US3636748A

US3636748A - Drawing of sheet metal

Info

Publication number: US3636748A
Application number: US809493A
Authority: US
Inventors: George Roberts Hall; Robert Alexander Lyall
Original assignee: Individual
Current assignee: Individual
Priority date: 1969-03-24
Filing date: 1969-03-24
Publication date: 1972-01-25
Anticipated expiration: 1989-01-25

Abstract

The disclosure relates to an apparatus for the cold drawing of sheet metal consisting of a plurality of punches adapted for mounting on a crosshead of a press and telescopically received within one another for intermittent relative movement, said punches being arranged to cooperate with a plurality of stationary dies of progressively decreasing size, whereby to draw an initially flat or substantially flat workpiece of sheet metal into the shape of a container, a control circuit being provided for each telescoping punch, which circuit or circuits embody at least one energy-storage section adapted to contain a compressible fluid as an energy-storage medium.

Description

United States Patent Hall et al. 1 Jan. 25, 1972 [54] DRAWING 0 SHEET METAL 2,989,019 6/1961 Van Sciver ..72/351 3,167,044 l/l965 l-lenrickson.... 72/349 [72] Inventors: George Roberts Hall, 32. Amesbury Road, 3,453,848 7/1969 Williamson.... 72/349 l y. g m, 3; R r Alex- 3,470,725 10/1969 Brown et al ...72/34 ander Lyall, 22 Morven Road, Sutton 3,509,754 5/1970 Massingill et al. ..1 13/120 Coldfield, Warwickshire, both of England FOREIGN PATENTS OR APPLICATION [22] Filed: Mar. 24, 1969 s 223,430 10/1924 Great Britain ..72/349 [21] Appl. No.: 809,493

Related US. Application Data Continuation-impart of Ser. No. 752,010, Aug. 12, 1968, abandoned.

Primary Examiner-Richard J. Herbst Attorney-Scrivener, Parker, Scrivener and Clarke [57] ABSTRACT The disclosure relates to an apparatus for the cold drawing of sheet metal consisting of a plurality of punches adapted for mounting on a crosshead of a press and telescopically received within one another for intermittent relative movement, said punches being arranged to cooperate with a plurality of stationary dies of progressively decreasing size, whereby to draw an initially flat or substantially flat workpiece of sheet metal into the shape of a container, a control circuit being provided for each telescoping punch, which circuit or circuits embody at least one energy-storage section adapted to contain a compressible fluid as an energy-storage medium.

FIG .2.

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PATENTEB JANZS 1972 .llu-llll I I II Nmm DRAWING 01F SHEET METAL This is a continuation-in-part of application Ser. No. 752,010 filed Aug. 12, I968, now abandoned.

The present invention relates to the deep drawing of sheet metal to form cup-shaped metal containers.

The invention particularly relates to an apparatus and method for the deep drawing of sheet metal blanks into containers by the use of specifically designed presses.

Deep drawing metal presses having a number of hydraulically controlled punches connected for telescoping movement are known in the art. However, in arrangements used hitherto, upon release of one or more of the hydraulic circuits which control operation of the punches, the hydraulic fluid has been drained to a hydraulic fluid reservoir, and thus when a further punch operation has been required it has been necessary to reenergize the appropriate hydraulic circuit.

It will be seen therefore that with previous presses, the excess energy beyond that required to deform the workpiece system has been released and therefore wasted, since subsequent operations of the punches have required the hydraulic control circuits to be reenergized.

Thus previous presses have consumed large amounts of power and the present invention seeks to provide an apparatus for attachment to the press head of a deep drawing press the power consumption of the press and the apparatus being low compared with conventional presses.

One advantage of the present invention is that the apparatus can be employed with either a mechanical or a hydraulic press.

According to the present invention then an apparatus for the cold drawing of sheet metal comprises a plurality of punches adapted for mounting on a crosshead of a press and telescopically received within one another for intermittent relative movement, said punches being arranged to cooperate with a plurality of stationary dies of progressively decreasing size, whereby to draw an initially flat or substantially flat workpiece of sheet metal into the shape of a container, a control circuit being provided for each telescoping punch, which circuit or circuits embody at least one energy-storage section adapted to contain a compressible fluid as an energy-storage medium.

In one embodiment of the invention each telescoping punch control circuit additionally comprises at least one hydraulic, energy-transfer section including a chamber containing hydraulic fluid and being collapsible in response to movement of a punch relative to a press head or to another punch during.

one part of a drawing operation. In this embodiment of the invention the energy-storage section preferably comprises an accumulator directly connected to said collapsible chamber so as to receive and store energy transferred thereto upon relative movement of the punches of the press, thereafter retuming said energy to pressure responsive means for use in another part of the drawing operation.

Preferably holddown means are provided for holding the workpiece in position on at least the first die. I-Iolddown may be effected on subsequent dies by employing the punch immediately preceding that which is effecting the formation of the workpiece at the die.

The holddown pressure applied to the workpiece may be controlled by a spring-loaded attachment unit which comprises a pair of members resiliently spaced apart, one of said members being adapted to be fixedly connected to the press frame of said press, and the other of said members being adapted to be engaged by an abutment effecting holddown at that die, whereby to provide a workpiece holddown pressure less than the drawing pressure of said press.

Preferably each of the punches and dies section along at least part of its length.

In a preferred embodiment of the invention a double-acting press is used and two sets of telescopically received punches are coaxially mounted on said press head, which punches are arranged to cooperate with two opposed sets of stationary dies to produce two containers on each working stroke of the is of circular cross press. In this embodiment of the invention the or each energytransfer section associated with each punch of one of the sets of punches is connected to the hydraulic energy-transfer section of the corresponding punch on the other of said sets of punches.

In a still further embodiment of the invention a double-acting press is used and four sets of telescopically received punches are coaxially mounted in two rows on said press head which punches are arranged to cooperate with two opposed pairs of sets of stationary dies to produce four containers on each working stroke of the press.

