Method and apparatus for forming easy opening container walls

Abstract

A method and apparatus are provided for forming a sheet metal easy opening container wall in which an annular groove is formed around the periphery of a depressed central portion of a blank, a planar lip and an upstanding chuckwall are formed around the outer edge of the groove in the blank, the groove is reformed by moving portions of it radially outwardly to form a Z-wall connecting the center portion of the blank to the lip, a score line is formed in the lip to define a removable panel and the Z-wall is collapsed to form an annular folded band adjacent the score line. The annular folded band is designed to shield the raw score edge on the central panel portion after separation of the panel from the can end.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to containers and in particular to a method and apparatus for forming an easy opening end for a container having an annular folded band in the removable portion thereof to shield a raw score edge upon removal of a portion of the can end.

2. Brief Description of the Prior Art

It is known to provide an annular folded band of metal adjacent a weakening line or score line in an easy opening container end to shield the raw score edge after severance of a removable panel from the container end as is disclosed in U.S. Pat. Nos. 3,303,958, 3,434,623, 3,630,408 and 3,696,961 among others. In the absence of such a folded band of metal or a plastic protective strip for shielding the raw score edge, the consumer can be accidentally cut by the raw score edge. It has been known to provide such an annular folded band on either the removable or the non-removable portion of a can end, or on both the removable and non-removable portions.

Methods and tools for forming annular folded bands for shielding of a raw score edge are known as are disclosed in U.S. Pat. No. 3,696,961. That patent discloses a method for forming the band on the non-removable portion only of a can end. Methods and apparatus are also known for forming an annular folded band of material in a removable portion adjacent the score for shielding the score on such removable portion. However, there has heretofore been no known method for forming an annular folded band on a removable panel portion adjacent the score line around such panel portion in which a protective coating on the can end will not be damaged by forming of such annular folded band.

Annular folded bands for shielding raw score edges are used mainly on can ends in which a large central portion of the end is removable for gaining access to the contents of a container. Ends of this type are used on cans or containers for food products, and such can ends must usually have protective coatings on their interior surfaces in order to prevent corrosion and perforation of the can ends by the food products. It is desirable to be able to coat the sheet metal from which can ends are to be formed prior to forming of the ends, and to avoid the need to repair the can ends after they have been formed.

The prior art is lacking in a disclosure of a method and apparatus for forming an easy opening container end wall from coated sheet material wherein the coating on the sheet material will not be damaged by the forming operations.

SUMMARY OF THE INVENTION

This invention provides a method and tools for forming a sheet metal easy opening container end wall by drawing an annular groove into a blank as the blank is being formed into an end shell, forming a planar lip on the end shell between the annular groove and an upstanding chuckwall around the end shell, forming a score line in the lip around the end shell to define a removable panel portion, reforming the groove by moving a portion of it radially outward to form a Z-wall connecting the central portion of the end shell with the lip, and collapsing the Z-wall to form an annular folded band adjacent the score line in the removable panel portion. A pull tab may then be secured to the removable panel portion to complete the conversion of the sheet metal blank into an easy opening container end wall.

Accordingly, an object of this invention is to provide a method and apparatus for forming an easy opening can end having an annular folded band in the removable portion thereof adjacent the score line without damaging the coating on the sheet metal from which the end is formed.

Another object of this invention is to provide a method and apparatus for forming an easy opening container end for use on containers of food products in which a relatively large portion of the end is removed from the end for providing access to the contents of the container, and in which the removable panel has an annular folded band thereon for shielding the raw score edge after removal of the panel.

A further object of this invention is to provide a method and apparatus for forming an easy opening can end having an annular folded band on the removable portion in which a minimum number of operations and tools are required.

The above and additional objects and advantages of this invention will be more fully understood and appreciated with reference to the following description and the drawings attached hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of an easy opening container wall which has been formed in accordance with this invention.

FIG. 2 is a bottom plan view of the container wall of FIG. 1.

FIG. 3 is an enlarged partial cross-sectional view taken along line 3--3 of FIG. 1.

FIG. 4 is an enlarged partial cross-sectional view taken along line 4--4 of FIG. 1.

FIG. 5 is an enlarged cross-sectional view through dies for cutting a blank from a sheet of metal and forming the blank into an end shell.

