US3568555A

US3568555A - Guidepost construction for die sets

Info

Publication number: US3568555A
Application number: US758981A
Authority: US
Inventors: Werner H Stroh
Original assignee: Porter Precision Products Co
Current assignee: Porter Precision Products Co
Priority date: 1968-09-11
Filing date: 1968-09-11
Publication date: 1971-03-09
Anticipated expiration: 1988-03-09
Also published as: DE1945799A1; CH476572A; SE358101B; BE729806A; FR2017754A1; NL6904970A; GB1283717A; JPS4813510B1

Abstract

A die set including upper and lower die shoes respectively mounting a punch and die and a plurality of guideposts interconnecting the upper and lower shoes. The lower die shoe is adapted to be mounted upon a press platen. The upper die shoe carries a backup plate which is adapted to be engaged by the press ram, but is not connected thereto. The upper and lower die shoes are interconnected by a plurality of guidepost assemblies. The guidepost assemblies perform three functions, i.e. they maintain the upper and lower die shoes in alignment, they provide a spring force for opening the die, and they provide a stripping force for stripping the work from the punch member. Each guidepost assembly includes a hollow tube mounted on the upper shoe and a bushing mounted on the lower guide shoe which telescopically receives the tube. A stationary pin extends into the tube and abuts the lower end of a spring, such as a urethane spring member. The urethane spring member is of a configuration smaller than the space in which it is confined when the die is open. Upon closure of the die, the urethane spring member is deformed. When the ram is raised, the urethane member returns to its original shape, forcing the die open and stripping the work from the punch.

Description

United States Patent [72] Inventor Werner H. Stroh Cincinnati, Ohio [2]] Appl. No. 758,981 [22] Filed Sept. 11,1968 [45] Patented Mar. 9, 1971 [73] Assignee Porter Precision Products Co.

Cincinnati, Ohio [54] GUIDEPOST CONSTRUCTION FOR DIE SETS 11 Claims, 7 Drawing Figs.

[52] US. Cl 83/146, 83/588, 83/590, 83/637 [51] Int. Cl B26d 7/06 [50] Field of Search 83/582, 588,590,145,146, 635, 637, 685

[56] References Cited UNITED STATES PATENTS 616,733 1898 Rogers 83/590 1,995,466 1935 Bishop... 83/685X 2,108,253 1938 Dense..... 83/588 3,345,896 1967 Bennett.. 83/637X 1967 Danly 83/637X Primary Examiner-Andrew R. Juhasz Assistant Examiner-James F. Coan Attorney--Wood, Herron and Evans ABSTRACT: A die set including upper and lower die shoes respectively mounting a punch and die and a plurality of guideposts interconnecting the upper and lower shoes. The lower die shoe is adapted to be mounted upon a press platen. The upper die shoe carries a backup plate which is adapted to be engaged by the press ram, but is not connected thereto. The upper and lower die shoes are interconnected-by a plurality of guidepost assemblies.

The guidepost assemblies perform three functions, i.e. they maintain the upper and lower die shoes in alignment, they provide a spring force for opening the die, and they provide a stripping force for stripping the work from the punch member.

Each guidepost assembly includes a hollow tube mounted on the upper shoe and a bushing mounted on the lower guide shoe which telescopically receives the tube.

A stationary pin extends into the tube and abuts the lower end of a spring, such as a urethane spring member, The urethane spring member is of a configuration smaller than the space in which it is confined when the die is open. Upon closure of the die, the urethane spring member is deformed. When the ram is raised, the urethane member returns to its original shape, forcing the die open and stripping the work from the punch.

Patented March 9, 1971 7 3,568,555

3 Sheets-Sheet 1 INVENTOR.

Patented March 9, 1971 3 Sheets-Sheet 8 INVENTOR.