Also according to the present invention there is provided a method of forming a container from a sheet metal workpiece which comprises introducing the workpiece onto a first die, advancing a plurality of interconnected telescopically arranged punches as a composite punch towards said first die and drawing said workpiece therethrough, advancing said punches to a second die, storing energy created by relative movement between one of said punches and said innermost punch by compressing a fixed quantity of a fluid medium in a sealed volume, and utilizing said energy stored within the fluid medium for a further part of the operation.

The invention will now be further described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic and explanatory illustration partly in section of a punch and die arrangement embodied in the presentinvention,

FIG. 2 is a diagrammatic illustration of a press provided with an energy-storage section and a hydraulic, energytransfer section according to one embodiment of the present invention,

FIGS 3 and 4 are sketches illustrating the progressive stages in the operation of the arrangement illustrated in FIG. 2,

FIG. 5 is a diagrammatic and composite illustration of the punches and dies during each of the several stages of the drawing operation, and also illustrates (on the lower half of the Figure) the progressive development of a workpiece W during drawing,

FIG. 6 is a plan view of a double-acting hydraulic press provided with an energy-storage section and a hydraulic, energytransfer section according to a second and preferred embodiment of the invention,

FIG. 7 is a sectional view on the lines 7-7 of FIG. 6,

FIG. 8 is a sectional view on the lines 88 of FIG. 6,

FIGS. 9 to 14 are diagrammatic illustrations of the operation of the embodiment illustrated in FIGS. 6 to 8,

FIG. 15 is a schematic illustrated of a third embodiment of the invention,

FIG. 16 is a schematic illustration of a fourth embodiment of the invention which is only provided with an energy-storage section,

FIG. 17 illustrates an apparatus for initially displacing a completed workpiece from a punch of the press prior to stripping therefrom,

FIG. 18 illustrates a spring-loaded holddown arrangement for varying the holddown pressure acting on a workpiece W, and

FIG. 19 illustrates a length of sheet metal strip on which is shown the most economical arrangement for the layout of blank workpieces.

In the arrangement illustrated in FIG. 1, three telescopically engaged punches are shown as 10, 12 and 14. The punch 12 is provided at one end with a radially extending flange 19 which slidably engages within a casing 16 as a piston. The punch 14 is connected by two

guide rods

20 and 21 to

pistons

22 and 23 which slidably engage within two

further casings

15 and 17. The

casings

15, 16 and 17 are mounted on the press head 18 of a single-acting, vertical hydraulic or mechanical press (not shown in full) and define collapsible chambers with the

pistons

22, 19 and 23 respectively. The punch 10 is also provided with a flange 24 which is rigidly attached to the press head 18 externally of the casing 16.

Two

apertures

26 and 27 are provided in the upper region of the sidewall .of the casing and 17, in the region of the press head 18, while a further aperture 30 is provided in the upper region of the sidewall of casing 16.

Hydraulic fluid is fed through a conduit 29 to cylinder 16 and through a common conduit 25 to feed

cylinders

15 and 17.

When the conduits connected to

apertures

26, 27 and 30 are closed, the three

punches

10, 12 and 14 are locked solid as a single composite punch. Relieving one or both of the

conduits

25 or 29 enables relative movement of the punches to take place, as hereinafter described.

The three

telescopic punches

10, 12 and 14 are arranged to cooperate with four fixed, spaced dies 50, 52, 54 and 56 (shown diagrammatically) of progressively diminishing size. The dies 50, 52 and 54 are draw dies while the die 56 is an ironing die and has a diameter only slightly less than that of the preceding draw die 54.

A holddown arrangement shown generally as 100 is provided to hold a workpiece W in position on the first draw die 50. Again, the holddown arrangement will be described in more detail hereafter.

The arrangement so described operates as follows:

A workpiece W (normally a metal blank of tin plate, steel or aluminum for example and of substantially circular configuration) is initially placed in position on the first draw die 50, as illustrated in FIG. 1. As the press head 18 commences to move downwards (as viewed in FIG. 1), the holddown arrangement I00 operates to clamp the workpiece W in position against the upper face of the first draw die 50. Continued downward movement of the press head 18 causes the three punches l0,

12 and 14 to move as a single composite punch to draw the workpiece W through the first draw die 50. Towards the end of this draw, the workpiece W is forcedly drawn from beneath the holddown arrangement 100, so that it then lies in a substantially cylindrical shape around the outermost punch 14. The press head 18 continues to move downwardly until the composite punch approaches the second die 52, whereupon the conduit connected to the

apertures

26 and 27 is relieved to allow the outermost punch 14 to act against the upper face of die 52 as a holddown device for the workpiece while the

punches

10 and 12, acting as a composite punch, draw the partially formed workpiece through the second die 52 to reduce it in size once again.

Continued downward movement of the press head 18 against the outermost punch 14 causes it to slide relative to the two

innermost punches

10 and 12 so that the punches l0 and 12 move in unison to draw the workpiece entirely through the second die 52.

Thereafter the intermediate punch 12 acts against the upper face of die 54 to act as a holddown for the workpiece while the conduit connected to the aperture 30 is relieved to allow the inner punch 10 to draw the workpiece through the third draw die 54.

Finally, the now cylindrical workpiece is drawn through the ironing die 56 by the innermost punch 10 to give to the workpiece a substantially uniform wall thickness.

When the drawing operation has been completed, the cylindrical workpiece is removed in known manner from the innermost punch 10 by means of a stripper ring 58. Thereafter the press head 18 moves back to its initial position (as illustrated) thereby also withdrawing the punches l0, l2 and 14 back through the dies 56, 54, 52 and 50. At the same time hydraulic fluid is supplied to

conduits

25 and 29 to telescope the punches back to their original positions within their housings.

