US2040731A

US2040731A - Hydraulic metal drawing press and method for shaping metal articles

Info

Publication number: US2040731A
Application number: US329765A
Authority: US
Inventors: Ernst Walter
Original assignee: HYDRAULIC PRESS CORP Inc
Current assignee: HYDRAULIC PRESS Corp Inc
Priority date: 1929-01-02
Filing date: 1929-01-02
Publication date: 1936-05-12
Anticipated expiration: 1953-05-12

Description

May n? 1936- w. ERNST A I 2,040,731l 'Y HYDRAULIC METAL DRAWING PRESS AND METHOD FOR SHAPING METAL ARTICLES Filed Jan. 2,- 1929 s sneetsfsheet 1 mvenfor v Gttornegs,

May 12, 1936. w. ERNST 2,040,731

HYDRAULIC METAL DRAWING' PRESS AND METHOD FOR SHAPING METAL ARTCLS Filed Jan. 2, 1929 3 Sheets-Sheet 2 j, Envenktor,

Gttornegs.

w. ERNST 2,040,731

HYDRAULIC METAL DRAWING PRESS AND METHOD FOR SHAPING METAL ARTICLES May 12., 1936.

Filed Jan. 2, 1929 3 Sheets-Sheet 3 UNITED ,STATES PATENT oFElCE HYDRAULIC METAL DRAWING' rREs's AND METHOD Foa snAPING METAL ARTICLES Walter Ernst,-Mount Gilead, Qhio, assigner, by mesne assignments, to The Hydraulic Press Corporation, Inc., Wilmington, Del., a corporation of Delaware 4 Application January 2, 1929, Serial No. 329,765

22 Claims. (Cl. 113-45) Thisinvention relates to hydraulic drawing presses and more particularly to drawing presses including male and femaledies, one of whichis attached to a stationary table fixed to the press frame-and the other of which is carried by a platen mounted on the press frame for reciprocatory movements towards and away from the station- I ary die, and in which press there is provided a 'hydraulically operated die cushion for clamping the work against the moving die and thus holding the work in proper position relative to the dies "during the drawing operation.

When shaping metal into Various forms by the drawing process, it is customary Ato employ a pair: ofdies consisting of a female die and a male die,

one being fixed to a stationary part of a press and the other being carried by the press platen and adapted to move towards and away from the fixed die so-that the male die enters the female die and shapes or draws a blank placed on the xed die to the desired form. When the drawing operation requires -what is known as a' deep draw, there is a. tendency for the blank to wrinkle. In order to overcome this tendency, various devices known as blank holders have been used to yieldingly clamp the blank against the female die. Some of these previously used blank hold- 4 rs have been operated by mechanical means lncluding links and toggles, others by spring loaded 0 devices, and still others by air or hydraulic pressure loaded pistons or rams. The `chief disadvantage of all such devices heretofore used is that, each time the nature of the drawing operation is changed, as, for instance, when a heavier 5 or lighter blank is-to vbe drawn, or when a dinerent set of dies is to be used, the blank holdlerv operating means must be adjusted so that the blank holder will clamp the blank under a pressure best suited for theparticular drawing opera'.-

tion to be performed. l

.'I'he main object of the present invention is to provide in a drawing press a die cushion, or blank holder, so arranged that the pressure exerted by 45 the blank holder will always bear a constant ratio to the pressure exerted on the blank by the moving die, so that the blank will automatically" be clamped against 4the female die under onlyl such pressure as is necessary for preventing 50 wrinkling-of the blank'. y

Among other objects of the invention are tol provide a press for drawing metal adapted to ausmtomajlgally perform an indeterminate number of drawing opitionsateashigh speed. and to pro- 55 vide such a press in which the speed of the mov- (191.'7, granted vto Hele-Shaw et al.`

ing die is automatically reduced as the resistance to drawing increases. y

v With these and other objects in view, the nature of which will more fully appear, the invention will b e understood from the following description, the 5 appended c1aims,and the several views illustrated lin the drawings, in which: t

Figure 1 is a front elevation of a hydraulic press, showing some essential operating parts thereof, some parts being shown in section; 10

Figure 2 is an enlarged partial Iside elevation taken at right angles to Figure 1, 'with certain parts shown in section; l

Figure 3 is a fragmentary vertical sectional view of the lower portion of the press, drawn on 15 an enlarged scale and showing die cushion cylinders in detail; I

`Figure 4 is adiagrammaticview of the hydraulic circuit, certain of the yparts being shown in section; i L 20 Figure 5 is a longitudinal `sectional view oi a reversing valve;

Figure 6 is a sectional view taken on the line 6 6 of Figure 5;

Figure 7 lis a detail View of a manually oper- 25 able control lever; y i Figure 8 is a planview of a p ump cross head;

Figure 9 is a detail view showing the relative positions of a male and a female die and a blank being drawn at an intermediate point in the drawing operation, and;

Figure 10 is a view similar to' that shown in Figure 9, the parts being shown in the positions occupied at'the end of the drawing operation.

Like numerals designate corresponding Parts in the several views illustrated.

Hydraulic presses have been previously built which were capable of automatically performing an indeterminatenumber of pressing operations;

usually employed to furnish the pressure for operating such presses, it has heretofore not been found possible to operate these presses at ahigh speed, except in the case'of small presses where the inertia of ythe moving parts, and especially that of the pump cross head, is comparatively small.

In connection with'such automatic presses it has been usual, to employ a variable discharge, reversible pump of the type described in U S; 5o Letters Patent No. 1,250,170, of December 18, Pumps of this type are provided witha cross-head, the shifting of which reverses theilowof the fluid in Y the hydraulic circuit, the reversals producing the reciprocatory motion of the press platen.

While the construction of this type of pump is now well known to those skilled in the art, for

the sake of clearness attention is called to the fact that in such pumps there is usually provided a spring adapted to yieldingly hold the pump cross head in a position permitting the pump to deliver its full discharge,l there being also provided either mechanical Yor pressure operated means adapted to move said cross head against the pressure of said spring, thereby progressively reducing the discharge of the pump to zero, and then progressively increasing the discharge of the pump in the opposite direction.

As stated above, when the system is comparatively small, the inertia of the pump cross head is also small, so that it may be quickly shifted to reverse the ow of the uid'under pressure, and a high press operatingvspeed may be thereby attained. It is obvious that-/where the press used is large, and the pump cross head correspondingly large, the cross head has an inertia suflicient to oppose the shifting thereof, and to thereby cause a considerable time lag to occur between the strokes of the platen, which naturally is objectionable since it slows down the operating speed of the press.

