Abstract:
A punch and die set is provided for use in a stamping press having a punch assembly and a die assembly reciprocated by a driving mechanism. The punch and die assemblies are aligned to a common center and are structured to slidably engage one another for positive guidance of the punch and die tools without the need for other guidance by shafts, bars or the like. One of the punch assembly and die assembly can be non-fixedly carried by the drive mechanism, allowing the guidance of the engaged punch and die assemblies to define the relative positions of the tools. This arrangement eliminates any stack-up of tolerances between the assemblies and substantially reduces misalignment during stamping, including any misalignment that may be introduced by the press driving mechanism.

Description:
BACKGROUND OF THE INVENTION 
     1. Field Of The Invention 
     The invention relates to metal forming and stamping machines in which opposed punch and die tools are brought together on a malleable work piece such as a length of sheet metal. According to an aspect of the invention, cooperating tools such as a punch and complementary die are carried on opposed tool carrying structures that are independently complementary, namely being engaged with one another around a periphery for guidance in a male-female guiding arrangement that precisely and repeatably determines the relative positions of the punch and die tools as they are brought together at the work piece in the stamping operation. 
     2. Prior Art 
     In a conventional technique for the manufacture of certain articles, particularly from flat strips of metal, blank stock is fed into a specially manufactured tool called a stamping press, which carries a stamping die. The stamping die and other associated structures have shaped forming edges and surfaces that respectively support or strike the stock. Through the pressure and motion of the device, the tool cuts out and/or forms the stock into the metal parts or components of the required size and shape. 
     The stamping press has driving elements that impart the necessary motion and tonnage to force the flat metal strip into the desired shape in conjunction with the tool structures, typically moving one of two interengaging tools in an oscillatory displacement against an opposed tool which is mounted on a stationary support. Typically the motion involves the vertical oscillation of a forming tool against a fixed tool on a horizontal bed. One or a number of forming operations can be accomplished in a stroke, plural operations being accomplished by placing tools configured for successive forming steps laterally adjacent to one another along a feed path of the stock. 
     Stamping presses are available in a wide variety of sizes and capabilities, depending upon the size and complexity of the required parts, as are the tools. Stamping presses can produce small parts at very high rates, and may operate at over 3,000 vertical strokes per minute. Metal stamping dies are used to manufacture parts ranging from very small and/or sophisticated components for the electronics industry, to large shapes such as portions of an automotive body. 
     Metal stamping dies typically comprise two associated halves, which together are referred to as a “punch and die set.” A conventional punch and die set has an upper shoe and a lower shoe to which the metal forming tools are mounted, and guide posts and bushings for holding the upper and lower shoes, and therefore the tools, in precise alignment during die construction, die maintenance, die setting and in use to form parts. 
     The number of guide posts and bushings varies according to the accuracy required and the size of the die set. In a typical vertically-oriented stamping die, the upper half of the stamping die holds a punch-set, and is usually the portion that is attached to the movable part of the stamping press, known as a “ram.” The ram moves the punch-set up and down relative to the lower half of the stamping die (referred to as the die-set), which is stationary on a heavy bolster plate defining a fixed bed. Metal stamping dies perform different processes upon the flat metal strip, depending on the configuration of the surfaces that contact the work piece. The processes include, without limitation, coining, drawing, blanking, piercing, notching, embossing, and similar types of bending, forming and cutting operations, etc. The tools that perform the foregoing processes require machining and mounting to very precise tolerances. For example, to cut through the work piece an appropriate clearance between passing edges of the punch and die tools might be less than two tenths of one thousandth of an inch. Depending on the thickness of the stock and other parameters, a relatively wider clearance between the same passing edges may not cut through the stock at all, and instead will bend or draw the stock without parting it. For dependable correct operation, the dimensions and relative positions of the punch and die tools can be critical. In addition, a lack of sufficient clearance, or even contact between punch and die portions that are intended to pass one another, can wear or destroy the punch and die sets. 
     The tolerances can be very demanding. A punch and die set is preferably capable of being precisely opened and closed and will correctly form parts repeatedly, for hundreds of thousands of successive strokes of the stamping press. The punch and die set structures must be precisely and accurately positioned in the stamping press and the movable and stationary parts of the press that carry the punch and die sets must be moved precisely and accurately to ensure that the punch and die structures meet and/or pass in the exact same relative position each and every time the stamping press cycles. This is necessary to prevent the stamping die from damaging itself as well as to correctly form the parts. 