FIG. 6 is a cross-sectional view similar to FIG. 5 with the end shell partially formed.

FIG. 7 is a cross-sectional view similar to FIGS. 5 and 6 showing completion of the end shell.

FIG. 8 is an enlarged cross-sectional view through a second set of dies and end shell positioned therein preparatory to reforming of the annular groove around the end shell.

FIG. 9 is a cross-sectional view similar to FIG. 8 showing completion of the reforming of the groove around the end shell.

FIG. 10 is an enlarged cross-sectional view through a third set of dies preparatory to further reforming of the end shell.

FIG. 11 is a cross-sectional view similar to FIG. 10 showing completion of forming of the end shell to produce an annular folded band in the removable panel adjacent the score line.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

In order to facilitate understanding of the subject invention and in the interest of clarity, the terms upper, upwardly, lower and downwardly will be herein employed to delineate directions relative to the plane of a can end wall as positioned as it would be when secured on the top of a cylindrical container. The terms inner, (radially) inwardly, outer and (radially) outwardly will be employed to delineate directions toward and away from the center of the can end or end wall.

Referring to FIGS. 1-4, an easy opening container end 10 is illustrated which has been formed in accordance with this invention. The easy opening container end 10 is made of sheet material, and preferably of aluminum or an alloy thereof, and has a protective coating 11 of plastic material such as a polyolefin approximately 3 mils thick adhesively bonded on its inside or undersurface to prevent attack and corrosion of the metal by the contents of the container. The plastic coating 11 has sufficient extensibility to permit fabrication of an easy opening container end in accordance with this invention and still retain coating integrity. Food contents in containers are frequently chemically acidic in character and can corrode metal container components unless the components have their interior surfaces coated with such a plastic material.

The easy opening container end 10 has a line of weakening in the form of a score line 12 in it which defines a relatively large tear panel 14 which can be removed from the container wall. An annular lip 16 extends radially outwardly from the score line 12 around the removable panel 14 and connects the removable panel with an upstanding chuckwall 18 and a seaming flange 20 around the periphery of the can end. Flange 20 can be double seamed on a container body 22 as is illustrated in FIG. 3. The container body 22 illustrated in FIG. 3 preferably has an inwardly projecting annular rib 24 on it which underlies lip 16 for shielding the raw score edge on such lip after panel 14 has been removed from the container.

A tab 26 is attached to panel 14 in any suitable manner such as by an integral rivet 28. Tab 26 which has been selected for purposes of illustration is constructed from a piece of sheet metal and includes a tab body in the shape of a ring 30 and an attaching portion 32 through which rivet 28 passes for attachment of the tab to the removable panel 14. The tab has a downwardly projecting rib 34 for facilitating rupture of the score line 12 when the tab ring 30 is lifted in the conventional manner. Tab 26 further has a downwardly convex hub 29 around the rivet aperture to hold the tab in a parallel relation with respect to the plane of removable panel 14 as is best illustrated in FIG. 3.

Removable panel 14 has a downwardly embossed central portion 15 and two upwardly embossed buttons 17 for facilitating gripping of ring 30. The removable panel 14 also preferably includes two downwardly embossed ribs 19 extending radially along opposite sides of rivet 28 and a downwardly embossed quarter moon shaped bulge 21 adjacent the rivet toward the center of the removable panel. The ribs 19 and bulge 21 help to control bending of the removable panel 14 along a choral line between the ribs and the bulge when tab 26 is lifted. Controlling bending of panel 14 facilitates rupture of score line 12 and helps to prevent undesirable separation of the tab from the removable panel.

In accordance with this invention, removable panel portion 14 includes an annular folded band 36 therearound adjacent score line 12 for shielding the raw edge of the panel after rupture of the score line. As best illustrated in FIG. 4, folded band 36 includes radially outwardly projecting smooth or dull edge surface 38 which preferably projects outwardly beyond score line 12 in the container end so that such dull surface will be contacted by the finger of a user before the raw score edge, which could cut the finger of the user, is contacted by the finger.