I have found that, by arranging such a pump to discharge in one direction only, and by providing means whereby the uid discharged by the pump may be directed alternately to the pressing cylinders and to the push back cylinders operating the press platen, it is possible to attain a high operating speed with a large press.

When operating a large hydraulic press, it is of course essential that the discharge of the pump be reduced as the press platen nears the end of the up and the down strokes, since aV sudden reversal of flow of the fluid under pressure when thepump is delivering its full discharge would result in a, shock or water hammer in the hydraulic system, such shock being injurious to the various associated parts.

It is to be understood that in the description which is to follow the term automatic operation means that kind of operation in which the reciprocatory platen continuously performs an indeterminate number of pressing operations, and the term semi-automatic operation means that kind of operation in which the platen performs one complete pressing cycle, and is then brought to rest in its uppermost position.

The invention mayv be embodied in various types of hydraulic presses, but in the accompanying drawings it is illustrated in connection with a press of the four column downward pressure type. Referring to the drawings, there is shown a hydraulic press A, having a base B, a stationary table C, a press head D connected to said table by four strain rods E, a reciprocatory platen or movable die support F, and a die cushion G. The die supportF is guided on the strain rods E in the usual'manner. An annular female die H having a lower face h and an inner downwardly facing surface h is secured to the under side of the platen, which in effect is a movable support table and located directly over an opening therein. A circular sheet metal blank K is shown in Figures 1 and 3 as being positioned on the punch shape assumed by the blank during the drawing operation.

The die cushion G is carried by a supporting plate I, suspended from lugs 2 or the press frame by means of strain rods 3 threadedly connected at their lower ends to lugs 4 on the supporting plate. A cushioningl cylinder 5 is carried by the supporting plate and is preferably positioned directly beneath the punch I, and also carried by the supporting plate on opposite sides of the cushioning cylinder are blank holder returning cylinders 66, equally spaced from the cushioning cylinder and-preferably of somewhat lesser diameter than the latter. Mounted for reciprocation in the cylinder 5 is a cushioning plunger or ram 1, and in the cylinders 6-6 blank holder returning rams v8 8 are mounted. The rams I and 8-8 are connected at their upper ends to a yoke 9. Connected to the yoke by means of pins I0 extending through openings II in the die support or bolster plate is a blank holder or clamp- 'ing ring I2 concentrically arranged around the the punch, the blank K which is positioned on the clamping ring will be clamped between the latter and the lower face of the female die. A plurality of vertically disposed guide standards I3-I3 bolted to the bolster plate and arranged circumferentially around the clamping ring guidesthe said ring during its reciprocatory movements, thus relieving the pins I0 of any lateral thrust to which said pins might otherwise be subjected.

A variable discharge pump I4 of the type above referred to is connected to a surge tank I5 by means of a suction pipe I6, as shown in Figure 4. The discharge of the pump -is directed through a pipe line I 'I which is connected to a reversing Valve I 8. The valve I8 also has connected to it a pipe line I9, which leads to booster cylinders 20 and to one side of a. surge Shifting valve 2|, located in the surge tank I5, a pipe line 22 which leads to push back or die returning cylinders 23 and to the other side of the surge shifting valve 2i, and apipe line 24 which leads to and opens into the surge tank I5. The surge shifting valve 2| is preferably mounted directly on top of a main pressing cylinder 25 and is arranged to communicate therewith by means of a port 25a. As will be hereinafter described, the reversing valve I8 is adapted to direct fluid under pressure alternately to the pressing cylinder 25 and to the diereturning cylinder 23 to effect reciprocations of `the movable die support F, the two-cylinders thus line 2S, and, since there are no valves in this pipe line, the cushioning cylinder and the pressing cylinder are always in direct communication, and

it is therefore apparent that the unit pressure in the cushioning cylinder will always be the same as that in the pressing cylinder. The cushioning ram 1 is of smaller diameter than the main pressing ram 21 so that the total pressure exerted upwardly on the cushioning ram will be at all times less than the pressure exerted upon the pressing ram, and as a result the clamping ring will be v forced downwardly by the .female die when .the

die descends. Because of the constant open communication between the cushioning cylinder and the main pressing cylinder 25, the total effective pressure exerted on the cushioning ram '8 will always bear a constant ratio to the total effective pressure exerted on the main pressing ram 21. In other words, when the drawing pressure is. large and results ina marked 'tendencyy for the blank to wrinkle, the pressure exerted upon the blank by the clamping ring will also be large, and wrlnkling of the blank will be veffectively prevented. When the drawing pressure -is relatively small, the clamping pressure will also be relatively small and the blank will not be unnecessarily squeezed.

The construction and the operation of the; reversing valve I8 will be hereinafter described in detail, but for the 'sake of clearness it will, for the present, be suiiicient to say that the valve is adapted to be set in either 'of -two positions, in the rst of which positions the pipe line I1 is placed in communication with the pipe line I9,

and the pipe line 22 with the pipe line 24, and in the second of which positions the pipe line I1 is placed in communication with the pipeline 22, and the pipe line I9 with the pipe line 24.

The surge shifting valve 2| is provided with a valve casing 29 having a valve chamber 38 which communicates with the surge tank I5 by means of a port 3|, and with the main cylinder 25 of the press by means of the port 25a. Slidably mounted in the chamber 30 is a balanced piston valve 32, said valve being provided at one of its ends with a tail rod 33, the tail rod being slidable in a bore 34.v 'Ihe bore 34 communicates with the chamber 30 by means of the passage 35, and also with the pipe line I9. The valve 32 is also provided with a second tail rod- 36 which extends through a chamber 31 into a bore 38 in a casing 39 attached to the casing 29, and into a chamber 49 in said casing 39, the chamber 40 cornmunicating at its outer end with the pipe line 22. It may be `noted that, when the piston valve 32v is in the position shown in the drawing, the main cylinder 25 communicates with the surge tank .I5 by means of the port 25a, the chamber 30 and the port 3| but, when the piston valve is caused to be shifted to the left inl a manner to be hereinafter described, the cylinder 25 will communicate with the pipe linev I9 by means of the port 25a, the chamber 38', the passage 35, and the bore 34.

