US3357228A

US3357228A - Method and means for making metal forgings

Info

Publication number: US3357228A
Application number: US462277A
Authority: US
Inventors: Harrison George; Nelson K Harrison
Original assignee: IMP Eastman Corp
Current assignee: IMP Eastman Corp
Priority date: 1961-09-01
Filing date: 1965-06-08
Publication date: 1967-12-12
Anticipated expiration: 1984-12-12

Description

Dec. 12, 1967 R S ETAL 3,357,228

METHOD AND MEANS FOR MAKING METAL FORGINGS Ori inal Filed Sept. 1, 1961 2 Sheets-Sheet 1 INVENTORS fiEORGE HARRISON Dec. 12, 1967 V HARRlSON ET AL 3,357,228

METHOD AND MEANS FOR MAKING METAL FORGINGS 7 Original Filed Sept. 1, 1961 2 Sheets-Sheet 2 INVENTORS GEORGE HARRISON 7 NELSON K. RR!

,4 I, ATTY.

United States Patent ABSTRACT OF THE DISCLOS Apparatus for making metal forgings comprises a chilled permanent mold in which the metal is cast and in which the forging is made while the metal retains its heat of casting. The forging mechanism comprises a punch and a counterpunch for forming a bore and a counterbore in the forging. The punch is slidably telescoped within the counterpunch and the hydraulic driving mechanism for the two operates to maintain the punch always at least as far advanced into the forging as the counterpunch.

This application is a division of our copending application Ser. No. 146,391, filed Sept. 1, 1961, now Patent No. 3,228,073.

This invention relates generally to metal working, and more particularly to a method and apparatus for making metal forgings from castings that were made in permanent molds.

It is an object of the present invention to provide a method of making metal forgings in which a hot solidfied casting is worked while still in the casting mold to cause a more faithful conformance of the metal to the contour of the mold cavity walls.

It is a further object of the present invention to provide a method of the type stated in which the solidified casting may be forged into a desired shape while the casting remains within the mold in which it was formed.

In many instances it is desired to make a casting with a hole or bore therein, and for this purpose a core is used in the mold. As the casting metal solidifies it contracts around the core, and since the core is usually incompressible, stress concentrations are set up around the core resulting in a weakening of the metal of the casting surrounding the bore or hole. Oftentimes the shrinkage may be suiiicient to cause the casting to crack. It is an object of the present invention to provide a method of making metal objects by a combined casting and forging operation in which the product may be cast without a bore and then forming the bore by a forging or punching operation while the object is still hot in the mold.

Broadly speaking, the method of the present invention comprises the casting of molten metal in a permanent mold and after the casting has solidified and while it is still in the mold and still retains a large portion of its heat of casting, applying to the solidified casting sufficient mechanical pressure to cause the hot solidified metal to flow to all parts of the casting mold and faithfully conform to the contour of the mold cavity. The mechanical pressure may also forge the solidified casting into a preselected shape, and, if desired, form an opening which extends into or through the casting. In the apparatus of the present invention, the mechanical pressure may be imposed by one or more forging punches. As the punch or punches work the casting, some of the solidified metal may be forced out of the cavity, preferably through the opening through which the mold cavity is filled with molten metal. A

"ice

It is still a further object of this invention to provide a machine of the type that includes a male punch, with a metal casting mold so arranged that the male punch extends into the mold cavity and can be used to shape or work the metal in the mold cavity. A further object lies in the shaping and locating of the metal gate of the mold in line with the punch and of a shape which is a counterpart of the punch so that the gate constitutes the female member that cooperates with the male punch in its operation of punching a hole through a casting in the mold.

It is a more specific object of the present invention to provide a method and apparatus for punching a metal work piece with a punch and counterpunch in which the punch makes a sliding fit within the counterpunch and supports the same against radially inward collapse as the two punches are advanced into the workpiece. In accordance with this object of the invention, punch and counterpunch are operated in overlapping timed relationship while maintaining the punch always at least as far advanced as the counterpunch.

It is an additional object of the present invention to provide a punching apparatus and method of the type stated in which the movement of the punch controls the movement of the counterpunch and wherein the movement of the counterpunch may be disabled to cause continued movement of the punch after termination of the stroke of the counterpunch.

The attainment of the above and further objects of the present invention will be apparent from the following specification taken in conjunction with the accompanying drawing forming a part thereof.

