US 2318819 A
Description (OCR text may contain errors)
May 11, 1943. D. c. VERSON MULTIP LE A CTION PUNCH PRESS DIE AND CUSHION Filed Dec. 12, 1940 3 Sheets-Sheet 2 y 1943. D. c.. VERSO N 2,318,819
MULTIPLE ACTION PUNCH PRESS DIE AND CUSHION Filed Dec. 12, 1940 3 Sheets-Sheet 3 M. i 0 nah ,0 d mmww Z I WM) a w .z a .r a 0 I a %m Patented May 11, 1943 UNITED STATES PATENT OFFICE MULTIPLE ACTION PUNCH PRESS DIE AND CUSHION 7 Claims.
This invention relates to the metal drawing art, and is concerned with the provision of a multiple action die cushion and die set for use therewith. By use of a. device incorporating this invention, it is possible to draw in a single punch press stroke objects formerly requiring several successive strokes.
In the interest of clarity, the present invention is illustrated and described as incorporated in a set of dies and cushions to be used therewith for drawing a cylindrical steel can approximately ten inches long and five inches in diameter out of 21- plate gauge steel drawing stock. t is to be understood, however, that this invention is not limited to any such specific use. In order to draw such a can from a fiat blank, it is necessary that the blank be made into a shallow dish and that by successive drawing operations this shallow dish be gradually reduced in diameter and drawn out in length until the final long, narrow can is.
The device of the present invention is particularly adapted for use with long stroke hydraulic presses or with a long stroke press of the type described in the copending application of Albert Clements, entitled. Screw Press, filed November 22, 1940, and given Serial No. 366,610. These two types of presses are mentioned as examples, although any press having a long stroke and sufficient capacity can be used with this device.
It is, therefore, an object of the present inven tion to provide a novel device that enables the drawing in one punch press stroke of objects formerly requiring a plurality of separate drawing operations.
Another object of the present invention is to provide a novel die set adapted for a plurality of successive drawing operations.
Still another object of the present invention is to provide an improved device which will cut a blank from a flat metal plate and then by successive drawing operations draw this blank into a long, thin object.
Yet another object of the present invention is to provide a novel multiple action die cushion together with means for controlling the action of such a cushion.
An additional object of my invention is to provide a multiple action die cushion and a die set cooperating therewith, such that some of the members of the die set will at one time act as punches to draw the metal, and will at other times act as draw rings around which the metal is drawn by a successive punching operation.
Other objects and advantages will become apparent from the following description of a preferred embodiment of my invention taken in conjunction with the accompanying drawings in which:
Fig. l is a vertical longitudinal sectional view through a die cushion and die set constructed to embody the present invention;
Fig. 2 is a somewhat diagrammatic sectional view of one set of duplicate control valves for use with the die cushion of the present invention;
Figs. 3, 4, 5, and 6 are vertical longitudinal sectional views similar to Fig. 1 showing successive positions of the various elements of the device during the course of a drawing operation.
Referring to Fig. 1 of the drawings, the punch press, of which only a portion is shown since it forms no part of the present invention, includes a bed I0 and a slide I2. An upper die member I4 is secured to the lower surface of the slide, while a lower die set l5 rests upon and is secured to a bolster plate l8, which, in turn, is secured to the press bed It. The multiple action die cushion, indicated generally by the numeral 29, is comprised of a base 22'hung from the bed Ill upon a plurality of steel rods 24, so that the load tending to move the die cushion downwardly will be carried directly by the bed I I] through these rods. The base 22 supports an inner cylinder 26, while around this inner cylinder, a second cylinder 28 is positioned, both of these cylinders being secured to the base 22. Since the cylinder 28 is considerably larger in diameter than the cylinder 26, an annular space 30 will be provided between these cylinders, while a cylindrical space 32 will be provided within the cylinder 25.
At its lower end, the cylinder 28 has an outwardly extending flange 34 that provides a cylindrical surface which fits closely within a third cylinder 36 while at its upper end this third cylinder 3t has an inwardly extending flange '38 which closely fits the outer cylindrical surface of the second cylinder 28. Thus, between the cylinder 36 and the cylinder 28, a third annular space 40 is provided.
