US2431173A - Apparatus for stretch-shaping metal blanks to conform to convex curved dies - Google Patents

Description

Nov. 18, 1947. -r. a. HAWKES APPARATUS FOR STRETCH-SHAPING METAL BLANKS T0 CONFORM TO CONVEX CURVED DIES Filed Jan. 29, 1943 4 Sheets-Sheet 1 INVENTOR 'r. 1 BY Wm ATTORNEYS N 1947- r. B. HAWKES APPARATUS FOR STRETCH-SHAPING METAL BLANKS TO CONFORM TO CONVEX CURVED DIES 4 Sheets-Sheet 2 Filed Jan. 29, 1943 Nov. 18, 1947. 1'. a. HAWKES APPARATUS FOR STRETCH-SHAPING IETAL B LANKS TO CONFORI TO CON VEX CURVED DIES Filed Jan. 29, 1943 4 Sheets-Sheet 4 ATTORNEYS- Patented Nov. 18, 1947 APPARATUS FOR sras'rcmsrmrmo MET- AL BLANKS 'ro CONFORM 'ro convex CURVED DIES Thomas Blair Hawkes, Champlain, N. Y., assignor of one-half .to The Sheridan Iron-Works and one-half to T. W. & C. :B. Sheridan Company, both corporations of New York Application January 29, 1943, Serial No. 473,943

Q 20 Claims. (Cl. 153-48) This invention relates to the stretch-shaping of metal bars, sheets and the like, having reference both to a novel stretching and shaping apparatus or power press and to a method of shaping or curving various pieces of workbythe aid of stretching operations, to conform the metal blanks to convex curved dies.

Power-operated presses or machines for such purposes constitute a well known class, characterized in that the work-piece without the need of heating may be bent, curved or otherwise shaped, by causing it to conform to the contour of a preconstructed templet, convex pattern or male die, without the need of a complementary means or female die but by apowerful pulling and stretching action, causing theworkpiece to be modelled, disposed and reshaped to the tions or the coaction of a complementarydie or pressure member, and the pull upon and reshaping of the work may be along one or several directions. In the case of an elongated workpiece, hereinafter called a bar, and which may be a simple strip or on the other hand a structural angle bar, T-bar, U-bar or channel, prefabricated by extrusion, rolling or otherwise, the ends of the bar may be gripped and simultaneously'stretched and shaped, usually by a simple curving or bending action in contact against the pattern or die, but sometimes with also a twist, to the predetermined contour or form. As an industrial example, the shaped and curved or twisted bars may serve to constitute the frame members or skeleton of a structure, for instance the fuselage, wing or pontoon of an aeroplane, while the shaped sheets may constitute the shell or skin of such product supported by and attached to such frame members.

While various apparatuses and methods have been heretofore devised for the general field and purposes thus set forth, these have usually involved certain practical drawbacks in structure, operation or control, to the impairment of the product and detriment to the operation and output of the apparatus. The general object'therefore of the present invention is to afford a stretchforming apparatus and method which are of improved efliciency whereby to deliver more uniformly satisfactory products and at a high output in operations per hour. A further object is to vaiford an increased scope or range in the variety of products that can be turned out in a single apparatus, and as well to afford high convenience of operation and control, and adaptation of apparatus to various specific purposes.

Another object is to afford, in apparatus of the :class mentioned, improved reliability and accuracy of operation withconsequent uniformity andhieh quality of product. Another object is to eliminate to maximum extent the tendency to buckling or wrinkling that is liable to occur without effectively coordinated stretching and curving actions and which greatly weakens the products. It is to be understood that, depending upon the properties of the metal worked upon, the stretch-shaping may be performed somewhat in excess, beyond the exact desired contour, thereby to allow for a slight return of shapin which however in some cases may be negligible.

Further objects and advantages of the present invention will be explained in the following description of one or more illustrative embodiments of the invention or will be understood by those conversant with the subject matter. To the attainment of such objects and advantages the present invention consists in the novel stretch-shaping apparatus, press or machine, as well as the method of operation, and the novel features of combination, arrangement, construction and mode of action, herein illustrated or described.

In the drawings:

Fig. 1 is a perspective view of a preferred form of stretch-shaping press embodying the present invention.

Fig. 2 is a fragmentary section showing an illustrative workpiece engaged upon the die of the press.

