US2167941A - Double-acting press - Google Patents

Description

Aug. l, 1939. w. ERNST DOUBLE-ACTING PRESS 3 Sheets-Sheet 3 Filed Sept. l5, 1936 /N VEA/TOR l/VA LTER EHA/5 7' Smal SM v A TTORNEYS Patented ,Aiig.V 1 1939 UNITED ,STATES PATENT OFFICE ,nouxiafacrms ranssv Waiter Emst, Mount Gilead, ohio, minor a '.lhe Hydraulic Press Corporation, Inc., -Wil mlngton, Del., a corporation oi Delaware I RHSSUED Application September v16, 1936, Serial No. 101,110

' s claims.V (ci. 11a-45) Y ing pressures at different points onthe blank, thereby enabling the blank to lbe held more tight-a lll` lyy along different portions of its periphery.

Another object is to provide a hydraulic press having a drawing plunger and a plurality of clamping plungers, together with means for maintaining diilerent pressures in the different 16 clamping plungers so as to hold the blank with different .clamping pressures at different points,

each clamping cylinder being arranged to enable the pressure therein to be adjusted independently ofthepressures in the other clamping 20 cylinders.

Another object. is to provide a hydraulic press having a drawing plunger anda plurality oi clamping plungers, together' with means for maintaining diierent pressures in the clamping plungers so asto maintain diillerent clamping forces at different parts of the blank, additional -means being provided to prevent the release of pressure from the clamping cylinder from tending to equalize the-pressure in other clamping blank, means being provided for releasing pres-- sure-fluid from the different clamping cylinders o at diierent predetermined pressures so as to enable4 the blank to be held at dierent points by different clamping pressures. i

-`Afnother object is to provide a hydraulic press l.having a drawing plunger and a plurality of clamping plungers operating in drawingvan'd clamping cylinders, respectively, the pressure for operating theclamping cylinders being provided by the action of the drawing plunger in forcing the clamping plungers downwardly against the blank, means being provided for releasing pressure uid from the different clamping cylinders at different predetermined pressures so as to en able the blank to be held at diierent points by diierent clamping pressures, the press being providedwith means whereby a part of the pressure generated in the clamping cylinders is utilized to force the clamping member downwardly, and thereby to assist the action of the drawing plunger instead of opposing it, as in other types of presses. A b Another object is to provide a hydraulic press lhaving a drawing plunger and a plurality of clamping plungers arranged to provide diflerent clamping pressures among themselves, together withrelease of pressure fluid therefrom on the 10 attainment of diilerent predetermined pressures therein, means beingv provided to prevent the escape of pressure fluid/upon the return strokeof the drawing plunger whenthe pressure-releaslng means-is set at a low amount, thereby coun- 15. teracting the effect of the pressure-releasing means during the return stroke of the press.

In the drawings: \.V

Figure l is a diagrammatic view, mainly in section, showing the w'orking elements of a hy- 20 draulic metal drawing press circuit arranged according to this invention, with the upper portion of the press framework omitted to show the con-'- l struction more clearly.

Figure 2 is a'horizontal section along vthe lline 2B 2 2 in Figure 1. v

Figure 3 is a view similar to Figure 1, but of a modified form of hydraulic drawing press circuit for accomplishing a similar result.. i

Figure 4 is a diagrammatic'plan viewv showing 30 the connections between the various cylinders of the press in Figure 3.

Figure- 5 is a view of a portion of Figure 3 oi modified construction as regards the clamping cylinder.-

Figure 6 is a vertical section through apres sure relief` valve employed in connection with the press circuit shown in Figure l. -A

In general, the press of this invention conl sists of a drawing plunger and a plurality of 40 clamping plungers having relief valves associated with each clamping plunger for release oi! the pressure uid therein at predeterminedpressures. thereby enabling the diierent clamping plunge ers to exert different clamping pressures upon 45 the blank. 'l'here is also provided a series of check valves adapted 'to prevent .the individual relief valves from interfering with the action oi' each other, thereby preventing equalization ofv pressure between the diiIerent clamping cylin- 50 ders by the discharges from their relief valves. A modiiied construction shown in Figure 3 also provides an arrangement .wherein the blank holder pressure is partially utilized to assist the action of the drawing plunger rather than to oppose it, 55

as in other types of presses. The arrangement of Figure 1 also contains a provision whereby the action of the various'relief valves is prevented during the return stroke by admitting fluid to the opposite side of the valve plunger, this arrangement enabling the moving parts to return on the return stroke, regardless of how low the relief valve setting may be.