A cylindrical piston 42 fits within the cylindrical space 32, while an annular piston 44 fits within the annular space 30. An annular ring 46, somewhat smaller in external diameter than the external diameter of the cylinder 26, is secured to the upper end of cylinder 25 and is provided with a circular opening 48 somewhat smaller in diameter than the internal diameter of cylinder 26. An upward extension 50 of the piston 42 of smaller diameter than the piston extends through the opening 43, and thus, the extension 50 is free to move upwardly and downwardly within the opening 48, while the ring 46 serves as a stop to limit the upward movement of the piston 42. A similar annular ring 52 is secured to the upper end of cylinder 28. The central opening 54 in this ring is smaller in diameter than the internal diameter of cylinder 23, and thus the ring limits the upward movement of piston 44. An annular extension 56 of the piston 44, having an external diameter somewhat smaller than the internal diameter of the ring 52, extends through this opening 54 and is free to move upwardly and downwardly through this opening. The external diameter of the ring 52 is somewhat greater than the external diameter of cylinder 29, and thus limits the up ward movement of the outer cylinder 36 in a like manner, while an annular member 56 is secured to the top of the flange 38 and extends upwardly beyond the ring 52.
Each of the pistons 42 and 44 is sealed within its respective cylinder by means of cup washers 69 held in place by annular rings 62 in a wellknown manner. flange 34 of cylinder 28 is sealed by means of a cup washer 64 and ring 66 against the inner side wall of the outer cylinder 36. Similarly also, the upper flange 38 of the outer cylinder is sealed by means of a cup washer 68 and ring I9 to the extemal cylindrical surface of the intermediate cylinder 28.
For convenience in further discussion of the present invention, the cylindrical space 32, the annular space 30, and the annular space 49 will be referred to, respectively, as cylinders A, B,
and C. I a
From the above discussion it will be seen that in the absence of pressure within these cylinders, the pistons 42 and 44 and the annular outer cylinder 36 will be free to move upwardly and downwardly within limits established by the rings 46 and 52 and the bottoms of the several cylinders. Likewise, the vertical positions of the upward extensions 59, 56, and 58 can be determined by the positions of their respective pistons 42, 44, and 36. For convenience, the outer annular cylinder 36 will be referred to as a piston hereafter, since its action in this device is somewhat similar to pistons 42 and 44, and since it moves relative to the base 22.
When the piston 42 is at the top of its cylinder, the top end of the upward extension 59 will be spaced a short distance below the bolster plate I8 and will be in axial alignment with the upper die member I4. An annular crosshead I2 is secured to the upper end of the annular extension 58 and lies with its upper surface in approximately the same plane as the upper surface of the extension 59. A similar annular crosshead I4 is secured to the upper end of the annular extension 56 and lies somewhat beneath the crosshead I2. This latter crosshead 14 has a central opening provided with a bushing I6 fitted to the cylindrical extension 59. Thus, the extension 59 and the crosshead I4 are enabled to move vertically relative to each other, although relative movement in other directions that would cause misalignment is prevented. A similar opening I8 is provided in the center of the crosshead I2 to permit the passage of the extension 59 and also to permit the passage of a plurality of vertically extending circumferentially arranged rods to be described presently. The outer annular extension 58 is guided for vertical movement by the bed I9 of the punch press through which it passes, or, if desired, by a specially constructed bearing member secured to the press bed I9.
A pipe 80 communicates at one of its ends with the interior of cylinder A while its other end leads to a solenoid valve 82. In a similar manner, a second pipe 84 connects the cylinder B to a second solenoid valve 86. The two solenoid valves 82 and 86 are substantially identical and thus a description of one of these valves. will suflice.
Referring to Fig. 2, which shows the construction of the solenoid valves diagrammatically, a
In a similar manner the lower closed oil reservoir 88 contains a quantity of oil maintained under a pressure of approximately 80 pounds per square inch. This pressure is maintained by connecting the reservoir to an air receiver, not shown, so that the space above the liquid in the reservoir contains air forced into I the reservoir from the air receiver. A pipe 99 extends into the reservoir and has its lower end below the liquid level'therein, while its upper end is connected to a forward chamber 92 of a pneumatically controlled hydraulic valve body 94. This valve body is also provided with an intermediate cylindrical chamber 96 and a rearward cylindrical chamber 93. The chambers 96 and 98 are in axial alignment and for the particular embodiment of the invention here shown, the chamber 96 is of somewhat greater diameter than the chamber 98. 'A valve rod I99 extends axially through these two chambers and into the forward chamber 92 where at its end it carries a conical valve plug I92. This conical plug seats in a complementary conical valve seat I94 at the forward end of the chamber 92 and this valve seat in turn communicates through the valve body with a pipe fitting I06 connected in turn to either the pipes or 84, asth'e case may be.
