Die-shaping apparatus and process

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, 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 strip of relatively stiff material includes a series of consecutive discs formed along the length thereof, at least two adjacent discs having the laterally extending slot therebetween and the 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, and shaping the discs between the bridges.

Description: This invention relates to a progressive die and a shaping process using such a die. While the die and process described and claimed herein have utility in other fields, the specific example described 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 14.699cm (5.787"); a spacing of 14.699cm (5.787") ± 0.00508mm (.0002") between stations one and two; and, because the tolerance is nonaccumulative, a spacing of 44.097cm (17.361") ± 0.00508mm (.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 0.0508mm (.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 in the discs. The result has been a disruption of the punching operation and a loss of strip metal. US-A-3 107 566 discloses a progressive die and, according to the patent, a method of correcting a camber problem in a strip of metal. Two slots 14 are cut across the width of the strip, leaving a connecting neck 16. The connecting neck 16 is supposed to bend or flex and thereby enable the strip to straighten out and eliminate the camber. While it is not certain whether the method disclosed would correct for camber in actual practice, the method would not correct for a progression problem. The connecting neck 16 of the patent is too wide to permit an adjustment in the center-to-center distances between the lamination blanks as would be required to correct a progression problem. DE-A- 1652940 forms the base of the pre-characterising features of claims 1 and 12 According to one aspect of the present invention there is provided a progressive die for shaping a consecutive series of adjacent discs in a strip of relatively stiff material, said die having a series of adjacent die stations including a slot cutting station and a plurality of shaping stations which follow said slot cutting station, said strip having an imaginary center line and each of said discs having a geometric center, and said slot cutting station including slot cutting means for cutting a plurality of slots in said strip between adjacent discs, characterized in that: said slot cutting means cuts said slots extending substantially aligned laterally of said strip center line and leaving a plurality of narrow deformable bridges connecting said adjacent discs, said bridges extending across said slots and connecting said adjacent discs, the die further having pilot means at said shaping stations for engaging and accurately locating said discs to coincide with said shaping stations, and said slot cutting means shaping said bridges with a lateral width and thickness sufficient to enable deformation thereof to either increase or decrease the distances between said centers of said discs, whereby said discs coincide with said shaping stations despite any variations in the distances between said centers of said adjacent discs. According to another aspect of the present invention there is provided a process for shaping a consecutive series of adjacent discs in a strip of relatively stiff material using a die having a series of adjacent die stations including a slot cutting station and a plurality of shaping stations which follow said slot cutting station, said strip having an imaginary center line and each of said discs having a geometric center, and said slot cutting station including slot cutting means for cutting a plurality of slots in said strip between adjacent discs, characterized by the steps of: cutting said slots to extend substantially aligned laterally of said strip center line and leave a plurality of narrow deformable bridges connecting said adjacent discs, said bridges extending across said slots and connecting said adjacent discs, engaging and accurately locating said discs to coincide with said shaping stations, and cutting said bridges such that they have a lateral width and thickness sufficient to enable deformation thereof to either increase or decrease the distances between said centers of said discs, whereby said discs are made to coincide with said shaping stations despite any variations in the distances between said centers of said adjacent discs. In the accompanying drawings, Fig. 1 illustrates a prior art apparatus and method for die forming metal laminations. This apparatus is described below, and thereafter, for a better understanding of the invention and to show how the same may be carried into effect, reference will be made, by way of example, to Figs. 2 to 7 of the accompanying drawings, in which: 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. l 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. l). 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 lO (Fig. l), 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 10a to l0f, l0h and l0i 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 ll to l4 (see disc 10a), 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 10a 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 and sensors are provided to turn off the machine if the discs are not properly located 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 10c and l0d. 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 l0e removing fragments 3l and a thin ring of material 35 is removed from the center of disc l0e 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 frequently 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 and the sensors detect a misalignment, 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 l0 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 40a, 40b, 40c, 40h and 40i 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 features 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 5l which extends into the pilot hole 42 of the disc 40a. In addition, four straddle pilots 52 (Fig. 2) engage the sides 43 of the disc 40a, the pilots 5l and 52 serving to locate and orient the disc 40a properly. The punch assembly includes four punches 53 (Fig. 3) which punch four pilot holes 54 in the disc 40a. 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 6l between the discs 40 and 40a. 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, or a part of a bridge may be arcuate or straight and another part angular, for example. 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 0.635 ± 0.0762 mm (.025 ± .003"), each bridge has a lateral width in the range between 1.27 and 1.778 mm (.050 and .070"), a lateral width of 1.524 mm (.060") 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 and/or straddle pilots are provided at the sides of the discs, 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 40c, 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 1/2 57 in each of the discs 40H and 40I. In the example illustrated the two endmost bridges 58 and 6l 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 14.699 cm (5.787") ± 0.00508 mm (.0002"), and the spacing between the first and fourth stations is 44.097 cm (17.361") ± 0.00508 mm (.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 40b and 40c 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 simultaneously stretch (since they are deformable) to the dashed line positions 76, thereby increasing the separation between the discs 40b and 40c and the center-to-center distance between them. 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 8.001 mm (.315") in lateral width. The discs or sections of the strip may have shapes other than that shown in Figs. l 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 8l 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. In a progressive die as described herein, the lamination strip is pushed (not pulled) through the die, and the pushing is accomplished by a feeder mechanism (not illustrated) which may have a conventional design. Since the strip is being pushed, the connecting bridges must be sufficiently sturdy to push a number of lamination discs ahead of it. It will be apparent therefore that a balance must be achieved in the size of the bridges, because they must be sturdy enough to push the forwardly located discs and at the same time be thin enough to deform and correct for a progression error as described herein.

