US 2783727 A
Description (OCR text may contain errors)
March 5, 1957 O. HOFFMANN CUSHION DIE STRUCTURE FOR APPARATUS FOR PRESSING SHEET METAL SHAPES Original Filed Sept. 12, 1951 2 Sheets-Sheet 1 INVENTOR. flt giw AffdF/YZYS'.
March 5, 1957 o. HOFFMANN 2,783,727 CUSHION DIE STRUCTURE FOR APPARATUS FOR PRESSING SHEET METAL SHAPES IN V EN TOR. 012; M
@ivmdjw United States Patent '0 CUSHION DIE STRUCTURE FOR APPARATUS FOR PRESSING SHEET IWETAL SHAPES Otto Hofimann, Kenmore, N. Y., assignor to Lake Erie Engineering Corporation, Buffalo, N. Y., a corporation of New York Original application September 12, 1951, Serial No. 246,229. Divided and this application September 13, 1952, SerialNo. 309,501
2 Claims. (Cl. 113-44) This invention relates to a cushion die structure for apparatus for pressing sheet metal shapes.
This application is a divisional application of my copending application for Apparatus for Pressing Sheet Metal Shapes, Serial No. 246,229, filed September 12, 1951, and to which reference is made for a more detailed description of the apparatus in which the cushion die structure of the present invention is adapted to be used.
The invention generally relates to a cushion die structure in the form of a metal holder containing a resilient pad or cushion of rubber backed with a liquid and against which resilient pad or cushion the metal blank to be formed is placed, and a punch forcing the blank into the pad of the cushion die structure against controlled relief of the liquid so that the pad of the cushion die structure wraps the blank around the punch to form it to a corresponding shape. Apparatus having such a cushion die structure is particularly useful with unusual or complicated shapes which can be formed in one operation with such apparatus but which would require a number of separate operations with a corresponding large number of dies if done with male and female metal dies.
An object of the present invention is to provide such a cushion die structure including a liquid backed rubber body, in which the rubber body is not subject to tearing or impairment in use.
Another object of the invention is to provide such a cushion die structure adapted to operate under relatively high pressure, such as 6,000 to 10,000 pounds per square inch or more.
Another object is to provide such a liquid backed cushion die structure which tends to seal itself against the escape of liquid.
Another object is to provide such a cushion die structure which utilizes both the flow of rubber and the back pressure of a liquid backing for the rubber, or other rubberlike flexible substance to wrap the blank around a punch entering the cushion die structure.
Other objects and advantages of the invention will be apparent from the following description and drawings in which:
Fig. 1 is a fragmentary vertical section through the ram of a hydraulic press and through a unit for pressing sheet metal shapes which has a cushion die structure ern- 'bodying the present invention. in this view theparts are shown in the position occupied at 'the start of the pressing stroke.
Fig. '2 is a view similar to Fig. 1 but showing the position of the parts and acorresponding deformation of the blank at the middle of the pressing stroke.
Fig. 3 is a view similar to Figs. 1 and 2 and shows the position of the parts on completion of the pressing stroke and showing the blank fully formed to the desired shape.
Fig. 4 is a horizontal section taken generally on line '4-4, Fig. l to show the pad of the cushion the structure in plan.
The cushion die structure of the present invention is shown as contained in a low, relatively broad unit adapted to be interposed between the ram 10 and stationary :platen (not shown) of any standard hydraulic press having a.
sufii'cient opening to receive the unit. The cushion die structure of the present invention comprises an .upperpad or cushion holder 12 secured to the ram 10 of the press and which is preferably in the form of a rectangular metal casting having an upper flat face 13 which engages the lower face of the ram 10. This pad or cushion holder 12 is provided in the center of its lower face 14 witha large pocket or recess extending upwardly therefrom and which forms a chamber 18 containing a body of oil 19. This pocket can be of any shape in horizontal section to suit the shape of the workpiece, this pocket being shown as being round in horizontal section although it can :be square, oval, elongated rectangular, diamond shaped or of any other horizontal section best suited to the shape of the article being formed. The oil 19 isretained in this chamber 18 by a rubber pad or cushion 20 and for this purpose therecess .or chamber 18 is bell-shaped having an upper face 21 of relatively small diameter from which a frusto-conical side wall 22 flares downwardly and outwardly and the lower end of this frusto-conical side wall 22 terminating in a generally vertical annular wall ,'23 which extends to the lower flat face 14 of the padjor cushion holder. This lower annular wall 23' of'the chani-,
ber 18 can be also provided with annular channels 24 which are preferably of saw tooth form and have 'horizontal lower faces against which annular beads 25 around the perimeter of the rubber cushion 20 fit so as to hold the cushion 20 within the recess or chamber 18. It has been found, however, that such beads are not essential to retain the cushion 20, the cushion being self-retaining in the pocket 18 without these beads as hereinafter described in greater detail. Also while this cushion 2.0 is preferably made of rubber it can be in the form of a member composed of any soft, resilient and readily distortabl'e but substantialy incompressible material.