The cylinder 98 contains a piston I98 fixed to the rearward end of the valve rod I90, while a second piston H9 is fitted within the intermediate cylinder 95 and is also secured to the valve rod I00. These two pistons are so positioned upon the rod I09 that when the conical valve plug I92 is seated in the valve seat I04, these two pistons will be at an intermediate point in their cylinders.
An air line II2 leads from an air receiver not shown, but which is maintained under approximately 80 pounds per square inch pressure, to a two-position valve II4. This valve, when in the position shown in Fig. 2, has a passage H6 in a rotary member II8 which conducts the air from the air line II2 to a conduit I29 so as to place the conduit under 80 pounds per square inch pressure. When the rotary member II8 of this valve is rotated in a clockwise direction, a matter of 99, the passage II6 connects the conduit I20 to the atmosphere through a valve opening I22, thus placing the conduit I29 at substantially atmospheric pressure. The conduit I29 is' connected at its opposite end to the valve body 94 in such a position that it communicates with the intermediate cylinder 96 in a position behind the piston II9, so that, when the valve I I4 is in the position shown in Fig. 2, the piston IIO will be urged forwardly, thus seating the valve plug I02 in its seat I94.
A second air line I24 leads from the air receiver not shown and also carries air under approximately 80 pounds per square inch pressure to a second two-position valve I26. Within the valve I26 a rotary member I 29 is provided with two passages. When this valve is in the position shown, one of these passages, indicated by the numeral I39, connects the air line I24 with a conduit I32 which leads to the rearward cylinder 98 at a position behind the piston I98, thus tending to urge the piston forwardly when the valve is in the position shown. A second passage I34, within the rotary member I28, connects a valve opening I36 leading to the atmosphere to a conduit I38 connected in turn to the forward portion of the intermediate cylinder 96. Thus, with the valve in the position shown, the forward portion of cylinder 96 is vented to the at mosphere.
When the rotary member I28 is swung through an angle of 90 in a clockwise direction, the conplug can be maintained in its seat by air pressure behind cylinders H and 98, or both of them, even though this air pressure is many times less than the back pressure in the pipes 80 or 84, as the case may be.
The operation of this portion of the device is as follows: first, assume that both the rotary valve members H8 and I are rotated through an angle of 90 in a clockwise direction from the positions shown. With the valve in this position, the rearward portions of cylinders 06 and 98 will be connected to the atmosphere, while the forward portion of cylinder 96 will be connected to the air line I24 and will, therefore, be under a pressure of 80 pounds per square inch. The pressure on the forward side of piston 96 will move the valve plug I 02 rearwardly and oil witha in the reservoir 88, since it is under approximately 80 pounds per square inch pressure, will move upwardly through the pipe 90, into the chamber 92 and thence through the pipe 80 or 84 to either cylinder A or B, as thecase may be.
This oil under 80 pounds per square inch pressure in the cylinders A and B will move the pistons 42 and 44 upwardly against the stops provided by the rings 46 and 52. the cycle, both the rotary members H2 and 28 are rotated into the positions shown by solenoid actuating means not illustrated. The forward portion of cylinder 95 is, therefore, vented to the atmosphere while the rearward portions of cylinders 56 and 98 are placed under 80 pounds per square inch pressure. Pistons H0 and I 08, therefore, move forwardly and seat the valve plug I02 tightly in its seat 504. The relative areas of piston 42, valve plug 02, and pistons I I0 and 108 of valve 82 are such that under these conditions it will require a downward pressure on piston 42 of 21 tons to unseat valve plug I02 and permit the hydraulic fluid to be forced around this valve member and into the reservoir 88. Similarly, the relative areas of piston 44;; valve member I 02, and pistons I03 and H0 in valve 65 connected to cylinder B are such that under similar conditions it will require tons pressure to move piston 44 downwardly .to unseat valve member I02.
