US2865626A - Cushion for power presses - Google Patents

Description

Dec. 23, 1958 F. J. RODE CUSHION FOR POWER PRESSES Filed Feb. 9, 1955 INVENTOR. 56 FRED d. R005 die member.

United States Patent CUSHION FOR POWER PRESSES Fred J. Rode, Chicago, Ill., assignor to Niagara Machine & Tool Works, Buffalo, N. Y.

Application February 9, 1955, Serial No. 487,166

1 Claim. (Cl. 267-1) This invention relates to power presses and particularly to a novel cushion arrangement for the beds of such presses.

It is conventional and well known to provide yieldable cushion means in or beneath the beds of power presses, such cushions being generally employed to yieldably support draw rings in connection with the use and operation of metal drawing dies although they may be employed for various purposes. The yieldable medium employed in power press cushions of this general type is most commonly air under pressure, the air in the cushion being compressed or additionally compressed during the working portion of a press cycle and acting to return the cushion and the parts supported thereby to their initial positions during the return portion of a cycle of operation.

In what is probably the most common form of draw die apparatus the male die member is fixed to the bed of the power press and the female member is fixed to the reciprocable slide above and in registry with the lower A draw ring surrounds the male die member with its upper surface at or above the upper surface of the male die, so that a work sheet placed in the die rests on the draw ring and is gripped between the draw ring and the marginal surfaces of the female die member as the latter descends.

During further downward movement of the female die, after the work sheet is initially clamped between the draw ring and the female die, the draw ring is moved yieldably downward and the marginal portions of the metal of the workpiece are frictionally gripped between the draw ring and the female draw die in such a way that the metal may slide between the draw ring and the female die as it forms over the male die, more or less as additional metal is needed to produce the desired male die form.

If the pressure between the draw ring and the female die is too greatthe metal will not feed inwardly enough and the work sheet will tear or become unduly thin in places. If the pressure is not great enough the metal will slide between the draw ring and the female die too readily and wrinkles will result in the drawn piece.

As an additional means of producing enough gripping action between the draw ring and the female die it is known to provide their meeting surfaces with complementary groove and bead formations, the bead being in either the draw ring or the female die and the mating groove in the other. Such beads need not be continuous about the draw ring and may be located only where needed to properly restrain inward feeding of the work metal during drawing. Furthermore, the bead and groove formations may be varied as to depth to impose only the desired degree of restraint in this connection.

A common difficulty which finds no satisfactory solution in the practical prior art arises from the fact that the yieldable means supporting the draw ring, by the very nature of its yieldability, does not offer enough resistance or reaction force, at the time when the female die first meets the draw ring and the workpiece supported thereon,

to properly form the restraining beads in the workpiece.

For instance, and of course merely by way of example, the actual drawing operation may dictate the use of a cushion for supporting the draw ring with a resistance of say 20 tons, whereas proper formation of the marginal restraining beads in the workpiece, which of course must come at the very beginning of the drawing operation to be useful, may require a pressure between the draw ring and the female die of 50 tons.

The present invention provides simple and effective means whereby power press cushions used in metal drawing operations are arranged to offer a much higher yieldable resistance at the very beginning of the downward movement of the cushion, so that initially the draw ring affords enough resistance to the pressure of the female die to fully form the draw beads.

This is accomplished in such a way that only the normal resistance of the cushion is present immediately after the beginning of the working engagement between the female die and the draw ring is past. Furthermore, the arrangement of the present invention is such that the distance through which the greatly increased initial resistance is effective may be readily adjusted to suit a particular draw die set-up and insure power draw bead formation without imposing the increased initial resistance of the draw ring any longer than is necessary to secure full formation of the draw beads.

The arrangement of the present invention, in the form set forth herein by way of example, is further such that the degree of increased or augmented initial resistance is readily adjustable without affecting or disturbing the normal cushion resistance, design and arrangement.

A single embodiment of the present invention is shown somewhat schematically in the accompanying drawing and is described in the following specification. However, it is to be understood that such embodiment is by way of example only and that the principles of the invention are limited only as defined in the appended claim.

The single figure of the drawing is a fragmentary front elevational view of a power press provided with one form of the cushion control means of the present invention.

The power press illustrated fragmentarily in the drawing is a double crank or two-point eccentric straight side press which would normally be provided with two air cushions of the general type here under consideration. The drawing shows only the right-hand portion of the press in cross-sectional detail but it is to be understood that the left-hand side of the bed of the press would in the present instance be provided with a duplicate cushion and a single description will sufi'ice for both.