To prevent tearing or rupture of this rubber cushion 20 and to provide adequate contact between this-rubber cushion and the internal side walls 22, 23 of the pad or cushion holder 12, this central part of the rubber pad or cushion 20 'is in the form of a relatively 'thin section 28 diaphragm-like form while its marginal portion 29 is thickened to provide a thick marginal rim the circular perimeter of which corresponds to the internal frustoconical and vertical faces 22, 23 of the pad or cushion holder 12. This thickened rim portion 29 is of sub stantially greater thicknessthan said diaphragm-like cenrim 31 of upwardly diminishing cross section, this rim, :in
turn, terminating in a relatively thin edge 32. It wi'llbe seen that the pressure of the fluid body 19 tends to press the upwardly tapering relatively thin-edged rim 32 of the cushion 20 against the internal frusto-conical side wall '22 of the-chamber or recess 18 and hence iprovide a seal against the escape of fluid between the walls of this pocket-or chamber 18 and theperimeterof-the'ruhber pad or cushion 20.' I
The movement ofthe liquid 19 into and out of the chamber Hi-is through a vertical bore 33 communicating with a horizontal bore 3-4 one end of which is connected with ;-a line 35, and the-other end of which coin inunicates With a relief valve 36 which is of such form as to restrict the escape of fluid from this chamber an accordance with the'vertical .position of .a plunger .18.?! depending :from the xvalve 3,6 and carrying a;,ro;1l.er :38.
The relief valve :is :such "that the l'higher .the rpositionof its plunger 37 the more isits resistance to the escape of the liquid 19 from the chamber 18 and this relief valve is controlled automatically by a cam as hereinafter described.
A blank plate 40 is shown as provided for supporting a blank 43 and while the upper surface of this blank plate can be fiat it is shown as provided with a central annular raised portion 41 which fits within the lower rim portion of the recess or pocket 18 for the rubber pad or cushion 20 and the central part of this raised portion 41 is recessed,
fas indicated at 42, to provide an indented surface on which the blank 43 is placed. If the upper surface of the blank plate is'fiat, the undersurface of the rubber pad or cushion .26 is arranged, of course, flush or coplanar with the underface of the cushion holder 12.
The blank plate is secured, as by screws 44, to the upper face of a blank bolster 45 which is of flat rectangular'form. The blank plate 40 and blank bolster 45 are provided centrally with registering openings 46 and 48, respectively, these openings jointly forming a downwardly and outwardly enlarging through opening in which the punch 50 is arranged.
This punch 50 is externally shaped to correspond to the shape of the pressed piece and is shown as having a pyramidal upper portion from the lower edge of which vertical side walls extend downwardly. This punch is secured in any suitable manner (not shown) on a punch bolster S1 and this punch bolster can be supported on the stationary platen of the press by the multiple cylindex-structure (not shown) forming the'subject of my said parent application of which this is a division.
The relief valve 36 is shown as controlledby a bell crank lever 94 pivoted, as indicated at 95, to a vertical guide 92 on the cushion holder 12. The upper horizontal arm 96 of this bell crank lever engages the roller sees the plunger 37 of the relief valve 36. The depending arm 97 of the bell crank lever 94 carries a roller 98 in contact with the working face 99 of a cam plate 103. This cam plate is suitably. secured to one side of an upwardly moving control bar 91 guided in the guide 92, and the working face 99 of the cam plate 100 is formed to correspondto the pressure requirements of the part being pressed. Thus infforminga sharp corner a greater degree of back pressure is required and hence when the blank 43 engages such a sharp corner of the punch 50 the roller 98 will encounter a salient part .of the working face 99 of the cam 100 so as to lift the plunger 38 of the relief valve 36 and thereby restrict to a greater degree the escape of fluid from the chamber 18 and build up a higher back pressure in this chamber. The bar 91 and cam plate 100 can be controlled by the mechanism shown in my said parent application.