Mounted onthe top of the valve casing 29 and adapted to commmunicate with the chamber 31 is a check valve 40, which comprises a casing 4I, ports 42, 42, and 43, and a valve ball 44 which is urged to closed position by a spring 45, the tension of which spring may be adjusted by means of athreaded plug 46 for a purpose hereinafter specified. It is to be noted that, when thevpiston valve 32 is moved to the left in the plane of the drawings, fluid contained in .the chamber 31 will,

' chamber 31 through said check valve.

Mounted on the bottom of the casing is a second check valve 41 adapted to communicate with the chamber 31 by means of the port 48 and with the surge tank I5 by means ofthe port 49. It is to be noted that, though no lHuid will be discharged from the chamber 31 through the valve the ball 58 will be lifted from its seat by the suc- Ltion created in the chamber 31, .thus allowing fluid to flow from the surge tank I5 through the ports 49 and 48 into the chamber 31.

With more particular reference to the reversing valve I8, there is shown inFigures 5 and 6 a valve casing 5| having a central chamber 52 and a piston valve 53 slidable longitudinally in the bore forming said chamber, and being closely tted therein. In order to facilitate the connecting of the control valve I8 to the pipe lines VI9 and 22, there are provided detachable plates 54..which.are

' bolted orA otherwise attached to the valve casing -5I,` tongue and groove connections 55 forming pressure tight joints between the plates 54 and the valve casing 5|. The plates 54 are provided with threaded bores which receive the ends of the pipes I9 and 22, thereby placing said pipes' in communication with the valve chamber 52 by means of ports 56 and 51 respectively. The pipe line I1 communicates with the valve chamber 31 by means of a port 58, and it is to be noted that movesto the right in Ithe plane of the drawingl when the piston valve 53 is in the position shown.,`

in Figures 5 and 6 the pipe line I1 communicates with the pipe line I9 by means of the port 58, the valve chamber 52, and the port 56. When the piston valve is'` moved to the right in the plane of the drawing in,a manner to be hereinafter described, the pipe line I1 will' be placed in communication with the pipe line 22 by means of the port 58, the valve chamber 52, and the portu 51.

In one end of the valve casing 5| is a bore 59 into which is -closely fitted a 'ring`60 provided the pipe 24, thus placing said pipe in communication with the valve chamber 52 by means of a port 65 which extends through the plate 64 and the ring |50, and the passage 62. With the piston valve 53 in the position shown in Figures 5 and 6, the pipe line 24 communicates with the pipe line 22 by means of the port 65, the passage 62, the valve chamber 52, and the port 51. When the piston valve 53 is moved to the right from the position shown in the drawings, the pipe line 24 is placed in communication with the pipe line I9 by means of the port 65, the valve chamber 52, and the port 56.

At one end of the piston valve 53 there is provided a rod 66 extending through the valve chamber 52 and beyond the valve casing 5|, the rod 66 sliding in a bore 61. provided with a suitable packing gland 68. At the outer endoLthe rod 66 there is provided a collar 69 rigidly attached to said rod by a pin or other suitable attaching means.

The valve casing 5| yis provided with chambers *10, 16 communicating with pipe lines 1|, 1| by means of ports 12, 12. The pipe lines 1|, 1| cornmunicate at all times with the pipe line I9 so that the same iiuid pressure is caused to exist in the chambers 10, 18 as in the pipe line I9.

Adapted to slide in packing glands13 in the valve casing 5|, and projecting into the chambers 10, are

plungers

14, 14, said plungers `sliding inbearings 15 in a bracket 16 bolted to a flange 11 on the valve casing' 5|. A cross bar 18 is attached to the

plungers

14, 14 by means of

nuts

19, 19.

Slidably mounted on the plungers 14 and the rod 66 is a cross head 88 equipped with suitable bushings 8|. The plungers 14 are provided with collars 82 adapted to abut the cross head 88 and to thereby move said cross head to the right in the plane of the drawing when said plungers are caused to be moved to the right.

A spring loaded compressible link 83 is loosely pivoted at one end to the cross head 88 and at its other end to a pin 84 on the bracket 16, while a second and similar link 85 is loosely pivoted at one end to the cross head 88 and at the other end is xed toy a rock shaft 86 journaled in the' bracket 16. It'is to be noted that the

links

83 and 85, and the cross head 88, which in effect is Aalso a link, comprise a spring loaded toggle, so

l center of the cross head 88 will eventually reach a point just to the right of a line connecting the centers of the pivot pin 84 andthe rockshaft 86,

at which .time the toggle will quickly snap to its extreme position, whereby the cross head 88 will strike the collar 69 on the rod 66 and move said rod and the piston valve 53 to the right. By rocking the shaft 86 in a counterclockwise direction by means hereinafter described, the toggle will be caused to move in the opposite direction, nally snapping to the left and causing the cross ,head to abut a shoulder 81 on thevrod 66, thereby shifting the piston valve 53 to the left.

Mounted in a boss 88 on the bracket 16 and extending longitudinally of the rod 66 is a stem 89 provided at its inner end with aA shoulder 98 abutting a shoulder 9| in the boss 88, a clampingnut 92 being threaded to the stem 89 and serving to hold the shoulder 98 against the shoulder 9|, thereby locking the stem 89 to the boss 68. I A set screw 93 in the boss 88 prevents-the stem 89 from turning relative to said boss. 1n the inner end of the stem 89 there is provided a recess 94 permitting the rod 66 and the collar 69 to move to the right, the bottom of said recess limiting the movement of said rod and nut in that direction.

Slidably mounted on a reduced portion of the stem 89 is a collar 96" which is urged against a shoulder 91 on said stem by means of a coll Aspring 98. A hand wheel 99 is -threaded on the outer end of the stem 89 and is adapted to' vary the expansive force of said spring.- A spring seat |88 and a thrust bearing |8| are interposed between the hand wheel and the spring to facilitate the turning of said hand wheel, and a nut |82 prevents the hand wheel from being accidentally removed from the stem 89.

Referring to Figure 1, there is shown a vertically disposed operating rod |83, slidably mounted in lugs |84 and |85 on the` stationary table C and the press head D respectively, the downward movement Aof said rod being limited by a collar |86 adjustably fixed to the rod. The operating rod |83 is constantly urged to its lowermost position by gravity and also by means of a coil spring |81 mounted on said rod between the lug |85 and a collar |88 also on said rod. A boss |89 on the movable die support is arranged to slide freely on the operating rod |83. Adjustably attached to the-rod |83 is a collar ||8 which is adapted to be engaged by the boss |89 when the movable support has reached a predetermined hollow coupling ||1, the latter being plvotally connected at ||8 to a manually operable control lever H9. A tensioned coil spring |28 interposed between the press base B and the shorter arm of the bell crank lever tends to cause a lug |2| on said handle to abut a lug |22 on the base B, thereby normally maintaining the bell crank lever in the position shown in the drawing.