While the dies 50, 52 and 54 are so spaced in relation to the size of the workpiece that the workpiece is drawn through only one die at any one time (i.e., that the upper edges of the partially formed workpiece are drawn out from the previous holddown device before the workpiece enters the next successive die) it is envisaged that a workpiece may be' drawn through two or more dies simultaneously.

punches 10 and 14 have been shown together with two dies 50 and 54 in order to facilitate an understanding of the embodiment. It will be understood, however, that any number of punches and dies may be used. The blank holddown circuit of FIG. 1 comprises a blankholder 101 which is shown as an annular ring having an upstanding flange at its inner radius. The blank holder 101 is normally biased upwardly of the first die 50 by two double-acting hydraulic cylinders 102. The hydraulic cylinders 102 are connected through a pair of hydraulic lines 28, a two-position valve 104, which is operated by part of the press head assembly 105, and a hydraulic fluid pump 44 to a hydraulic reservoir 40. If difficulty occurs in accurately positioning the cam-operated valve 104, it may be replaced by a solenoid-operated valve. An accumulator 106, a nonretum valve 110 and a pressure sensitive control valve 108 provide a hydraulic fluid power circuit for the blank holddown as hereinafter described.

The aperture 26 in the casing 16 is connected to a hydraulic line 34 and thence to a cam-operated valve 36 which is actuated by part of the press head assembly 37. The side of the valve 36 remote from the press is connected to a hydraulic accumulator 38, which in turn is connected to two bottles of compressed

nitrogen gas

39 and 39A. It will be readily understood from FIG. 2 that at the upper part of the accumulator 38 as illustrated there is compressed nitrogen gas, and on the lower part there is the hydraulic fluid of the system. The nitrogen gas and hydraulic fluid are separated by a free-floating piston 41.

The nitrogen bottle 39A is a high-pressure bottle and contains pressurized nitrogen, and the bottle 39 is a lower-pressure bottle. When it is desired to apply a preloading pressure to piston 41, valve cock 43 is opened and valve cock 45 closed. Thus a predetermined mass of gas is introduced into bottle 39 to give a preloading pressure on piston 41.

A hydraulic fluid makeup circuit is provided for the hydraulic circuit of the punch 14 which hydraulic circuit is defined by casing 16, valve 36 and accumulator 38 and hydraulic makeup fluid is fed into the circuit by conduit 49 between the valve 36 and the accumulator 38. The makeup circuit comprises a nonretum valve 60 and a pressure-responsive control valve 62. These are connected to the hydraulic reservoir 40 via the pump-44, as was the case with the holddown fluid power circuit.

The arrangement so described operates as follows.

A workpiece W is initially placed in position on the first draw die 50 and the press head 18 is lowered towards the workpiece W. The cam-operated valve 104 is actuated by press part 105 and permits oil to pressurize and load each of the hydraulic cylinders 102. It will be apparent that if a solenoid-operated valve is used, press part 105 will not be required. This causes the blankholder 101 to lower and clamp the workpiece W on the first draw die 50. The value of the holddown pressure applied to the workpiece W depends upon such factors as the cross-sectional area of the cylinders 102 and the operating pressure of valve 108. A gas-loaded accumulator 106, is included in the makeup circuit to increase the speed of response of the blankholder 101. Continued downward movement of the press head 18 causes actuation of the cam, or solenoid-operated valve 36 on press part 37 to lock the hydraulic line 34, so that the

punches

10 and 14 act upon the workpiece W as a solid composite punch to draw it through die 50 into a substantially dished condition asillustrated in FIG. 3. When the punch 14 reaches the second draw die 54, it acts as a holddown for the initially formed workpiece and the cam-operated valve 36 opens to permit hydraulic fluid to pass by way of aperture 26 from the collapsible chamber defined by casing 16 directly into the accumulator 38, the piston 41 of which rises against the nitrogen gas loading pressure to accommodate an increased volume of hydraulic fluid. A holddown pressure is maintained on the workpiece W by the punch 14 while the punch continues to draw the workpiece through the second die 54 (FIG. 4). It may thus be seen that the nitrogen gas above the piston 41 in accumulator 38 and in the cylinder 39 acts as an energy-storage medium for storing energy created during the downward movement of the punch 10 through the die 54 while the punch 14 is acting as a holddown for the workpiece W on the die 54. Furthermore, the hydraulic control circuit for punch 14 acts as a hydraulic, energy-transfer section for transferring energy from punch 14 to the energy-storage medium.

On the return stroke of the press head 18 hydraulic fluid stored in the accumulator 38 passes through the valve 36 to recharge the hydraulic circuit of the punch 14 which then moves to the end of its travel within the casing 16. Thus, when the press head 18 returns to its initial position, the punches automatically return to their rest position ready to commence a further drawing operation. From the foregoing description it will be seen that the whole of the power required for operating the hydraulic circuit associated with the punch .14 has come from the press, no additional power having been injected into the hydraulic circuit of punch 14.

The pressure-controlled regulating valve 62 senses if hydraulic fluid leakage has occurred from the hydraulic circuit, and if leakage has occurred it is made up from the pump 44 via the pressure-controlled regulating valve 62 and the nonreturn valve 60.

The camor solenoid-operated valve 104 permits hydraulic fluid to pass from the cylinders 102 to drain, thereby enabling the blankholder 101 to be raised from the die 50 to permit a further flat workpiece W to be placed in position on the first die.

In the embodiment described with reference to FIGS. 2 to 4, the cam, or solenoid-operated valve 36 has been described as essential to the invention, since it was necessary to keep the workpiece holddown pressure less than the drawing pressure of the press.

However, if the valve 36 is omitted, the preloading gas pressure on the piston 41 of the accumulator 38 determines the available drawing pressure at the first die 50 and the holddown pressure which will be applied to the workpiece W at draw die 54 by the outermost punch 14. Thus with a high-preloading gas pressure at the accumulator 38, created by a relatively high pressure in bottle 39, the holddown pressure will become greater than the immediately preceding drawing pressure. It is therefore desirable to reduce the holddown pressure at the second die 54, and this may conveniently be accomplished by including a spring-loaded arrangement 250 to be described hereinafter with reference to FIG. 18.

In FIG. 5 there is shown diagrammatically the various stages in the drawing of a workpiece using a three punch, four die arrangement including the positions of the

punches

10, 12 and 14 during each drawing stage. After the workpiece has been clamped by the blank holddown (not shown), it occupies the, position shown as W on the lower half of the figure. On completion of the first drawing operation the punch 14 comes to rest against the second die 52 and the workpiece occupies the position illustrated as W1. On completion of the second drawing operation, the punch 12 occupies the position illustrated against the third die 54, the workpiece then occupying the position W2 and having a diameter approximately equal to the punch 12. Thereafter the workpiece is drawn, by the innermost punch 10, through the third die 54 when it has the shape corresponding to W3, and thereafter through the ironing die 56 which serves both to reduce the wall thickness of the container and to provide the base of the container and the upper walls thereof with slightly thicker metal, in order to provide a reinforced base and a reinforced rim at the top of the container which rim can then be flanged to allow a lid to be sealed thereonto. The completed container is illustrated at W4.