At a later point in the cycle of the machine,
to be described in greater detail subsequently,
the rotary member I I8 of valve I I4 is rotated 90 in a clockwise direction, thus connecting the rearward portion of cylinder 96 to the atmosphere. Under these conditions, the force tend;- ing to urge valve plug I 02 into its seat will be exerted solely by piston I08 and it will therefore require less hydraulic back pressure to unseat the valve I02. The relative areas of the piston H0 and I08 are such that with the valve in the position last mentioned, a pressure of only tons will be required to move cylinder 42 down wardly, while a pressure of 7 /2 tons will move piston 44 downwardly. That is, these pressures At this point in' will be sufiicient to unseat the valve I02 and permit oil to flow from cylinders A and B around their respective valve members 102 and into the reservoir .88.. p
The space C in the die cushion of the present embodiment is connected directly to the air re ceiver and the area of the piston working in this space is such that a pressure of 10 tons is required to move the piston 36 downwardly against the air pressure of 80 pounds per square inch in this space.
The upper member I4 of the die set consists of a hollow punch I42 secured to the slide I2. At its lower end the external face of this punch provides a cylindrical surface I 44 of the proper diameter to shear a circular blank from a strip of stock to be used to form the can. Above this surface I44 the external face of the punch is relieved somewhat at I46 in the usual manner. The lower portion of the punch is provided with a cylindrical cavity I48 somewhat broader than it is deep and of the proper shape to form the first draw from the circular blank. Above this cavity I48 is a second cylindrical cavity I50 which is somewhat narrower and deeper than the cavity I48. This cavity is of the proper shape to reduce the diameter and elongate the dish formed by the first drawing portion I48. Above the cavity I50 is a third cavity 452 which is narrower and deeper than the cavity I50 and is of the proper shape to form the can to its required final dimensions. In each instance the punch at the juncture between different sizes of cavities is provided with a radius of curvature so that no sharp edges are present.
The lower die set I6 comprises a cylindrical sleeve I54 secured to the bolster plate I8. At its upper end the sleeve l54 is provided with an inwardly flanged edge I56 having a circular opening therein fitted to the cylindrical surface I44 of the punch I42 so that as the punch moves downwardly with a strip I58 placed between the die members, the end of the punch in conjunction with the upper face of the flange I56 will 7 shear a circular blank I59 of proper sizefrom the strip.
An outer draw ring I60 has a cylindrical opening I6| therethrough somewhat smaller in diameter than the cylindrical opening of the cavity I48 in the punch I42. The lower portion of this draw ring is flanged outwardly somewhat so that the shoulder of the flange I56 will prevent the draw ring I60 from being raised substantially above the level of the top of the sleeve I54. This draw ring is secured to the upper ends of a plurality of circumferentially arranged rods I62 extending downwardly through the bolster plate I8 and connected at their lower ends to a ring I64 secured in turn to the upper face of the crosshead 12. Thus the draw ring I60 can be moved downwardly by the punch I46 against a resisting force of ten tons.
An annular punch I66 has its external face fitted to the internal surface "H of the draw ring 160. The external diameter of this punch is such that the punch functions properly in drawing a sheet metal blank into the lower cavity I48 of the upper punch I42. The internal diameter of the annular punch I 66 is somewhat smaller than the intermediate cavity I50 of the punch I42 and fitted to this internal surface is a second annular punch I68 of proper size to draw the dish formed in cavity I48 into the intermediate cavity I50. A third punch I10 of proper size to draw the dish formed in the intermediate cavity I50 into the final cavity I52 is fitted to the internal surface of the annular punch I68 and at its lower end is secured to the bolster plate I8. The external annular punch I66 is secured to vertical rods II2 which extend downwardly through the bolster plate and through the crosshead I2 and are connected at their lower ends to a ring I14 secured in turn to the crosshead I4. In a like manner, the annular punch I68 is supported upon rods I'I6 attached at their lower ends to a ring "8 secured to the upper end of the inner piston extension 50.
When all of the members of the lower die set are in their maximum upper positions, the upper end of annular punch I65 is about two inches above the upper end of annular punch I68while the latter in turnis approximately two inches above the upper end of the central punch II0. In each instance the noses of the punches are rounded off so that there will be no sharp corners present to tear the metal being drawn.
The operation of this device is as follows: Assuming that the die set and air cushion described are properly secured in place in a punch press of adequate capacity having a stroke of approximately 34 inches, and also assuming that the slide I2 is in its upper position and that rotary valve members H8 and I28 are in the positions shown in Figure 2, a strip I58 of sheet metal of proper gauge is inserted to cover the opening in the upper end of the sleeve I54. The press is then set in operation to cause the slide I2 carrying the punch I42 to move downwardly.