Claims: A progressive die for shaping a consecutive series of adjacent discs (40a to 40i) in a strip (40) of relatively stiff material, said die having a series of adjacent die stations (A to I) including a slot cutting station and a plurality of shaping stations which follow said slot cutting station, said strip having an imaginary center line and each of said discs having a geometric center, and said slot cutting station including slot cutting means (56) for cutting a plurality of slots (57) in said strip (40) between adjacent discs (40a to 40i), characterized in that: said slot cutting means (56) cuts said slots (57) extending substantially aligned laterally of said strip center line and leaving a plurality of narrow deformable bridges (58, 59, 60, 61) connecting said adjacent discs (40a to 40i), said bridges (58, 59, 60, 61) extending across said slots (57) and connecting said adjacent discs, the die further having pilot means (62) at said shaping stations for engaging and accurately locating said discs to coincide with said shaping stations, and said slot cutting means shaping said bridges with a lateral width and thickness sufficient to enable deformation thereof to either increase or decrease the distances between said centers of said discs, whereby said discs coincide with said shaping stations despite any variations in the distances between said centers of said adjacent discs. A progressive die according to Claim 1, and further characterized by pilot means (52) adjacent said slot cutting means (56) for engaging and accurately locating a disc while said slot cutting means (56) is cutting said slots (57). A progressive die according to Claim 1 or Claim 2, characterized in that at least some of said bridges (59 to 61) include portions which are disposed at an angle relative to said center line to facilitate said deformation. A progressive die according to Claim 3, characterized in that said portions have the shape of a chevron. A progressive die according to Claim 3, characterized in that said portions are arcuate portions (81). A progressive die according to Claim 1 or Claim 2, characterized in that said deformation is in the form of a bulge or buckle (77) out of the plane of said strip. A progressive die according to Claim 1, characterized in that said strip (40) is scroll shaped, said series of stations further including a station (A) including punches (53) for forming pilot holes (54), said station (A) further including straddle pilots (52) for locating a disc (40a) during the formation of said pilot holes (54). A progressive die according to Claim 7, characterized in that said slot cutting means (56) and said punches (53) are at said slot cutting station (A). A progressive die according to Claim 7, characterized in that said shaping stations (B to I) include pilot pins (62) extending into said pilot holes (54). A progressive die according to Claim 1 or Claim 2, characterized in that said slot cutting means (56) forms at least four of said bridges (58 to 61), said bridges being spaced apart on opposite sides of said center line of said strip (40). A progressive die according to Claim 1, characterized in that said shaping stations are at fixed and equal distances apart. A process for shaping a consecutive series of adjacent discs (40a to 40i) in a strip (40) of relatively stiff material using a die having a series of adjacent die stations (A to I) including a slot cutting station and a plurality of shaping stations which follow said slot cutting station, said strip having an imaginary center line and each of said discs having a geometric center, and said slot cutting station including slot cutting means for cutting a plurality of slots (57) in said strip (40) between adjacent discs (40a to 40i), characterized by the step of: cutting said slots (57) to extend substantially aligned laterally of said strip center line and leave a plurality of narrow deformable bridges (58, 59, 60, 61) connecting said adjacent discs (40a to 40i), said bridges (58, 59, 60, 61) extending across said slots (57) and connecting said adjacent discs, engaging and accurately locating said discs to coincide with said shaping stations, and cutting said bridges such that they have a lateral width and thickness sufficient to enable deformation thereof to either increase or decrease the distances between said centers of said discs, whereby said discs are made to coincide with said shaping stations despite any variations in the distances between said centers of said adjacent discs. A process according to Claim 12, and further characterized by the step of engaging and accurately locating a disc while said slot cutting means (56) is cutting said slots (57). A process according to Claim 12 or Claim 13, characterized by the step of cutting at least some of said bridges (59 to 61) with portions which are disposed at an angle relative to said center line to facilitate said deformation. A process according to Claim 14, characterized in that said portions have the shape of a chevron. A process according to Claim 14, characterized in that said portions are arcuate portions (81). A process according to Claim 12 or Claim 13, characterized in that said deformation is in the form of a bulge or buckle (77) out of the plane of said strip. A process according to Claim 12, wherein said strip (40) is scroll shaped, and further characterized by the step of forming pilot holes (54) in said discs at a station (A) and accurately locating a disc (40a) during the formation of said pilot holes (54). A process according to Claim 18, characterized in that said slots (57) and said pilot holes (54) are formed at said slot cutting station (A). A process according to Claim 12, characterized in that at least four of said bridges (58 to 61) are formed and are spaced apart on opposite sides of said center line of said strip (40). A process according to Claim 1, characterized by the step of providing said shaping stations at fixed and equal distances apart.

Inventors: FOSNAUGH DAVID L, FOSNAUGH, DAVID L.
Applicants: FRANKLIN ELECTRIC CO INC, FRANKLIN ELECTRIC CO., INC.
Application year: 1992
Main classification: B21D28
IPC codes: B21D28