In the drawing:

FIG. 1 is a diagrammatic vertical sectional view showing an apparatus for performing the method of the present invention;

FIG. 2 is a diagrammatic top plan view of the ladle receiving box of FIG. 1 with a ladle therein;

FIG. 3 is a fragmentary view of a portion of the structure of FIG. 1 with the parts thereof moved to an alternate position;

FIG. 4 is a view of the machine of FIG. 1 with the parts thereof in the position immediately following the discharge of a finished forging.

Reference may now be made more particularly to the drawings wherein like reference numerals represent like parts throughout.

In FIG. 1 the machine is shown in its normal position for receiving a ladle of metal preparatory to starting a cycle for operating the machine. The machine includes a base 1 on which there is mounted metal forging and casting apparatus 2 and supply apparatus 3 for supplying liquid metal to the casting and forging apparatus 2. The metal supply apparatus includes an open top box or cup 5 that is mounted on a piston rod 6 of a hydraulic cylinder 7 that is operated by oil pressure selectively supplied to an oil line 8 or an oil line 9 that lead respectively .to opposite sides of a piston 10 Within the cylinder 7 for actuating the piston rod in its upward or downward movement, as the case may be. The flow of liquid to the cylinder 7 is controlled by valves 12 and 13 which may be conventional electromagnetically controlled valves or hydraulically of pneumatically controlled valves. The purpose of this arrangement is to raise or lower the box 5 under control of the valves 12 and 13. The box 5 includes a cradle 20 of suitable heat insulating material which is adapted to receive a ladle 22 (FIGS. 2 and 3) containing the liquid metal to be cast, in this instance brass. The ladle includes a handle 23 that rests in a slot 24 at the top of the box on one side thereof, a gasket 25 being interposed. A flexible hose 28 of rubber or the like supplies air under pressure to the inside of the box, the supply of air being controlled by a valve 29.

At the top of the base 1 there is firmly secured an open ended forging cylinder 33 which is closed at its top by a cylinder head 34 and at its bottom by a die carrying cylinder head 35. The upper and

lower cylinder heads

34 and 35 are firmly bolted or otherwise rigidly secured to the top and bottom of the cylinder 33. The cylinder 33 has a lower piston 37 slideably mounted therein which piston includes a circular counterbore punch or piston rod 38 that is slideable through the lower cylinder head 35. An upper piston 40 is also slideable within the cylinder 33, said upper piston including a piston rod or through punch 41 that slides through the piston 37 and through the piston rod 38. The lower end of the counterbore punch 38 and the through punch 41 are flush with one another when both pistons are in their elevated pistons illustrated in FIG. 1.

A top molding and forging die 45 is secured to the underside of the lower cylinder head 35. A bottom molding and forging die 46 is secured to or carried by a platen or plate 37 that is in turn carried by a pair of slide rods 50-50 that extend through aligned holes in the cylinder 33 and the upper and

lower cylinder heads

34 and 35. The slide rods 50 are connected togther by a cross bar 51 at their upper ends. Means is provided for reciprocating the slide bars 50 and thus raising or lowering the bottom molding and forging die 46. This includes a double acting power cylinder 53 that has a double acting piston therein which it moved upwardly or downwardly by pressure such as oil pressure, through

lines

54 and 55 respectively, under control of

valves

56 and 57 respectively. The piston within the cylinder 53 raises or lowers a piston rod 59 that is connected at its upper end to the cross bar 51. Thus the piston 53 through the slide rods 50 raises or lowers the mold bottom or bottom die 46 from the position illustrated in FIG. 1 to a lowered position as illustrated, for instance, in FIG. 4.

Secured to the bottom side of the die carrying platen 47 is a sealing or gasketing plate 62 that carries a sealing ring or gasket 63 for making an air-tight or semi air-tight fit with the top of the box 5. A thin metal tube 67, the lower end of which is of larger diameter than the upper end, projects downwardly from the bottom of the plate 62 and is adapted to be immersed in the liquid metal in the ladle 22 as will be hereinafter more fully explained. The upper end of the tube 67 opens into a gate 69 that leads to the mold cavity 70. The gate 69 is in line with the punch 41 and of a shape that is the counterpart of the bottom of the punch 41, so that the punch and the gate constitute the male and female parts of a cooperatin'g punch set.

The two

pistons

37 and 40 are moved downwardly together (not necessarily at the same speed) by the application of oil under pressure to the portion of the cylinder above the piston 40 as through a hydraulic line 75. The two pistons are moved upwardly together to the position illustrated in FIG. 1 by supplying oil under pressure to the portion of the cylinder 33 immediately below the bottom piston 37, through an oil line 76. The space between the two pistons, indicated at 77, is filled with oil which may move into that space or out of that space through an oil line 78. The

lines

75, 76 and 78 are controlled by

valves

79, 80 and 81.