The reason for providing a different clamping pressure at different portions of the blank arises from the fact that it is found that in drawing irregular work-pieces it is often desirable to hold one portion of the periphery of the blank with a tighter clamping force than other portions. In the ordinary .types of presses, wherein the same clamping pressure is provided on all portions of the blank, this variable blank-holding force cannot be supplied. In the present invention, however, each individual clamping cylinder is equipped with its own relief valve and its own check valve so that a different clamping pressure can be built up on each one of the several clamping plungers.

Referring to the drawings in detail, Figure l shows diagrammatically a hydraulic metal drawing press having a base/member I0 connected to a top member II (reduced in size for clearness of showing) by means of tie rods I2, the latter being secured in position by means of the nuts y I3 upon the ends thereof. Mounted in the base member I0 is a drawing die I4 having a die cavity I5 for receiving the blank-I6. Associated with the die cavity I5 isa plunger I1 adapted to support the tip of the blank as it is being drawn, and passing through a bore I6 to its operating cylinder (not shown). The details of the supporting plunger I1 form no part of the present invention, and are shown in my copending application, Ser. No. 74,742, flied April 16, 1936.

The present invention may be employed either with fiat blanks or with blanks which have already been subjected to one or more drawing operations. For convenience of disclosure, blank I6 is shown as having been subjected to one drawing operation,and in position for another drawing operation which will elongate it and cause it to be drawn downwardly into the die cavity I5.

Associated with the top member I I of the press is a surge tank III for containing they fluid by which the press is actuated. Also associated with the top member I I is the drawing or main cylinder 20, having a bore 2I within which reciprocates the double-acting drawing plunger 22 having av piston head 23 thereon. The cylinder 20 is provided with upper and lower ports 24 and 25 on opposite sides of the piston head 23, and adapted by means of pipes 26 and 21 to supply pressure fluid to advance or retract the drawing plunger 22, according to the manner in which the four-way valve 28 is manipulated. This valve 23 is of any suitable type known to those skilled in the art, and its details form no part 'of the present invention.

vLeading from the four-way valve 26 is the pressure line `2!! connected at its opposite end to the pump 30. A discharge line 3I, also connected to the four-way valve 28, leads into the interior of the surge tank I9. The pump 30 is also provided with a suction line 32, likewise leading into the interior of the surge tank I9. The drawing cylinder 20 is supplied near the mouth of its bore 2I with a packing ring 33, beyond which isa packing 34 adapted to be compressed by a gland 35 so as to prevent leakage around the drawing plunger 22. Connected to the drawing plunger 22 is the platen 36, within which are arranged the clamping cylinders 31 having clamping plungers 33 operating therein. Each clamping plunger 33 is provided with a packing 39 and gland 40 for the prevention of leakage. Secured'to the platen 3'6 is a drawing plunger or punch 4I having a nose portion 42 corresponding to the diev cavity I5, and adapted to pass through an aperture 43 in the clamping member 44 secured to the outer ends of the clamping plungers 33.

Each of the clamping plungers 33 is provided with a fluid passageway 45 leading by way of an 'outwardly opening check valve 46 to a common passageway 41, which extends upwardly through the drawing plunger 42 and opens into the drawing cylinder bore 2| immediately beneath the drawing plunger head 23. Consequently, fluid is free to pass from the pull-back or return side of the drawing plunger 23 into the clamping cylinders 31, but is prevented from passing in the opposite direction by the action of the check valves 46. Also passing outwardly from each clamping cylinder 31 is a fluid conduit 43 leading to an intermediate portion of a pipe 49, having on l one end a safety valve and on the other end a pressure relief valve 5I. Leading from the discharge side of the safety valve 50 is a discharge line 52 connected to the discharge side of the relief valve 5I by the line 53.

