 2 . 
   The strip  40  is fed into the progressive die with each disc having the initial configuration illustrated by the disc at the far left in  FIG. 2 . It includes a centrally located pilot hole  42 , four angled sides  43 , and a connecting side  44  which is joined with the next adjacent disc. This initial configuration is referred to in the trade as a scroll or zigzag shape, and it is cut from a wide sheet of lamination steel by a scroll die. 
   The progressive die set  41  ( FIG. 3 ) includes an upper punching assembly  46  and a lower die assembly  47 . Except for the feature described hereinafter as the invention, the die may otherwise have a conventional design. In addition to the two parts  46  and  47 , the die may also include a stripper (not illustrated) between the strip  40  and the punch assembly. 
   At station A, the punch assembly  46  includes a pilot pin  51  which extends into the pilot hole  42  of the disc  40   a . In addition, four straddle pilots  52  ( FIG. 2 ) engage the sides  43  of the disc  40   a , the pilots  51  and  52  serving to locate the disc  40   a  properly. The punch assembly includes four punches  53  ( FIG. 3 ) which punch four pilot holes  54  in the disc  40   a . In addition, slot piercing punches  56  pierce a series of slots  57  through the strip  40 , the slots extending laterally across the width of the strip at the connecting side  44 . The slots  57  leave a plurality (in this specific example, there are four) of narrow width bridges  58  to  61  between the discs  40  and  40   a . The bridges  58  to  61  preferably have an angled or chevron shape as illustrated in  FIG. 2 , but this is not necessary because they could instead be arcuate, straight longitudinal, etc., as illustrated in  FIGS. 6 and 7 . As will be described in connection with  FIGS. 4 and 5 , the bridges  58  to  61  are sufficiently thin and narrow (in the lateral dimension) to be deformable, and the lateral dimension needed to permit such deformation will depend on the thickness of the strip and the type of metal. As a specific example, for motor lamination steel having a thickness of 0.025±0.003 inch, each bridge has a lateral width in the range between 0.050 and 0.070 inch, a lateral width of 0.060 inch being preferred. This example is for standard material known as cold rolled semi-processed motor lamination steel. 
   It should be apparent that strips of other thicknesses, materials and stiffness should have other bridge dimensions. The bridges must be wide enough to hold adjacent discs together during the punching operation but sufficiently narrow that they may be deformed as will be described. Aside from the narrow bridges, the strips are otherwise stiff and not materially deformable to enable them to accommodate a misalignment of the pilots. 
   Following the punching of the pilot holes  54  and the slots  57 , further punching operations are performed at the subsequent stations. At each station, pilot pins  62  extend into the pilot holes  54  in order to orient the discs. As examples of further punching operations, at station B a large center hole  66  is formed by a punch  67 , at station C segments  67  are trimmed from the outer sides of the disc  40 C, at station H, a number of winding slots  68  are formed, and at station I the forwardmost lamination is severed from the strip by making a lateral cut (using a punch  69  in  FIG. 3 ) through the centers of the bridges  59  and  60  leaving one-half slots ½  57  in each of the discs  40 H and  40 I. 
   In the example illustrated the two endmost bridges  58  and  61  are relatively close to the sides  43 . When the segments  67  are punched out, the cut along the dashed lines  71  extends to the slots  57  and thus removes the bridges  58  and  61 , leaving only the two center bridges to connect adjacent discs. 
   The chevron shape of the two bridges  59  and  60  result in a dove-tail shape slot  72  ( FIG. 2 ) at the sides of a stack of the laminations, which may receive a banding strip as previously mentioned in connection with the opening  26  shown in  FIG. 1 . The punches  56  instead may be shaped to produce longer slots  57  and only one deformable bridge, or more than two narrow deformable bridges, for example. 