Fig. 3 is a central longitudinal section of certain parts seen in Fig. 1, taken on the line 3--3 of Fig. 4; while Fig. 4 is a left end elevation, partly in section and with parts omitted, of the structure shown in Fig. 3, and Fig. 5 is a right end elevation of the upper parts of Fig. 3.

Fig. 6 is a diagrammatic front view, partly in section, of a preferred hydraulic system of operation and control of the press; and Figs. '7 and 8 are sectional views showing difi'erent positions of a 3-way valveseen in Fig. 6.

Fig. 9 is a top plan view, partly in central section, of the lefthand work gripper device seen in Fig. 1; while Fig. 10 shows such gripper in central section taken at right angles to Fig. 9; Fig. 11 is an enlarged fragmentary section like part of Fig. 10 but showing the gripper in its work gripping position; and Fig. 12 is a reduced partial right end elevation of the gripper of Figs. 9-11, with the work omitted.

Figs. 13, 14 and 15 are diagrammatic front views showing successive positions of the press parts in one mode of operation; and Figs. 16, 1? and 18 are analogous diagrams showing successive positions in another mode of operation.

Fig. 19 is a partial top plan view, and Fig. '20 a front elevation, showing a self-acting contrivance for uptilting each gripper during operation.

While the longitudinal lay of the press is shown horizontal and the stretching actions are in general horizontal but with certain rising or slanting movements, in using relative terms of direction or position, as upward, downward, above, below, horizontal and the like, these are not intended as limitations but are used as a matter of convenience in description.

As a preliminary outline, the press comprises, near the center, the given male or convex die or templet, positioned and resting upon a. supporting saddle, table or bench which is fitted for ascending and descending movements and has means for its power actuation to cause rising and lowering of the die; together with a work gripping system or means which includes edge grippers or devices for engaging and holding the opposite ends of the workpiece during the stretching operations, with the die saddle beneath or adjacent the work between such end grippers; a longitudinally shiftable or traveling carriage for at least one and preferably both of said opposite end grippers, each carriage having means for power actuation to shift or retract the carriage and gripper device and to reset the same to initial position; and certain mountings for each gripper device upon its retractible carriage including a tiltable head carrying the gripper device, and means mountin this head to swing up and down upon the carriage thereby to vary or adjust the position or angle of action of the gripper device relatively to the die and workpiece.

For convenience the bar or other blank to be shaped by stretching is indicated by the reference letter B, the interchangeable die or pattern for the work by the reference D and each of the work gripper devices by the letter G.

In Fig. 1 the blank or bar B is shown overlying the die or templet D, in a longitudinal direction, with a gripper G engaged with each end of the bar. The apparatus as a whole may be of a relatively low type, giving clear vision of the operations, which may be controlled manually or Semiautomatically, through hydraulic or electrical operating or controlling means, for example from a control stall or instrument panel 20 at the front of the machine.

The frame comprises a base 2! composed of two heavy I-beams spaced apart and suitably interconnected as by cross walls 22. Associated with the cross wall near each end of the machine is a base or platform 23 for a motor to be described. Attached to the base beams 2| are a pair of opposite upright plates or strips 24 constituting tracks for the carriages to be described. Near the center of the apparatus and secured on top of the longitudinal beams 2i is a heavy base or plate 25 giving support, through bearings 26, to the upright rams or vertically moving plungers 21 which, at their upper ends, carry the saddle or table 28 upon which is mounted and attached the interchangeable die D. While usually the saddle and die may be elevated with a parallel motion, there are cases wherein it is desirable to give thereto a tipp or tilting motion during ascent, permitted by the cross pins or pivots 29 as shown in Fig. 13, the two rams 21 being independently liftable to deliver substantially any desired tipping action of the rising and lowering die. Diagrammatically the die D is shown in Fig. 6 as rising vertically by the ascent of its two rams 21, the latter being shown sliding within hydraulic cylinders 30, the connection and operations of which will be further described.

The traveling or retractible carriages are shown as a left end carriage 3| and a right end carriage 32, these being in longitudinal line with each other and with the central mountings of the saddle and die. The carriages are shown symmetrically arranged and may be alike, each being shown as comprising two upright side plates 33 arranged directly over, so as, to slide upon, the fixed tracks 24. Each carriage may be positively guided upon its tracks by a shouldered construction, the carriage having an upper shoulder 34 which'overlies the track and an under shoulder 35 which underlies the track; the two side plates being rigidly interconnected as by cross bars 36 upon which, as by a flange or plate, is mounted the threaded nut 31 by which the carriage shift is preferably effected, the two carriages being independently operable.