The discharge line 52 passes upwardly into the telescoping cylinder 54, thereby forming a slip connection, enabling the telescoping cylinder 54 and the pipe 52 to move vertically relatively to each other, an action which necessarily occurs when the platen 36 'moves downwardly in response to the action of the drawing plunger 22. A discharge line 55 leads from the telescoping cylinder 54 into the interior of the surge'tank I9 and serves to discharge fluid expelled from the presdangerous pressure within the corresponding clamping cylinder 31 and a failure of the corresponding pressure relief valve 5I to act.A It will be seen from Figures l and 2 that each clamping cylinder is provided with its own pressure relief valve 5I and safety'valve 50 so that a different pressure release point may be given to each clamping cylinder. 'I'he pressure relief valves 5I are connected to the drawing plunger passageway 41 by conduits 56 for the purpose of counteracting the action of the relief valves 5I during the return stroke of the drawingplunger 22, as is discussed below in connection with the description of the details of the relief valve.5I.

The relief valve 5I is shown in vertical section in Figure 6, and consists of a casing having a bore 6Iv within which reciprocates a valve plunger 62. Arranged between the valve plunger 62 and the bore 6I is a tubular member 63 having a longitudinal bore 65 and a cross bore 63, communicating therewith and opening into a transverse bore 61 in the casing 60. 'I'he end connection of the pipe 4 9 is held in communication with the bore 6I by means of the collar 63 Within the can` 12 is la coil spring 14, one end of which engages an enlargement 15 upon the upper end of the valve plunger 62. whereas the opsite end engagesla button 16 in contact with an'adjusting screw 11 threaded Vthrough a bore 18 in the upper end ofthe cap 12. Surrounding and covering the adjusting screw 11 is a hollow nut 19 which serves to project the adjusting screw 11 and also to lock it in its adjusted position. The cap 12 is provided with a\port 88 receiving and communicating with the pipe 56 leading to the pull-backside of the drawing plunger 22, as shown in Figure 1.

Thus, when 'the same pressure uid is admitted simultaneously'to the valve 5|, by way of the pipes 49 and 56 during the pull-back stroke of the press, the'valve plunger 62 will be prevented from opening by means oi' this counteracting arrangement, as is more fully described under the oeration thereof. 'I'he pipe 56 also serves durin \the return stroke of the press to receive and transmit the fluid which leaks into the interior of the cap 12 past the valve plunger 62.l Thus, each safety valve may be adjusted to discharge pressure fluid at a different predetermined pressure by differently` adjusting the adjusting screw 'll to compress the springs 14 by different amounts. The clamping member 44 is provided with rods 9| passing through the vertical bores 82 in the platen 36, and having the nuts B3 on the upper ends thereof. The rods 8|"llmit the extent to which the clamping member 44 can move relatively to the platen 36.

In the operation of the form of press shown in Figures l1 and 2, the pump 361s started and delivers pressure iluid to the four-way valve 28, which in turn, 'is set to deliver pressure fluid through the line 26 and port 24 into the space above the drawing plunger head 23. This presl sure forces the drawing plunger 22 and platen 3E ldownwardly, carrying with them the clamping-member 44. When the latter engages thel periphery of the blank l5 and clamps lt tightly against the die member |4, the clamping member 44 halts, but the platen 36 continues to move downwardly, forcing its drawing `die or punch 4| into engagement with the blank I6; As the punch 4| moves downwardly it forces the centralv portion of the blank I6 into the die cavity I5 and overcomes the resistancev of the'supporting plunger I1, which protects the tip of the workpiece or blankIB.

Meanwhile, pressure has been built up in the clamping cylinders 431 by reason ofthe relative motion between the vplaten 36 and the clamping member 44 to which the clamping plunge'rs38 are attached, and the fluid inthe clamping cylinders 31` has been prevented from escaping by the closing of rthe outwardly opening check valves 46. When the pressure within each clamping cylinder 31 reaches the amount for `which its corresponding relief valve 5| is set, the latter opens and discharges fluid through the line 53, into the discharge line l52 leading to the telescoping cylinder 54, and thence by the lline 55 to the surge tank |9. In this manner each clamping plunger 38 may be caused to exert a different force upon the portion of the blank periphery which is engaged by the clamping member 44 -in its vicinity.