As previously indicated the beads 25 in the annular channels 24 are not necessary to retain the cushion 20 in the pocket 18. The rim area of the pocket 18 which contains these annular channels 24 is substantially per peudicular to the lower face 14 of the cushion holder 12 and this perpendicular rim area extends a substantial distance into the pocket. The thickened rim portion 29 of the rubber cushion 20 has a substantial rim area of conforming shape engaging this perpendicular rim area ,of the pocket 18 and the'cushion 20 is forced into the pocket 18 under pressure so that the thickened rim portion 29 of the cushion is under internal compressive force which provides sufficient frictionalcontact between the contacting rim areas of the cushion and pocket to insure retention of the cushion in the pocket when the cushion holder 12 is elevated to an inoperative position. It
push the cushion 20 down and out of the pocket 18 is its own weight and the weight of the body of fluid 19. Wall friction between the rims of the cushion 20 and pocket 18 has been found to be sufiicient to sustain these weights when these rims are generally perpendicular to the lower face 14 of the cushion holder 12 as described.
In the operation of the apparatus as above described, the ram 10 of the press is raised high enough to separate the pad or cushion holder'12 from the blank plate 40 sufiiciently far to permit removal of theformed workpiece 43 and to insert a blank workpiece 43 inthe recess 42 of the blank plate 40.
In this fully open position of the press ram 10 and the unit having the cushion die structure forming the subject of the present invention, the blank bolster 45 and the blank plate 40 carried thereby are supported in the elevated position shown in Fig. 1. At this time delivery of fluid under high pressure through the line 35 is cut off and the pad cavity 18 has been filled from an oil supply tank (not shown) through the line 35.
The ram 19 of the press is brought down so as to bring the lower face 14 of the pad 'or cushion holder 12 into contact with the upper face of the outer part of the blank plate 40' and so as to bring the central raised part 41 of this blank plate 40 into mating relation with the lower part of the pocket or recess 18 of the pad or cushion holder 12 and the upper face of this raised part 41 into contact with the bottom face of the rim portion 29 of the rubber pad or cushion 20. This position of the parts is illustrated in Fig. 1. At this time also the upper extremity of the punch 50 is in closely spaced relation to the'bl'ank 43 as also illustrated in Fig. 1. Following this, oil under pressure is admitted from the line 35 to build up pressure in the chamber 18 behind the rubber cushion 20. This pressure is determined by the setting of the relief valve 36. Thus, at this position of the parts, the relief valve 36 is held at the desired setting by virtue of the roller 98 of the bell crank lever 94 riding on the upper receding part 99a of the working face 99 of the cam 100 and hence releasing the plunger 37 of the relief valve to a corresponding downwardly projected position.
The continued downward movement of the ram 10, forces, through the multiple piston structure shown in-my said parent application, the punch bolster 51 upwardly. Accordingly the punch bolster 51 is elevated while the ram 10 is descending and the blank or workpiece 43 is deformed by the punch 50 as a function of the combined downward movement of the blank or workpiece and the upward movement of the punch 50. The halfway position of the parts is illustrated in Fig. 2. i
As the punch 59 so moves upwardly relative to the workpiece or blank 43, the liquid backed rubber cushion 20, 19 causes the blank 43 to be wrapped around this punch 59 and to take the form of the punch. To do this the blank 43 and punch 50 must enter the liquid backed cushion 20, 19, as illustrated in Figs. 2 and 3, and to permit this, liquid pressure must be built up in the cavity 18 and this pressure should be controlled to provide the optimum back pressure corresponding to the work being done by the punch 50 at any particular time. Thus as a sharp corner is produced in the blank 43 the back pressure of the liquid 19 should be higher than when a shallow deformation of the blank is being made. This variable back pressure is under control of the relief valve 36 and its controlling cam 100, the working face 99 of this controlling cam being shaped to conform to the pressure requirements of the particular punch 50 being used. The movement of the controlling cam 100 can be effected as described in my saidparent application. v
The cam plate shown is provided with an initial receding position 99a which, through the'bell crank lever 94, holds the relief valve 36in such position that a relatively low back pressure is maintained in the cavity 18 during the initial part of the pressing stroke; At this time the workpiece 43 is being pressed over the pyramidal top part of the punch 50 and relatively small back pressure is required for this shallow deformation. However in forming the angular corner between, the base of the pyramidal top of the punch and its side walls greater back pressure is required and at this time the roller 98 of the bell crank lever rides up on the intermediate salient part 99b of the cam plate 100 and hence moves the plunger 37 of the relief valve 36 upwardly to establish a higher back pressure in the chamber 18. In forming the final flange or rim (Fig. 3) on the workpiece a still higher back pressure is required and at this time the roller 98 rides up on the trailing salient 99a of the cam plate 100. This operates to elevate the plunger 37 still higher and close the relief valve still further and establish this still higher back pressure in the cavity 18. Each punch 50 will, of course, have an individual cam plate 100 shaped to conform to it, the punch and cam plate shown being merely illustrative.