For some applications it is necessary to dimple the base of the container and this may be done by suitably shaping the end of the innermost punch 10. Any desired shape of base may be produced by suitably shaping the end of punch 10, and arranging for a shaped forming tool to cooperate with the punch 10 to shape the base of the drawn container.

In the second embodiment of the invention illustrated in FIGS. 6 and 7 and 8, there is shown a horizontally operating hydraulic press shown generally as 200. The press comprises a frame 202 to which two horizontal

hydraulic cylinders

204 and 206 are attached. Supported between the two hydraulic cylinders is a ram 208 connected to the press head 209, for horizontal reciprocal movement within the press frame 202. Supported at either side of the press head 209 are two punch sets 211 and 213 respectively. FIG. 7 illustrates the punch sets which each carry three

hydraulicpunches

210, 212 and 214 similar to those described in connection with the previous embodiment. Spaced outwardly of, and in the same horizontal axis as the two punch sets 212 and 214 are two die boxes 216 and 218. The die boxes 216 and 218 contain three spaced draw dies, 50, 52 and 54 and an ironing die 56, similar to the dies illustrated with respect to the first embodiment. A stripper ring 58 is provided for stripping a completed container from the innermost punch 210 of each punch set.

A blankholder is provided on each punch set 211 and 213., for holding a workpiece in position on each first draw die 50. The blankholder conveniently takes the form of an annular ring 220 which is actuated by the piston 221 of a double-acting hydraulic cylinder which is located concentrically of each punch set.

Thus it will be seen that the embodiment of FIGS. 6, 7 and 8 provides a'doubling-up of the first embodiment described with respect to FIGS. 2 to 4 inasmuch as two separate punch assemblies are used in conjunction with two die boxes. Two separate hydraulic circuits (not shown on FIGS. 6 to 8) are employed and each of these is provided with an

accumulator

238 and 239 respectively which are both similar to that shown as 38 in FIG. 2, one of these accumulators 239, being for storage of energy created at the second draw die 52, and the other accumulator 238 for storage of energy created at the third draw die 54. Each of the two accumulators store and release energy associated with the two

punch assemblies

211 and 213, and, as with the embodiment of FIG. 2 no additional power is injected into any of the hydraulic control circuits, so that all of the power required for the drawing operations is supplied from the basic hydraulic press 200.

The operation of the embodiment described with reference to FIGS. 6, 7 and 8 will now be described through a complete operating cycle with reference to FIGS. 9 to 14. To facilitate an explanation of the operation, the parts of the press on the right as viewed have been suffixed by the letter A.

The hydraulic cylinder chambers for

outer punches

214, 214A have been noted as 230, 230A, and the hydraulic cylinder chambers for the intermediate punches have been noted as 232, 232A.

Outer punch

214, 214A is illustrated as connected to a

piston

234, 234A by a connecting

rod

236, 236A. The

chambers

230, 230A are connected to the accumulator 238 by conduit 240, and

chamber

232, 232A is connected to the accumulator 239 by conduit 242. FIG. 9 illustrates a workpiece W which is initially placed in position on the first die 50 and is clamped thereon by means of the blankholder 220. It will be assumed that a workpiece WA has just been completed on the right-hand punch set and that this is to be subsequently removed from the punch 210A.

As the press head 209 moves in the direction of the arrow, the workpiece W is drawn through the first draw die 50 (FIG. 10) by the

punches

210, 212, 214 acting as a composite punch, and at the right side of the apparatus the punch 210A commences to withdraw, the stripper 58A engaging the workpiece WA so that is is gradually removed from the punch 210A as the punch withdraws. The

punches

212A and 214A however remain pressed against dies 54A and 52A by the hydraulic fluid which acts on the flanged part of punch 212A and on the pistons 234A respectively-It will be noted that the action of the

punches

212A and 214A acting on their respective dies assists the movement of the press head 209 in the drawing direction. The volume of the chambers 230A and the chamber 232A commence to increase, the additional volume of hydraulic fluid required being provided by the two

accumulators

238, 239, the levels of which will be noted to have fallen from those shown in FIG. 9.

FIG. 11 illustrates the effect of continued movement of the press head 210, the punch 214 having been arrested at die 52 and the punch 212 having drawn the workpiece through the die 52 to the third draw die 54. As the movement of the press head has continued from the position shown in FIG. 10, the volumes of the chamber 230 have decreased by an amount proportional to the spacing between the second and third draw dies 52 and 54. Meanwhile, on the right-hand side of the press the workpiece WA has been removed from innermost punch 210A, and the volumes of

chambers

230A and 232A have also increased, all of the additional hydraulic fluid required for the

chamber

230A and 232A having been provided by the fluid exhausted from the

chamber

230 and 232.

FIG. 12 illustrates the punch 212 having been arrested at the third die 54 and the innermost punch 210 having drawn the workpiece through the die as far as the ironing die. The chambers 230 have decreased in volume during the whole of this movement and the chamber 232 has decreased in volume from the time that the movement of the punch 212 was arrested. At the right-hand side of the apparatus the punch 210A has further retracted and the volumes of the

chambers

230A and 232A have further increased, all of the additional hydraulic fluid required having come from their

counterpart chambers

230 and 232 on the drawing side of the press. It will be noted that the punch 212A is about to be withdrawn from die 54A, and that thechamber 232A is now at its maximum volume.