Folded band 36 includes upper and lower layers 40 and 42 respectively, an intermediate layer 44 and inner and outer reverse bends 46 and 48 respectively which interconnect the upper, lower and intermediate layers of the band. At all locations along the score line 12 except for the region adjacent the rupturing rib 34 on the tab 26 (FIG. 3), the layers 42 and 44 are flattened against the intermediate layer 44 as shown in FIG. 4. At the region of the score line 12 adjacent the rupturing rib 34 on the tab, the intermediate layer 44 is not bent into tight supporting engagement with the upper layer 40. Instead, as shown in FIG. 3, the intermediate layer 44 projects radially outwardly and axially downwardly in extending from bend 46 to bend 48. With this construction, the intermediate layer 44 is not backed up or supported immediately radially inwardly of the score line 12. This absence of support for the upper layer 40 beneath the rupturing rib on the tab facilitates initiation of severance of the sheet material at the point of initial rupture beneath the rupturing rib. If the intermediate layer 44 were in tight engagement with the upper layer 40, the support provided by such intermediate layer would resist the inwardly directed force against the upper layer applied by the rupturing rib on the tab.

This invention is directed to providing a method and apparatus for forming an annular folded band on a removable panel in an easy opening can end from a sheet of metal in such a manner that a protective coating on the side of the sheet which is to be the inside surface of the can end is not damaged during the forming operation. FIGS. 5-7 illustrate opposing dies which are employed to cut a blank 50 from a sheet of metal 52 and partially reform the blank into an end shell which will eventually become an easy opening can end. The lower dies include a die core insert 54 with a planar top surface 56 and a rounded outer corner 57, an annular die core ring 58 around insert 54, a draw ring 60 around the die ring 58 and an annular cutting die 62 around the draw ring 60. Die ring 58 includes an inner upwardly facing rim surface 64 and an inner inwardly facing wall surface 66 which together form a groove 67 with the outer surface 68 of die core insert 54. The die ring 58 further includes a rounded corner 65, an intermediate upwardly facing rim surface 70, an intermediate inwardly facing wall surface 72 and a curvilinear shoulder 74 which faces generally upwardly. The bottom die members 54, 58 and 62 are all held in fixed position for forming blank 50 against the upper punch members. Draw ring 60 is supported by springs or the like not shown so that it can move downwardly when an upper die member is moved thereagainst.

The upper dies include a punch insert 76 having a downwardly projecting annular tongue 78 thereon for mating with groove 67 in the lower dies. The tongue 78 preferably has a rounded nose 80 on it having a radius of curvature of approximately 0.030 inch. The upper dies further include a punch ring 82, a knockout ring 84, a punch cutting ring 86 and a stripper ring 88. Punch ring 82 has a downwardly facing substantially planar surface 90 for mating with inner rim surface 70 on the die core ring 58, a radially outwardly facing wall surface 92 for mating with intermediate wall surface 72 on the die core ring and a curvilinear shoulder 94 for mating with the inner portion of curvilinear shoulder 74 on the die core ring. As mounted in a press, all of the upper dies are mounted on the top die shoe or holder for vertical movement with such die holder. Punch ring 82 and cutting ring 86 are solid with the die holder (no springs), and punch insert 76, knockout 84 and stripper 88 are spring loaded so that their downward travel can be arrested by the resistance of the bottom dies.

As illustrated in FIG. 5, the upper tools have just commenced their downward travel, and the cutting edges on upper and lower cutting rings 86 and 62 have cut a blank 50 from metal sheet 52. The peripheral edge portion of blank 50 is engaged between the top surface of draw ring 60 and cutting ring 86. Springs or the like, not shown, support the draw ring against the downward travel of cutting ring 86 whereby the peripheral edge portion of the blank can be drawn inwardly from between the draw ring and cutting ring during drawing of the blank to form an end shell.

FIG. 6 illustrates an intermediate stage in the drawing of the blank into an end shell which is to be subsequently made into an easy opening container end. During die travel to the position illustrated in this figure, knockout 84 first bottomed against die core insert 54 shortly after the end blank was cut from the sheet of metal, followed by punch insert 76 bottoming against die core insert 54. The springs between the upper die holder and the knockout and punch insert are compressed as the die holder continues its downward travel. The punch insert 76 has drawn the center of the blank downwardly with respect to its peripheral edge portions and the rounded nose 80 of the punch insert has drawn an annular groove 96 in the blank into groove 67 provided by die core insert 54 and die core 58. The rounded corners 57 and 65 on die core insert 54 and die core 58 and curvilinear shoulder 74 on the die core permit the metal from the blank to be drawn into such annular groove 96 without tearing or otherwise damaging the blank or the protective coating on the blank. Punch 82 has not completed its downward travel to reform the portion of the blank outwardly of groove 96, so the metal in the blank is not restrained by such punch and can be drawn inwardly from the peripheral edges thereof to form groove 96.