As clearly shown in Figure 7, there is rigidly attached to the upper end of the rod ||6 a collar |23 which is adapted to slide within the hollow coupling ||1 and to abut the inwardly extending flange |24, thereby limiting the downward movement of the rod ||6 relative to theA coupling ||1. It is apparent that, although the control lever ||9 may be swung to the left and the rod ||6 thereby elevated, an upward movement of the rod I |6 will not cause the control lever to be moved. Thus, when the rod ||6 is caused to perform a reciprocatory motion during constant operation of the press in a manner hereinafter described, there will be no Idanger of the control lever swinging outwardly and striking the operator.

In Figures 1, 2, and 8 there is shown a mechanism for controlling therate of discharge of the pump. This mechanism is provided with a. vertically disposed and longitudinally adjustable operating rod |25 slidably mounted in lugs |26 and |21 on the stationary tablel C and the press head D respectively. The downward movement of said rod is limited by collars |28 and |29 iixedly attached to the rod. The operating rod |25 is constantly urged to its lowermost position by gravity and by means of a. coil spring |38 mounted on said rod and interposed between the lug |21 and a collar 3| on the rod. 4A boss |32 on the movable support is arranged to slide freely on the operating rod |25. -Adjustably attached to the rod |25 is a collar |33 which is adapted to be engaged by the boss |32 when the movable support has reached a predetermined point in its upward travel, the rod |25 being thereby lifted. Rigidly attached to the base B directly below the lug |26 is a bracket |34 to which a bell crank lever |35 is'pivoted as at |36. A link |31 is pivoted to the operating rod |25 at |38 and Vto the bell crank lever |35 at |39.

whereby a. clockwise movement of the lever |42 will cause the pump cross head to be pushed towards the center of the pump, thus decreasing the discharge of the pump in a `manner well 'known to those skilled ih the art. As stated exerted onthe cross head by the lever |42, is removed. I Operation If it is desired that'the press operate under full automatic control, the collar III! is 'adjusted in a position on the operating rod permitting said collar to be engaged'by Atheboss |09 at the proper point in the up stroke of the movable support, and the motor driving the pump then started.

Assuming 'that this adjustment of the collar I I0 has been made, that the motor driving the pump has been started, and that the movable support F is travelling downward, the various parts comprising the automatic control mechanismwill be in the positions shown in the draw-v ings, the blank K will have been placed on the punch as shown in.Flgure -1, and the operation of the press will be as follows:

Thel pump I4 is set to deliver its full dischargev of huid under pressure through the pipe line I1 into the reversing valve.|8, the fluid then passing through the port 58, the valve chamber 52, lthe port 56, and the pipe line I9 and into the. booster cylinders 28, the fluid pressure thereby exerted in said booster cylinders causing the movable support to move downwardly. During lthis part of the down stroke of the support, liuid' from the surge tank I5 will owthrough the "port 3|, the valve chamber 30, and the port 25a into the main cylinder 25. It is to bevnoted that, during the down stroke of the support, the fluid which entered the die returning cylinders 23 andthe return cylinders 6, 6 duringthepreceding up stroke must escape from said cylinders, the fluid escaping from'the diel returning cylin- -ders` by means of the pipe line 22, the port 51,

the valve chamber 52, the passage 62, the port 65, andthe pipe line 24, which pipe line discharges said fluid into the surge tank I5, and

the fluid in the return cylinders escaping through j the pipe line s28 into the die returning cylinders and thence over the same path as the fluid which was in the die returning cylinder.

When the female die H contacts 'the blank K,`

further movement of the platen and the die will be resisted, firstly', by the resistance to bending ofthe blank-'which is supported on the fixed most position to its point of contact with the punch I, and, secondly,`by the clamping ring I2 contacting the blank K, the clamping ring being yieldably urged upwardly by pressure in theA cush ioning cylinder 5.l When the female die first engages the blank, the pressurein the cushioning cylinder 5 is small, being due only to the static head lof the fluid in the surge tank I5. It is to,v be noted that, in the interval during which the female die. is moving from its upperblank, the full discharge of the pump is directed to the boosterv cylinders, which are of relatively small diameter. This results in a-rapiddie travel during the inactive portion of the down or draw'- v ing stroke, so' that a minimum of ltime is consumed in bringing thedies into actual drawing relation.

As the drawing of the blank starts, the female die and* its movable support will encounter resistance to their downward travel', and the fluid pressure in the pipe lines I1 .and I9 l will build up until it reaches a predetermined value',` at which time said pressure, acting on the tail rod 33 ofthe surge shifting valve 2|, will'ucause the.. Vpiston valve 32 to be moved to theleft from the position shown in the drawing, thereby expelling the fluid. contained. in the chamber v31 through valve, and, `at the same time', said valve chamber 30 will be placed in communication with the pipe line I9 by means of the passage 35 and the bore 34, which bore has been vacated by the tail rodv 33. The maincylinder 25 now receives the .fluid under pressure from the valve chamber 38 through the port 25a. The movableI support, now, being forced downwardly by the combined action of the main and booster cylinders, continues said downward movement until the resistance to drawing causes the pressure to build up in the circuit" and then to act to move the pump cross head inwardly against the pressure of 'the cross head spring, thus ldecreasing thefrate of discharge from said pump and preventlngthe occurrence of yshocks of waterhammer which might otherwise take place when the flow of fluid under pressure isreversed to start the support on its upward movement'. During the drawing .of the blank, the building up of the pressure in the main pressing cylinder 25 has resulted in a proportional increase'in pressure in the cushioning cylinder 5, the blank-being thereby clamped between the v clamping ring I2 and the female die by a -force proportional 'to the drawing pressure, that is the ratio of the blank holding pressure tothe drawing pressure is constant for all values of drawing pressure, `and wrlnkling of the blank is thereby prevented.