Centrally of the width of the press, arranged to rotate in fixed bearings 38, are a lefthandfeed screw 39 engaging the nut 31 of the left carriage 3|, and driven by motor 40, and a righthand screw 4| engaging the nut of the carriage 32 and driven by a motor 42; the two motors being of reversible type so that the carriages may be shifted or ad- Justed either advancingly or toward the center of the machine or retractingly toward the ends thereof.

As a matter of terminology the "gripper means of the press comprises the opposite gripper devices GG. Each gripper device may include a single gripper G or several, and the term gripper also is used in that sense. The function of the grippers is to grip, i. e. grasp or otherwise engage, the opposite blank ends or edges; and to take part in various operations, including pulling retractingly to stretch the blank, or holding in a given position, or yielding under pulling resistance, and finally ungripping or releasing the shaped blank.

. The mountings and operative movements of the respective grippers upon their carriages may be varied considerably according to the intended stretching and shaping operations; and such movements may serve for adjustment in preparation for a stretching operation, or for adaptation of the location or posture of the gripper during the stretching, as well as for the stretching operation itself. Among particularly advantageous relative movements of each gripper upon its carriage, are, first, a tilting or swinging upwardly and downwardly, by means of a head 45 pivoted upon the carriage, and second, a longitudinal or axial movement of the gripper advancingly and retractingly relatively to the head and therefore relatively to the carriage, bymechanism to be described. A third movement, whether for its mountings upon the head 45. These. various movements, particularly in conjunction with the elevating and lowering of the die and preferably also with the carriage shifting movements make possible a great variety of effective stretchshaping actions.

The uptilting of each gripper device and its head during operation, as the die becomes active, permits the line of action or axial retraction of the gripper to be maintained in longitudinal line with the margin portion of the gripped blank; in other words tangential to the curved or shaped blank, so that the stretching operation involves a simple true pull by the gripper without bending of the margin.

- The tiltable head 45 is shown as a cylindrical member arranged generally longitudinally and formed hollow to serve as a hydraulically operable cylinder as will be described. The cylinder or head 45 is shown trunnioned upon the carriage by means of short axles 46 projecting horizontally from the sides of the cylinder turning within bearings 41 provided on the side walls or plates 33 of the carriage. By this arrangement the inner or proximal end of the cylinder may be swung upwardly and downwardly about the trunnion pivots; and this tilting action may be positively performed, or may be a passive action due to the pull of the workpiece upon the gripper and mountings during shaping operations, while the gripper remains in alinement with the end of the blank to be pulled. The trunnion pivot is so located that the natural tendency is for the gripper to swing down by gravity, for example from its operating position shown in Figs. 1, 14 and 15 to its initial position shown in Figs. 3 and 13; but to avoid too great a gravity force the trunnion may be set ratherwell forward on the cylinder, as shown in Figs. 13 to 15. When the headand gripper tilt downward to starting position a stop means and action may be employed to position them in a definite or horizontal posture, as for example in Fig. 13.

As an operating or controlling means for the tilting upwardly and downwardly of the head 45 and gripper, at each end of the press, there is shown a mechanism comprising primarily, at each side of the carriage, a segment gear 48 attached to each axle 46, each segment meshing with a rack 49 sliding, preferably horizontally, on the carriage adjacent to a side plate 33. By shifting, or controlling the movements of the two racks 49 the tilting of the head may be controlled; and for this purpose there is shown a hydraulic device comprising a plunger 50 movable with or attached to each rack and a barrel or cylinder 5| trated) on the carriage; and this is preferably the position inwhich a straight or flat blank, or bar is loaded horizontally into the press, as in Fig. 13 shown, preparatory tothrusting the die D.. gradua1ly up against the blankbetween the opposite gripper devices to. convert. it from straight to curved form.