     There are potential problems associated with punch and die sets that can cause finished part quality problems and punch and die set tool damage. A very reliable, extremely precise, and accurate alignment design is required in order to ensure that a stamping die is always correctly aligned. If a punch and die set is not aligned correctly, for whatever reason, expensive damage will occur. For example, punch tools and die sections can chip or break, or excessive wear of the tools will occur, necessitating frequent stoppages for maintenance. 
     On the other hand, the press driving and guiding structures must be heavy and durable if they are to survive a large number of operations. It can be all the more difficult to ensure accurate and repeatable motion in very heavy driving arrangements needed for durability and longevity. With these needs in mind, various methods have been employed in the prior art to prevent or reduce misalignment of punch and die tools. 
     Known stamping dies and presses typically comprises planar supporting structures such as a movable rectangular plate on the punch side and a stationary horizontal bed or support for the die. Driving mechanisms bring the supporting structures together relative to one another in a direction normal to the parallel planes of the movable plate and the bed. For guidance, the punch and die sets are usually connected, respectively, to the ram and to the bed or base of the stamping press and to one another, including by two, three or four vertical guide posts, for example at the corners of the punch and die set. The posts can be fixed in one of the movable and stationary sides and movable in an opening in the other. These vertical posts also can be configured in a male/female elongated arrangement with the top or punch-posts fitting over or inside the lower die-posts. p Both the stamping press and punch and die set depend upon the guide posts for alignment of the punch tools with the die tools, and the punch and die set with the stamping press ram. A number of guide posts are provided at positions spaced laterally from one another, defining a line along which the movable and stationary members come together, and fixing the relative orientation of the movable and stationary members as well. 
     A punch and die set may have inherent alignment problems due to their shape. For a punch and die set to make a viable component, the top half (e.g., the punch) must meet the bottom half (die) in a nearly perfectly parallel orientation (usually level horizontal). If, for example, one corner is lower than another, the angular error results in a corresponding side-to-side or front-to-back lateral error in the relative positions of interacting punch and die surfaces and edges. Even the slightest difference in angular relationship between the punch and die may damage the metal forming tools or result in poor quality parts. 
     A four-post die, punch and die alignment is considered appropriate to maintain relative positions and to prevent uneven closing of the punch and die set. The posts are typically located at or near the periphery of the bed, such as at the corners of a rectangular bed. In this arrangement, the guiding interactions of the individual posts are well spaced from one another, which spreads the guiding effect of the posts and tends to provide more positive support than a closer array or fewer guide posts. However, each post involves a limited mass of material and has a relatively small surface area in contact with the bore in the opposed structure or the like. The posts and their bores can wear at different rates, for example due to die imbalance or uneven buildup of grease and dirt along each post. Furthermore, with wear, the plates can tend to move out of a parallel orientation and become canted. This can cause uneven performance of the stamping die as well as an increased rate of wear on the guiding mechanism, resulting in increasingly poor or variable quality in the stamped parts. 
     Apart from the aspect of angular error between the punch and die set, the overall alignment of the press can vary and negatively affect the performance of the punch and die set, particularly where highly demanding tolerances are involved. For example, if the press ram has incurred an angular error, the thrust vector for the ram&#39;s vertical motion is not exactly perpendicular to the base of the press, this error in the alignment of operative forces is likewise translated to the punch and die set. 
     Prior art designers have developed methods of loosely suspending a punch and die set from the ram to eliminate a direct angular error. This improvement in alignment separates the matter of press alignment form punch/die plate alignment but has other drawbacks. Substantial complexity must be added to the punch and die arrangement, and even greater reliance for structural support and alignment is placed on the four guide posts. Thus suspending the punch to relieve ram alignment sensitivity may introduce angular errors by increasing wear and reliance on the guide posts. As a practical matter, this concept works only if every other component is in excellent condition and operates perfectly, and the press is only out of alignment by a minor span, such as a few thousandths of an inch. Such circumstances rarely occur in normal manufacturing. 
     Press manufacturers also have attempted to add dimensional stability and/or to reduce alignment errors by adding margins of safety to the various die and punch components. These efforts add cost and complexity to the punch and die. 