GIUWIEIPOST (IONSTIRUCTION FOR DIE SETS BACKGROUND OF THE INVENTION This invention relates to die sets of the type including a lower shoe mounting a die member and an upper shoe mounting a punch member, and is particularly directed to a novel guidepost assembly for interconnecting the upper and lower shoes of the die set.

The present invention is directed to a die set in which the upper and lower die shoes are held in alignment by a plurality of guidepost assemblies and in which the die set includes spring force members effective to open the die and to provide a stripping force effective to strip the workpiece from the punch.

One advantage of this general type of die set is that it does not require any attachment of the upper die shoe to the ram of a press. Rather, it is only necessary to clamp the lower die shoe to the press bolster plate. As a result, dies of this type can be quickly and easily set up as compared to conventional dies in which both the upper die shoe and lower die shoe must be carefully secured in alignment to the press ram and bolster plate. However, since the upper die shoe is not secured to the press ram, it is necessary that a substantial spring force be built into the die set to open the die shoes and strip the work from the punch. One of the disadvantages of previously proposed die constructions is that separate spring assemblies were required to provide this stripping and opening force. These spring assemblies were relatively expensive to fabricate and took up a portion of the otherwise usable space between the die plates.

SUMMARY OF THE INVENTION The principal object of the present invention is to provide a novel guidepost assembly which will perform three functions, i.e. (1) will maintain the upper and lower die shoes and hence punch the punch and die in precise alignment, (2) will provide a spring force for opening the dies when the ram pressure is released, and (3) will provide force for stripping the workpiece from the punch member.

More particularly, the present invention is predicated in part upon the concept of providing a plurality of guidepost assemblies, each of which includes a-hollow guidepost as opposed to the solid guideposts previously employed. The hollow tubular guidepost is mounted upon the upper shoe and carries an internal spring member. The guidepost is telescopically received within, and is guided by, a guide bushing mounted upon the lower guide shoe. These guideposts and guide bushings are effective to maintain the punch and die in precise alignment despite any misalignment of the press, ram and bolster plate, or wear of slides or other parts of the press.

In accordance with the present invention a stationary abutment, such as a headed pin, extends upwardly into the tubular guidepost. This stationary abutment member engages one end of the spring member disposed within the hollow guidepost. The other end of the spring member is in engagement with a backup plate secured to the upper shoe member. The spring is thus compressed when the upper and lower die shoes are brought together and stores energy which is subsequently used to strip the work from the punch and open the dies.

It is contemplated that the spring can be of several different types; for example. a polyurethane member, a rubber member, a coil spring, a plurality of disc springs, a compressible air spring or the like. The preferred form of spring, however, is a polyurethane spring member which is elongated and is of a length such that when it is in its extended position it supports the upper shoe member so that The polyurethane spring member is formed of any one of a number of polyurethane compositions, preferably of the order of 75 Shore D in hardness. These compositions have the property that they deform when pressure is applied to them, but yet return to their original shape when the pressure is released.

In accordance with the present invention, the polyurethane spring member is shaped so that it occupies a volume smaller than the volume within which it is confined, both when the die is in its raised or open position and when the die is in its lower or closed position. When the die is in its open position, the spring member is substantially relaxed. However, when the ram forces the upper die shoe downwardly, and forces the punch through the workpiece, the polyurethane spring member is deformed and foreshortened, storing a substantial spring force. When the ram is raised, the polyurethane spring member returns to its original elongated configuration, forcing the upper die shoe upwardly to open the die and to strip the workpiece from the punch.

One of the principal advantages of this guidepost construction is that it is extremely simple and economical to produce. For example, one preferred form of polyurethane spring member comprises a cylinder with tapered ends forming two frustoconical portions. This configuration can readily be molded or can readily be machined from a cylindrical rod of polyurethane material. The guidepost assembly comprises a minimum number of parts and can be quickly and easily repaired in the event that one or more parts shoulder become damaged.

A still further advantage of the present invention is that the guidepost assembly is extremely compact. More particularly, the springs are mounted within the guideposts and no external coil springs or other spring units are required. Consequently, a maximum usable space is made available between the upper and lower die shoes.