The peripheral edges of the blank are drawn from between the surfaces of the upper and lower die members as the center of the blank is drawn downwardly by punch insert 76 against die core insert 54. The upper and lower die members 58, 60, 84 and 86 are so designed that the peripheral edges of the blank will either be pressed between a fixed die and a resiliently mounted die or drawn from between two closely spaced surfaces as between die core 58 and cutting ring 86 so that such peripheral edges are so confined that they cannot wrinkle as they are being drawn inwardly. An outwardly projecting curvilinear flange 98 is formed on the blank over die core member 58.

FIG. 7 illustrates completion of the first stage of forming of a blank into an end shell 101. As illustrated here, punch 82 has completed its downward travel and has bottomed against die core 58 to form an annular lip 100 and an upstanding chuckwall 102 between groove 96 and peripheral flange 98. The metal for forming such lip and chuckwall is provided by drawing the peripheral edge portions of the blank further inward from between the surfaces of the top and bottom die members. Upon completion of forming the end shell, the upper dies are withdrawn upwardly, and knockout 84 pushes or knocks the end shell off the upper dies. As explained above, knockout 84 is spring loaded, and the springs have been compressed during the downward travel of the die holder. Consequently when the die holder is withdrawn upwardly, the springs are axially expanded which forces the knockout ring 84 downwardly with respect to punch 82 and punch cutting ring 86 to knock the end shell from the upper dies.

The end shell 101 is next removed from the dies illustrated in FIGS. 5-7 and positioned in another set of dies as illustrated in FIGS. 8 and 9. These dies include a die insert 104, an anvil 106, a combination punch and score indentor 108 and a spring-loaded locating ring 110. As the upper dies are moved downwardly toward the lower dies, the spring-loaded locating ring 110 first contacts the end shell 101 to center it in the dies and hold it in position for the combination punch and score indentor 108 to reform groove 96 in the end shell. As the upper die holder continues to move downwardly, the springs in the locating ring 110 are compressed permitting the combination punch and score indentor 108 to move downwardly with respect to such locating ring. As the combination punch and score indentor 108 completes its downward travel, the central portion of the end shell is flattened against the bottom die insert 104 which moves a portion of groove 96 radially outwardly to form a Z-wall 111 (FIG. a) connecting the center portion of the shell to annular lip 100 on the shell. At completion of the downward travel of the combination punch and score indentor 108, scoring rib 112 on such tool indents or cuts a score line 114 in lip 100 against the support provided by anvil 106. The upper dies are next withdrawn upwardly for removal of the end shell 101 from the dies.

The end shell 101 is next positioned in a third set of dies as illustrated in FIGS. 10 and 11. These dies include a platten 114, a spring-loaded pressure ring 116, a forming tool 118 and a locating ring 120. As the upper tools are moved downwardly toward the lower tools, the locating ring 120 first contacts the chuckwall 121 of the end shell 101 to center the end shell in the die and hold it in such position as illustrated in FIG. 10. When surface 122 on the locating ring 120 has moved downwardly to contact the upper surface of lip 100 on the end shell 101, the force of the locating ring begins to compress the springs under the pressure ring 116 to move such pressure ring downwardly with the forming tool and locating ring. During this last portion of the tool movement, the central depressed portion of the end shell is supported on platten 114 and cannot move. Consequently, the force of forming tool 118 against lip 100 on the end shell collapses Z-wall 111 to form an annular folded band 124 as illustrated in FIG. 11. Such annular folded band 124 comprises three layers of metal as is described with respect to the can end illustrated in FIGS. 1-3. The upper dies are then withdrawn upwardly for removal of the end shell 101 from the dies.

Upon completion of forming of the annular folded band 124, the desired embossments and an integral rivet are formed in the removable panel in the end shell, a pull tab is positioned on the end wall over the rivet and the rivet is headed or staked to secure the pull tab to the removable panel. The finished can end is then ready to be double seamed onto a filled container body in a conventional manner.

