BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to punch and die assemblies and, more specifically, punch and die assembly designs that incorporate precision cutting components.

Brief Description of the Prior Art For many years, punch and die assemblies have been used to produce a wide variety of stampings that are useful in the production of many products. During this time, various improvements have been made to the punch and die assemblies. For example, improvements such as illustrated in U. S. Patents 4,103,574; 5,860,315; and 5,423,641 relate to designs for more rapidly changing machine tooling. As another example, various types of guide systems and improvements thereto also have been developed. Still other improvements have been directe to modifications in material composition. For example, such improvements have included the use of Meehanite and, in limited applications, die set aluminum for the

manufacture of the shoes and other metallic components in the punch and die assemblies.

Some prior art improvements have been directe to the manufacture of stampings having precise tolerances and at relatively high production rates. For example, carbide cutting tools have been found to be useful in many applications to produce precision stampings in large volume and at relatively high rates of production.

Iypically, the carbide cutting tools have been used in combination with Meehanite metallic components and improved guide systems.

However, a persistent problem with the use of such precision stamping tools has been that such tools have tended to be subject to relatively rapid wear that degraded product quality and increased manufacturing costs. In prior art assemblies, one cause of accelerated tool wear was that the shoes and other metallic components would laterally deform as a result of compression forces.

This, in turn, caused the feed distance to change and resulted in loss of product quality and even product rejection.

Another cause of accelerated tool wear has been the thermal expansion and contraction of the assembly components during the course of operation. Such thermal variations arise due to friction and other exothermic causes that are inherent in the stamping process.

Over time, such thermal variations contribute to degraded accuracy of the punch and die apparats and loss of precision in the stampings that are produced.

Due to relatively high rates of tool wear in the prior art precision stamping tools, manufacturers were required to increase the frequency of tool maintenance. This, in turn, led to disadvantages of increased costs arising from higher maintenance costs, shorter tool life and more frequent periods of down time for the stamping machine.

Attempts in the prior art to avoid the disadvantages of the rapid wear associated with precision carbide cutting tools have included the use of ceramic cutting tools. It has been recognized that ceramic cutting tools tend to be more resistant to wear and therefore would potentially avoid some of the disadvantages of carbide cutting tools.

However, in many applications, the use of ceramic precision cutting tools has been unsuccessful because ceramic tools are subject to a somewhat different set of limitations. For example, ceramic cutting tools are relatively brittle in comparison to carbide cutting tools.

Ceramic cutting components have been commercially successful in some applications as, for example, the draw process that is used in the can industry where the ceramic component is not subject to the shock. However, such ceramic tools have not been successfully used in the pierce punch industry where the tool is expose to a sudden shock.

Ceramic cutting components have also been found to be more sensitive to thermal expansions and contractions in the punch and die apparats. Such thermal variations are especially significant in precision punch and die assemblies wherein the tolerances are typically on the order of 0.00008 in. whereas in non-precision punch

and die assemblies tolerances are more typically in the range of 0.001 to 0.002 in. In the same manner, the ceramic cutting tools are also more sensitive to mechanical vibrations and deflections in the punch and die apparats.

Accordingly, there was a need in the prior art for a punch and die apparats that would extend the useful life of precision cutting tools and, in particular, better enable the use of ceramic precision cutting tools.

SUMMARY OF THE INVENTION In accordance with the subject invention, a punch and die assembly for use in a press wherein the assembly inclues a punch sub-assembly, a plurality of guide assemblies, and a die sub- assembly. The punch sub-assembly has a translational axis that is generally parallel to the direction of movement of the material to be punched, the punch sub-assembly defining an array of guide assembly openings that are separated in the direction of the translational axis by a center-to-center distance in the range of substantially four to ten inches. The die sub-assembly has a translational axis that is generally parallel to the direction of movement of the material to be punched, the die sub-assembly defining a plurality of guide assembly openings that are separated in the direction of the translational axis by a center-to-center distance in the range of substantially four to ten inches. Each of the guide assemblies is secured within a respective opening of the punch sub-

assembly and is also laterally confine within a respective opening of the die sub-assembly.