These and other objects and advantages of the present invention will be more readily apparent from a consideration of the following detailed description of the drawings illustrating a preferred embodiment of the invention.

IN THE DRAWINGS FIG. I is a side elevational view partially in section showing one preferred form of punching die constructed in accordance with the principles of the present invention, the die being shown in the open position.

FIG. 2 is a view similar to FIG. 1 showing the die in the closed position.

FIG. 3 is a plan view of the die set taken generally along line 33 of FIG. 1.

FIG. 4 is a cross-sectional view taken along line 4% of FIG. 3 with the die in the open position.

FIG. 5 is a cross-sectional view similar to FIG. 4 with the die in the closed position.

FIG. 6 is a cross-sectional view similar to FIG. 4 showing a modified form of guide sleeve with the die in the open position.

FIG. 7 is a cross-sectional view similar to FIG. 6 with the die in the closed position.

Details of the guidepost assembly 10 of the present invention are best shown in FIGS. 4 and 5, while the manner in which the guidepost assembly is utilized in a die set II is shown in FIGS. 1 and 2. It is to be understood that the present guideposts are useful in conjunction with many different types of die sets, one example being the set shown in FIGS. 1 and 2. The present guide sleeve assembly can also be utilized in die sets in which the die opening is formed in a die button mounted in shoe 15 or in which the die opening is formed directly in a shoe member 15 made of a suitable alloy. Moreover, while the present guidepost assembly is shown in a piercing die, it can also be used in conjunction with blanking dies or combined punching and blanking dies.

More particularly, as is shown in FIGS. 1 and 2, the die set 11 comprises a backup plate 12 which is mounted above and secured in any suitable manner, such as by means of bolts 19, to an upper shoe or punch-carrying plate 13. Shoe 13 carries :1 depending punch 14 which is secured to the shoe in any suitable manner. The die set further comprises a lower shoe 15 which carries female die member 16, the die member being mounted upon the shoe in any suitable manner. Mounted above the die member 16 is a stripper plate 17. The stripper plate is provided with a horizontal channel opening 18 to receive the strip of work 20.

As is well known in the art, the opening 21 in the die member is essentially the same size as the punch 14. A slight clearance is provided between the punch and opening 22 in the stripper plate 17. The lower shoe is provided with a somewhat larger slug hole 23 for providing passageway for the slugs 24 sheared from workpiece 20 by the punch. In this embodiment, the upper and

lower shoes

13 and 15 are held in precise alignment by four guidepost assemblies 10.

It is to be understood that the present guideposts can be used not only in a four-post die set of the type illustrated, but also in a diagonal post-type die set in which only two guideposts are utilized, such as those identified as a and 10b in FIG. 3 Alternatively, the present guidepost can be utilized in a die set of the back-post type in which only two guideposts corresponding to guideposts 10b andlOc are utilized. Still another possibility is a center-post type of die set in which only two guideposts are provided, the two guideposts being positioned respectively between posts 10a and 10c and posts 10b and 10d as shown in FIG. 3.

The details of one preferred form of guidepost assembly are shown in FIGS. 4 and 5. It is to be understood that each of the guidepost assemblies is identical with one another so that only one will be described. As shown in FIG. 4, the guidepost assembly comprises a cylindrical tube 25 formed of steel. The tube 25 is secured to the upper shoe member 13 in any suitable manner, such as by being press fit in an opening in the shoe, or by being staked, welded or the like. Alternatively, a separate bushing can be utilized to mount the tube as shown in FIGS. 6 and 7 and explained in detail later.