When the drawing operation has been completed and the`female die has reached the posi-l tion shown in Figure 10, the blank (now drawn) will be subjected to a finishing, or pressing, operation. The formed blank will `be tightly pressed between the top surface i of lthe vpunch i and the inner downwardly-facing surface h' of the female die, a very smooth finished article,

free from wrinkles or other imperfections some` times caused by drawing, being thereby produced. This pressing of the blank between the two dies results in a building up of the pressure in the main cylinder, and the movable support will be reversed and returned to its upper or normal position as follows:

As has been heretofore stated, the chambers 10 are always in communication with lthe pipev line I9 by means of the ports 12 and the pipe line 1|,

cause the cross'bar -18 to slide on the stem 8,9,

and` the collars 82 to abut the cross head 80 'andithereby move said cross head to the right against the force exerted by the spring loaded

compressible links

83 and 85. When the vertical jso that, as the fluid pressure builds up in the center line of the cross head has reached a point just a little'tothe left of a plane containing the centers of the pin 84 and the rock shaft 86, the` cross bar 18 will abut the collar 95, the

lplungrs 14 being thereby held against furtler' movement to the right until the fluid pressure in the chambers 10 has further built up. When 75' pressure of the spring 98, thus allowingv the plungers 14 to move further to the right, until the cross head 80 has passed the plane containing the pin 14 and the rock shaft 86, at which time the spring loaded

compressible links

83 and 85 will cause the toggle to snap quickly to the right,

4the cross head 80 striking the collar 69 on the rod 66, moving said rod and' the piston valve 53 to the right.

From the foreging it is apparent that the travel ofthe platen and the female die is reversed upon the attainment of a definite pressure in the main pressing cylinder 25, and that the reversal is not directly dependent upon any distance control means. This characteristic will at once be seen as an important advantage when it is remembered that dies of any depth, within reasonable limits, may be placed on the machine and operated in the above manner withoutthe necessity of making new adjustments for each different set ofdies in order to properly control the length of stroke of the movable die.

Itis to be noted that, by turning the hand wheel 99 and thus varying the tension of the spring 98, the amount of pressure which must build up in the main and booster cylinders lbefore the valve I8 is reversed may be varied at will.

As has been descrlbed'above, when the piston valve^53 has been moved to the right, the pipe line |1 will communicate with the pipe line 22,

and the' pipe line I9 with the pipe line 24. In this position of the valve, the discharge of the pump is directed through the pipe lines I 1 and 22 into the die returning cylinders v23 and the chamber 40 in the surge shifting valve 2|. The fluid pressure in the chamber 40 acts on the tailrod 36 causing the piston valve 32 to be moved to the right, in other words, to the position shown in Figure 4. While the piston valve is moving to the l right, fluid from the surge tank I5 will enter the y rin chamber 31 through the check valve 41 as hereinbefore described. The iluidv under pressure in the die returning cylinders 23 then causes the movable support to move upwards, the iiuid contained inthe main cylinder 25 then being expelled-.therefrom into the surge tank I5 through the port 25a, the valve chamber 30, and the port 3|, and the uid in the booster cylinders 20 being expelled through the pipe line I9, the reversing valve I8, and the pipe line 24 into the surge tank I5.

Since the blarikjholder` returning cylinders 6- are in constant communication with the die returning cylinders by means of the pipe line 28, uid will enter the return cylinders 23 during the upwardmovement of the platen, and will move the s 8-8 'upwardly to return the clamping y f to its upper position. The upward move merit of the 'rams s-sv is limited by theyoke s contacting with 'the bolster plate J, and the pins Ifare of. such a` length that, when the return rms have reached their upper limit, the upper face of the clamping ring will liein substantially the same plane as the upper face of the punch.

It is to be noted that, since the pressure in the pipe line I1 is less at this time than it was at the time the movable support met resistance toits'downward travel,l the spring on the pump cross head will return said cross head to the position permitting maximum discharge by the direction by means of the link |31, the bell crank lever |35, and the link |40. By this movement of l the lever |42, the head |46 of said lever forces the cross head |41 of the pump inwardly against the force of the pump cross head spring, thereby reducing the rate of discharge from the pump preparatory to a. reversal of direction of travel of the movable support for the purpose stated above.

When the support has proceeded a little farther on its upward travel, and has reached a predetermined point, the boss |09 will strike the collar ||0 'on the operating rod |03, lifting said operating rod, whereby the collar I contacts withA the arcuate projection ||4 on the rocker arm ||3, causing said rocker arm tobe swung upwardly. thus turning the rock shaft 86 in a clockwise direction as viewed in Figure 1 and in a counterf clockwise direction as viewed in Figure 6. This turning of the shaft 86 causes the compressible link 85 .which is xed to the rock shaft to be swung to the left, whereby the cross head 80 will be also swung to the left, during which movement the cross head will strike the collars 82 on the plungers 14, and the shoulder 81 on the rod 68, thereby returning the plungers to their inner position and the piston valve 53 to the position shown in Figures 5 and 6; In this posi- 4the female die then return to its uppermost position and stop, the collar ||0 on the operating rod |03 isloosened and moved up into a position in which it Will not be engaged by the boss |09. Assuming that the"movable support is on its downward stroke, the completion of said downward stroke and the start of the upwardstroke will be executed in thesame manner as that described above. When the boss |32 strikes the collar |33 on the upward stroke o1' the support, the rod 25 willbe liftedand the pump cross head `|41 moved inwardly in the manner already described, until said cross head has reached a point at which the discharge of the pump is zero, the movable support then coming to rest.

To cause the movable support to descend 4to cause the dies to perform another drawing operation, the manually'operable control lever ||9 is swung to the left from the position shown in Figure 1, thereby raising the rod IIB, swinging thelever ||3 upwardly, and turning the rock shaft 86 in a clockwise direction as viewed in' Figure 1 and in acounterclockwise direction as lviewed in Figure 6. 'The piston valve 53 is thereby moved to the left in the manner described above, and the pipe line I1 will then communicategwith the pipe line I3. and the pipe line 22 with the pipe line 24. It may be noted that, though the valves I8 and 2| are now 'in a positionto allow fluid under pressure to produce a downward movement of the platen, the

iii.

die returning cylinders 23 with the surge tank l by means'of the pipe line 22, the valve I8, andl the pipe line 24, and thel booster` cylinders 20 with the surge tank by means of the pipe line I9, the valve I8, the pipe line I1, the pump Il, and the pipe line I6, there is no fluid pressure tending to hold the movable support up. The weight of the support itself will therefore cause the latter to coast downwardlyA until the operating rod I25`has been lowered and the pump cross head |41 thereby allowed to be moved outwardly by the cross head spring, `whereupon the pump will start to discharge and the operation will proceed in the manner already described.