     Improvements in the prior art to improve the alignment of punch and die sets with time and wear, have added substantially to the complexity of an already complicated technology. The practical improvement in accuracy has been modest by comparison. There is a need in the art to reduce or eliminate angular alignment errors and improve positioning accuracy, without adding substantial complexity to the structure of dies and presses. Conversely, there is a need for a less complicated and expensive arrangement for punch and die sets that is at least as accurate for punch/die positioning, and preferably is more accurate, than the conventional structure in which a plurality of spaced guide posts constrain the relative motion of the punch and die and their carrying structures. 
     SUMMARY OF THE INVENTION 
     The invention provides a punch and die set for use in a stamping press, comprising a self-guiding punch assembly and die assembly, eliminating stack-up of the tolerances associated with cooperative assemblies and substantially reducing misalignment during stamping. 
     In one embodiment, the punch assembly includes at least one tool that is adapted for engaging and altering a work piece such as a strip of metal, a punch shoe arranged to hold the tool on a first side and for operative engagement with a portion of the stamping press on a second side, with the first and second sides having a common center or reference. A stripper guide bushing surrounds and encloses the punch shoe so that the punch shoe and the stripper guide bushing are both symmetric about the common center or reference. The die assembly is disposed in coaxial confronting relation to the punch shoe, and includes a die nest having at least one through-bore that is sized and shaped to receive the tool, and a die nest guide bushing surrounding and enclosing the die nest. The die nest guide bushing is symmetric about the same common center or reference as the punch shoe, and is dimensioned relative to the punch shoe and the stripper guide bushing such that, when the punch and die set are mounted and assembled in a stamping press, the die nest guide bushing slidingly receives the punch shoe and the stripper guide bushing. The die nest guide bushing is rigidly fixed on one of the relatively movable members of the stamping press and positively guides the punch shoe and stripper guide bushing, which are fixed to the other of the movable members of the press, over the full stroke of the stamping press. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and advantages of the invention are more fully disclosed in, or rendered apparent by, the following detailed description of certain preferred embodiments of the invention, which are to be considered together with the accompanying drawings wherein like numbers refer to like parts, and wherein: 
     FIG. 1 is a front elevational view of a stamping press including a punch and die set in accordance with the subject invention; 
     FIG. 2 is a front elevational view, partially in phantom, of the punch and die set shown in FIG. 1, with the high speed stamping press removed for clarity of illustration; 
     FIG. 3 is an exploded, cross-sectional view of the punch and die set shown in FIG. 2; 
     FIG. 4 is a front elevational view of a tooling mount; 
     FIG. 5 is a side view, partially in phantom, of the tooling mount shown in FIG. 4; 
     FIG. 6 is a top view of an upper spring retainer; 
     FIG. 7 is a side view, partially in phantom, of the upper spring retainer shown in FIG. 6; 
     FIG. 8 is a bottom elevational view of a punch shoe formed in accordance with the invention; 
     FIG. 9 is a side view, partially in phantom, of the punch shoe shown in FIG. 8; 
     FIG. 10 is a top view of a ball cage; 
     FIG. 11 is a cross-sectional view of the ball cage shown in FIG. 10, as taken along line  11 — 11  in FIG. 10; 
     FIG. 12 is a cross-sectional view of a portion of the ball cage shown in FIGS. 10 and 11, showing the relationship of the wall of the ball cage and an individual ball bearing; 
     FIG. 13 is a top view of a lower guide bushing formed in accordance with the present invention; 
     FIG. 14 is a side view, partially in phantom, of the lower guide bushing shown in FIG. 13; 
     FIG. 15 is a top elevational view of a die nest according to the invention; 
     FIG. 16 is a side view, partially in phantom, of the die nest shown in FIG. 15; 
     FIG. 17 is a side view of a die shoe according to the invention; and 
     FIG. 18 is a top elevational view, partially in phantom, of the die shoe shown in FIG.  17 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following description of preferred embodiments of the invention is intended to be read in connection with the foregoing drawings and should be considered a portion of the entire written description of this invention. As used in the description, terms such as “horizontal, ” “vertical,” “left,” “right,” “up” and “down,” etc., are intended to refer to orientations illustrated in particular drawing figures and the like and do not limit the invention to particular orientations. Similarly, terms such as “inwardly” and “outwardly” generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate. Also, terms such as “coupled,” “connected” or “interconnected” are intended to describe a relationship between two or more structures, mean that such structures are secured or attached relative to each other either directly or indirectly through intervening structures and includes pivotal connections. The term “operatively” means that the foregoing direct or indirect connection between the structures allows such structures to operate as intended by virtue of such connection. 