   As previously mentioned, a progressive die assembly of the type used to cut the strips  10  and  40  includes a series of successive stations. The center-to-center distances between the stations is fixed, and the tolerances are non accumulative. In the example previously given, the spacing between the first and second stations is 5.787″±0.0002″, and the spacing between the first and fourth stations is 17.361″±0.0002″. The center-to-center distances between the discs are variable, however, and the variations may prevent the pins  62  from aligning with and entering the pilot holes  54 . This problem has resulted in disruption of the stamping process and considerable loss of lamination steel. 
   This problem is avoided in accordance with this invention by making the bridges  58  to  61  sufficiently narrow (taking into consideration the type, stiffness and thickness of the strip material) that the bridges are capable of deforming to make up for the differences in the spacing. With reference to  FIG. 5 , if the center-to-center distance between two adjacent discs  40   b  and  40   c  of the strip  40  is less than the center-to-center distance between two adjacent stations B and C of the die  41 , the bridges stretch (since they are deformable) to the dashed line positions  76 , thereby increasing the separation between the discs  40   b  and  40   c  and the center-to-center distance between them. As is apparent from the foregoing and from  FIG. 2 , the strip  40  and the die stations A, B, etc. have a center line extending through substantially the centers of the discs  40   a ,  40   b , etc. and the stations, and the centers of the discs remain substantially on the center line when the bridges  58  to  61  deform. The amount of the stretch is sufficient to enable the pilot pins  62  to enter the pilot holes  54  and orient the discs at the adjacent stations. The outer ends of the pilot pins  62  may be conical to enable them to enter the pilot holes and then deform the bridges as the pins fully enter the holes. 
   In the event the center-to-center distance between the adjacent two discs is greater than the center-to-center distance between the adjacent two stations, the bridges deform to decrease the distance between the two discs. As shown in  FIG. 4 , the deformation may take the form of an upward (or downward) bulge or buckle  77  of the bridges, or the bridge may deform laterally to sharpen the angle of the chevron-shaped bridges. In the latter situation, the bridges may deform to the dashed line, positions  78  in  FIG. 5 . In an alternative construction where the bridges extend straight lengthwise between the discs (see  FIG. 7 ), the bridges would bulge upwardly or downwardly as shown in  FIG. 4 . Where the bridges are arcuate (see  FIG. 6 ) or chevron shaped ( FIG. 5 ), the deformation may be a combination of the two forms shown in  FIGS. 4 and 5 . 
   As is clearly shown in  FIGS. 2 and 4  to  6 , the length of each of the bridges  58  to  61  and  81  is greater than the width of the slots  57  punched between adjacent discs. This greater length of each bridge is due to its having at least a portion which is out of alignment with the longitudinal center line of the strip, as illustrated by the chevron and arcuate shapes shown in  FIGS. 5 and 6 . This greater length than the slot width (or distance between the adjacent edges of two discs) enhances the ability of the bridges to stretch or contract (see  FIG. 5 ) and thereby change the width of the slots and the between-center distance between adjacent discs. 
   While the prior art strip included sections  32  between adjacent discs, the connecting sections  32  are too wide and stiff to permit their deformation as is the case with the narrow deformable bridges in accordance with this invention. As an example, the connecting sections of the prior art have been approximately 0.315 inch in lateral width. 
   The discs or sections of the strip may have shapes other than that shown in  FIGS. 1 and 2 .  FIGS. 6 and 7  respectively show examples where the discs have square and round shapes.  FIG. 6  further illustrates discs connected by two deformable bridges  81  which have arcuate shapes.  FIG. 7  illustrates round discs connected by a single deformable bridge  82  and in this example the bridge  82  is straight longitudinal. 
   The discs shown in  FIGS. 6 and 7  may also have pilot means cut into them for orientation at the die stations, or the die stations may be provided with straddle pilots such as the pilots  52 . 
   While the slots forming the deformable bridges have been described as being cut at an initial station of a progressive die, it will be apparent that such slots could be cut by a separate die prior to being introduced into the progressive die. For example, these slots could be cut by the scroll die which cuts the strip  40  from the wide metal band, or a separate die may be provided for cutting such slots and pilot holes in the discs.