While one method of carrying out Amy invention has been herein described, it is of course to bel understood that the details of structure and arrangements of parts may be variously changed and modified without departing from the spirit and scope of my invention.

I claim:

1.A In a drawing press including a. movable die and amovable blank holder; the combination with hydraulic actuating means for moving said die towards said holder; loi? a source of fluid pressure connected to said means; hydraulic cushioning means associated with said blank holder for yieldably urging said blank holder towards said die; and hydraulic connections between said actuating means and said cushioning means for maintaining at constant ratio the hydraulic pressures therein.

2. In a drawing press including a reciproca tory die and a movable blank holder, the combination with hydraulic actuating means for re-v ciprocating said die towards and away from said holder; of a source of fluid pressure connected to said actuating means; hydraulic cushioning means associated with said blank holder for -vyieldingly urging said. blank holder towards said die during movement of the die towards said holder, and for moving the blank holder towards the die whileA the die is moving away from said holder, and hydraulic connections between said hydraulically actuated die moving means and said hydraulic cushioning means for maintaining at a constant ratio the hydraulic pressures therein. Y l

3. In a drawing press, including a press frame, the combination with a pair of die supports mounted on the frame, one oi' said supports being movable towards and away from the other: of hydraulic actuating meansE for effecting alternate drawing and return strokes of said movable support, said actuating means including a main pressing cylinder; a die fixed to each support; a source of fluid pressure; means forming with the pressing cylinder and with said source of fluid pressure a hydraulic circuit; a blank holder adapted to clamp a blank against oneof the dies; va cushioning cylinder; hydraulically actuated means mounted for reciprocation in, said cushioning cylinder and connected to s'aid blank holder for resisting kmovement of said holder during the drawing stroke;-hydraulic connections betweenl the pressing cylinder and the cushioning cylinder for maintaining proportionate pressures therein-and circuit controlling Cil meansoperatively connected with the circuit for causing said hydraulically actuated means to effect' alternate drawing and return strokes of the Ymovable support.

4. In adrawing press, including a press frame, y

, 'adapted to clamp a blank against one of the dies,

said holder being also adapted to be moved away from its normal position by the die during the drawing stroke of the latter; a cushioning cylinder; hydraulically actuated means mounted for reciprocation. in said cushioning cylinder and connected to said blank holder for resisting movement of said holder during the drawing stroke; hydraulic connections'between the press- 1 ing cylinder'and the cushioning cylinder for maintaining proportionate pressures therein; hydraulically actuated means associated with the blank holder and connected to -said` hydraulic circuit for returning said holder to its normal position during the return stroke of the movable l support; and 'circuit controlling means operatively connected with the circuit for causing said hydraulically actuated means to effect alternate drawing and return strokes of the movable support. 4

5: In a drawing press, including a press frame, the combination swith a pair of die supports mounted on the frame, one of said supports being movable towards and away from the other; of

' hydraulic actuating means for eiecting alternate drawing and return strokes of said movable support; said actuating means including a main pressing cylinder, and a die returning cylinder; a

,die xed to each support; a source of fluid pressure; means forming with the pressing cylinder and with said source of fluid pressure a hydraulic circuit; a blank holder normally occupying a position at rest and being adapted to clamp a blank against one of the dies; a cushioning cylinder; hydraulically actuated means mounted for reciprocation in said cushioning cylinder and connected to ksaid blank holderl for resisting movement of said holder d ing the drawing stroke; hydraulic connection etween the pressing cylinder and the cushioning cylinder for maintaining proportionate pressures therein; a blank holder returning cylinder; hydraulically actuated means mounted for reciprocation in said blank holder 4returning cylinder and'connected to the blank holder forv returning the latter toits normal position during the return stroke of the the combination with abolster plate connected to the frame and having an opening; of ,a die connected to the upper face of the bolster plate; a movable die support mounted on the frame vfor performingvdrawing and return strokes respectively towards andawayirom said die; a second die mounted on said support; hydraulic actuating ,said support, said actuating means including a main pressingA cylinder; a source of fluid pressure; means forming with the pressing cylinder and with said source of fluid pressure a hydraulic circuit; a cushioning cylinder connected to said frame below the bolster plate; cushioning means mounted in said cushioning cylinder for reciprocatory movements; a blank holder adapted to clamp a blank against the moving die, said blank holder beingk arranged in cooperative relation with the die on the bolster plate; means extending through the opening and connected to said reciprocatory cushioning means and to the blank holder for resisting movement of said holder during the drawing stroke; hydraulic connections between the pressing cylinder and the cushioning cylinder for maintaining proportionate pressures therein; and circuit controlling means for causing said hydraulic actuating means to eiect drawing and return strokes of the movable support.

'7. In a drawing press'including a press frame, the combination with a bolster plate connected to the frame and having openings; of a die connected to the upper face of the bolster plate; a movable vdie support mounted on the frame for performing drawing -and return strokes respectively towards and away from vsaid die; a second die mounted on said; support; hydraulic actuating ,'means for effecting reciprocatory movements of said support, said actuating means including a main pressing cylinder and a die returning cylinder; a source of fluid pressure; means forming with the pressing cylinder and with said source of fluid pressure a hydraulic circuit; a cushioning cylinder connected to said frame below the bolster plate; a cushioning ram mounted in said cushioning cylinder for reciprocatory movements; a blank holder returning cylinder connected to the frame and disposed adiacent the l cushioning cylinder; a ram mounted for re'ciprocatory movements in said returning cylinder; a blank holder for clamping a blank against the moving die and arranged in cooperative relation n with the die on the bolster plate; means extending through the'openings in the bolster plate and connecting said blank holder to the blank holder -to the frame and having openings; of a die connected to the upper face of the bolster plate; a movable die support mounted on the frame for performing drawing and return strokes respectively toward and away from said die; a second die mounted on said support; hydraulic actuating means for effecting reciprocatory movements of said support, lsaid actuating means including a main pressing cylinder and a die returning cylinder; a source of fluid pressure; means forming with the pressing cylinder and with said source of fluid pressure a hydraulic circuit; a cushioning cylinder connected to said frame below the bolster plate; a cushioning ram mounted in said cushioning cylinder for yreciprocatory movements; a blank holder returning cylinder coni nected to the frame and disposed adjacent the cushioning cylinder; a ram mounted for reciprocatory movements in said returning cylinder; a blank holder for clamping a blank against the moving die and arranged in cooperative relation with the die 'on the bolster plate; a yoke connected to said'cushioning ram and to said blank l.holder returning ram, said yoke being arranged in substantial parallelism with the bolster plate, and being adapted to engage said plate to limit the movement of said rams in one direction; means extending through the openings in the bolster plate and connecting the blank holder to said yoke; hydraulic connections between the maintaining proportionate pressures therein to urge the blank holder against the moving die;

hydraulic connections between the die returning cylinder and the blank holder returning cylinder; and circuit .controlling means for causing said hydraulic actuating means to effect drawing and return strokes of the movable die.

