Abstract:
A modular cutoff die unit features square-ended punch and die steels, which are supported by and sized relative to their respective retaining shoes such as to provide four reversable cutting edges and to allow plural cutoff dies to be arranged in tandem.

Description:
SUMMARY OF THE INVENTION 
     The present invention is directed towards a modular cutoff die unit, which is particularly adapted to provide a &#34;cutting off&#34; capability for magnetic punch holder and die holder assemblies of the type disclosed for instance in U.S. Pat. Nos. 3,089,376 and 3,782,166. 
     In an illustrated form of the present invention, the modular cutoff die unit comprises a punch blade-retaining shoe positionally located by a conventional punch templet and held against a punch shoe by magnetic means: a punch steel or blade removably fixed to the punch blade-retaining shoe; a die blade-retaining shoe positionally located by a conventional die templet and supported by a die shoe; a die steel or blade removably fixed to the die blade-retaining shoe; and a presser-foot assembly, which is mounted on the punch blade-retaining shoe and cooperates with the die blade-retaining shoe to positionally clamp a workpiece during a cutting operation. 
     A particularly important feature of the present invention is that the punch and die steels, which may be interchangeable, are shaped and supported relative to their associated shoes such as to provide four reversable cutting edges, which may be resharpened without necessitating change of reference spacing between the punch and die shoes. 
     A further feature of the present unit is its modular construction and the square-end design of the punch and die steels, which enable units to be arranged in tandem to form an overall cutting edge whose length is a multiple of the length of each punch and die steel. 
     While a presently proposed commercial form of the present modular cutoff die unit will be hereinafter described in detail, it is anticipated that the novel features of the present invention may be incorporated within cutoff die units of otherwise diverse construction. 
    
    
     DRAWINGS 
     The nature and mode of operation of the present invention will now be more fully described in the following detailed description taken with the accompanying drawings wherein: 
     FIG. 1 is a side elevational view of a die set mounting a modular cutoff die unit formed in accordance with the present invention; 
     FIG. 2 is an enlarged view of the modular cutoff die unit shown in FIG. 1, but with parts broken away for purpose of clarity; 
     FIGS. 3 and 4 are sectional views taken generally along the lines 3--3 and 4--4 in FIG. 1, and further illustrating punch and die units, respectively, arranged in tandem; and 
     FIG. 5 is a sectional view taken generally along the line 5--5 in FIG. 3. 
    
    
     DETAILED DESCRIPTION 
     Reference is first made to FIG. 1, wherein a conventional die set is generally designated as 10 and shown as mounting therewithin a modular cutoff die unit, which is formed in accordance with the present invention and generally designated as 12. A workpiece, such as a piece of sheet metal, on which a cutting operation is to be performed, is generally designated at 14. 
     Die set 10 is shown in FIG. 1 as generally including a punch shoe 16, which is adapted to be suitably secured to a press ram, now shown; a die shoe 18, which is adapted to be suitably secured to a press bolster, also not shown; a plurality of shoe guide assemblies 20, which include a die shoe mounted guide post 22 and a punch shoe mounted guide post receiving bushing 24; a punch templet 26, which is adapted to be releasably secured to punch shoe 16 by a plurality of templet support or locator posts 28; and a die templet 30, which is adapted to be removably secured to die shoe 18 by a plurality of templet support or locator posts 32. A more complete description of the construction of die set 10 may be had by reference to U.S. Pat. Nos. 3,089,376 and 3,782,166, whose disclosures are incorporated by reference herewithin. 
     In FIGS. 2-4, templets 26 and 30 are specifically shown as being formed with locator holes 26a and 30a and clearance openings 26b and 30b, which are sized, shaped and arranged to accommodate a plurality of identically sized modular cutoff die units 12 arranged in tandem. However, it will be understood that the specific design of these templets will vary with press setup requirements, that is, the number and relative size or cutting lengths of the modular cutoff die units to be employed and whether additional operations, such as perforating, notching, embossing, lancing, forming, knock-out, stamping, etc. are to be simultaneously performed on workpiece 14. 
     By viewing FIGS. 1-4, it will be understood that each modular cutoff die unit 12 includes a pair of associated punch and die units 40 and 42, which are adapted to be suitably affixed to facing surfaces 16a and 18a of punch and die shoes 16 and 18, respectively, such that they are arranged in operative vertical registration in order to effect cutting-off of workpiece 14, whenever punch shoe 16 is caused to reciprocate between its upper or die set open position shown in FIG. 1 and its lower or die set closed position shown in FIG. 2. 