     FIG. 1 shows a self-guiding punch and die set  1  structured in accordance with the invention, installed for use in a stamping press  10  of a type that apart from the invention is conventional in the art. Stamping press  10  includes a ram  15  coupled to a drive operable to move ram  15  toward and a away from a bolster plate  20 , for example at a rate in the range from approximately 5 to 5,000 strokes per minute. The length of the stroke may be in the range from about 0.5 to 10 inches. An electric motor  25  is coupled to a drive shaft  30  having an eccentric  35  which drives ram  15  by means of a crank  37 . A flywheel  38  stores kinetic energy from electric motor  25  and assists in moving ram  15  toward and away from bolster plate  20 . Drive shaft  30  and crank  37  can be journaled in hydrostatic bearings and ram  15  likewise can be journaled in a linear hydrostatic bearing, including fluid conduits, all of which are designed to allow stamping press  10  to operate at the above-mentioned 5 to 5,000 strokes per minute. An upper tooling mount  40  is attached to and carried by ram  15 , via through-bores in mount  40  and bolts or the like (not shown). 
     Referring to FIGS. 1-3, punch and die set  1  comprises a punch assembly  100 , a die assembly  200 , and a spring  300 . Punch assembly  100  is secured to tooling mount  40 . Die assembly  200  is secured to bolster plate  20 , and spring  300  is interposed between the punch assembly and the die assembly and bears resiliently against them. Preferably, punch assembly  100  and die assembly  200  define a common center  50  (see FIGS. 1 and 2) and axes-of-symmetry X-Y (see FIGS. 4,  6 ,  8 ,  10 ,  13 ,  15 , and  18 ). In the exemplary embodiment shown such symmetry is circular. Other symmetric relationships between punch assembly  100  and die assembly  200  may be adopted for use with the invention, including, e.g., elliptical, hexagonal, octagonal, or any other shape that provides  360  degrees of bearing surface between punch assembly  100  and die assembly  200 . 
     Punch assembly  100  and die assembly  200  may be formed from any of the well known tool steels or similar, relatively hard and/or durable metals that are well known in the art. A strip of relatively hard metal (not shown) is disposed between the forming tools and die. An indexing mechanism (not shown) is provided to move the strip of metal or other blank or preformed stock through stamping press  10  and to bring the stock between punch assembly  100  and die assembly  200  in a manner that is well known in the art. 
     Punch assembly  100  includes an upper spring retainer  103 , a punch shoe  106 , a stripper guide bushing  109 , and a ball cage  112 . In the embodiment shown, all conform to a substantially circular symmetry defined about axes of symmetry X-Y passing through punch and die set center axis  50 . More particularly, upper spring retainer  103  comprises a generally circular plate having an upper surface  115  and a recessed lower surface  118  projecting radially outwardly from an outer surface of punch shoe  106  (FIG.  7 ). A ram coupler  124  projects outwardly from a central portion of upper surface  115 . Ram coupler  124  is adapted to non-fixedly engage a complementarily shaped recess on tooling mount  40  of ram  15 . The engagement is such that the ram can force the tooling mount generally axially downwardly, and limits the axially upward displacement of the tooling mount due to spring  300 . However, some relative motion is permitted by the coupling, between the ram and punch assembly  100 . Ram coupler  124  may be formed, for example, as a bulbous protrusion such as a chord of a sphere on upper surface  115 , and tooling mount  40  may be formed as a complementary recess  125  on ram  15  confronting the protrusion (FIGS. 2,  3 ,  4 - 7 ). 
     As best shown in FIG. 3, recessed lower surface  118  of upper spring retainer  103  is sized and shaped to receive punch shoe  106 . Through-bores  119  communicate between upper surface  115  and recessed lower surface  118 , and are adapted to receive fastening means, such as bolts or the like, for affixing spring retainer  103  and punch shoe  106 . 