An exhaust air line 82, regulated by a needle valve 83 and controlled by a magnetic or pneumatically actuated valve 84, leads to the cavity 70, the exhaust opening or openings being small enough to prevent the flow of liquid metal therethrough but large enough for air to move therethrough.

for casting a mass of molten metal and forging the casting while it is still in the molding die and still retains its initial heat of casting. The metal used is brass. To commence the operation the tube 67, which is of stainless steel, is preheated so that when the first liquid metal flows upwardly through the tube, the metal will be excessively chilled. Thereafter, the tube 67 absorbs suflicient heat during each casting operation so that it is maintained sufficiently hot for the next casting operation. Using the ladle 22, a mass of molten metal is dipped from an open top melting furnace or crucible. The ladle is then placed in the box 5, with the open spoon portion of the ladle resting on the cradle 20 and the handle portion resting on the gasket 25, the top of the handle of the ladle being slightly below the top at the box 5 at the place where the handle of the ladle extends outwardly from the box. The piston 10 of the cylinder 7 is actuated to raise the box and bring it into engagement with the bottom of the plate 62. The box makes a substantially good fit with the sealing gasket 63 so that there can be only a small leakage of air from the box. At the same time, the tube 67 enters the liquid metal within the ladle. Pressure of air, or of an inert gas such as nitrogen, is then applied to the line 28 to place the interior of the box under an air pressure of a number of pounds, for instance four pounds of air pressure. At the same time, a small vacuum may be applied to the mold cavity to control the escape of air from the mold cavity. The vacuum is applied through the valve 84 and the line 82 that extends through the lower cylinder head 35 to and through the upper forging the 46 and opens into the cavity 70 through fine openings, as previously stated. If desired, the needle valve 83 may be omitted in which case a smaller vacuum pump will suffice, or the vacuum pump may also be omitted. However, it is preferable to control the air flow by using a source of very high vacuum connected to the valve 84 and throttle the negative pressure to produce in the passageway 82 a pressure only a small fraction of a pound below atmospheric pressure. By this arrangement, if there should be clogging of any of the fine air passageways leading from the mold cavity 70, the vacuum in the line 82 will increase almost to the vacuum of the vacuum pump, thereby tending to force the clogging material out and clear the passageways. Also, by this arrangement the negative pressure in the line 82 increases slowly as the mold cavity completely fills. A pressure gauge 88 therefore indicates a filling of the mold. The needle valve is regulated so that it is almost completely closed. By producing a slight scratch on the needle of the needle valve there is enough leakage past the small scratch when the needle valve is closed to produce the desired choking effect. The gas pressure in the box 5 forces liquid metal to fiow from the ladle upwardly through the hot tube 67 into the mold cavity 70 at a rate controlled by the controlled rate of escape of air from the mold cavity so that the flow of metal into the mold cavity is without turbulence. The mold of the present machine is a metal mold and being watercooled the liquid metal with the mold cavity solidifies rather quickly. Thereafter the box 5 is lowered, at least partially, although it may be completely returned to the position of FIG. 1.

When the box 5 has been lowered from contact with the plate 62 and the metal within the mold cavity has hardened, the machine proceeds to force the metal casting within the mold cavity. This forging operation is obtained by applying pressure to the top of the piston 40, through the line 75, while the space 77 between the two pistons is full of oil which is held against escape by maintaining the valve closed. The pressure exerted against the top of the piston 40 causes it to descend, causing the punching piston 4 1 to descend into the metal casting 70. The. descent of the piston 40 transmits pressure to the oil in the space 77 which forces the lower piston 37 downwardly, thus causing the counterpunch 38 also to descend into the solidified metal in the mold cavity.

The descent of the two pistons produces two results. First, it forges the metal and forces the plastic metal into firm contact with the mold cavity Walls. This assures a faithful conformance of the casting with contour of the walls of the mold cavity. Excess metal that is displaced by the descent of the punch 41 and counterpunch 38 is pushed out or extruded through the gate 69 and the tube 67. The punch 41 may and does descend faster than does the counterpunch 38 because the piston 40 is of a smaller diameter than the piston 37, so that a given descent of the piston 40 produces a somewhat lesser descent of the piston 37 while maintaining the volume of the space 77 between the two pistons constant. Ultimately, the bottom of the piston 37 reaches the cylinder head 35 and can descend no further. This limits the desent of the counterpunch 38 into the casting. The valve 80 is now open and the continued pressure on the top of the piston 40 causes it to descend until it engages the top of the bottom piston 37. At this time, the bottom of the inner punch 41 has completely penetrated the casting in the molding cavity 76. The solidified metal that has been punched from the casting within the mold cavity drops into the ladle 22.