The tube extends downwardly through a guide bushing 26 mounted in an opening in the lower shoe member 15. It is to be understood that guide bushing 26 can be secured to the lower shoe in any suitable manner, such as by press fitting, staking, welding or the like. Alternatively, if the lower shoe is fabricated from an appropriate material, the guide bushing can be constituted by the plate itself, i.e. a bore is drilled through the plate to receive the tube 25 directly. The tube 25 is slidable within guide bushing 26 but is at all times maintained in axial alignment with the bushing. Guidepost 25 depends below lower shoe and receives a pin 27. Pin 27 is provided with a head 28 only slightly smaller than the inner diameter of tube 25 and a reduced diameter shank portion 30. The lowermost end of shank 30 abuts bolster plate 31 of the press. Pin 27 is maintained in assembled relationship with the guide tube 25 by means of an O-ring 32 seated in an internal peripheral groove within the lower end of tube 25.

Also mounted within tube 25 is a urethane spring member 33. This urethane spring member can be formed from any number of suitable polyurethane compositions. The polyurethane material has a high degree of tensile strength and impact resistance; and does not compress, but rather flows and displaces under stress. When the stress is relieved, the urethane member returns to its original shape.

I have found that the preferred urethane material has a hardness of the order of 75 Shore D. One such suitable material is sold under the trade name Flex-I-Cast." Other examples of suitable materials are given in U.S. Pat. No. 2,234,835. Data on other suitable urethane materials is provided in Du- Pont publication Engineering Properties of Urethane Elastomers." Those skilled in the art can readily determine which urethanes are preferable for a given application. In this application and the claims, the term urethane" is utilized as a generic term to cover any of the suitable polyurethane compositions.

As shown in FIGS. 4 and 5, the urethane spring member 33 is of an appreciably smaller volume than the volume within space 34 defined by tube 25, the bottom surface 35 of backup plate 12 and the upper surface 36 of head 28. At the same time, in the embodiment shown, the combined lengths of pin 27 and urethane spring member 33 is equal to the desired spacing of upper shoe 13 from bolster plate 31 when the die is in the open position. Since, as is explained below. lower shoe 15 is clamped to the bolster plate, this combined length assures that the desired die opening is obtained at the end of each stroke. One preferred construction of urethane spring, as shown in FIGS. 4 and 5, comprises a cylindrical central portion 37 having truncated

conical end portions

38 and 40. The diameter of the central cylindrical portion 37 is preferably slightly less than the inner diameter of tube 25, while the end surfaces of

portions

38 and 40 are only a fraction, for example one-half, of the diameter of tube 25.

As is best shown in FIGS. 1 and 3, the lower die shoe 15 is preferably rigidly secured to bolster plate 31 in spaced relationship therewith by means of clamping assemblies indicated generally at 41 and 42. As there shown, each clamping assembly comprises a spacer block 44 which rests on bolster plate 31 and engages the undersurface of the lower shoe member 15. A clamp bracket 45 engages the upper surface of shoe 15 while a bolt 46 threadably engaging the bolster plate is utilized to draw the clamping member 45, lower shoe l5 and spacer block 44 tightly together and to hold them rigidly in place with respect to the bolster plate.

As is shown in FIGS. 1 and 2, no permanent connection is made between the upper shoe member 13 or backup plate 12 and ram 47 of the press. Rather, backup plate 12 is disposed in a horizontal plane parallel to the lower face 48 of the ram. The ram is spaced from the backup plate when the ram is at the top of its stroke. However, as the ram is advanced, it engages the backup plate forcing it downwardly.

FIGS. 6 and 7 illustrate one of many possible modifications of the present guidepost assembly. As there shown, backup plate 12 is mounted above and secured to an upper shoe member 13 in any suitable manner. A guide tube 25 extends through an opening in upper shoe 13 and abuts the undersurface of backup plate 12. The guide tube in this embodiment is secured in place by means of a mounting bushing 51. The guide tube 25 is press fit or otherwise secured to the mounting bushing in any suitable manner. The bushing in turn is bolted to the upper shoe member as by means of bolts 52. As shown, the mounting bushing has a shoulder 53 which seats within opening 54 formed in the upper shoe member.