Preferably, the punch sub-assembly inclues a punch shoe made of mold plate aluminum and a cutting tool that is connecte to the punch shoe. The punch sub-assembly also inclues a stripper plate that is flexibly connecte to the aluminum punch shoe and mechanically biased away from the punch shoe. The punch shoe and the stripper plate both include respective guide assembly openings that are separated in the direction of the translational axis by a center-to-center distance in the range of substantially four to seven inches. The die sub-assembly inclues a die shoe that is made of mold plate aluminum and a die that is secured to the die shoe. The die shoe inclues guide assembly openings that are separated in the direction of the translational axis by a center-to-center distance in the range of substantially four to seven inches. The guide assembly inclues a leader pin that has a bushing at one end and a bearing assembly at the opposite end. The leader pin is connecte to a respective guide assembly opening of the stripper plate, the bushing is connecte to a respective guide assembly opening in the punch shoe, and the bearing assembly is connecte to a respective guide assembly opening in the die shoe.

More preferably, the cutting tool that is connecte to the punch shoe is made of ceramic material. Most preferably, the guide assembly opening in the punch sub-assembly and in the die sub- assembly are separated in the direction of the translational axis by a

center-to-center distance of substantially four to six inches and the pre-load of the bearing assembly is in the range of substantially 0.0002 inch to 0.0006 inch.

Other objects and avantages of the invention disclosed herein will become apparent to those skilled in the art as a description of a preferred embodiment of the invention proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the presently disclosed invention is shown and described in connection with the accompanying drawings wherein: FIG. 1 is a bottom plan view of the punch shoe that is included in the apparats of the present invention; FIG. 2 is a partial end view of the punch and die apparats disclosed herein taken along the translational axis A-A'of Figure 1 with portions thereof broken away; and FIG. 3 is a parital side view of the apparats herein disclosed taken along the cross-axis B-B'with the portions thereof broken away to show the mechanism for biasing the stripper plate away from the punch shoe.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A presently preferred embodiment of the disclosed invention is shown in Figures 1-3 wherein a punch and die assembly is shown.

As will be apparent to those skilled in the art, the disclosed punch and

die assembly is used in connection with a vertical punch press to produce stampings of various types, depending on the dies that are used. The punch and die assembly inclues a punch sub-assembly 10 in combination with a die sub-assembly 12 and a plurality of guide assemblies 14 as are hereinafter more fully described.

Punch sub-assembly 10 inclues a punch shoe 16 that is flexibly connecte to a stripper plate 18. Punch shoe 16 has a translational axis A-A'and a cross-axis B-B'. Axis A-A'is generally parallel to the direction of movement of the material that is to be punched and cross-axis B-B'is substantially orthogonal to axis A-A'.

As will be apparent to those skilled in the art, material that is to be stamped is fed from a spool or web toward the punch sub-assembly substantially in the direction of translational axis A-A'.

As hereinafter is more fully explained, stripper plate 18 is flexibly connecte to punch shoe 16 by means of guide assemblies 14, a plurality of bolts 20 that cooperatively serve as a stop, and a spring 22 or other biasing means that mechanically biases stripper plate 18 away from punch shoe 16. A precision tool such as a ceramic punch 24 is secured to punch shoe 16. Stripper plate 18 is provided with an opening that receives punch 24 so that stripper plate 18 serves as a guide for precision punch 24.

In the example of the preferred embodiment, punch 24 is made of"Z-MAT 250"ceramic material such as is available from Norton Company or equivalent. Punches made of this material and used in the punch and die assembly that is herein described have been found

to have a useful life that is approximately five times longer than precision punches made of carbide material. The longer life of ceramic punch 24 is due, in part, to less frequent tool sharpening for the ceramic tools than for the carbide tools. Moreover, it has also been found that, to achieve a sharpened edge, it is necessary to remove less material from ceramic tools than from carbide tools.