After the upper punch has moved downwardly approximately inches or so, the lower end of the punch will come in contact with the sheet metal strip I58 and will clamp the strip I58 between the lower end of the punch and the upper face of the draw ring I60. Upon slight additional downward movement, the punch acting in conjunction with the sleeve I54, will shear a circular blank I59 of proper size from the strip I58. This blank is carried downwardly against the upper end of the outer annular punch I66 which is maintained against downward displacement by a pressure of approximately 30 tons. Under these condition no appreciable downward movement of the punch I66 will take place. The sheet metal blank is, therefore, drawn radially inwardly across the contiguous faces of the draw ring I60 and the punch I42 and into the depression I48.
After the blank I59 has been fully drawn into the depression I48 the punch I66 can move no farther into the die I42 and will, therefore, start to move downwardly against the 30 tons ressure exerted by piston 44. The relative position of the parts at this point in the-cycle are shown in Figure 3. At this point in the cycle of the machine a limit switch establishes an electrical circuit which energizes the solenoid valve portion H4 of control valve 86 so that the rotary member H8 is rotated 90 in a clockwise direction from the position shown in Fig. 2. This establishes a connection between the rearward portion of cylinder 86 in the valve body and the atmosphere and as has been previously explained causes the pressure exerted by the piston 44 in an upward direction to drop from 30 tons to 7 /2 tons.
Since it takes an appreciable interval of time to cause the valve 86 to be shifted in the manner described, the upper end of. punch I66 is spaced approximately two inches above the upper end of punch I68. Thus, sometime before the bottom of the dish formed by the punch I66 has been brought against the end of the intermediate punch I68, the pressure tending to prevent downward movement of the punch I66 will have dropped from 30 to 7 /2 tons. The outer punch, therefore, under this reduced pressure acts as a second draw ring as the second punch I68 draws the dish formed by the outer punch into the intermediate recess I50. The positions of the parts at one point in this stage of the draw are shown in Figure 4.
When the punch I68 has reached the bottom of the recess I50 and can go no farther, a limit switch operates valve 82 in the same manner that valve 86 was previously operated. That is, the rotary member H8 in this valve is rotated through an angle of 90 in a clockwise direction to connect the rearward portion of cylinder-96 to the atmosphere. As has been explained previously, this causes the pressure tending to maintain the punch I68 against downward movement to be dropped from 21 tons to 5% tons. Continued downward movement of the punch I42 brings the bottom of the dish formed in cavity I50 against the upper end of the inner punch I10. The positions assumed by the parts at this point in the cycle are shown in Figure 5.
Since the pressure now tending to prevent downward movement of the annular punch I66 has dropped to 5 tons, this member will act as a third draw ring and will cause the metal in the dish to be smoothly drawn into the uppermost recess I52 by the innermost punch I10. At the completion of the press stroke, the can for which these dies are made will be completely formed. The positions assumed by the parts at the end of the drawing cycle are shown in Figure 6.
As the slide I2 starts its upward movement, the rotary valve members I28 in both valves 82 and 86 will be caused to rotate in a clockwise direction from the position shown in Figure 2 and as has been previously described, oil under pressure in reservoir 88 will return the several elements of the die cushion to their original starting positions as the slide I2 moves upwardly. As in the previousinstances, the shifting of the valve members I28 is accomplished by a limit switch which is tripped when the slide I2 reaches the lowest position in its stroke.
When the slide has reached a point near the top of its stroke, a limit switch will be tripped which will cause both the solenoid valves 82 and 86 to return their rotary members H8 and I28 to the positions shown in Figure 2, thus conditioning the multiple action die cushion and the die set for a succeeding draw.
In order to insure the finished can being ejected from the upper punch I42 as the upper punch moves upwardly, a knock-out bar I extends axially from above into the upper recess I52 of the punch I42. This knock-out bar operates in the conventional manner in that during the upward movement of the slide I2, this knock-out bar impinges against a stationary member which permits the upper die to move upwardly while for a moment the knock-out bar remains stationary. The knock-out bar, therefore, pushes the can from the inner recess I52.
No detailed description of the limit switches and the solenoid valve shifting elements or the circuits connecting these members is here given inasmuch as the arrangement and detailed construction of these members is a matter well within the skill of anyone familiar with this art. That is, limit switches and solenoid valves are,
commonly used to institute and stop various cycles of operation in automatic and semiautomatic machines, including metal deforming machines, and the particular design and arrangement of these elements in any particular machine is largely a matter of choice and not a matter requiring invention.
From the above description of a preferred embodiment of my invention, it will be seen that I have provided a device which enables a sheet metal blank to be drawn through several drawing stages during a single stroke of a metal drawing press, and that this invention accomplishes all of the objectives set forth at the beg nnin of this specification.