FIG. 13 illustrates the workpiece W having been drawn through the ironing die 56, and the fact that the

chamber

230 and 232 have decreased still further in volume. On the righthand side of the press the punch 212A has been withdrawn from die 54A and the pistons 234A have reached the limit of their stroke within their respective cylinders. Thus the

chambers

230A and 232A are now all at their maximum volumes. The chamber 232 having decreased in volume, but the volume of its counterpart chamber 232A remaining constant, the volume of oil removed from the chamber 232 is stored in accumulator 239. The additional hydraulic fluid required for chambers 230A having been provided by the fluid transferred from chamber 230.

FIG. 14 is a view similar to FIG. 9 with the press head 210 in its left-hand limiting position, and ready to commence a further drawing operation in the' right-hand direction as viewed. The workpiece W is ready to be stripped from innermost punch 210 by the stripper ring 258, and the volumes of the

chambers

230 and 232 have decreased to their minima. The volume of fluid which has been removed from the

chambers

230 and 232 between the positions in FIGS. 13 and 14 has been transferred through the

conduits

240 and 242 and stored in the

accumulators

238 and 239. The gas in the accumulators has thus been compressed and therefore the accumulators have acted as an energy store. On the right-hand side of the apparatus the

punches

210A, 212A, 214A have returned to the positions illustrated in FIG. 9 for the

punches

210, 212, 214 and are ready to draw a further workpiece WA into a container.

The operation of the apparatus in the reverse drawing direction is similar to that described hereinabove and will not therefore be described in any detail.

lt-is desirable that the total gas capacity of the

accumulators

238 and 239 is sufficiently large such that the increase in gas pressure due to displacement of oil from the hydraulic circuits is kept at a low figure, thereby maintaining the holddown pressure approximately constant throughout the stroke of the press. It has been found that a maximum compression of 3 percent is desirable.

It will be appreciated that while the above embodiment has been described as containing two

hydraulic cylinders

204 and 206, one such cylinder could be used to drive the press head 209.

It will further be appreciated that the ancillary features of the invention, such as the hydraulic fluid makeup circuits, described with respect to the first embodiment can be embodied in the second embodiment described hereinabove.

The third embodiment of the invention illustrated in FIG. 15 is mounted on the press head 318 of a double-acting hydraulic press (not shown). The embodiment comprises a cylindrical casing 316 having two sets of punches 300 and 302 respectively, coaxially mounted therein. Each set of punches 300 and 302 consists of three

punches

310, 312 and 314 similar to those illustrated as 10, 12 and 14 in the previous embodiments, the punches of punch set 302 being designated 310A, 312A and 314A. Each of the

punches

312, 312A and 314, 314A is internally formed with a flanged part 31 1 which is arranged to cooperate with a spring attachment unit 250 to be described in more detail hereinafter with respect to FIG. 17. The

innermost punches

310 and 310A of the two punch sets are screw-threaded onto a center flange member 320 which is fixedly attached to the center of the casing 316. The

punches

312, 312A and 314, 314A, of each punch set are capable of sliding in the casing 316, and each punch is connected to a source of hydraulic fluid by a hydraulic circuit. The hydraulic circuit for the

punches

312 and 312A is a common one and consists of a pair of axially extending bores 322 in the member 320, one of the bores 322 being connected by a radially extending bore 324 to a hydraulic conduit 326. The conduit 326 is connected to a nitrogen-loaded accumulator 338 which is provided with a free-floating piston 341. Accumulator 338 is the equivalent of accumulator 38 of the previous embodiment. A first chamber 328, 328A is defined between the

punches

312, 312A, the greater volume of the chamber alternating on either side of the member 320 depending on the position of the press head 318.

The hydraulic circuits for the

punches

312 and 312A of each punch set comprises a pair of

ports

330, 330A which are formed in the walls of the casing 316. A-pair of conduits 340

connect corresponding ports

330, 330A of the first and second punch sets 300 and 302. Second chambers 332, 332A

separate punches

312, 314 and 312A, 314A respectively, and a third chamber 334, 334A is formed between an end wall of casing 316 and one or other of the

punches

312, 312A, the

volume of the chamber 334, 334A, alternating from one end to the other of the casing 316 depending upon the position of the press head 318.

To facilitate an explanation of the invention the inner and outer surfaces of the

punches

312, 312A and 314, 314A have been suffixed 1 or 0 respectively. Thus the inner surface of punch 312 for example will be referred to as 312,.

In the position illustrated the chamber 334, 334A, is on the left of the Figure and is therefore designated 334.

In operation, a workpiece WA is initially placed on first draw die 50A and is clamped thereat by a blankholder 101, previously described with respect to FIGS. 2 to 5. When the press head 318 commences to move to the right in the direction of the arrow as illustrated, the

punches

310A, 312A and 314A move as a composite punch to and through the first draw die 50A as hereinbefore described. The flanged parts 311 of the

punches

312 and 314 however are pressed against their respective spring units 250 by the action of hydraulic fluid pressure which acts on their flanged parts at chambers 332 and 328' in the following manner. Hydraulic fluid is present in both chambers 328 and 332 and at the same pressure, and chamber 334 is at atmospheric pressure. Considering punch 312 then, because the surface 312,, has a greater area than surface 312 the punch 312 is pressed into contact with spring unit 250. Similarly the surface 314,, of punch 314 has a greater surface area than surface 31 so that punch 314 is pressed into contact with spring unit 250. Thus themovement of the press head 318 to the right as viewed is assisted.

At the second draw die 52A, the forward movement of outer punch 314A is arrested but punch 312A continues its movement with the press head 318 so that the flanged part of punch 312A commences to move towards the flanged part of punch 314A within the casing 316. Thus the volume of the chamber 332A decreases and continued movement of the press head 318 causes hydraulic fluid from chamber 332A to transfer through

conduits

340 and 326 to chamber 328 the volume of which is continuously increasing as the press head 318 continues to move to the right as viewed. However the volume of the chamber 328 is expanding more rapidly than the volume of the chamber 332, is decreasing, so that the remaining volume of fluid required to completely fill chamber 328 is introduced from the accumulator 338, the piston 341 of which moves to the left as viewed under the nitrogen loading pressure. As in the case of drawing the workpiece through the first draw die 50A, the pressure in the hydraulic system acts upon the innermost flanged part 312 of the punch 312 the flanged part 311 of which acts upon the spring unit 250, thereby assisting the movement of the press head 318 in the drawing direction.