When the drawing stroke of the press has been completed the setting of the four-way valve 28 is reversed so that pressure fluid flows through the line 21 and' portA 25, into the space beneath the drawing plunger head 23, causing the drawing cylinder 31.

iugplunger 22 to move upwardly. A portion of this pressure fluid. however. passes downwardly through the plunger passageway 41, the outwardly opening relief valves 46,to the passageways 45,. into the clamping cylinders 31, causing their plungers 38 and the clamping member 44 to remain in clamping engagement with the blank I6 while the punch or drawing die 4| is withdrawn from the cavity I5 of the die 4. If ,the relief valves 5| have been set for a low clamping pressure' it would,. at first glance, seem that pressure uid during the pull-back stroke would pass from the clamping cylinders 48 through the relief valve 5| and lines 52, 53 and 55, back into the surge tank |9, thus preventing the return of the moving parts. This,v however, is prevented by the operation of the pipe line 56 leading from the valve cap 12 of the valve 5| to the passageway 41 within the drawing plunger 22. Consequently, during the pull-back stroke pressure fluid is applied simultaneously upon opposite sides of the valve plunger 62 within the relief valve 5|, and prevents its opening regardless of lhow low a clamping pressure is provided by the setting of each relief valve 5|. When the platen 36 has moved upwardly along the rods 8| it will engage the nuts 83 and lift the clamping member 42 free from engagement with the work-piece i6, thereby enabling the operator to remove the blank holder assembly as a unit.

The modified form of press shown in Figures 3 and 4 has a base portion |0,vtle rods I2, die i4 and vsupporting plunger I8 similar to those of the press shown in Figure 1. A pump 38 and four-way valve 48 are similarly provided, and

work-piece and also'lifting the entire platen andV the latter hasy similar forward and reverse pressure lines 26 and 21, respectively, leading to the opposite sides of the drawing plunger head- 23 within the drawing cylinder 2|). Other corresponding parts are given like reference numerals. In this form of press, however, the drawing plunger22 is of solid construction, and the clamping plunger cylinders 31 are provided with passages 81 leading into tubular plungers 88 mounted upon the upperside of the platen 36, and having bores 89 therethrough. The hollow plungers 88 pass through glands 90 and packings 9| into cylinders 92 arranged on the press top member li and within the surge tank I9. From each cylinder 92 the line 93 leads through the check valve 94 to the interior of the surge tank i9. Each check valve 94 opens in the direction of the cyl- `inder 93 so that the latter may draw in fluid upon the descent of the hollowplungers 88. The check valves 94, however, will close upon the ascent of the plungers 88.

From each cylinder 92 a T-shaped line`95 also leads to a safety valve 96 and a pressure relief valve 91. 'I'hese valves 96and 91 are similarto the safety valves 58 and pressure relief valves 5I described in connection with Figure 1, with the exception of the fact that the connection 56 to the port 89 in the valve cap .12 is omitted. The valves 96 Aand 91 discharge into the discharge line 98 leading to the interior of the surge tank I9. A pressure gauge 99 is provided in each line j 95 to indicate the pressure existing in the clamp- Extending from each cylinder 92 is, a line |80 having therein a check valve ||l| opening in a direction away from the cylinder SI2. Beyond the check valves IDI the lines |00 join a common line |02 leading to a normally open valve |83, having a dischargline |64 leading therefrom to the surge tank I9. The valve |03 is provided with a valve rod |05 having an adjustable stop |06 thereon adapted to be engaged by the end |01 of a platen arm |08 secured to the platen 36. The platen 36 is provided with bores |09 adapted to receive the rods I|0, the lower ends of which are secured to the clamping member 44, and the upper ends ofy which are provided with nuts threaded thereon. The upper ends of the rods ||0 are also provided with threaded sockets ||2 in which are inserted the threaded rods ||3. This arrangement enables an adjustment of the effective length of the rods ||0 and enables the point at which these-rods ||0 serve as knock-out rods to be varied as desired.