Having described my invention, what I claim as new and useful and desire to secure by United States Letters Patent, is:
1. A punch press device comprising a central immovable punch, an annular punch surrounding said immovable punch and adapted for movement relative to said immovable punch, a die cushion piston adapted to support said annular punch with its outer end beyond the outer end of said immovable punch, and means cooperating with said die cushion piston to enable said piston to support difierent degrees of pressure during different portions of the punch press stroke, the last said means comprising a cylinder fitted to said piston, means to fill said cylinder with hydraulic fluid, escape valve means adapted to retain fluid in said cylinder until a predetermined cylinder pressure has been reached after which said valve means is adapted to open to permit escape of fluid under restraint, and means subsequently operative during the press stroke to cause said valve means to release said fluid at a positive pressure lower than said predetermined pressure.
2. In a multiple action die cushion, a die cushion cylinder, a hydraulic conduit leading from said cylinder, a valve to close said conduit against back pressure from said cylinder, said valve being seated against said back pressure by a plurality of cooperating force producing cylinders so arranged that one of said force produring cylinders acting alone will hold said valve in its seat against a certain amount of back pressure, while both of said force producing cylinders acting together will hold said valve in its seat against a different degree of back pressure, and means to actuate first both and then one of said force producing cylinders.
3. In a multiple action die cushion, a die cushion cylinder, a hydraulic conduit leading from said cylinder, a valve to close said conduit to prevent flow from said cylinder when the force acting upon the die cushion side of said valve tending to push said valve from its seat is less than the force tending to seat said valve, a plurality of cooperating air cylinders adapted to seat said valve so arranged that one of said air cylinders acting alone will hold said valve in its seat against a certain degree of back pressure from said die cushion cylinder, while both of said air cylinders acting together will hold said valve in its seat against a different degree of back pressure, and means to connect first both and then one of said air cylinders to a source of air under pressure.
4. In a punch press device, an inner punch and an outer punch, said outer punch being adapted to reciprocate relative to said inner punch, hydraulic cylinder means to support said outer punch to inhibit said relative reciprocation, relief valve means adjusted at the beginning of a drawing operation to prevent escape of fluid from said hydraulic cylinder means until a certain predetermined cylinder pressure has been reached and to permit escape of fluid from said cylinder at said predetermined pressure, and means subsequently operative during the drawing operation to permit the escape of said fluid from said cylinder at a positive pressure substantially less than the first said pressure.
5. A punch press die cushion comprising a plurality of cylinders, a plurality of pistons adapted to reciprocate in said cylinders, means to fill said cylinders with a hydraulic fluid so as to move said pistons outwardly, escape valve means adapted when in closed position to prevent escape of fluid from said cylinders and when in open position to permit the escape of fluid therefrom, said valve means being so arranged that pressure in said cylinders tends to force said valve means toward open position, resilient loading means adapted to apply a force to urge said valve means toward closed position, means adapted when operated to decrease the force applied by the loading means, and means operated by the punch press mechanism during the course of a punch press stroke for actuating the last said means.
6. In a multiple action die cushion, a die cushion cylinder, a hydraulic conduit leading from said cylinder, valve means to close said conduit against back pressure from said cylinder, said valve means being so arranged that pressure from said cylinder will tend to open said valve means to permit the escape of fluid from said cylinder, force producing means adapted resiliently to bias said valve means toward closed position against the pressure in said cylinder so that the pressure developed in said cylinder before opening said valve means depends upon the pressure exerted by said force producing means, and means to develop a certain degree of force in said force producing means andsubsequently a less degree of force in said force producing means.
'7. In a punch press device, a plurality of concentric metal drawing punches, said concentric punches being movable relative to each other and being telescoped when at rest with each successively outwardly spaced punch having its outer end extending a substantial distance beyond the outer end of the adjacent inner punch, die cushion means supporting said movable punches and adapted to resist movement of the latter, said die cushion means being adapted to oifer different degrees of resistance to movement of said movablepunches at different positions in the press stroke, whereby the outermost of said concentric punches will be yieldingly restrained against movement for a portion of a punch press stroke and will subsequently be permitted to move under less restraint during the remainder of the punch press stroke so that the outermost of said concentric punches will first act as a yieldingly supported drawing member and later as a draw ring while another of said punches is acting as a drawing member.
DAVID C. VERSON.