Because the accumulator 338 provides the difference in volume required in the hydraulic fluid between the two punch sets 300 and 302, the nitrogen gas in the accumulator 338 may be considered to have acted as an energy store for the difference in hydraulic fluid in the two punch sets created by the relative movement of

punches

312A and 314A. That is the accumulator 338 may be considered to have stored the difference in energy between the left and right sides of the drawing apparatus as viewed in FIG. 15.

The continued movement of the press head 318 to the third die 54A arrests the movement of punch 312A, which causes a decrease in volume of the chamber 328A. Part of the hydraulic fluid from chamber 328A passes to chamber 328, and part of the fluid passes to accumulator 338 for storage. As was the case with previous draws, hydraulic fluid acts upon the innermost flanged part 312 of piston 312, which assists the movement of the press head 318 and consequently the drawing of the workpiece at die 54A.

Thus at the end of the working stroke of press head 318,

punches

314A and 312A have moved inwardly towards center member 320, and in so doing have drawn a workpiece W into the shape of a container.

Punches

314 and 312 have moved outwardly relatively to member 320 to a position corresponding with that of

punches

314A and 312A at the commencement of the stroke, and are therefore ready to commence a further drawing operation. No power has been introduced into the hydraulic circuits, and all the power required for drawing the workpiece has been provided by the basic press, much of the poser for the drawing operation having been provided by the action of the

punches

312 and 314 on their respective spring-loaded units 250.

At the end of its working stroke to the right as viewed, the direction of movement of the press head 318 is reversed, thereby drawing a further workpiece by means of the punch set 300 in a similar manner to that previously described.

It will be appreciated that while the embodiment has been described in conjunction with three punches, any number of punches could be employed by providing a pair of

ports

330, 330A for each additional punch. Again, the ancillary features of the invention such as the hydraulic fluid makeup circuits can be embodied in the third embodiment of the invention described above.

Furthermore, in view of the relatively small size of the punch apparatus, two sets of punch apparatus can be fitted on one press head 318 so that four containers are produced on each full working stroke of the press head.

If desired, an accumulator may be provided for each corresponding pair of hydraulic punch circuits, so that in the embodiment of FIG. 15 for example two accumulators would be employed.

By employing an accumulator as an energy-storage device, great savings in the power requirements for deep drawing are made. For example a known deep drawing press requiring about 250 hp. available input to produce containers/min, could be replaced by a press requiring about l00 hp. available input when embodying the features of the present invention.

FIG. 16 illustrates a fourth embodiment of the invention which closely corresponds with the first embodiment, but in which the hydraulic, energy-transfer circuit has been omitted. As in F 161 '2, the embodiment has been described with respect to two punches to facilitate understanding.

A pressure regulating valve 43A is included between a high pressure nitrogen bottle 39A and the lower pressure bottle 39. The valve 43A is manually adjustable and controls the pressure applied to the punch 14 and therefore the drawing pressure of the punch.

Thus, in operation the press head 18 moves downwardly to and through the first die 50 as described hereinabove. At the second die 54 movement of punch 14 is arrested, but continued movement of the press head 18 causes punch 10 to draw the workpiece through the second die 54. Accordingly the volume of the chamber formed in casing 16 decreases, and gas previously in the chamber is transferred directly through conduit 34 to gas bottle 39. Thus, as in the previous embodiments, the gas becomes compressed and acts as an energy store, which energy is then used to return punch 14 to the end of its stroke in casing 16.

The loss of any nitrogen gas from the system during operation is sensed by the pressure-regulating valve 43A, whereupon valve 43A operates to supply makeup nitrogen. As in the previous embodiments an ironing die 56 and stripper ring 58 can be provided together with a workpiece holddown circuit.

It will be appreciated that while the gas employed with each of the above embodiments of the invention has been nitrogen gas, any gas may be used, provided that it exhibits appropriate characteristics.

It is envisaged that the embodiment described with respect to FIG. 16 may be mounted on a double-acting press and be connected in a similar manner to the second and third embodiments described above. It is also envisaged that the power requirements for arrangements built in accordance with the fourth embodiment will be even less than those of embodiments previously described.

In each of the above-described embodiments of the invention when the drawing operation has been completed, it is necessary to remove the completed drawn workpiece from the innermost punch. This may be achieved in known manner for example by the use of a stripper ring 58 (FIG. 5) which acts upon the open end of a drawn container to remove it from the punch 10. However, where the drawn container fits tightly round the innermost punch, a stripper ring has tended to damage the upper walls of the completed container.

Accordingly, a stripping arrangement similar to that illustrated in FIG. 17 may be employed which for the sake of understanding has been described with respect to the first embodiment described with reference to FIGS. 2 to 4. The stripping arrangement comprises a spring-return hydraulic cylinder 263 which is connected to the press head 18. The hydraulic cylinder 263 has an actuating rod 262 which extends through the innermost punch 10 and terminates in a plunger 264 which locates over the end of the innermost punch 10, so that the sides of the workpiece are drawn around the sidewalls of the innermost punch 10 and the base of the workpieceis drawn by the plunger 2641. When the drawing operation has been completed, the hydraulic circuit 261 feeding the hydraulic cylinder 263 is actuated, causing the plunger 264 to project from the end of the punch 10 carrying with it the completed container. In this way the completed container is loosened from the sidewalls of punch 10 and the container is removed from the plunger 264 on the return stroke of the press head 18 by means of a conventional stripper ring 58.

In FIG. 18 there is shown a spring-loaded attachment unit by means of which the holddown pressure acting on a workpiece can be varied. It will be recalled that with the embodiment of FiGS. 2 to 4 for example, with the valve 36 omitted a holddown pressure greater than the immediately preceding drawing pressure is obtained. By using the unit of FIG. it is possible to obtain a holddown pressure on die 54 which is less than the immediately preceding drawing pressure. The unit 250 is threadedly located by means of screw threads 257 on the press frame 252. The unit 250 comprises a cup-shaped member 254 in the form of an annular ring having a cylindrical sidewall 255. The member 254 is resiliently spaced apart from a further annular ring 256 by springs 258. Ring 256 is provided with a pair of radial walls, the wall located on the greater radius being arranged to cooperate with the sidewall 255 of the member 254. A number of circumferentially spaced guide rods 260 are located on the ring 256 upon which the member 256 is free to slide. The arrangement is such that as the press moves towards a die, for example die 54, the unit becomes loaded by means of an abutment 259 located on the first drawing punch 14, so that the effective holddown pressure on the workpiece at die 52 is the difference between the pressure required for the preceding draw and the pressure loading on the unit 250. Thus the holddown pressure acting on the workpiece is less than the pressure required for the preceding draw.