After the forging operation has been completed, the piston within the cylinder 53 is actuated to move downwardly and, acting through the piston rod 59 and the slide rods t), it lowers the platen 47 carrying the bottom molding die 46, to separate the bottom molding die from the top molding die. The two molding dies are now in the position illustrated in FIG. 4 while the punch and the counterpunch are in the position of FIG. 3, because as the bottom molding or forging die 46 recedes from the top forging die 45 the casting 85 remains around the punch 41 and the counterpunch 38. A retrieving chute 90 is now moved into position between the top of the lower die 46 and the bottom of the upper molding and forging die 45. Thereafter, by the application of oil pressure to the

lines

76 and 78 the two pistons 37 and 4d are raised or returned to the position of FIG. 1. This strips the workpiece from the punches. The workpiece then drops onto the retrieving chute 96 on which it slides to a collecting bin (not shown).

The retrieving chute 90 carries at 92 a pair of nozzles, one of which is directed upwardly towards the bottom of the top molding and forging die 45 and the other of which is directed downwardly towards the top of the bottom molding and forging die 46. The nozzles 92 are connected through a pipe line 94 to a source of air or other inert gas under pressure, say a pressure of ninety pounds per square inch. Mixed with this gas or air is a mold release agent which comes through the nozzle 92 in the form of a fine spray that covers the mold cavity surfaces. The mold release agent may be any of the known agents for this purpose particularly adapted for use in the chill casting of a metal such as brass. Generally, such mold release agents are also lubricants. It may be a spindle oil such as, for instance, the Excel brand of spindle oil of Standard Oil Company of Indiana, or it may be the material sold as Cellube made by Celanese Corporation of America, or it may be a phosphate ester which chlorinated hydrocarbons (Monsanto Chemical Co.s Pyroll). Or it may be a mold release agent such as described in the Patents 2,618,530 that issued Nov. 18, 1952, or 2,923,041 that issued Feb. 2, 1960, or 2,592,337 that issued Apr. 8, 1952. The mold release agent is a volatile material and to the extent that it does evaporate during the molding operations the resulting vapor is drawn from the mold cavity by the vacuum in the line 82. We have found that it is not necessary to apply the mold release agent for every operation. It may be supplied once for every few operations, say every third or fourth operation, or even less frequently.

During the casting operation some of the zinc of the casting brass may condense or precipitate out and coat the wall or walls of the mold cavity either with powdered zinc or a compound of zinc. If this is allowed to accumu late within the mold it does become a matter of concern. We have found that this accumulation of zin or zinc compound within the mold is eliminated by reason of the forging operation. When the punch or counterpunch enters the workpiece it deforms the workpiece into firm, high pressure contact with the wall of the mold cavity and therefore into firm and high pressure contact with any precipitate or condensate of zin or a Zinc compound that may have formed on the mold cavity wall. Later, upon cooling of the casting and consequent shrinking thereof from the mold wall, the receding casting tends to carry with it the powdered precipitate or condensate of the zinc or zinc compound, which then appears as an unobjectionable film or layer on the outside of the finished product.

The sequence of operation of the machine of FIG. 1 is in general as follows. The operator places a ladl of metal onto the cradle 20 in the box 5. Thereafter, the operator commences the cycle of operation of the machine by actuating the valve 13. The piston in the cylinder 7 raises the box 5 to a position where the box engages the gasket 63 of the gasketing plate 62. At this time, or immediately before this position is reached by the box 5, the valve 84 is operated to apply vacuum to the mold cavity 70, and the valve 29 is operated to apply air pressure to the box 5. At the same time, water is being circulated throu h the molding dies, the water fiowing from the line 85 through the die 45 and hose connection 86 to and through the die 46 and then out through the line 87. The liquid metal rises in the mold cavity at a rate sufficiently slow to prevent turbulence of the liquid metal, as controlled by the permissive rate of escape of air from the mold cavity 70. If desired, the vacuum applied by the line 82 may be on all the time since the power required to maintain this air flow at all times is quit low. The vacuum pump draws air at a high vacuum but the permissive rate of air flow through the restricted scratch opening in the needle valve 83 is very low so that only a small vacuum can be built up in the mold cavity during the time the liquid metal is entering thereinto. After a time sumcient for solidification of metal within the mold cavity the piston in the cylinder '7 is actuated to draw the box 5 down.