The illustration herein of a double crank or two-point eccentric press and a dual cushion arrangement is again merely by way of example and the cushion control principles set forth herein may be applied to any type of power press or similar machine where a cushioning means of the type set forth herein may be gainfully employed. Furthermore, the principles of the present invention are the same and are equally applicable where, one, two or any other number of cushions are employed 1n a press.

Referring to the drawing, the power press fragmentarily depicted therein is entirely conventional excepting for the cushion apparatus and comprises a bed 10, side columns, one of which is designated 11, and a vertically reciprocable slide 12 having a die or punch holding platen 13 at its lower face. The bed 10 is provided with a die receiving bolster 14 in conventional manner and the slide 12 is reciprocated by cranks or eccentrics disposed at the upper portion of the press (not shown) and is connected to the cranks or eccentrics by the usual connections or pitmans, one of which is designated 15 in the drawing.

The bed structure of the press is provided with a'paii of air cushion cylinders 16 which are fixed with respect to the bed as by bolts and tie rods designated fl in the drawing. A drum-type piston member 18 enters the upper end of each of the cylinder members 16 and is provided with a head plate structure 19 which will usually, although 7 not necessarily, be square or rectangular in shape and extend into an opening of corresponding shape in the upper plate member of the bed, so that headplate 19 of the cushion is disposed moreor less directly beneath bolster 14 when the press is in a rest position, as shown in the drawing. p ,7

The bottom endsof the cylinders 16 are provided with heads or closure plates 22 and the bearing surfaces 9f piston members 18 'and cylinders 1 6 are provided with suitable; bearing and packing or sealing means as at 24 and 25in the drawing.

The foregoing cushion constructions are entirely con ventional. Inoperatipn any desired degree of airpressure is maintained in the cylinders 16 'to urge the pistons 18 upwardly with the required force toaccomplish proper draw ring operation and to return them to their upper idle positions after the pistons have been depressed during a cycle of operation of the power press in conventional manner. So muchof thecushionpistonand cylinder construction. as has been thus far described is conventional and well known in the prior art.

By Way of illustration the drawing shows a male draw die member positioned on the bolster 14 with a complementary female draw die member 31'fixed to the 'platen 13 of slide 12 of the press. A draw ring 33 is supported upon the upper ends of a series of pressure pins 34 which extend slida bly through suitable openings in bolster 14 and rest at their lower ends upon the upper surfaces of cushionplate 1 9. Thus the downward pressure of female die 31 againstdraw ringr33, with-a work sheet normally held between these two members, is resiliently opposed by thefair pi'essure in cylinder 16. v I I Dnaivrin'g 33 i'sfshown-provided with a draw bead 35 and the etigagin'gs urface of female draw die member =31 is provided with a corresponding groove 36, these formations being provided to produce the draw beads hereinfore referred to for restraining the slippage ofthe metal betweenthe draw-ring- 33 and the lower surface of female draw die 31. As fprthe'r mentioned above, the'bead and groove formations 35 and 36 may be reversed, may be disposed intermittently at various places about the draw die'a's the'need presents'itself, and may be of' any desired depth to producea given desired restraining action.

The means provided by the present invention in the form set forth herein by way of example forestablishing an initial cushionresistance substantially exceeding the normal cushion resistance, for the purpose of forming the draw head as describedgenerally above, comprises a hydraulic systern'which now be described and which is housed generally in a cylindrical casing 40 which is fixed a'iiially to the bottom end of each cushion cylinder 16. p p i V Hydraulic cylinder 40 is provided with a:-p ist0n 41 which -is fixed for.movement withpcushion head 19 by means of'a connecting shaft 42. The piston 41 is not packed or sealed with. respect to the wallsof 'cylinder 40 "and is provided with a slight clearance with respect thereto. The oil level in cylinder 40 is-indicated at 44.