9.` In a drawing press, including a press frame, the combination with a pair of die supports mounted on the frame, one of said supports being movable towards and away from the other; of hydraulic actuating means for effecting alternate drawing and return strokes of said movable support, said actuating means including a main pressing cylinder; a die fixed to each support; a

source of iiuid pressure; means forming with the pressing cylinder and with said source of fluid pressure a hydraulic circuit; a blank holder adapted to clamp a blank against one of the dies; a cushioning cylinder; hydraulically actuated means mounted for reciprocation in said cushioning cylinder and connected to said blank holder for resisting movement of said holder during the drawing stroke; hydraulic connections between the pressing cylinder and the cushioning cylinder for maintaining proportionate pressures therein; circuit controlling means operatively connected with the circuit for reversing the direction of fluid travel to reciprocate the movable support; and means responsive to the uid pressure in the circuit for decreasing the speed of travel of the movable support when said support approaches the limit of its drawing stroke.

10. In a drawing press, `including ,a press framle, the combination with a pair of die supports mounted on the frame, one of said supports be- Y ing movable towards and away from the other; of hydraulic actuating means for effecting alternate drawing and return strokes of said movable support, said actuating means including a main pressing cylinder; a die iixed to each support; a source of fluid pressure; means forming with the pressing cylinder and with said source of fluid pressure a hydraulic circuit; a blank holder adapted to clamp a blank against one of the dies; a cushioning cylinder; hydraulicallyactuated means mounted for reciprocation in said cushion? ing cylinder and connectedrto said blank holder for resisting movement of said holder during the drawing stroke; hydraulic connections between the pressing cylinder and the cushioning cylinder for maintaining proportionate pressures therein; means operatively connected in the circuit and responsive to the fluid pressure therein for reversing the direction of fluid travel upon the building up in the circuit of a predetermined pressure; and means actuated by the movable4 support and operable at the end of the returnl uid pressure a hydrauliccircuit; a blank holder adapted to clamp a blank against one of the dies; a cushioning cylinder; hydraulically actuated means mounted for reciprocation in said cushioning cylinder and connected to said blank holdl er for resisting movement of said holder during the drawing stroke; hydraulic connections between the pressing cylinder and the cushioning cylinder for maintaining proportionate pressures therein; means operatively connected in the cir- 'cuit and responsive to the fluid pressure therein for reversing the direction of fluid travel when the drawing stroke has been completed; and means Vactuated by the movable support and operable at the end of the return stroke 'for reversing thel direction of fluid travel.

12. In a drawing press, including a press frame, the combination with a pairof die supports mounted on the frame, one of said supports being movable towards and away from 'the other; of hy. draulic actuating means for effecting alternate drawing and return strokes of said movable support, said actuating means including a main pressing cylinder; a die xed to each support; a source of iiuid pressure; means forming with the pressing cylinder and with said source. of iiuid pressure a hydraulic circuit; a blank holder adapted to clamp a blank against one of the dies; a cushioning cylinder; hydraulically actuated means mounted for reciprocation in said cushioning cylinder and connected to said blank holder for resisting movement of said holder during the` drawing stroke; hydraulic connections between the pressing cylinder and the cushioning cylinder for maintaining proportionate pressures therein;

means operatively connected in the circuit andi the combination with a pair of die supports mounted on the frame, one of said supports being movable towards and away from the other; of hydraulic actuating mearis for eiecting alternate drawing and return strokesof said movable support, said actuating means including a main pressing cylinder; a die iixed to each support; a `sourceof fluid pressure; meansl forming with the pressing cylinder and with said source oi.' fluid pressure a hydraulic circuit; a blank holder adapted to clamp a blank against one of the l dies; a cushioning cylinder; hydraulically-actuated means mounted for reciprocat'ion in said cushioning cylinder and connected to said blank holder for resisting movement of said holder during the drawing stroke;l hydraulic connections between the pressing cylinder and thecushioning cylinder for maintaining proportionate pressures therein; circuit controlling means operatively connected with the circuit forreversing the direction of iiuid travel to reciprocate the movable support; and means actuated by the movable support for decreasing the speed of travel of said support when the latter approaches the limit of its return stroke.

14. In a drawing press, including a press frame, the combination with a pairof die supports mounted on the frame; one of said supports being movable towards and away from the other; of hydraulic actuating means for eiecting alternate drawing and return strokes of said movable support, said actuating means including. a main pressing cylinder, a die iixed to each support; a source of uid pressure; means forming with the pressing cylinder and with said source of iluid pressure a hydraulic circuit; a blank holder ada'pted to` clamp a blank against one of the dies; l

' therein; circuit controlling means operatively connected with the circuit for reversing the direction of fluid travel to reciprocate the movable support; means responsive to the iiuid pressure in the circuit for decreasing the. speed of travel of the movable support when said support approaches the limit oi its drawing stroke; and means actuated by the movable support for decreasing the speed of travel of said support when thev latter approaches the limit of its return stroke.

15. Ina drawing press including a press frame, the combination with a pair of die supports mounted on the frame; one of said supports being movable towards and away from the other; of hydraulic actuating means for effecting alternate drawing and return strokes of said movable support, said actuating means including a main pressing cylinder and a die returning cylinder; a die xed to each support; a source of fluid pressure; means forming with the pressing cylinder and with said source oi fluid pressure a hydraulic circuit; a blank holder normally occupying a po- CTI ment of said holder during the drawing stroke;

hydraulic connections between the pressing cylinder and the cushioning cylinder for maintaining proportionate pressures therein; -a blank `holder` returning cylinder; hydraulically actuated means mounted for reciprocal-,lon in said blank holder returning cylinder and connected to the blank holder for returning the latter to its no1'- mal position during uthe, return stroke of the 'movable support; hydraulic connections between the die returning cylinder and the blank holder returning cylinder; and circuit controlling means operatively connected in the circuit for reversing the direction of fluidtravel to alternately direct iluid under pressure into the pressing cylinder and then into the die returning cylinder.