Still further details concerning the comparative performance of selected ceramic punches are as follows: Ceramic Material Performance; (all punches were 2. 00" long with .580" sweeps) Number of Punch Stvle MateXal Cveles Results Square (. 010"x. 015") Enomoto UTZ-30 2 Broke Square (. 010" x. 015") Zircoa Zircon L 100 Fracture Square (. 010"x. 015") Norton Z-MAT 250 1000 Like New Round (. 060") Enomoto UTZ-30 100 Chipped Round (. 060") Zircoa Zircon L 240 Fracture Round (. 060") Norton Z-MAT 250 1000 Like new Blade (. 050" x 2.000") Enomoto UTZ-30 5 Broke Blade (. 050" x 2.000") Zircoa Zircon L 305 Chipped Blade (. 050" x 2.000") Norton Z-MAT 250 1000 Like new

The properties of the ceramic material are: Hardness Vickers 13.5Gpa (Rockwell A 90) 4 Point Bend Strength 210 Ksi (1440 Mpa) Fracture Toughness 8 Mpa. m l/2 Fully Dense Fine grain size (< 1 micron) Punch shoe 16 defines an array of guide assembly openings 28.

Guide assembly openings 28 are arrange in rows along the A-A'axis and in columns along the B-B'axis. The presently preferred embodiment discloses an array of two rows and three columns although other arrays having additional columns are also within the scope of the invention that is herein disclosed. Also in the preferred embodiment, the guide assembly openings 28 are separated in the direction of the translational axis by a center-to-center distance that is substantially in the range of four to ten inches. More preferably, the

guide assembly openings 28 are separated in the direction of the translational axis by a center-to-center distance that is substantially in the range of four to seven inches. Most preferably, the guide assembly openings 28 are separated in the direction of the translational axis by a center-to-center distance that is substantially in the range of four to six inches.

In a manner similar to punch shoe 16, stripper plate 18 is also provided with an array of guide assembly openings 30. The relative location of guide assembly openings 30 substantially corresponds to the location of guide assembly openings 28 such that guide assembly openings 30 are arrange in rows along the A-A'axis and in columns along the B-B'axis. The presently preferred embodiment discloses an array of two rows and three columns although other arrays having additional columns are also within the scope of the invention that is herein disclosed. Also in the preferred embodiment, the guide assembly openings 30 are separated in the direction of the translational axis by a center-to-center distance that is substantially in the range of four to ten inches. More preferably, the guide assembly openings 30 are separated in the direction of the translational axis by a center-to-center distance that is substantially in the range of four to seven inches. Most preferably, the guide assembly openings 30 are separated in the direction of the translational axis by a center-to-center distance that is substantially in the range of four to six inches.

As also shown in Figures 1-3, each of the guide assemblies 14 are precision guide pin assemblies of a type that is commercially available from Steinel or equivalent. Guide assemblies 14 include a leader pin 32 that is secured within a respective guide assembly opening 30 of stripper plate 18. Preferably, leader pin 32 is press fitted into guide assembly opening 30 such that it is securely fastened therein.

Guide assemblies 14 further include a bushing 34 that is concentrically arrange on a first end 36 of leader pin 32 and slidably located thereon. Each of bushings 34 is confine within a respective guide assembly opening 28 of punch shoe 16. Furthermore, leader pin 32 has an outside diameter that is approximately 0.0005 in. smaller than the inside diameter of bushing 34 to provide a more precise sliding fit.

Guide assemblies 14 further include a bearing assembly that inclues a ball cage 38 and a bushing 42. Ball cage 38 is concentrically arrange about a second end 40 of leader pin 32 where the second end 40 of leader pin 32 is oppositely dispose from the first end 36. Ball cage 38 inclues a number of bearings that are in rolling contact with the surface of leader pin 32 and also with the internal surface of bushing 42 such that the leader pin 32 is moveable in a longitudinal direction with respect to a bushing 42.

Bushing 42 of the bearing assembly is secured within guide assembly opening 50 of die shoe 44. In this way, bushing 42 and die shoe 44 are stationary with respect to the press bed of the press.

Stripper plate 18 of punch sub-assembly 10, which is secured to leader pin 32, is moveable with respect to die shoe 44 in the direction of the longitudinal axis of leader pin 32 because the second end 40 of leader pin 32 is longitudinally moveable within ball cage 38. Punch shoe 16, which is flexibly secured to stripper plate 18, is also moveable with respect to die shoe 44 in the direction of the longitudinal axis of leader pin. 32.