The forging operation now commences by the actuation of the valve 79 to apply oil pressure to the top of the piston 40. At this time, the valve 80 is closed thereby preventing the escape of oil from the space 77 between the two

pistons

40 and 37 and the valve 81 is open to permit the escape of liquid from the portion of the cylinder below the piston 37. The descent of the piston 40 thus forces the punch 41 into the solidified metal in the mold cavity, and pressure from the piston 49 is also applied to the incompressible liquid in the space 77 to force the piston 37 downwardly. The piston 37 moves downwardly at a rate slightly lower than the rate of descent of the piston 49 because the piston 37 is of larger diameter than the piston 40. Therefore, the bottom of the punch 41 always reenforces the bottom of the counterpunch 38 as the two descend into the hot casting within the mold cavity 79. It is permissible that the punch shall advance with respect to the counterpunch but it is not permissible that the counterpunch shall advance with respect to the punch because if that were to happen then the very bottom of the counterpunch would no longer be supported by the punch against radially inward collapse and such collapse might take place. By keeping the bottom of the punch always at or below the bottom of the counterpunch we are assured that the punch will always reenforce the counterpunch against inward collapse. This punching operation continues until the piston 37 abuts against the top of the cylinder head 35 whereupon it can descend no more. The valve 80 then open thereby permitting escape of liquid from the space 77 between the two pistons so that the piston 49 can continue to descend under the continued hydraulic pressure to which it is being subjected. The punch 41 thus continues to descend and to extrude metal through the gate 81. The extruded metal drops into the ladle 22. Thereafter the valve 56 opens to force the piston within the cylinder 53 downwardly, thus drawing the platen 47 and with it the bottom die 46 downwardly. At this time the punch and counterpunch are in the position illustrated in FIG. 3 because they have not yet been retracted to the position of FIG. 1. The metal of the casting 88 grips the punch and counterpunch so that the bottom die 46 is stripped from the casting. At this time a hydraulic mechanism (not shown) moves an inclined chute into a position between the lowered bottom die 46 and the upper die 48. Any desired mechanism for accomplishing this movement may be provided, for instance a mechanism such as shown in the patent to George Harrison 2,863,188 that issued Dec. 9, 1958. Thereafter, pressure on the line 75 is relieved and pressure is applied to the line 76 which causes the piston 37 to rise and also causes the piston 40 to rise. At the same time, a small pressure is applied to the line 78 which causes the piston 40 to separate from the piston 37, bringing those pistons back to their position of FIG. 1 or 4. This strips the casting 87 from the punch and from the counterpunch. The casting then drops onto the inclined chute 90 and slides down this chute to a bin. Thereafter, the chute 90 is retracted and the piston within the cylinder :53 actuated to raise the platen 47 back to the position of FIG. 1. In the meantime, the operator has manually removed the ladle 22 from the box 5, emptied the ladle of its contents and dipped out a fresh ladle full of metal from the open top liquid metal furnace or crucible and replaced the ladle into the box 5. The operator then again initiates the operation of the machine for a repetition of the cycle above described.

In compliance with the requirements of the patent statutes, we have herein shown and described a preferred embodiment of our present invention. This is merely illustrative of the principles of the invention. What is considered new and sought to be secured by Letters Patent 1. In combination with a machine for punching metal including a punch and a die having a hole of a shape that is a counterpart of the cIOSS section of the punching end of the punch and in the path of movement thereof, a counterpunch surrounding the punch, the punch making a snug sliding fit in the counterpunch and reenforcing the punching end thereof against radially inward collapse, means for moving the punch in its punching operation, means controlled by movement of the punch for moving the counterpunch, and means for disabling said last means whereby the continued movement of the punch becomes ineffective to cause further movement of the counterpunch.

2. In combination with a punch and a counterpunch with the punch making a snug sliding fit within the counterpunch, and reenforcing the counterpunching end thereof against radially inward collapse, and means for moving the two together in their punching operations and then advancing the punch for continuing its punching operations after the counterpunch has completed its punching advance, said means including a cylinder and a pair of spaced apart separately movable pistons in said cylinder, there being an incompressible liquid separating said pistons, and means for controlling the amount of said liquid.