When the abutment 259 is withdrawn it occupies the posi tion illustrated dotted in FIG. 18 so that the unit is no longer loaded.

The holddown pressure which acts upon the workpiece is varied either by altering the stiffness of the springs 258 or alternatively by altering the relative positions of the press frame 252 and unit 250 by screwing the unit 250 on screw threads 257 into or out of the press frame. By screwing the unit 250 into the press frame, the workpiece holddown pressure is decreased, and by screwing the unit 250 out of the press frame the holddown pressure is increased.

In an alternative construction the springs 258 can be replaced by an elastomeric material.

It will be appreciated that such a spring unit 250 may be provided for reducing the holddown pressure between any drawing punch and subsequent die.

It is envisaged that the holddown arrangement described with respect to FIG. I8 when used in conjunction with the press of FIG. will provide a relatively cheap, high-speed, container producing unit having low power requirements.

In the embodiments of the invention which have previously been described, the workpiece has been in the form of a flat metal disc W. This feature however is not essential since the workpiece may be fed to the machine as a sheet or strip instead of in the form of a blank, and this sheet may conveniently be in the form illustrated in FIG. 19. The cutting into narrow strips as shown by full lines being performed before the strip is fed to the press. By feeding the workpiece to the press in this manner the sheet metal may be used more efficiently.

We claim:

l. Ina method of deep drawing a container from a sheet metal workpiece which comprises introducing the workpieceonto the first die of one set of punches of a deep drawing press having two opposed sets of interconnected, telescopically arranged punches relatively movable to an innermost punch, advancing a set of punches as a composite punch towards said first die and drawing said workpiece therethrough and advancing said punches to a second die, the improvement comprising the steps of storing energy created by relative movement between one of said punches and said innermost punch by compressing a fixed quantity of a compressible fluid medium, and transferring part of said energy directly to a punch in the opposed set of punches to assist movement of at least one of the telescoping punches of said opposed punch sets relative to the innermost punch of said opposed set of punches.

2. Deep drawing press apparatus of the type including a press head, at least one set of a plurality of telescoping punches carried by the press head for cooperation with a plurality of stationary draw dies whereby an initially substantially flat metallic workpiece supported on a first die is drawn progressively by said punches through said die to form a container upon movement of said press head towards said dies, at least one of said punches being movable in opposite directions relative to said press head during parts of the drawing operation, a control system for a relatively movable punch including means for storing energy generated in response to movement of said punch relative to said press head during one part of a drawing operation, said energy storing means comprising an accumulator containing a substantially fixed quantity of compressible fluid medium, a collapsible chamber containing a substantially fixed supply of a hydraulic fluid medium, means affording a direct and unrestricted connection between the collapsible chamber and said accumulator whereby a decrease in volume of said collapsible chamber effects a corresponding increase in pressure of the compressible fluid in said accumulator, means responsive to movement of said punch relative to said press head in.one direction during a part of a drawing operation to collapse said chamber and increase the pressure in said accumulator in proportion to said relative movement, and fluid pressure-responsive means connected to said accumulator and constructed and arranged to receive the energy stored therein and assist in the further operation of said press, thereby decreasing the energy input requirement to the press substantially by the energy stored in the accumulator during the first-mentioned part of the drawing operation.

3. An apparatus as set forth in claim 2 wherein a hydraulic fluid makeup circuit is provided for supplying hydraulic makeup fluid to each control system.

4. An apparatus as set forth in claim 3 wherein the hydraulic makeup fluid circuit comprises a nonretum valve and a pres sure-sensitive relief valve operatively connected to a hydraulic reservoir.

5. An apparatus as set forth in claim 2 wherein holddown means are provided for holding the workpiece in position on at least the first die.

6. An apparatus as set forth in claim 5 wherein the holddown means comprises a blankholder operable by means of a hydraulic control circuit to move between a position in which the blankholder is biased away from the die and a clamping position in which said blankholder is adapted to hold a workpiece in clamping relationship with said die.

7. An apparatus as set forth in claim 6 wherein the blankholder is in the form of an annular ring.

8. An apparatus as set forth in claim 6 wherein a hydraulic fluid makeup circuit is provided for supplying hydraulic makeup fluid to the hydraulic circuit controlling the blankholder. L

9. The press of claim 2 including a plurality of punches relatively movable with respect to said press head, and a control system for each of said punches.

10. An apparatus as set forth in claim 8 wherein the hydraulic fluid makeup circuit associated with the holddown means comprises a two-position valve for controlling actuation and relief of the hydraulic control circuit controlling operation of said blankholder, a hydraulic accumulator connected to the valve on the side thereof remote from the blankholder, and a nonretum valve and a pressure-sensitive control valve arranged fo connection to the hydraulic control circuit at a position between the valve and the accumulator and connectable to an hydraulic reservoir.

11. An apparatus as set forth in claim 9 wherein workpiece holddown means are provided on second and subsequent draw dies, holddown being effected by the punch immediately preceding that which is effecting the formation of the workpiece at that die.

12. An apparatus as set forth in claim 1 1 wherein the holddown pressure applied to the workpiece at any one of said dies is controlled by a spring-loaded attachment unit which comprises a pair of members resiliently spaced apart, one of said members being adapted to be fixedly connected to the press frame of said press, and the other of said members being adapted to be engaged by an abutment on the punch effecting holddown at that die, whereby to provide a workpiece holddown pressure less than the drawing pressure of said press.

13. An apparatus as set forth in claim 2 wherein each of the punches and dies are of circular cross section along at least part of its length.