It is seen that a method and apparatus have been illustrated and described which may be used to form an annular folded band in a removable panel on an easy opening container end in which a protective coating on the sheet metal from which the end is formed is not damaged during the forming operation. The sheet metal is not stretched significantly, but instead is drawn and reformed into an annular groove in the sheet metal whereafter the groove is reformed and collapsed to form three folded layers of metal adjacent the score line around the removable panel. Such annular folded band of metal includes an outer smooth edge which substantially underlies the score line for shielding the raw score edge after severance of the score line.

Although a preferred embodiment of the invention has been illustrated and described, it will be apparent to those skilled in the art that numerous variations can be made in the method and apparatus without departing from the scope of the invention or of the claims appended hereto. For example, upon forming the end shell with a peripheral groove in it, the center portion of the end wall within the outline of the groove can be depressed and the groove collapsed in one operation using a single set of tools, rather than in two sets of tools and two operations as is illustrated and described. If this is done, the score line around the end wall is preferably formed after forming of the end shell with the groove therein and before depressing the center portion of the end wall and collapsing of the groove. In another alternative method, the score line can be cut in the end wall radially inwardly of the annular band which will then shield the raw score edge on the non-removable portion of the container wall. The can ends which are formed in accordance with this invention may also be of various shapes and designs, as may the tabs on the ends. For example, the layers of metal in the annular folded band may be flattened against one another adjacent the entire length of the score line instead of being loosely folded beneath the nose of the tab as is illustrated in FIG. 3. It has been found that with some can end and tab configurations, flattening the layers of metal in the band beneath the nose of the tab does not adversely affect the force required to initiate rupture of the score line, and may even reduce the magnitude of such force.

Claims

What is claimed is:

1. In a method of forming a sheet metal easy opening container end wall having an annular score line therein defining a removable panel, an annular folded band in the removable panel adjacent the score line to shield the raw score edge on the panel after removal from the end wall, an upstanding chuckwall around the removable panel and a peripheral flange extending outwardly from the chuckwall for securement of the end wall to a container body, the steps comprising:

drawing the center portion of a generally circular sheet metal blank downwardly with respect to the peripheral edge portions of the blank,

drawing an annular U-shaped groove in the blank around the periphery of the center portion of the blank,

forming an annular lip and an upstanding chuckwall around the outer edge of the groove,

depressing the center portion of the blank and the inner wall of the groove to move portions of the groove radially outwardly to form a Z-wall connecting the center portion of the blank to the lip of the blank,

forming a score line in the lip around the blank and

collapsing the Z-wall to form an annular folded band adjacent the score line.

2. A method as set forth in claim 1 in which the blank has a plastic coating on the surface thereof which is to be the inside surface of the can end.

3. A method as set forth in claim 1 in which the annular band is formed closely adjacent the score line and has a smooth outer edge which projects radially outward beyond the score line.

4. A method as set forth in claim 3 in which the score line is cut in the outer surface of the lip around the complete circumference of the can end to define a relative large panel which is completely removable from the can end.

5. In a method for forming a sheet metal easy opening container end wall having an annular score line therein defining a removable panel, an annular folded band in the removable panel adjacent the score line to shield the raw score edge on the panel after removal from the end wall, an upstanding chuckwall around the removable panel and a peripheral flange extending outwardly from the chuckwall for securement of the end wall to a container body, the steps comprising:

providing a first die set including a substantially planar first surface perpendicular to the direction of die travel, an annular groove around said planar surface, an annular rim surface around the outer edge of the groove, an annular radially inwardly facing wall surface around the outer edge of the rim surface substantially perpendicular to said first surface and an annular shoulder around the top of said wall surface, and a second opposing die set including a punch having an annular projecting tongue mating with said groove in said first die set, an annular forming ring around said punch including a planar rim surface in opposed relation to said rim surface of said first die set and annular radially outwardly facing wall surface in parallel radially inwardly spaced relation to said wall surface of said first die, and a clamping ring around said forming ring in opposed relation to said shoulder of said first die set;