In ordinary drawing presses. it will be seen that i during a drawing operation the pressure exerted `within the clamping cylinders 31. Where the sired proportion of the clamping pressures are low, the effect of this arrangement is not serious. If, however, a high pressure is employed 'for clampingthe blanks the reduction in drawing force by the withdrawal of force for the clamping plungers may be quite serious. It is for this reason that the modified arrangement shown in Figure 3 was devised. The pressure generated bythe relative motion between the platen 36 and the halted blank holder or clamping member 44 still produces the blank holder clamping pressure, but this pressure now hows through the hollow plungers 88 and helps to advance the p laten 36 by operating on the annular heads of the plungers 88. Any de pressure on the clamping plungers 38 can thus be balanced, andthe main or drawing plunger 22 will only have to overcome the difference between the pressures on the ends of the plungers 38 and 88. In this manner it is possible to exert very great clamping pressures with comparatively small main or drawing plunger pressures.

In the operation of the pressand circuit shown in Figures 3 and 4, the pump 30 is started and valve 28 isset to discharge pressure fluid through the forward `line 26 leading to the space abovev the drawing plunger head 23. The drawing plunger 22 then moves downwardly, carrying with it the platen 36 and the hollow plungers 88. The suction thereby created in the cylinders 92 opens the check valves 94 and causes fluid to be drawn into the cylinders from the surge tank I9. When the blank holder or clamping member 44 descends to a point where it engages the work-piece |6, however, a relative motion occurs between the now halted blank holder 44 and platen 36 as the latter continues to advance and move its drawing die or punch 4I into engagement with the workpiece I6.

Pressure thus accumulates in the clamping cylinders 31 and is transmitted through the passages 89 of the hollow plungers 88 into the cylinders 92. Normally this pressure would be free to pass through the lines |00, check valves |0|, line |02, normally open valve |03 and line |04 into the surge tank I9. By this time, however, the platen 36 has descended to a pointwhereat the end |01 of the platen arm l|08 has engaged the stop |06 and moved the valve rod |05 downwardly, thereby closing the normally open valve |03 and cutting off this means of escape for the fluid from the cylinders 92. 'I'he check valves 94` -settng of its relief valve 91, the latter will open and discharge fluid through its discharge line 98 into the surge tank I9. In the event that the pressure relief valve 91 jams or fails for other reasons, the safety valve 96,` which is set for a higher pressure, will open and discharge the fluid, thereby preventing damage to the press.

By adjusting the relief valves 91 to discharge atl different pressures the clamping cylinders 31 and their clamping plungers 38 may be caused to exert different" clamping pressures upon the clamping member of blank holder 44, and hence, apply different amounts of pressure to different points on the peripheryuof the work-piece I8. The check valves |0| prevent the equalization of pressures between the several cylinders 92, consequently, the intensified pressure built up in the clamping cylinders 31 acts against the clamping plungers 36 to clamp the work-piece I6. At the same time aportion of this pressure uid passing through the bore 89 of each hollow plunger 88 acts against the annulartop surface thereof, and urges each plunger 88 in a downward direction, thereby assisting the action of the main or drawing plunger 22.

As soon as the drawing completed the operator shifts the four-way control valve 28 to cause the pump 30 to discharge operation has been beneath the drawing plunger head 23. This pressure raises the drawing plunger 22 and the platen 36, together with the hollow plungers 88. At the start of this operation, however, the platen arm .|08 is still holding the normally open valve |03 in a closed position, hence, the plungers 88 cannot return against the pressure already built up in the cylinders 92 without displacing fluid into the clamping cylinders 31 within the platen 36. This pressure fluid,V so displaced, acts against the clamping plungers 38 and tends to separate the platen 36 and the clamping member or blank holder 44 until b oth havetraveled a distance sufficient to enable the platen arm |08 to release the stop |06 upon the valve rod |05 and permit the valve |03 to resume its normally open position. When this occurs the fluid can escape from the cylinders 92 through the lines |00, the check valves |0|, the line |02, the valve |03 and the line |04 into the surge tank |9, permitting. the entire assembly to execute its return stroke. The adjustable arrangement shown on the rods |I0 serves to separate the platen 38 and the blank holder 44 in a positive manner in case both of these should be held together by reason of the vwork-piece |6 adhering to the drawing die or punch 4 I.