In this embodiment, a boss bushing 55 is bolted to lower die shoe member 15 as by means of bolts 56. The lower die shoe is provided with an opening 57 which receives the lower end ofa tubular guide bushing 58 which is press fit or otherwise secured to boss bushing 55. A plurality of precision ball bearings mounted in a conventional cage (not shown) engage the inner surface of guide bushing 58 and the outer surface of tube 25. As a consequence, the tube 25 is rigidly axially aligned within guide bushing 58, but is free to shift axially relative thereto through the rolling contact of ball bearings 60.

As in the embodiment shown in FIGS. 4 and 5, a headed pin 27 extends upwardly into tube 25. The head 28 ofthe tube engages the lowermost end of truncated surface 40 of a polyurethane spring member 33. This member is identical with spring member 33 described above. The upper end of spring member 33 engages the undersurface of the backup plate 12 as described previously. It is to be understood that the die assembly partially shown in FIGS. 6 and 7 is otherwise substantially identical with that shown in FIGS. 1 and 2 with the lower shoe member 156 being clamped to the bolster plate of the press and pins 27 being in abutting engagement therewith.

FIG. 7 shows the position of the guidepost assembly when the die is in its closed position. It will be noted that the urethane spring member 33 has been deformed, but still does not completely fill the space 34 defined by the cylindrical tubing 25, the lower surface of backup plate 12 and the head 28 of pin 27.

In operation, the embodiment shown in FIGS. l-S and the embodiment shown in FIGS. 6 and 7 function in the same manner. Consequently, only the operation of the embodiment shown in FIGS. l-5 will be described in detail. More particularly, when the press ram 47 is in its raised position, it is spaced from backup plate 12 and the die set is in its open position illustrated in FIG. 1. In this position punch 14 is clear of the work feed channel 28 so that a work strip 20 can be advanced through the channel to a position over the opening 21 in die member 16. As the ram 47 is lowered, it engages backup plate 12., forcing that plate downwardly together with shoe member 13 and punch 14. During downward movement, the guidepost assemblies maintain the punch 14 in precise alignment with the die opening 21. Specifically, during this movement tubes 25 slide downwardly within guide bushings 26 and are maintained in precise axial alignment therewith.

As backup plate 12 is shifted downwardly, it deforms urethane spring member 33 until at the bottom of the ram stroke the urethane member 33 is deformed to a configuration somewhat like that shown in FIG. 5. The urethane member, however, is not deformed beyond its elastic limit and does not till the space 34 defined by tube 25, backup plate 12 and head Ztl of pin 27. It will be appreciated that during its downward movement, punch member 114 is forced through work strip 20 and shears a slug 24 from work strip 20. This slug passes downwardly through slug opening 23.

As the ram 47 is raised, the urethane members 33 function as spring members, i.e. they return to their original elongated condition shown in FIG. 4. These urethane spring members provide the force for raising upper die shoe l3 and backup plate 12 to their open position shown in FIG. 1. The urethane spring members also provide the stripping force required to strip the workpiece 20 from die member 1-4. At the same time, the inner engagement of tubes 25 with guide sleeves 26 maintain the upper and lower shoes in precise alignement during opening of the die.

From the upper disclosure the general principles of the present invention and the preceding detailed description of two preferred embodiment, those skilled in the art will readily comprehend various modifications to which the present invention is susceptible. Thus, for example, if in a particular embodiment additional stripping force is required, it can easily be obtained by mounting annular urethane spring members around tubes 25. These spring members are of a height so that they are deformed when the die is closed and, hence, tend to force the dies open when the ram pressure is released. Therefore, I desire to be limited only by the scope of the following claims.