In the embodiment of the presently disclosed invention, it is preferred that the bearings are maintained in the ball cage 38 by a ball cage retainer 41. It has been found that the use of the ball cage retainer 41 allows the use of a longitudinally longer ball cage 38. In this way, the guide assemblies 14 provide more stable guidance between the die sub-assembly 12 and the punch sub-assembly 10.

The bushing 42 is concentrically located about ball cage 38 with bushing 42 having an internal diameter that is larger than the outside diameter of the second end 40 of leader pin 32 such that bushing 42 and leader pin 32 define an aperture 42a therebetween. Aperture 42a has a radial width 42b that is slightly smaller than the diameter of the bearings that are contained in the ball cage 38. The difference between the radial width dimension of aperture 42a and the diameter of the bearings in ball cage 38 defines the"pre-load"for the guide assembly.

It has been found that, in contrast to the punch and die assemblies of the prior art, it is preferred that the pre-load of the guide assemblies is greater than 0.0002 in. because this affords

adequate stability for the guide assemblies 14. In this way the guide assemblies 14 can maintain sufficient lateral stability between the punch sub-assembly 10 and the die sub-assembly 12 in the precision punch and die assembly. More preferably, the pre-load of the guide assemblies 14 is in the range of 0.0002 in. to 0.0006 in. because it has also been found that when the pre-load is greater than 0.0006 in. the guide assemblies tend to conduct mechanical vibrations to an undesirable degree.

Further comparative information regarding selection of an optimal precision guide assembly is as follows: Brand Ball Number Name Size Pre-load/Lateral of Cycles Results Danly. 1875". 001". 0003"500 Lightwear Danly. 1875". 0014". 00015" 500 Heavy wear Danly. 1875". 0005". 0005" 500 Very light wear Lempco. 1875". 001" .0003" 500 Light wear Lempco. 1875". 0014". 0001" 500 Medium wear Lempco. 1875". 0005". 0005" 500 Very light wear Agathon. 157". 0002". 0001" 500 No wear Steinel. 157". 0002". 0001" 500 No wear

The. 1875"diameter balls were not available from either Agathon or Steinel and their standard pre-load is. 0002"-. 0003". The Danly and Lempco systems are not available in the smaller diameters.

The smaller diameter balls are preferred due to the extra surface contact per cage length. Danly/Lempco have 131 balls per cage.

Agathon/Steinel have 182 balls per cage affording 39% greater additional surface contact.

All tests employed guide pins of 1.500" diameter.

The die sub-assembly 12 of the disclosed punch and die assembly inclues a die shoe 44 and a die 46 that is secured to die shoe 44. Die 46 has a cavity 48 that receives the punch 24 at times when the punch shoe 16 is closed toward die shoe 44. Die shoe 44 has a translational axis A-A'that is generally parallel to the direction of movement of the material that is to be punched. Die shoe 44 also has a cross-axis B-B'that is substantially orthogonal to the translational axis.

In a manner similar to punch shoe 16 and stripper plate 18, die shoe 44 is also provided with an array of guide assembly openings 50.

The precise location of guide assembly openings 50 substantially corresponds to the location of guide assembly openings 28 and 30 such that guide assembly openings 50 are arrange in rows along the A-A'axis and in columns along the B-B'axis. The presently preferred embodiment discloses an array of two rows and three columns although other arrays having additional columns are also within the scope of the invention that is herein disclosed. Also in the preferred embodiment, the guide assembly openings 50 are separated in the direction of the translational axis by a center-to-center distance that is substantially in the range of four to ten inches. More preferably, the guide assembly openings 50 are separated in the direction of the translational anis by a center-to-center distance that is substantially in the range of four to seven inches. Most preferably, the guide assembly openings 50 are separated in the direction of the translational axis by a center-to-center distance that is substantially in the range of four to six inches.