14. An apparatus as set forth in claim 1, wherein the control system associated with each punch of one of the sets of punches is connected in common with the corresponding punch of the other of said set of punches.

15. An apparatus as set forth in claim 9 wherein a doubleacting press is used and four sets of telescopically received punches are coaxially mounted in two rows of said press heads, which punches are arranged to cooperate with two opposed pairs of sets of stationary dies to produce four containers on each working stroke of the press.

16. An apparatus as set forth in claim 2 in which the punches are directed for either horizontal or vertical operation.

17 A method as set forth in claim 1 which further comprises removing a drawn workpiece from the innermost of the telescoping punches.

18. A method as set forth in claim 1 wherein the drawn workpiece is removed by ejecting same from the innermost of the telescopic punches by hydraulic and mechanical means.

19. A method as set forth in claim wherein the hydraulic means comprises a plunger acting on the base of the drawn workpiece.

20. A method as set forth in claim 15 wherein the mechanical means comprises a stripper ring acting on the periphery of the open end of the drawn workpiece.

21. The press of claim 2 wherein said punch is movable between extended and retracted positions relative to said press head and wherein said punch is adapted to retract during the movement of said press head toward said dies and by engagement with a die of lesser cross-sectional dimension, said collapsible chamber being constructed and arranged to be collapsed in response to said retraction of said punch.

22. The press of claim 2 wherein said direct connection includes a cam-operated valve responsive to movement of said press head for locking the hydraulic fluid in said control system to prevent relative movement of a punch during a part of the drawing operation.

23. A press as set forth in claim 22 wherein at least some of the relatively movable punches are provided with radially extended flanges, a common casing formed as a cylinder slidably receiving said flanges, said flanges and easing defining each collapsible chamber operable during said one part in the drawing operation to increase the pressure in the accumulator, said casing and flanges also defining said pressure-responsive means for receiving the energy stored in said accumulator.

24. An apparatus as set forth in claim 2 including a second set of telescoping dies coaxially mounted on said press head in opposition to said first set and arranged to cooperate with a second set of opposed stationary dies to produce a container on each stroke of the press in opposite directions.

Claims

1. In a method of deep drawing a container from a sheet metal workpiece which comprises introducing the workpiece onto the first die of one set of punches of a deep drawing press having two opposed sets of interconnected, telescopically arranged punches relatively movable to an innermost punch, advancing a set of punches as a composite punch towards said first die and drawing said workpiece therethrough and advancing said punches to a second die, the improvement comprising the steps of storing energy created by relative movement between one of said punches and said innermost punch by compressing a fixed quantity of a compressible fluid medium, and transferring part of said energy directly to a punch in the opposed set of punches to assist movement of at least one of the telescoping punches of said opposed punch sets relative to the innermost punch of said opposed set of punches.

2. Deep drawing press apparatus of the type including a press head, at least one set of a plurality of telescoping punches carried by the press head for cooperation with a plurality of stationary draw dies whereby an initially substantially flat metallic workpiece supported on a first die is drawn progressively by said punches through said die to form a container upon movement of said press head towards said dies, at least one of said punches being movable in opposite directions relative to said press head during parts of the drawing operation, a control system for a relatively movable punch including means for storing energy generated in response to movement of said punch relative to said press head during one part of a drawing operation, said energy storing means comprising an accumulator containing a substantially fixed quantity of compressible fluid medium, a collapsible chamber containing a substantially fixed supply of a hydraulic fluid medium, means affording a direct and unrestricted connection between the collapsible chamber and said accumulator whereby a decrease in volume of said collapsible chamber effects a corresponding increase in pressure of the compressible fluid in said accumulator, means responsive to movement of said punch relative to said press head in one direction during a part of a drawing operation to collapse said chamber and increase the pressure in said accumulator in proportion to said relative movement, and fluid pressure-responsive means connected to said accumulator and constructed and arranged to receive the energy stored therein and assist in the further operation of said press, thereby decreasing the energy input requirement to the press substantially by the energy stored in the accumulator during the first-mentioned part of the drawing operation.

4. An apparatus as set forth in claim 3 wherein the hydraulic makeup fluid circuit comprises a nonreturn valve and a pressure-sensitive relief valve operatively connected to a hydraulic reservoir.

8. An apparatus as set forth in claim 6 wherein a hydraulic fluid makeup circuit is provided for supplying hydraulic makeup fluid to the hydraulic circuit controlling the blankholder.

10. An apparatus as set forth in claim 8 wherein the hydraulic fluid makeup circuit associated with the holddown means comprises a two-position valve for controlling actuation and relief of the hydraulic control circuit controlling operation of said blankholder, a hydraulic accumulator connected to the valve on the side thereof remote from the blankholder, and a nonreturn valve and a pressure-sensitive control valve arranged for connection to the hydraulic control circuit at a position between the valve and the accumulator and connectable to an hydraulic reservoir.

12. An apparatus as set forth in claim 11 wherein the holddown pressure applied to the workpiece at any one of said dies is controlled by a spring-loaded attachment unit which comprises a pair of members resiliently spaced apart, one of said members being adapted to be fixedly connected to the press frame of said press, and the other of said members being adapted to be engaged by an abutment on the punch effecting holddown at that die, whereby to provide a workpiece holddown pressure less than the drawing pressure of said press.

15. An apparatus as set forth in claim 9 wherein a double-acting press is used and four sets of telescopically received punches are coaxially mounted in two rows of said press heads, which punches are arranged to cooperate with two opposed pairs of sets of stationary dies to produce four containers on each working stroke of the press.

17. A method as set forth in claim 1 which further comprises removing a drawn workpiece from the innermost of the telescoping punches.

19. A method as set forth in claim 15 wherein the hydraulic means comprises a plunger acting on the base of the drawn workpiece.

23. A press as set forth in claim 22 wherein at least some of the relatively movable punches are provided with radially extended flanges, a common casing formed as a cylinder slidably receiving said flanges, said flanges and casing defining each collapsible chamber operable during said one part in the drawing operation to increase the pressure in the accumulator, said casing and flanges also defining said pressure-responsive means for receiving the energy stored in said accumulator.