lclaim:

i. A die set comprising spaced parallel upper and lower shoe members, a punch carried by said upper shoe member, a cooperating die carried by said lower shoe member, a plurality of guidepost assemblies interconnecting said upper shoe member and said lower shoe member, said lower shoe member being adapted to be mounted upon a bolster plate of a press, said guidepost assemblies holding said punch and die in alignment, each of said guidepost assemblies comprising a tubular post member carried by said upper shoe member, and a guide bushing carried by said lower shoe member, said guide bushing telescopically engaging the outer periphery of said tubular post member, upper abutment means extending across the upper portion of said tubular post, a lower abutment member immovable with respect to said lower shoe member and being disposed within said tubular post member, said lower abutment member extending below said lower shoe member and being adapted for engagement with the bolster plate, and spring means disposed within said tubular post member in engagement with said lower abutment member and said upper abutment means, said spring means being effective to urge said upper die plate away from said lower die plate, whereby said punch is spaced from said die.

2. A die set comprising spaced parallel upper and lower shoe members, a punch carried by said upper shoe member, a cooperating die carried by said lower shoe member, a plurality of guidepost assemblies interconnecting said upper shoe member and said lower shoe member, each of said guidepost assemblies comprising a tubular post member carried by said upper shoe member, and a guide bushing carried by said lower shoe member, said guide bushing telescopically engaging the outer periphery of said tubular post member, upper abutment means extending across the upper portion of said tubular post, a lower abutment member immovablewith respect to said lower shoe member and being disposed within said tubular post member, and spring means disposed within said tubular post member in engagement with said lower abutment member and said upper abutment means, said spring means being effective to urge said upper die plate away from said lower die plate, whereby said punch is spaced from said die, a stripper plate carried by said lower die shoe, said spring member being effective to provide a stripping force causing a workpiece to be stripped from said punch.

3. A die set comprising spaced parallel upper and lower shoe members, a punch carried by said upper shoe member, a cooperating die carried by said lower shoe member, a plurality of guidepost assemblies interconnecting said upper shoe member and said lower shoe member, each of said guidepost assemblies comprising a tubular post member carried by said upper shoe member, and a guide bushing carried by said lower shoe member, said guide bushing telescopically engaging the outer periphery of said tubular post member, upper abutment means extending across the upper portion of said tubular post, a lower abutment member immovable with respect to said lower shoe member and being disposed within said tubular post member, and spring means disposed within said tubular post member in engagement with said lower abutment member and said upper abutment means, said spring means being effective to urge upper die plate away from said lower die plate, whereby said punch is spaced from said die. said spring member being formed of urethane and occupying a space smaller than the space within said tube between said upper abutment means and said lower abutment means.

4. The die set of claim 2 in which said spring member is formed of urethane and occupies a space smaller than the space within said tube between said upper abutment means and said lower abutment member.

5. The die set of claim 3 in which said spring comprises a generally cylindrical center section and tapered endwise portions.

6. The die set of claim 2 in which said spring comprises a urethane member having a generally cylindrical center section and tapered endwise portions 7. The die set of claim 6 in which said upper abutment means comprises a backup plate secured to the upper surface of said upper shoe member.

8. A guide bushing for use in dies of the type having spaced upper and lower shoe members, and having a punch secured to said upper shoe member and a die secured to said lower shoe member, said lower shoe member being adapted to be mounted upon a bolster plate of a press, said guidepost assembly comprising a hollow tubular post member secured to said upper shoe member, a guide bushing carried by said lower shoe member and telescopically engaging the periphery of said tubular guide post, and upper abutment member extending across the upper end of said tubular post, a lower abutment member stationary with respect to said lower shoe member, said lower abutment member extending below said lower shoe member and being adapted for engagement with the bolster plate, and a spring disposed interiorly of said hollow guidepost in engagement with said upper abutment means and said lower abutment member, said spring being effective to urge said upper die shoe member away from said lower die shoe member to a position in which said punch is separated from said die, said tubular post and said guide bushing being effective to hold said punch and die in alignment at all times.

9. The guidepost assembly of claim 8 in which said spring member comprises a urethane member, a guide bushing car ried by said lower shoe member and telescopically engaging the periphery of said tubular guide post.