     Referring to FIGS. 2,  3 ,  8 , and  9 , punch shoe  106  defines an upper surface  133 , a lower surface  136 , a tooling recess  137 , and a side wall  138 . Side wall  138  of punch shoe  106  defines a surface of substantially circular symmetry defined about axes of symmetry X-Y passing through center  50 . In the embodiment shown, side wall  138  defines a smooth curved surface, namely a circular cylindrical surface, but other shapes are possible as provided herein. Blind bores  142  are located in upper surface  133 , and have a depth that is adapted for receiving fastening means, such as, bolts or the like. A plurality of stripper spring bores  143  are formed in lower surface  136 , and are adapted to receive a plurality of stripper spring compression sets (not shown). The stripper spring compression sets are known in the art for use in maintaining a stripper plate in position on the metal strip during stamping. Tools (not shown) are fastened, within tooling recess  137  of punch shoe  106  in a predetermined order and pattern. Tooling recess  137  may comprise a polygonal peripheral shape, e.g., rectangular as shown in FIGS. 2,  8 , and  9 . Tools that are releasably fastened within tooling recess  137  typically include punches and forming tools that are adapted for piercing, drawing, blanking, forming or otherwise displacing selected portions of the metal strip in order to alter its shape, as is well known in the art. 
     Referring to FIGS. 2,  3 ,  13 , and  14 , stripper guide bushing  109  comprises a cylindrically shaped shroud having a curved outer wall  147  and a bottom annular wall  149 . Stripper guide bushing  109  also comprises a substantially circular symmetry defined about axes of symmetry X-Y, passing through punch and die set center  50 . Outer wall  147  includes an annular recessed shoulder  151  adjacent to a top annular edge  153 . The surface of outer wall  147  is substantially smooth as is the inner surface. A chamfered annular corner  155  is disposed about the lower edge of stripper guide bushing  109 , at the intersection of outer wall  147  and bottom annular wall  149 . Bottom annular wall  149  projects inwardly from the inner surface of outer wall  147  and defines an opening  157  that communicates with the interior of stripper guide bushing  109 . Opening  157  is sized and shaped to correspond to tooling recess  137  of punch shoe  106 . An internal shoulder  159  is formed between a first annular vertically oriented wall  161  and a second annular vertically oriented wall  163 . Inner surface  165  of bottom annular wall  149  comprises a plurality of spring pockets  167  that are adapted to accept conventional compression springs (not shown). In a preferred embodiment, at least  8  spring pockets  167  are circumferentially disposed about opening  157 . A pair of anti-rotation bores  170  are defined in bottom annular wall  149  in diametrically opposed, spaced relation to one another. The anti-rotation bores receive corresponding angular anti-rotation pins (not shown) when stripper guide bushing  109  is assembled within punch and die set  1 , as will hereinafter be disclosed in further detail. An “O” ring  172  is disposed on shoulder  151  during assembly. 
     Referring to FIGS. 2,  3 , and  10 - 12 , ball cage  112  comprises a cylindrical bushing defined by a cylindrical wall  182  having a plurality of transverse bores  180  disposed throughout its circumference that are sized and shaped to house individual ball bearings  185 . Portions of each ball bearing  185  project outwardly from both sides of wall  182 . Ball cage  112  has an inner diameter sized to accept stripper guide bushing  109 . p Referring to FIGS. 3,  15 - 18 , die assembly  200  comprises a die shoe  203 , a die nest guide bushing  206 , and a lower spring retainer  209 , all having substantially circular symmetry defined about axes X-Y passing through punch and die set center  50 . The die nest guide bushing  206 , stripper guide bushing  109  and punch shoe  106  are complementary male/female structures, movably carried on one another in a telescopic guiding arrangement, with ball cage  112  reducing friction and wear. 
     Die shoe  203  comprises means for fixation to bolster plate  20 , e.g., through-bores  215  and associated bolts (not shown). A centrally positioned scrap port  218  is formed within die shoe  203 . Scrap port  218  provides an exit path for portions of the metal strip that are cut loose by the forming tools located in punch shoe  106 . A pair of anti-rotation bores  270  are positioned in die shoe  203  so as to be coaxially aligned with antirotation bores  170  when punch and die set  1  is assembled. 
     Die nest guide bushing  206  comprises a cylindrically shaped receptacle including a curved outer wall  220  and an annular bottom wall  222 . More particularly, curved outer wall  220  comprises an inner surface  224  and an outer surface  226 . Annular bottom wall  222  projects inwardly from the lower portion of outer wall  220 . The inner diameter of die nest guide bushing  206  is sized to accept stripper guide bushing  109 , as will be disclosed in further detail. An annular chamfered corner  227  is formed at the inner intersection of outer wall  220  and bottom wall  222 , and is complementary to chamfered corner  155  of stripper guide bushing  109 . An access/inspection port  228  is provided in the side of die nest guide bushing  206 . Access/inspection port  228  provides a press operator with means for viewing the stamping operation and for accessing tools and/or die shoe  203  for repair or adjustment. A metal strip entrance port  230  and a metal strip exit port  232  are formed in diametrically opposed, coaxially aligned relation to one another within outer wall  220  of die nest guide bushing  206 . 