3. The method of making a bore and a counterbore in a metal member which comprises, performing in overlapping timed relationship by moving a punch relative to a counterpunch a punching operation for forming the bore and a counterpunching operation for forming the counterbore.

4. The method of making a bore and a counterbore in a metal member which comprises sliding a punch and surrounding counterpunch relative to each other and by said relative sliding, performing in overlapping timed relationship a punching operation for forming the bore and a counterpunching operation for forming the counterbore, and maintaining the punching always at least as far advanced as the counterpunching operation whereby the punch always reenforces the counterpunch, and completing the counterpunching operation before the completion of the punching operation.

5. The method of making a bore and a counterbore in a metal member which comprises moving a punch and counterpunch relative to each other and by said relative movement punching a bore in the member and while the punching operation is taking place starting and finishing a counterbore punching operation. 6. The method of making a bore and a counterbore In a metal member which comprises advancing both a punch and a counterpunch part way through the memher and then advancing the punch but not the counterpunch the rest of the distance through the member.

7. The method of making a bore and a counterbore in a metal member which comprises first punching the counterbore part way through the member and then punching a bore of smaller cross section than that of the counterbore the rest of the distance through the member, and during both punching operations extruding the excess metal through the same hole in a die.

8. A machine for punching metal including a punch and a die for holding a workpiece to be punched, said die having a hole of a shape that is a counterpart of the cross section of the punching end of the punch and is initially spaced therefrom and is in the path of movement thereof, a counterpunch surrounding the punch, the punch making a snug sliding fit in the counterpunch and reenforcing the punching end thereof against radially inward collapse, means for moving said punching end in its punching operation to said hole to punch a hole through said workpiece and eject punched metal through said hole, means controlled by movement of the punch for moving the counterpunch to form a counterbore extending partially through the workpiece and coaxial with the hole formed by the punch, and means for disabling said last-named means to terminate the stroke of the counterpunch whereby continued movement of the punch is ineffective to cause further movement of the counterpunch.

9. A machine for punching metal including a punch and a die for holding a workpiece to be punched, said die having a hole of a shape that is a counterpart of the cross section of the punching end of the punch and is initially spaced therefrom and is in the path of movement thereof, a counterpunch surrounding the punch, the punch making a snug sliding fit in the counterpunch and reenforcing the punching end thereof against radially inward collapse, means for moving the punch and counterpunch together in their punching operations to form a counterbore extending partially through the workpiece and then advancing the punch for continuing its punching movement to said hole after the counterpunch has terminated its stroke to form a bore in the workpiece that extends axially from said counterbore to said hole and to eject punched metal through said hole, said means including a first piston connected to the punch, a second piston connected to the counterpunch, a cylinder housing said pistons, incompressible liquid separating the pistons, and means for expelling said liquid after the counterpunch has completed its stroke.

10. A machine according to claim 9 in which said pistons and cylinders are of such size and shape that the punch piston moves faster than the counterpunch piston when the two are moving together.

11. A machine for punching metal including a punch and a die for holding a workpiece to be punched, a counterpunch surrounding the punch, the punch making a snug sliding fit in the counterpunch and reenforcing the punching end thereof against radially inward collapse,

means for moving said punching end in its punching operation, means controlled by movement of the punch for moving the counterpunch to form a counterbore extending partially through the workpiece and coaxial with the bore formed in the workpiece by the punch, and means for disabling said last-named means to terminate the stroke of the counterpunch whereby continued movement of the punch is ineffective to cause further movement of the counterpunch, means for moving the die relative to the two punches to separate the punched metal piece from the punches, said last-named means including means for retracting the punches from the metal piece.

References Cited UNITED STATES PATENTS 1,458,294 6/1923 Hook 72354 2,396,108 3/1946 Loewy 72345 2,726,560 12/1955 Roux 72-345 2,928,450 3/1960 Belding 72358 from the die, and means for stripping the metal piece 10 CHARLES W. LANHAM, Primary Examiner.

Claims

1. IN COMBINATION WITH A MACHINE FOR PUNCHING METAL INCLUDING A PUNCH AND A DIE HAVING A HOLE OF A SHAPE THAT IS A COUNTERPART OF THE CROSS SECTION OF THE PUNCHING END OF THE PUNCH AND IN THE PATH OF MOVEMENT THEREOF, A COUNTERPUNCH SURROUNDING THE PUNCH, THE PUNCH MAKING A SNUG SLIDING FIT IN THE COUNTERPUNCH AND REENFORCING THE PUNCHING END THEREOF AGAINST RADIALLY INWARD COLLAPSE,