Thus by the present invention a full blankholding pressure can be exerted by supplying only a fraction of it by means of the main or drawing plunger 22, through the aid ofthe hollow plungers through the line 26. It will be understood, however, that a surge valve may be mounted in the top oi.' the cylinder 20 and operated in the man'- Y ner shown in my copending application, Ser. No.

74,742, filed April 16, 1936, thereby enabling the descent of the drawing plunger 22 by gravity and the Vpreflling of the cylinder 20 through such a surg valve. This surge valve has been omitted from t e present circuits for the purpose of s implifying the showing.

The modified construction shown in Figure 5 has the same purpose as the hollow plungers 88 and cylinders 92 in Figure 3. 'In this arrangement, however, the blank holder or clamping member 44 is provided with clamping cylinders H6 in upwardly projecting portions ili, adapted to enter corresponding recesses `i I8 in the platen 36. Glands H9 and packings |20 prevent the escape of fiuid from around the hollow clamping plungers i 2|, these being mounted in bores lf2 ln the upper walls of the recesses 'H8 in the platen 36. Each plunger i2| is provided with an enlargement i23 adapted to `engage the upperor end wall of the recess i I B. Formed integral with Wthe clamping plungers `I'2I, in thisarrangement,

and extending vertically upward therefrom are the hollow plunger portions |24 leading into the cylinders 92, previously described. While this construction is a modification of that shown -in Figure 3, the operation is substantially identical and requires no additional description.

It will be understood that a separate pressure i may be applied to each clamping plunger by emthe cylinders`92, such as, for example, a flexible Y playing a different pump for each clamping plunger rather than a single pump with four different pressure relief valves. In this manner each pump may be set to deliver the predetermined and desired pressure to its own particular., clamping plunger. In Figure 3, instead of the hollow plungers shown, solid plungers may be used with any suitable arrangement for conducting fiuid from the clamping cylinders 31 to conduit.

It will be understood that I desire to comprehend within this invention such modifications as come within the scope of the claims and the invention. v

Having thus fully described myinvention, what I claim as new and desire to secure by Letters Patent, is:

1. In combination in a drawing press, a press frame having a main cylinder and an auxiliary cylinder, a main plunger in said main cylinder, a platen operated thereby, a hollow auxiliary plunger connected to said platen and reciprocable in said auxiliary cylinder, a clamping cylinder associated with said platen `and communicating with said hollow auxiliary plunger, a clamping plunger adapted to clampthe workpiece during the drawing operation, and an adjustable pressure relief valve for said clamping cylinder adapted to effect the discharge of pressure uid from said clamping cylinder at a predetermined pressure, the working surfaces on the heads of said auxiliary plunger and main plunger being positioned in similar directions relatively to said platen whereby the*y pressure fluid generated in said clamping cylinder during theclamping operation acts against said auxiliary plunger to assist the urge imparted to said platen by said plunger, clamping'piston and cylinder assemblies associated with said platen and' operated by the motion thereof, auxiliary cylinders mounted on said press head, auxiliary hollow plungers connected to said platen and communicating with said clamping cylinders and reciprocable in said auxiliary cylinders, and a pressure relief device foreach auxiliary cylinder adapted to discharge fluid therefrom in response to the attainment of .a predetermined pressure therein, the working surfacesv on the heads of said auxiliary plunger and said drawing plunger being positioned in similar directions relatively to said platen, whereby the pressure duid generated in said clamping cylinders during the clamping operation acts against said auxiliary plungers to assist the urge imparted to said platen by said main plunger.

3. In combination in a drawing press, a drawing cylinder, a drawing plunger therein, a platen operated by said drawing plunger, clamping piston and cylinder assemblies associated with said platen and operated by the motionthereof, auxiliary cylinders, auxiliary hollow plungers connected to said clamping cylinders and reciprocable in said auxiliary cylinders, a pressure relief device for each auxiliary cylinder adapted to discharge fluid therefrom in response to the attainment of a predetermined pressure therein, a conduit adapted to discharge fluid from said auxiliary cylinders, a normally open valve in said conduit, and means responsive to the attainment of a predetermined position of said platen for closing said normally open valve to prevent the further discharge of the fluid through said conduit. f'