     Annular bottom wall  222  defines a central opening  234  that is defined by a first annular vertical wall  236  and a second, larger diameter annular vertical wall  238 . A shoulder  240  is defined between annular vertical walls  236  and  238 . Metal strip exit port  232  allows finished components to exit punch and die set  1 , for example to a reeling operation or the like. 
     Referring to FIGS. 3,  7 , and  18 , lower spring retainer  209  comprises an annular plate projecting radially outwardly from outer wall  220  of die nest guide bushing  206 , and includes an upper surface  251 , a lower surface  254  and an annular wall  256 . Lower spring retainer  209  is positioned on outer wall  220  of die nest guide bushing  206 , just above access/inspection port  228 , and is adapted to support spring  300 . 
     Referring to FIGS. 1 and 2, spring  300  comprises a helically formed rod of spring quality material, e.g., spring steel. Spring  300  is normally biased in compression and comprises an upper ring  310 , a lower ring  320 , and one or more turns forming a helical beam  330 . The diameters of upper ring  310  and lower ring  320  are sized to circumscribe ball cage  112  and die nest guide bushing  206 . 
     Punch assembly  100  and die  200  are assembled in the following manner. Referring to FIGS. 2 and 3, die nest guide bushing  206  is first bolted to die shoe  203  so that scrap port  218  is disposed in coaxial relation with a corresponding scrap part in bolster plate  20 . In this position, die nest guide bushing  206  opens upwardly, as best shown in FIG.  3 . Once die nest guide bushing  206  is securely fastened to bolster plate  20 , die sections, which are the female cutting components that correspond to the tools disposed in punch shoe  106 , (not shown for clarity of illustration) are mounted to die nest guide bushing  206 , completing the assembly of die assembly  200 . 
     Punch assembly  100  is assembled by first mounting the male cutting components (e.g., pierces, punches, forming tools, etc.) in tooling recess  137  of punch shoe  106 . Once this has been completed, a plurality of stripper spring compression sets are mounted within bores  143  of punch shoe  106 . A plurality of stripper inserts (not shown, for clarity of illustration) are then mounted to stripper guide bushing  109 . Stripper inserts are known in the art for use in removing the pierced metal strip from around the punches, etc., so as to allow the metal strip to advance through the die. Once the stripper inserts have been mounted to stripper guide bushing  109 , stripper guide bushing  109  is mounted to punch shoe  106  so as to surround and enclose punch shoe  106 . Bolts or the like having a length sufficient to extend through-bores  167  are provided to fasten guide bushing  109  to punch shoe  106 . Once this point in the assembly has been reached “O” ring  172  is placed in firm engagement on annular recessed shoulder  151  of stripper guide bushing  109 . 
     Upper spring retainer  103  is mounted to punch shoe  106  by at least one bolt extending through-bore  119  into bore  142 . To compete the assembly of punch and die set  1 , spring  300  is positioned in lower spring retainer  209  such that lower ring  320  is disposed on lower surface  254 . Spring  300  is disposed on lower spring retainer  209  in an initially unbiased condition. Once spring  300  is in position, punch assembly  100  is placed into die assembly  200 . As this occurs, angular positioning anti-rotation pins (not shown) are oriented so as to be disposed in anti-rotation bores  170 ,  270  within stripper guide bushing  109  and die nest guide bushing  206 . The angular guide pins and angular guide bushings are known in the art for use in maintaining an appropriate angular orientation between the male and female portions of a punch and die set that are circular in cross section. The pins and bores serve to prevent relative rotation of the circular punch and die and are not provided to guide the punch and die in a longitudinal sense. Longitudinal guidance is provided by the engagement of the punch shoe, stripper guide bushing and die nest guide bushing. The anti-rotation pins and bores also obviously are unnecessary if the punch/die cross section is some shape other than circular. It will be understood that when punch assembly  100  enters die assembly  200 , spring  300  will be compressibly biased. In order to maintain punch assembly  100  in position within die assembly  200 , it is necessary to lock them in place in order to counteract the biased load exerted by spring  300 . 