In the operation of the preferred embodiment of the disclosed invention, the material that is to be stamped (not shown) is fed into the punch and die assembly in the direction of the translational axes A A'of punch shoe 16, stripper plate 18, and die shoe 44 and between stripper plate 18 and die shoe 44. The material is positioned within the punch and die assembly where it is to be stamped according to various guides and locaters as will be known and

understood to those skilled in the art. At this time, punch shoe 16 and die shoe 44 are spaced apart such that there is a gap between the stripper plate 18 and the die shoe 44. The gap between stripper plate 18 and die shoe 44 is sufficiently wide to allow the material to pass therebetween.

When the material is positioned for stamping, the press moves the ram downward and the punch shoe 16 and stripper plate 18 are thereby closed toward die shoe 44. This movement of the punch shoe 16 and stripper plate 18 closes the gap between stripper plate 18 and die shoe 44 so that the work material is placed in compression between stripper plate 18 and die face 46 according to the bias force of springs 22. Leader pin 32 moves with stripper plate 18 and also with punch shoe 16 during this portion of the downward stroke. At the same time, leader pin 32 moves freely in the longitudinal direction with respect to die shoe 44 because the end 40 of leader pin 32 is set within ball cage 38.

After the material has been placed in compression between the stripper plate 18 and the die face 46, the press ram continues to move in a downward stroke and closes punch shoe 16 toward die shoe 44.

As punch shoe 16 continues to close toward die shoe 44 on the downward stroke, stripper plate 18 maintins a substantially constant position against die face 46 because stripper plate 18 is flexibly connecte to punch shoe 16 through springs 22 and bolts 20. As punch shoe 16 continues to advance downwardly, punch 24 moves through aperture 26 of stripper plate 18, pierces the material, and

then enters the cavity 48 of die 46 before the completion of the downward stroke.

When the press lifts the press ram, the first end 36 of leader pin 32 moves longitudinally within bushing 34 and the punch shoe 16 opens with respect to die shoe 44. However, the stripper plate 18 maintins compression against the material due to the loading of springs 22. This movement allows the punch 24 to be withdrawn from the cavity 48 in die 46 and also from the material before the material can move laterally with respect to the punch. As the punch shoe 16 is opened further, springs 22 bias stripper plate 18 away from punch shoe 16 until stripper plate 18 is biased against stop 20. As punch shoe 16 continues to open, stripper plate 18 maintins its position with respect to punch shoe 16 and stripper plate 18 opens with respect to die shoe 44 so that the material is no longer in compression between stripper plate 18 and die shoe 44.

As herein previously described, in the preferred embodiment the guide assembly openings 28,30, and 50 are separated in the direction of the translational axis by a center-to-center distance of substantially in the range of four to ten inches More preferably, the center-to- center spacing is in the range of four to seven inches and, even more preferably In the range of four to six inches. This center-to-center spacing is contrary to the spacing for guide assemblies in precision punch and die assemblies known in the prior art. In such prior art assemblies the typical center-to-center spacing was twelve to fourteen inches and even greater.

The reason for the larger center-to-center spacing in prior art devices was that the precision guide assemblies are relatively extensive. To minimize the die costs as well as overall production costs, it has been the practice in the prior art to maintain relatively large center-to-center spacing between the guide assemblies and thereby limit the number of guide assemblies that are required.

However, surprisingly, it has been found that increasing the number of precision guide assemblies actually reduces the overall costs of production! By sufficiently increasing the number of precision guide assemblies, the surface contact of the guide assemblies is also increased to limit unwanted lateral movement of the punch sub-assembly with respect to the die sub-assembly.

Apparently, in the prior art such lateral movement has contributed to unwanted excessive wear of the punch and has resulted in more frequent machining of the punches, shorter life of the punch components, and shorter production runs; all resulting in total production costs that are actually higher than if a greater number of precision guide assemblies are used! The surprising result of using more closely spaced guide assemblies is completely contrary to the teaching and practice of the prior art.

As a result of the improvements to the punch and die assembly herein described, it is anticipated that the precision guide assemblies located on center-to-center spacing of seven inches or less as herein described will increase the operating life of the punch and die assembly by an order of magnitude as, for example, increasing the

useful life of the apparats from approximately ten million cycles to about one hundred million cycles.