4. In combination in a drawing press, a drawing cylinder, a drawing plunger therein. a platen operated by said drawing plunger, clamping piston and cylinder assemblies associated with said platen and operated by the motion thereof, auxiliary cylinders, auxiliary hollow plungers connected to said clamping cylinders and reciprocable in said auxiliary cylinders, a pressure relief device for each auxiliary cylinder adapted to discharge fluid therefrom in response to the attainment of -a predetermined pressure therein, a

conduit adapted to discharge fluid from said auxiliary cylinders, a normally open valve in said conduit, means responsive to the attainment of a predetermined position of said platen for closing said normally open valve to prevent the further discharge of the fluid through said conduit,

to prevent the flow of fluid from one auxiliary cylinder to another auxiliary cylinder.

5. In combination in a drawing press, a drawing cylinder, a drawing plunger therein, a platen operated by said drawing plunger, clamping pis-A ton and cylinder assemblies associated withsaid platen and operated by the motion thereof,V auxiliary cylinders, auxiliary hollow plungers con` nected to said clamping cylinders and reciprocable in said auxiliary cylinders, a pressure relief device for each auxiliary cylinder adapted to discharge fluid therefrom in response to the attainment of a predetermined pressure therein, a fluid tank, a conduit connecting each auxiliary cylinder with said fluid tank, and a check valve y in said conduit for permitting the drawing in of fluid in response to thesuction created in said auxiliary cylinders by the descent of said auxiliary plungers.

6. In combination in a drawing press, a press head having a drawing cylinder, a drawingplunger therein, a platen operated by said drawing plunger, clamping piston and cylinder assemblies associated with said platen and operated by the motion thereof, auxiliary cylinders mounted on said press head, auxiliary plungers movable in said auxiliary cylinders and connected to said platen, means for conducting fluid between said clamping cylinders and said auxiliary cylinders, and a pressure relief device for each auxiliary cylinder adapted to discharge fluid therefrom in response to the attainment .of a predetermined pressure therein, the working surfaces on the heads of said auxiliary plunger and said drawing plunger being positioned in similar directions relatively to said platen, whereby the pressure fluid generated in' said clamping cylinders 'during the clamping operation acts against said auxiliary plungers to assist the urge imparted to said platen by said main plunger.

7. In combination in a drawing press, a drawing cylinder, a drawing plunger therein, a platen operated by said drawing plunger, clamping piston and cylinder assemblies associated with said platen and operatedby the motion thereof, auxiliary cylinders, auxiliary plungers movable in said auxiliary cylinders, means for conducting fluid between said clamping cylinders and said auxiliary cylinders, a pressure relief device for each auxiliary cylinder adapted to discharge uid therefrom in response to the attainment of a predetermined pressure therein, a conduit adapted to discharge fluid from said auxiliary cylinders, a normally open valve in said conduit, and means responsive to the attainment of a predetermined position of said platen for closing said normally open valve to prevent the further discharge of fluid throughsaid conduit. n Y

8. In combination in a drawing press, a drawing cylinder, a drawing plunger therein, a platen operated by said drawing plunger. clamping piston and cylinder assemblies associated with said platen and operated by the motion thereof, auxiliary cylinders, auxiliary plungers rn'ovable in said auxiliary cylinders, means for conducting iiuidbetween said clamping cylinders and said auxiliary cylinders, a pressure relief device for each auxiliary cylinder adapted to vdischarge uid therefrom in -response to the attainment of a predetermined pressure therein, a conduit adapted to discharge fluid from said auxiliary cylinders, a normally open valve in said conduit, means responsive to the attainment of a predetermined position of said platen for closing said normally openvalve to prevent the further discharge of uid through said conduit, and uni-di rectional means in said conduit for permitting the iiow of fiuid from said auxiliary cylinders to said normally open valve but adapted to prevent the flow of fluid from one auxiliary cylinder to another auxiliary cylinder.

9. In combination in a drawing press, a drawing cylinder, a drawing plunger therein, a platen -operated by said drawing plunger, clamping pisduit for permitting the drawing-in of fluid in re sponse to the suction created in said auxiliary cylinders by the descent of said auxiliary plungers.

WALTER ERNST.

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