16. Ina drawing 'press including a pressirame, a combination with a. pairof die supports mountagainst one of the dies; a cushioning cylinder;

hydraulically actuated means mounted for reciprocation'in said cushioning cylinder and connected to said blank holder for resisting movement of said holder during the drawing stroke; hydraulic connections between the pressing cylinder and the cushioning cylinder for maintaining proportionate pressures therein; a blankv holder returning cylinder; hydraulically actuated means mounted for reciprocation in said blank holder returning cylinder and connected to. the blank holder for returning the latter to its normal position during the return stroke of the movable support; hydraulic connections between the die returning cylinder and the blank holder returning cylinder; and circuit controlling means operatively connected in the circuit for reversing the direction of fluid travel to alternatelyl direct fluid under pressure into the pressing cylinder and then into the die returning cylinder, said circuit controlling means including means responsive to the fluid pressure in the pressing cylinder for reversing thedirection of fluid travel upon attainment of a predetermined pressure in the presssure; means forming with the pressing cylinder and with said source of fluid pressure a hydraulic circuit; .a blank holder` normally occupying a position at rest and being adapted to clamp a blank against one of the dies; a cushioning cylinder;

hydraulically actuated means mounted for reciprocation in said cushioning cylinder and connected to said blank holder for resisting movement of said holder during the drawing stroke; hydraulic connections between the pressing cylinder'and the cushioningcylinder for maintaining proportionate pressures therein; a blank holder. returning cylinder; hydraulically actuated means mounted for reciprocation in said blankholder returning cylinder and connected to the blank holder for returning the latter to its normal pol sition during the return stroke. of thel movable support; hydraulic connections between the die returning cylinder and the blank holder returning cylinder; circuit controlling means operatively connected in the circuit for reversing the direction offluid travel to alternately direct fluid under pressure into the pressing cylinder and then into the die returning cylinder, said circuit y controlling means including means responsive to the fluid pressure in the pressing cylinder for reversingl the direction of uid travel upon attainment of a predetermined pressure in the pressing ed on the frame, one of said supports being movbeing performed; and means actuated by the movable support and operable when the support approaches the end of the return stroke for reversing the direction of fluid travel.

18.y In a drawing press including a press frame, the combination with a pair of die supports mounted on the frame, one of said supports being movable towards and away from the other; of hydraulic actuating means for effecting alternate drawing and return strokes of said movable support, said actuating means including a main pressing cylinder and a die returning cylinder; a die fixed to each support; a source of fluid pressure; means forming with the pressing cylinder and with said source of fluid pressure a hydraulic circuit; a blank holder normally occupying a position at rest and being adapted to clamp a blank against one of the dies; a cushioning cylinder; hydraulically actuated means mounted for reciprocation in said cushioning cylinder and connected to said blank holder for resisting movement of said holder during the drawing stroke; hydraulic lconnections between the pressing cylinder and the cushioning cylinder for maintaining proportionate pressures therein; a blank holder returning cylinder; hydraulically actuated means mounted for reciprocation in said blank holder returning cylinder and connected to the blank holder for returning the latter to its normal position during the return stroke of the movable support; hydraulic connections-between the die returning cylinder and the blank holder returning cylinder; circuit controlling means operatively connected in the circuit for reversing the Adirection of fluid travel to alternately direct fluid under pressure into the pressing cylinder and then into the die returning cylinder, and means responsive to the fluid pressure in the pressing cylinder g and operable upon attainment of a predetermined .pressure therein for reducing the rate of flow of fluid into the pressing cylinder when the movable support approaches the end of its drawing stroke.

19. In a drawing press including a press frame, the combination with a pair of die supports mounted on the frame, one of said supports being movable towards and away from the other; of hydraulic actuating means for effecting alternate drawing and return strokes of said movable support, said actuating means including a main pressing cylinder and a die returning cylinder; a die fixed to each support; a source of fluid pressure; means forming with the pressing cylinder and with said source of fluidpressure a hydraulic circuit; a blank holder normally occupying a position at rest and being adapted to clamp a blank against one of the dies; a cushioning cylinder; hydraulically actuated means mounted for reciprocation in said cushioning cylinder and connected to said blank holder for resistingmovement of said holder during the drawing stroke; hydraulic 'connections between the pressing cylinder and the cushioningcylinder for maintaining proportionate pressures therein; a blank holder returning cylinder; hydraulically actuated means mounted for reciprocation in said -blank holder returning cylinder and connected to the blank holder for returning the latter to its normal position during the return stroke of the movable support; hydraulic connections between the die returning cylinder andthe blank holder returning cylinder; circuit controlling means operatively connected'in the circuit for reversing the direction of fluid travel to alternately direct fluid under Vpressure cylinder while thev drawing stroke of said die is into the pressing cylinder and then into the die 75 returning cylinder; and means actuated by the movable support for decreasing the rate of ow of iluid into thedie returning cylinder when the movable support approaches the end of its Jreturn stroke.

20. In a drawing press, the` combination with a main ram; of a cooperating main cylinder; a blank holder mounted for movements in opposition to said rain to engage and hold a blank; a blank holder cushioning cylinder; a ram connected to said blank holder and mounted for reciproc toryv movements in said cushioning cylinder; and' for eciprocatory movements and being connected to saidmovable die;` a cushioning cylinder,

a ram mounted therein for reciprocatory movements and being connected to said blank holder for yieldably urging the latter towards said mov-jable die to engage and hold a blank; means for supplying fluid under pressure to said main cylinder; and a hydraulic connection between the cushioning cylinderand the main cylinder for maintaining at a constant ratio the hydraulic pressures therein.- 22. A method ior shaping metal blanks which consists in drawing the blank to be shaped between cooperating dies, one of whichis movable and the other stationary, moving the movable die by hydraulic means, clamping a portion of the blank against only the movable dieby hydraulic means, and maintaining a free and direct interfiow of pressure fluid between the hydraulic drawing means and the hydraulic clamping means, whereby t transmit pressure therebetween in substantially undiminished condition, said interilow of pressure. iluid serving to clamp said blank during the drawing operation by a pressure which bearsl a constant ratio to the drawing pressure.

WALTER ERNST.