     Punch and die units 40 and 42 are similar in many respects. Therefore, in order to simplify the following description of the construction of unit 12, only punch unit 40 will be fully described in particular detail and the elements of die unit 42, which are of similar construction, will be designated in the drawings by like primed numerals. More specifically, punch unit 40 is similar to die unit 42 in that it generally includes an elongated steel or blade 44; a retainer shoe 46; and means in the form of a locator pin 48 and a plurality of bolts 50 for removable clamping and positionally orienting steel 44 relative to retainer shoe 46. Punch unit 40 principally differs from punch unit 42 in that its retainer shoe 46 is shaped to accommodate a workpiece presser-foot assembly 52, whereas the latter has its retainer shoe 46&#39; shaped to provide a support rib 54, which is formed with openings 55 for affording access to bolts 50 and defines a support surface 56 arranged to cooperate with its associated steel 44&#39; to provide a support for workpiece 14 in the manner best shown in FIGS. 1 and 2. 
     Reference is now made particularly to FIGS. 2, 3 and 5, wherein steel 44 is shown as being formed from a rectangular bar stock having squared ends, such that it assumes a rectangular parallelepiped configuration having parallel clamping or first surfaces 60, parallel bearing or second surfaces 62 and parallel end or third surfaces 64. Surfaces 60 and 62 cooperate at their junctures to define four cutting or shear edges 66a-66d, which extend lengthwise of the steel between end surfaces 64. Steel 44 is preferably provided with a plurality of mounting bore openings 70 and a single locator bore opening 72, which collectively open through clamping surfaces 60 and have their axes arranged in parallel and to lie within a common plane arranged equidistant from bearing surfaces 62. Moreover, as will be apparent from viewing FIG. 3, locator bore opening 72 is preferably disposed equidistant from end surfaces 64, and mounting openings 70 are arranged one-half on each side of the locator bore opening with the positional relationship of each half of such mounting openings relative to the locator bore opening being identical. 
     Retainer shoe 46 is shown as being in the form of a metal casting adapted to be removably fixed or suspended from the downwardly facing surface 16a of punch shoe 16 by means of magnet devices 73, which may be of the type disclosed for instance in U.S. Pat. Nos. 3,089,376 and 3,782,166, and to be horizontally positionally located within die set 10 to project downwardly through the temperate plate clearance opening 26b by means of locator posts 74 releasably locked within temperate locator openings 26a by snap rings 76. In that the force of gravity tends to maintain die retainer shoe 46&#39; in bearing engagement with the upwardly facing surface 18a of die shoe 18, it is normally not necessary to provide the die retainer shoe with magnet devices of the type described above. While the illustrated means for attaching and positionally locating retainer shoes 46 and 46&#39; is preferred, it will be understood that any other suitable means may be employed. 
     By now making reference to FIGS. 2 and 3, it will be seen that retainer shoe 46 is shaped to define a horizontally elongated and vertically disposed retainer clamping surface 78; a retainer bearing surface 80, which extends horizontally and in a right angular relationship from adjacent one marginal edge of surface 78; and a retainer clearance surface 82, which extends from adjacent an opposite and parallel marginal edge of surface 78 in a direction away from retainer bearing surface 80. Preferably, the lengthwise direction of retainer shoe 46, as measured horizontally and lengthwise of surfaces 78 and 80 between opposite ends of the retainer shoe, which are designated as 46a and 46b, is less than the lengthwise dimension of steel 44, as measured between end surfaces 64. Further, the widthwise or vertical dimension of retainer clamping surface 78 is substantially less than the widthwise dimension of clamping surfaces 60, as measured between bearing surfaces 62. Thus, when steel 44 is fixed to retainer shoe 46 in the manner to be described, the ends of the steel may be arranged to project outwardly beyond opposite ends 46a and 46b, and clamping surface 60, which engages with retainer clamping surface 78, has a portion thereof designated as 60a arranged to project beyond retainer clearance 82. 
     Retainer shoe 46 is also formed with a plurality of threaded openings 84 and a single locator receiving opening 86, which is preferably disposed equidistant from end surfaces 46a and 46b. Openings 84 and 86 collectively open through clamping surfaces 78 and have their axes disposed in a parallel relationship and to lie within a common plane, which is arranged parallel to retainer bearing surface 80 and spaced therefrom through a distance corresponding to a spacing between locator receiving bore opening 72 of steel 44 and steel bearing surfaces 62. 
     Retainer shoe 46 is additionally formed with a plurality of stepped diameter bore mounting openings 88, which are arranged in a parallel spaced relationship and open downwardly through retainer clearance surface 82 in the manner best shown in FIGS. 2 and 3. By referring specifically to FIG. 2, it will be understood that each of mounting openings 88 includes an enlarged diameter upper portion 88a, an enlarged diameter lower portion 88b and a reduced diameter central or connecting portion 88c, which cooperate to define upwardly and downwardly facing annular shoulders or abutment surfaces 88d and 88c disposed concentrically of central portion 88c. 