In addition to the spacing of guide assemblies 14 as described above, bearings in ball cage 38 are used to locate the second end 40 of leader pin 32 in die shoe 44 as previously described herein. The ball cage 38 is retained by ball cage retainer 41. The use of the ball cage retainer allows the longitudinal length of ball cage retainer to be greater. This, in turn, allows the use of a greater number of bearings which affords improved guidance of the punch shoe 16 and the stripper plate 18 before the punch 24 penetrates the material.

Additional unexpected benefits that have been realized from the disclosed embodiment also include a reduction in wear on the die sections of die 46. Also, the incidence of"burrs"on the produced parts has been greatly reduced.

Also preferably, the punch shoe 16, stripper plate 18, and die shoe 44 are made of mold plate aluminum such as Alcoa gC7 or commercially available equivalent. For use in the precision punch and die assemblies as disclosed herein, mold plate aluminum has been found to have lower lateral deformation than Meehanite and also to hold more precise tolerances than the aluminum die set materials that are known and used in the prior art. The mold plate aluminum is denser than the aluminum typically used for die set material and is also surface hardened by anodizing. It has been found that the yield strength, tensile strength, density, modulus of elasticity, and the coefficient of thermal expansion of such material are also preferable to

those of the Meehanite material that is often preferred in punch and die assemblies that were used in the prior art.

More specifically, a comparison of the mold plate aluminum and the Meehanite materials is as follows: MEEHANITE ALUMINUM Tensile 65,000 psi 85,000 psi Strength Yield 45,000 psi 77,000 psi Strength Elongation 12% min. 8% max.

Brinell 153-207 167 Hardness Modulus of info not available 10.3 x 10 (6) psi Elasticity Thermal info not available 12.8 x 10 (-6) in/in/degree F Expansion 4"x 6"2"thick test piece. Both pieces had 1"diamenter holes located using 2"centers. Each part was subject to 250 degrees for 30 min, then hole locations and center distances checked. The aluminum moved. 000070" the Meehanite moved. 0002" which is 65% additional movement.

The results from the use of mold plate aluminum are conter- intuitive to what would be expected from this substitution of materials. It would be expected that the thermal variations of aluminum would be greater than for Meehanite. However, they are, in fact, smaller. It is believed that this is the result of the greater heat conductivity of the mold plate aluminum such that heat developed in the stamping process is more efficiently conducted away.

In addition, the mold plate aluminum affords further avantages in that it is lighter and therefore easier to secure the punch sub-assembly 10 and the die sub-assembly 12 to the press ram and the press bed. The lighter weight of the punch sub-assembly 10 and die-subassembly 12 also allow operation of the press at higher speeds. Another avantage of the mold plate aluminum punch sub- assembly 10 and die sub-assembly 12 is that they afford higher damping of mechanical vibrations generated in the stamping process to better protect the punch, particularly when the punch is compose of a ceramic material that is more sensitive to mechanical vibrations.

Additional comparative information regarding the optimal selection of the die set material is as follows: Aluminum Material Performance vs Meehanite; Test pieces had 1/a"diameter holes bored on 6"center distance.

Material & Size Temperature Tim. e Movement<BR> Meehanite 3"x 6"x 12"250 degrees 30 min.. 0024" Meehanite 3"x 6"x 12"150 degrees 1 hour. 0015" Meehanite 3"x 6"x 12"150 degrees 2 hours. 0015" Aluminum 3"x 6"x 12"250 degrees 30 min.. 0012" Aluminum 3"x 6"x 12"150 degrees 1 hour. 0005" Aluminum 3"x 6"x 12"150 degrees 2 hours. 00052" The mechanical properties of the Aluminum QC 7 Mold Plate are; Nominal Density. 10 llb per cu. in., Coefficient of Thermal Expansion 12.8 x 10-6 in./in./degree F, and Tensil strength 85, 000psi with a 8% elongation.

The mechanical properties of Meehanite are; Tensile strength 65,000 psi with a 12% elongation.

While a presently preferred embodiment of the invention has been disclosed and described herein, the invention is not specifically thereto, but can be otherwise variously embodied within the scope of the following claims.