On the completion of the pressing stroke the parts are in the position shown in Fig. 3 and the blank 43 fully formed. The ram of the press is then raised to effect its return stroke and at the same time the blank bolster is elevated to follow the rising ram 10 of the press and the cushion holder 12 by the mechanism forming the subject of my said parent application and the punch 50 is lowered toward the position shown in Fig. 1 to strip the finished workpiece 43 from the punch. As the ram 10 rises the cam plate 100 is moved downwardly relative to the roller 98 thereby to move the relief valve 36 toward its open position and at the same time the cavity 18 is being enlarged by the removal of the liquid displacing punch. New liquid from a supply tank (not shown) is introduced into the cavity 18 at this time.
The continued elevation of the ram 10 of the press and the cushion holder 12 continues until the cushion holder 12 is separated sufi'iciently far from the blank plate 40 to permit removal of the finished workpiece 43 and replacement of the blank. This completes the cycle of the operation.
It will be seen that the invention is essentially directed to the soft, resilient, and readily distortable but substantially incompressible die cushion member 20 adapted to be fitted in the bell-shaped pocket 18 in one face 14 of a cushion holder member 12 having a conduit 33 for passing liquid under pressure to and from the space in said pocket enclosed by said cushion member, the cushion member having one face 41 generally coplanar with the face 14 of the cushion holder member and comprising a central portion 28 integrally united to a thickened rim portion 29 having a substantial area in contact with the internal face of said pocket and said area terminating in an endless thin edge 32 of generally feather-like converging form in cross section and which edge projects into said pocket along said internal face to be held by the pressure developed in said pocket in sealed relation with said internal face.
From the foregoing it will be seen that the present invention provides a simple and effective cushion die struc- 6 ture for use in pressing shapes under high pressure and which uses both the flow of rubber and the flow of a pressurized liquid backing for the rubber to wrap the metal around the punch in producing shapes of unusual form in one operation.
1. A soft, resilient and readily distortable but substantially incompressible one-piece die cushion member adapted to be compressively fitted in and closing a pocket in one face of a cushion holder member to have frictional engagement with the internal face of said pocket, said cushion holder member having a conduit for passing liquid under pressure to and from the space in said pocket enclosed by said cushion member, said cushion member having one face generally coplanar with said one face of said cushion holder member and comprising a thin, diaphragm-like central portion integrally united to a thickened rim portion which is of substantially greater thickness than said diaphragm-like central portion both in the direction of depth of said pocket and in a direction across said pocket, said thickened rim portion being in the form of a gradual enlargement, in the direction of depth of said pocket, of said diaphragm-like central portion and having an external area around its rim, of substantial extent in the direction of depth of said pocket, in contact with a conforming area of the internal face of the rim of said pocket with substantial portions of these contacting areas being arranged substantially perpendicular to said one face of said cushion holder and held in frictional engagement with each other by the compressive force within said cushion member, said rim area of said thickened rim portion terminating in an endless thin edge which is of generally feather-like form in cross section and projects into said pocket along said internal face to be held by the pressure developed in said pocket in sealed relation with said internal face, said cushion being retained in said pocket essentially by frictional interengagement of said substantially perpendicular contacting areas ofsaid thickened rim portion and of said internal face of-said pocket.
2. A die cushion member as set forth in claim 1 wherein said pocket is of bell-shaped form with its widest part formed by the substantially perpendicular rim area thereof.
References Cited in the file of this patent UNITED STATES PATENTS 2,280,865 Stossel Apr. 28, 1942 2,313,689 Waters Mar. 9, 1943 2,317,869 Walton Apr. 27, 1943 2,369,643 Berger Feb. 20, 1945 2,431,935 Huck Dec. 2, 1947 2,550,672 Chyba May 1, 1951