     Locator pin 48 is best shown in FIGS. 3 and 5 as having a cylindrically shaped end portion 48a, which is sized to be snugly received within locator receiving opening 86, and an opposite, &#34;non-round&#34; end portion 48b, which is sized to be slidably received within locator bore opening 72. Preferably, end porton 48b is of a generally oval cross-sectional configuration and arranged such that it slidably engages only with facing wall surfaces of locator bore opening 72, which are arranged immediately adjacent opposite sides of a common plane passing through openings 70 and 72. This arrangement serves to accurately center steel 44 in a direction lengthwise of retainer shoe 46, such that the ends of steel 44 are equidistant from retainer shoe surfaces 46a and 46b, while at the same time not interfering with the seating of steel bearing surfaces 62 in surface-to-surface engagement with retainer bearing surface 80. 
     Again referring to FIGS. 3 and 5, it will be seen that bolts 50 are formed with threaded shank portions 50a, which are sized to be loosely accommodated within steel mounting openings 70 and be threadably received within retainer shoe openings 86; and enlarged head portions 50b, which are adapted to be arranged to clampingly engage that one of steel clamping surfaces 60 spaced from engagement with retainer clamping surface 78. It will be understood that the sole purpose of bolts 50 is to clamp steel 44 against retainer clamping surface 78 after such steel has been accurately located vertically and horizontally relative to retainer shoe 46 by retainer bearing surface 80 and locator pin 48, respectively. 
     The positional relationship of threaded openings 84 relative to locator receiving opening 86 and their positional relationship relative to retainer bearing surface 82 is preferably identical to the positional relationship of mounting bore openings 70 relative to locator bore opening 72 and their positional relationship to bearing surfaces 56. This permits clamping surfaces 60 to be alternately clamped against retainer bearing surface 78 with bearing surfaces 62 alternately disposed in bearing engagement with retainer bearing surface 80, whereby to selectively position cutting edges 66a-66d one at a time in an operative cutting position relative to retainer shoe 46, which is shown in FIG. 2 as being occupied by cutting edge 66a. Thus, that one of the four cutting edges, which at any given time constitutes the operative cutting edge of steel 44, is defined by that one of clamping surfaces 60, which is arranged in engagement with retainer clamping surface 78, and an outer one of bearing surfaces 62, which is spaced from engagement with retainer bearing surface 80. In the preferred form of the present invention, punch steel 44 and die steel 44&#39; are of identical size and construction in order to permit interchangeable mounting thereof on the punch and die retainer shoes. 
     It will be appreciated that the above described arrangement of parts permits resharpening of cutting edges 66a-66d by the simple expedient of grinding clamping surfaces 60; the resultant reduction in thickness of steel 44 being compensated for by forming threaded openings 84 of a depth sufficient to prevent bolt shank portions 50a from &#34;bottoming out&#34;, until the steel has been ground to some given minimum or design thickness requiring its replacement. Also, it will be appreciated that this mode of resharpening cutting edges 66a-66d does not change the placement of the operative cutting edge of the steel relative to either retainer clamping surface 80 or retainer bearing surface 82, and therefore avoids time consuming adjustment of units 40 and 42 relative to one another in a horizontal direction and/or adjustments of the die set closed position of punch unit 16, which would otherwise be required. Further, the above described method of sharpening the cutting edges of steels 44 and 44&#39; possesses the additional advantage that the coplanar relationship of rib support surface 56 and the upper steel bearing surface 62&#39; is not altered during the useful life of steel 44&#39;. 
     Again referring to FIGS. 2 and 3, it will be understood that workpiece presser-foot assembly 52 includes a presser-foot or plate having a generally rectangular and downwardly facing presser or pressure surface 92; a plurality of guide or support rods 94, which are slidably supported one within each of mounting openings 88 and serve to mount presser foot 90 within an elongated recess defined by retainer clearance surface 82 and projecting portion 60a of clamping surface 60 for vertically directed reciprocating movements between its extended and retracted positions shown in FIGS. 1 and 2, respectively; and suitable bias means, such as a plurality of coil type compression spring devices 96, which are operable to normally maintain presser foot 90 in its extended position. Each of support rods 94 includes rod head and shank portions 98 and 100, which are guided for vertically directed reciprocating movements within associated mounting opening upper and central portions 88a and 88c, respectively, such that each rod shank portion 100 extends downwardly through its associated mounting opening lower portion 88b and beyond clearance surface 82 for threaded attachment with presser foot 90. Spring devices 96 are arranged one concentrically of each of shank portions 100 for opposite end bearing engagement with downwardly facing annular abutment surfaces 88b and the upwardly facing surface of presser foot 90, and thereby normally serve to bias the presser foot into its above mentioned extended position, which is determined by engagement of rod head portions 98 with upwardly facing annular abutment surfaces 88d. 