Piston 41 is provided with a bore 46 and a plug valve 47 is disposed with its lower endin the upper-end of bore 46 when the power'press is in an initial position. Valve 47 is supported upon a stem 43 and'guided-at its upper end inthe bottom head 22 of cylinder 16 by virtue of'a further stem member 49. The lower end'of stem 48 is'provided with adjusting nuts. 50 by virt ue of which the vertical position ofvalve47 with respect topiston'41 may readily and accurately beadjusted I I It will be seen from'theffore'going that aninitial i rnpact'ag ai nst draw ring 33,which occ'urs wh'enfemaledie 31 engages the draw 'ring, or nio'r'eproperly the work I sheet resting thereon, at the beginning of a cycle of charation; occurs with plug valve 47 closing the bore 46 in P IOI 4. ,7 a, 7

Since the cushion can yield downwardly only by movement of piston 41 downwardly in hydraulic cylinder 40, downward movement of the cushion can occur only by the relatively restricted leakage of hydraulic fluid upwardly between the periphery of piston 41 and the interior wall of cylinder 40, albeit this clearance is sufficient to permit downward movement of the piston under a pressure at least high enough to fully form the draw beads through the means of the beads 35 and the grooves 36 in the draw ring and the female die, respectively.

The plug valve 47 is so adjusted that this initial resistance obtains just long enough t'o fully form the beads, whereupon piston 41 has moved downwardly a suflicient distance to open the bore 46, by movement thereof downwardly past plug valve 47. This opening of the bore 46 substantially neutralizes the deterrent effect of piston 41 and the remainder of the downward operation of the air cushion mechanism is conventional and takes place merely against the pneumatic resistance within cylinder 16.

Anadjustable pressure relief valve 55 is disposed in a bypass conduit 56 which communicates with cylinder 40 abovefa'nd below the pistonj ll. Adjustment of P i ssure reli efi valve 55 permits selective adjustment 'of 'the initial bead formingpressure or'resistance of the cushion, since any pressure developed against the draw ring in excess of the setting of relief valve 55 bypasses hydraulic fiuid'fro'm the bo t'tom to the top of cylinder 40.

In"a ,c'opending application filed of even date here with and bearing Serial No. 48711671 have disclosed and claimed a novel dash pot arrangement for slowing the return movement of 'the pressure pad of a punch press onithe upstroke of a power press as the pressure pad reaches its upper position. One form of this pressure pad return dashpot arrangement is illustrated herein in "conjunetion with my present invention, which thus relates primarily to theinitial'high pressure or high resistance operation of thefpressure pad and secondarily to thenovel combination whereby the high pressure operation and the return stroke dash pot operation are achieved in-a combined apparatus in a novel, simple and effective manner. I

In the drawing the numeral 60 designates-a collar which is fixed to the underside of the bottom head 22 of'cylinder 16 and has a reduced annular downward extension. The numeral 61 designates a cupshaped annular member which is fixed to the upper side of piston 41 or, in any event, to shaft 42, for movementtherewith. Thus each down stroke of the pressurepad results in the cupshapedmember 61 becoming filled with hydraulic fluid and as the terminal-portion of -the upstroke is approached, the reduced lower extension of collar 60 enters cupshaped member 61.

The hydraulic fluid thus trapped in the cup-shaped member has limited egress between the upper interior periphery of the-cup-shaped member 61 and the outer periphery of-the reduced-lower extension of collar 66, thus slowing the upward movement of piston '18 and pressure'pad 19, which'upw'ard movement is being accomplished 'under air pressure within the cylinder 16 and'within the body ofth'e piston "18.

What'is claimed is:

ln-afsh'eet metal draWing press, a die supporting bed having a pressure pad associated therewith, "fluid pressure nieans'for'yieldably resisting movement ofth'e pressure pad "in the'directio'n of a working stroke of said press,'and auxiliary resistance means comprising a hydraulic cylinder'and a piston'movable therein upon movement er said-pressure pad, relatively restricted hydraulic fluid passage means past saidpiston to permit movement thereof under a pressure against thepressure'pad in said working stroke direction substantially greater than the normal resistance of the first fluid pressure=-means,-and

hydraulic pressure relief means operable automatically References Cited in the file of this patent to neutralize said auxiliary resistance means upon completion of a predetermined initial movement of said pres- UNITED STATES PATENTS sure pad in said working stroke direction, and hydraulic ,74 49 Marghitan Feb. 4, 1930 dash pot means comprising a pair of relatively movable 5' 55 Rode Aug. 19, 1947 members associated with said cylinder and said piston, 8 ,339 Georgeii Feb. 5, 1952 respectively, and operable to damp the final return move- 2,605,731 501111126 e a1. 1952 ment of said pressure pad. 2, ,984 Zumwalt Dec. 1. 1953

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