drawing a generally circular blank of sheet of metal between said first and second die sets to form an end shell by moving said punch in said second die set against said first die set with the peripheral edge portions of the blank frictionally restrained between said shoulder and said clamping ring of said first and second die sets respectively to draw the center portion of the blank downwardly with respect to the peripheral edge portion thereof and draw a groove in the blank around the center portion, and thereafter moving the forming ring on said second die set against the annular rim and wall surfaces on said first die set to form a substantially planar lip and upstanding chuckwall around the outer edge of the groove which is formed in the end shell;

reforming the end shell by providing support under the lip on the shell and depressing the center portion of the shell within the outline of the groove therein to move portions of the groove in the shell radially outward and thereby form a Z-wall connecting the center portion of the lip in the shell;

forming a score line in the lip to define a removable panel; and

collapsing the Z-wall to form an annular folded band adjacent the score line.

6. A method as set forth in claim 5 in which the annular groove in the first die set has rounded corners leading into the die surfaces on either side of the groove and the projecting tongue on the second die set has a rounded nose to avoid damage to the blank or a protective coating on the blank.

7. A method as set forth in claim 5 in which the punch in the second die set includes springs for resiliently supporting it on the punch holder.

8. In a method of forming a sheet metal easy opening container end wall having an annular score line therein defining a removable panel, an annular folded band in the container wall adjacent the score line to shield the raw score edge after severance of the removable panel from the end wall, an upstanding chuckwall around the end wall and a peripheral flange extending outwardly from the chuckwall for securement of the end wall to a container body, the steps comprising:

drawing the center portion of a generally circular sheet metal blank downwardly with respect to the peripheral edge portions of the blank,

drawing an annular U-shaped groove in the blank around the periphery of the center portion of the blank,

forming an annular lip and an upstanding chuckwall around the outer edge of the groove,

depressing the center portion of the blank and the inner wall of the groove to move portions of the groove radially outward and

collapsing the groove to form an annular folded band around the center portion of the blank.

9. A method as set forth in claim 8 in which the blank has a plastic coating on the surface thereof which is to be the inside surface of the can end.

10. A method as set forth in claim 8 in which the annular band is formed closely adjacent the score line and has a smooth outer edge which projects radially outward beyond the score line.

11. A method as set forth in claim 10 in which the score line is cut in the outer surface of the lip around the complete circumference of the can end to define a relative large panel which is completely removable from the can end.

12. In a method for forming a sheet metal easy opening container end wall having an annular score line therein defining a removable panel, an annular folded band in the removable panel adjacent the score line to shield the raw score edge on the panel upon rupture of the score line, an upstanding chuckwall around the removable panel and a peripheral flange extending outwardly from the chuckwall for securement of the end wall to a container body, the steps comprising:

providing a first die set including a substantially planar first surface perpendicular to the direction of die travel, an annular groove around said planar surface, an annular rim surface around the outer edge of the groove, an annular radially inwardly facing wall surface around the outer edge of the rim surface substantially perpendicular to said first surface and an annular shoulder around the top of said wall surface, and a second opposing die set including a punch having an annular projecting tongue mating with said groove in said first die set, an annular forming ring around said punch including a planar rim surface in opposed relation to said rim surface of said first die set and annular radially outwardly facing wall surface in parallel radially inwardly spaced relation to said wall surface of said first die, and a clamping ring around said forming ring in opposed relation to said shoulder of said first die set;

drawing a generally circular blank of sheet of metal between said first and second die sets to form an end shell by moving said punch in said second die set against said first die set with the peripheral edge portions of the blank frictionally restrained between said shoulder and said clamping ring of said first and second die sets respectively to draw the center portion of the blank downwardly with respect to the peripheral edge portion thereof and draw a groove in the blank around the center portion, and thereafter moving the forming ring on said second die set against the annular rim and wall surfaces on said first die set to form a substantially planar lip and upstanding chuckwall around the outer edge of the groove which is formed in the end shell;

forming a score line in the lip to define a removable panel in the end shell;

depressing the center portion of the shell to move portions of the groove radially outward; and

collapsing the groove to form an annular folded band around the removable panel adjacent the score line.

13. A method as set forth in claim 12 in which the annular groove in the first die set has rounded corners leading into the die surfaces on either side of the groove and the projecting tongue on the second die set has a rounded nose to avoid damage to the blank or a protective coating on the blank.

14. A method as set forth in claim 12 in which the punch in the second die set includes springs for resiliently supporting it on the punch holder.