     By again referring to the drawings, it will be understood that the positional relationship of locator openings 26a and 30a relative to one another and locator posts 74 and 74&#39;, serves to horizontally positionally locate punch and die units 40 and 42 of each die unit 12 such that the axes of their locator pin receiving openings 86 and 86&#39; are parallel and lie within a common vertically disposed plane; retainer clamping surfaces 78 and 78&#39; are parallel and arranged to face in opposite directions; and presser surface 92 is disposed parallel to and arranged to bridge across rib support surface 56 and the upper bearing surface 62&#39; of steel 44&#39;. As a result, steels 44 and 44&#39; are positioned such that bearing surfaces 62 and 62&#39; are parallel; their respective end surfaces 64 and 64&#39; lie in a coplanar relationship; and clamping surfaces 60 and 60&#39;, which engage with retainer clamping surfaces 78 and 78&#39;, are parallel and face in opposite directions. The spacing between projecting portions 60a and 60a&#39;, as measured in a direction normal thereto, is such as to insure proper cutting off or shearing of workpiece 14 as portions 60a and 60a&#39; are moved between their offset and lapping positions shown in FIGS. 1 and 2, respectively. 
     By viewing FIGS. 3 and 4, it will be understood that the positional relationship of locator openings 26a and 30a relative to one another and locator posts 74 and 74&#39; additionally serves to horizontally positionally locate punch and die units 40 and 42 of adjacently disposed or tandemly arranged die units 12, such that the steel end surfaces 64 and 64&#39; of adjacent units are arranged in proximate surface engagement and the operative cutting edges of adjacent ones of steels 44 and 44&#39; are disposed in an aligned, end to end relationship in order to effect cutting-off of workpiece 14 along a line whose length corresponds to the sum of the lengths of the operative cutting edges of adjacent units. While it is preferable from the standpoint of manufacturing and inventory considerations to provide only a single size modular cutoff die unit, such that the total length of cut is a multiple of the length of the operative cutting edge of the die steels employed in each unit, it would, however, be possible to provide the units in various sizes as desired. 
     As indicated above, the positional location of the modular cutoff die unit 12 within die set 10 and the number of such units to be arranged in tandem will be determined by press set up requirements. Once these requirements have been determined, appropriately sized and arranged locator holes and clearance openings are formed in templets 26 and 30 to insure that punch and die units 40 and 42 of each unit 12 are arranged in operative vertical registration when these punch and die units are fixed to their associated templets and the latter fixed to the punch and die shoes in the manner shown in FIG. 1. Thereafter, a workpiece 14 to be severed is placed on die unit 42 for supporting engagement with rib support surface 56 and the upwardly facing bearing surface of steel 44&#39;. The workpiece may thereafter be severed by causing movement of punch shoe 16 downwardly towards die shoe 18 into the die set closed position shown in FIG. 2. During closing movements of punch shoe 16, presser foot 90 resides in its extended position relative to punch retainer shoe 46 until presser surface 92 is brought into engagement with the upper surface of workpiece 14, whereby to arrest continued downwardly directed movement of presser foot 90 while causing relative movement between presser foot 90 and punch retainer shoe 48 against the bias of springs 96, as the punch retainer shoe moves towards and into its die closed position shown in FIG. 2. The arrangement is such as to allow for the positive clamping of workpiece 14 prior to initiation of the cutting-off operation in order to prevent horizontal displacements of the workpiece, which would otherwise occur incident to the passage of steel 44 through the workpiece. 
     While a presently proposed commercial form of the modular cutoff die unit has been described in detail, it is anticipated that the several novel features of such unit may be incorporated within cutoff die units of otherwise diverse construction. Thus, as by way of example, the present die unit is not limited in use by the specific manner in which its associated punch and die units are positionally fixed within a die set nor by the construction of such die set. Moreover, it is anticipated that the feature of forming one or both of the punch and die steels with four selectively positioned cutting edges may be employed in cutoff units, which are not intended to be arranged in tandem and therefore may omit the locator pins or comparable steel centering devices. On the other hand, it is contemplated that punch and die steels characterized as having only a single cutting edge may be centered relative to their associated retainer shoes by means of locator pins or comparable devices in order to permit two or more cutoff die units to be arranged in tandem.