10. The guidepost assembly of claim 8 in which said spring member comprises a polyurethane member of generally cylindrical cross section at its center portion and having two frustoconical ends, said polyurethane member being deformed when said die is closed and returning to its original configuration when said die is open, a guide bushing carried by said lower shoe member and telescopically engaging the periphery ofsaid tubular guidepost.

Claims

1. A die set comprising spaced parallel upper and lower shoe members, a punch carried by said upper shoe member, a cooperating die carried by said lower shoe member, a plurality of guidepost assemblies interconnecting said upper shoe member and said lower shoe member, said lower shoe member being adapted to be mounted upon a bolster plate of a press, said guidepost assemblies holding said punch and die in alignment, each of said guidepost assemblies comprising a tubular post member carried by said upper shoe member, and a guide bushing carried by said lower shoe member, said guide bushing telescopically engaging the outer periphery of said tubular post member, upper abutment means extending across the upper portion of said tubular post, a lower abutment member immovable with respect to said lower shoe member and being disposed within said tubular post member, said lower abutment member extending below said lower shoe member and being adapted for engagement with the bolster plate, and spring means disposed within said tubular post member in engagement with said lower abutment member and said upper abutment means, said spring means being effective to urge said upper die plate away from said lower die plate, whereby said punch is spaced from said die.

2. A die set comprising spaced parallel upper and lower shoe members, a punch carried by said upper shoe member, a cooperating die carried by said lower shoe member, a plurality of guidepost assemblies interconnecting said upper shoe member and said lower shoe member, each of said guidepost assemblies comprising a tubular post member carried by said upper shoe member, and a guide bushing carried by said lower shoe member, said guide bushing telescopically engaging the outer periphery of said tubular post member, upper abutment means extending across the upper portion of said tubular post, a lower abutment member immovable with respect to said lower shoe member and being disposed within said tubular post member, and spring means disposed within said tubular post member in engagement with said lower abutment member and said upper abutment means, said spring means being effective to urge said upper die plate away from said lower die plate, whereby said punch is spaced from said die, a stripper plate carried by said lower die shoe, said spring member being effective to provide a stripping force causing a workpiece to be stripped from said punch.

3. A die set comprising spaced parallel upper and lower shoe members, a punch carried by said upper shoe member, a cooperating die carried by said lower shoe member, a plurality of guidepost assemblies interconnecting said upper shoe member and said lower shoe member, each of said guidepost assemblies comprising a tubular post member carried by said upper shoe member, and a guide bushing carried by said lower shoe member, said guide bushing telescopically engaging the outer periphery of said tubular post member, upper abutment means extending across the upper portion of said tubular post, a lower abutment member immovable with respect to said lower shoe member and being diSposed within said tubular post member, and spring means disposed within said tubular post member in engagement with said lower abutment member and said upper abutment means, said spring means being effective to urge upper die plate away from said lower die plate, whereby said punch is spaced from said die, said spring member being formed of urethane and occupying a space smaller than the space within said tube between said upper abutment means and said lower abutment means.

6. The die set of claim 2 in which said spring comprises a urethane member having a generally cylindrical center section and tapered endwise portions

7. The die set of claim 6 in which said upper abutment means comprises a backup plate secured to the upper surface of said upper shoe member.

9. The guidepost assembly of claim 8 in which said spring member comprises a urethane member, a guide bushing carried by said lower shoe member and telescopically engaging the periphery of said tubular guide post.

10. The guidepost assembly of claim 8 in which said spring member comprises a polyurethane member of generally cylindrical cross section at its center portion and having two frustoconical ends, said polyurethane member being deformed when said die is closed and returning to its original configuration when said die is open, a guide bushing carried by said lower shoe member and telescopically engaging the periphery of said tubular guidepost.

11. The guidepost assembly of claim 10 in which said upper abutment means compresses a backup plate secured to the top of said upper shoe member.