     Punch and die set  1  is assembled to high speed stamping press  10  in the following manner. Ram coupler  124  (disposed on upper surface  115  of upper spring retainer  103 ) is oriented so as to be in confronting relation with complementary recess  125  on ram  15 . Punch and die set  1  is first slid along bolster plate  20  of press  10  until tooling mount  40  is disposed in confronting relation with ram  15 . Once punch and die set  1  are in position with tooling mount  40  engaging ram coupler  124 , punch and die set  1  are releasably fastened to bolster plate  20  by dowel locating pins and securing bolts well known in the art. Once punch and die set  1  are secured, the stamping press  10  is activated so that ram  15  is moved to its full bottom position. Feeler gauges and die down stops (not shown) are used to set the depth of punch tool entry into die sections, as is well known in the art. Once the punch and die section depth settings are established, the lock-up device is removed from spring  300  so that punch assembly  100  is biased against ram  15  by spring  300 . Once this has occurred, punch and die set  1  is ready for use to fabricate metal parts. 
     More particularly, stamping press  10  is activated so as to move ram  15  into a fully top position, which opens punch assembly  100  and die assembly  200  by reducing the biased on spring  300 . With a strip of metal fed into die nest guide bushings  206 , via entrance support  230 , stamping press  10  is activated to move ram  15  into a fully bottom position, firmly holding the strip of metal between the stripper face plate and the die nest. This process is repeated several times with ram  15  reciprocating between a fully bottom position and a fully topped position as a material strip is incrementally slid through the die, where it is progressively formed by the various punch and die tools. The progress of the material through the die may be observed through viewing/access port  228  in die nest guide bushing  206 . Adjustments to the tools may also be accomplished via viewing/access port  228 , without the need to disassemble punch and die set  1 . Once punch and die set  1  has been adjusted to yield satisfactory components, stamping press  10  may be fully activated, for example reciprocating at a rate between 5 and 5,000 strokes per minute while synchronously indexing the stock material into and through the space between the punch and die, to produce parts. 
     Because of the extreme rigidity and circular symmetry of punch and die set  1 , the male cutting components of punch assembly  100  are guided into the female cutting components of die assembly  200  completely dependant upon the guidance provided by stripper guide bushing  109  and die nest guide bushing  206 , and completely independent of any inaccuracies inherent in press ram  15  or arises as a function of press ram wear. This system totally eliminates the need for extreme accuracy in the press alignment system. The necessary guidance is provided in the punch, die and stripper mountings. Advantageously, punch and die set  1  are disposed in independent relation to ram  15  since punch and die set  1  are not bolted to ram  15 . The linkage between ram  15  and punch and die set  1  shown in the Figures is more forgiving and compensates for press alignment inaccuracies. It will be understood that spring  300  may be replaced by employing spring compression sets located internally to the stripper spring guidance bushings. These internal spring compression sets may be mounted to the punch shoe  106  and act against pockets located in stripper guide bushing  109 . 
     A number of advantages are obtained by employing the present invention, which provides a self-guiding punch and die set which avoids all of the aforementioned problems associated with prior art metal stamping devices. The inventive self-guiding punch and die set reduces misalignment of die components by combining a cage structure of a die with the stripper assembly. The self-guiding punch and die set may be designed and constructed in a simpler fashion than punch/die arrangements having other mounting and guidance arrangements, combining the functions of the ball cage die structure with the stripper assembly. The inventive structure has fewer components subject to failure, and the components are more integral and therefore durable than more complex arrangements and are characterized by less expensive up-front acquisition costs. 
     One substantial advantage of the invention is that the self-guiding punch and die set as disclosed provides an independent alignment system which allows practical use of older, worn and less reliable stamping presses in the production of precision parts, without a corresponding reduction in the quality of the manufactured part. Old stamping press equipment may be utilized with the self-guiding punch and die set of the present invention without the expense of procuring new portions of the press to replace worn ones that admit of looseness or displacement of the ram, or otherwise repairing the worn press. This allows the design of a totally new type of simplified press that does not require the complex drive and controls of existence presses and the maintenance to the way and gibb alignment system. 
     The invention is by no means limited to the precise constructions specifically disclosed and shown in the drawings, but also encompasses modifications or equivalents within the scope of the appended claims.