The hydraulic principle of control or operation is preferably used extensively in the described press. j In its various places of use the'liquid is marked L, and may represent a thin oil. In Fig. 3 is indicated an oil reservoir or vessel 55 from which liquid may be drawn for the dashpot tilting control; but for this and theseveral other purposes a' common supply of liquid L, and a single reservoir .or vessel 55 may be employed, as shown also in the'hydraulic diagram Fig. .6, wherein the liquid is pumped through certain circuits to effect the lifting and lowering of the die saddle, and othercircuits to'eflect the advance and retraction of the grippers G with relation to the tilting heads 45 on carriages 'II and 32. For closing and opening the grippers in the specific illustration to be described hydraulic action is similarly. employed; but in that case the liquid supplying and pumping means are not shown but will be understood to be on the same general principles as in the cases of the die lifting rams and the gripper retracting cylinders.

The means for eifecting gripperadvancing and retracting movementsQin axial directions, relatively to the tilting head 45' and the workpiece is shown as comprising a hydraulic cylinder carried by the head 45; and in fact .such cylinder may constitute the tilting head. The cylinder comprises the cylinder wall 51 with its ends closed within which the plunger may slide, displacing or displaced by the liquid therein. For. example, the tilt-controlling device thus described may be such as to permit ready upswinging of the gripper as required by the progress of the work but operating as a cushion or dashpot to prevent sudden descent of the gripper and heavy parts associated therewith. A convenient arrangement for'this purpose is shown in Fig. .3 wherein the space within the barrel is arranged in communication witha supply vessel for the liquid or oil L through a check valve 52 permitting downflow from the vessel to the barrel and in parallel therewith a manually adjustable or needle valve 53 permitting return upfiow but at any desirably reduced rate.

When each head with its gripper tilts down to initial or horizontal position, it may be there stopped by a mechanical stop or ledge (not illusby a proximal wall 58 and a distal wall 59. there being a piston 0r ,p1unger 60 movable within the cylinder and having its connecting rod 6| extending through an aperture and packing in the proxi-.- mal end wall 58. The piston rod 6| may be attached to the stem 15 of the gripper to be described or the stem may be a simple continuation of the rod. By this arrangement the gripper can be bodily advanced toward the work or .retracted axially therefrom, under hydraulic control through pipes 7' and kshown in Figs. 1 and 3 comprised in a general hydraulc system as shown in Fig. 6. Thus the axial gripper movements may be variously utilized, for example to bring the gripper into position, and to take up initial slack which may exist in the work between the opposite grippers; and a further utility is that the hydraulic gripper control can function during the actual shapingoperations, either by bodily retraction of gripper to efiect stretching or by axially yielding advance under controlled resistance to maintain a desired pull or tens on on the work during certain stages of operation.

Another action or motion of tive to the carriage that is sometimes desirable is a revolution, part rotation or oscillation about its axis or pulling-line. This is provided by a revolubly mounted guide, bracket or turret 54. turning for example on the extended circular end 58 of the head 45, where its outer flange has a ring 65 attached for confining the revoluble guide upon the head. This ring 65 may be formed with external, teeth for purposes of rotary adjustment, and the ring gear thus constituted is shown as meshing with a pinion 66 mounted upon a fixed extension 81 attached to the proximal end wall 58 of the tilting head. This mechanism may be used operatively, as forgiving a twist to the work, or it may be used for initial adjustment to cone'ach gripper relaform the lateral angle of. the gripper to-the-work, thus to facilitate the initial engagement of the. work in the gripper. For these purposes the pin-ion 66 is shown having a shaft extension 68 with a squared end by which thepinion and" the revoluble guide may be turned as desired. When the guide or turret 64 has been brought to the desired rotated position, the parts may be there locked, for example by means of a locking tooth 69 manually adjustable by means of a locking screw H1, causing the tooth toenter between the two teeth of the pinion 66. andthus. holding the gears and turret against movement.

The described rotary adjustment of the guide,

or turret 64 is communicated to the gripper G by means of a bracketl2 extending axially from the turret and having a pair of guides or tracks I3 between or on which the gripper deviceslidesin its axial movements. As will be clear from Fig. 1 if the gearing 65, '66 be operated to rotate the turret 64 through a given angle, the bracket 12 will compel the gripper to turn with it and assume the same angle, being such; for example as to. facilitate the engagement of the gripper with the end of the workpiece. A further advantage of this arrangement is that the gripper, which is efiectively at the end of the pistonrod, and capable of turning, is prevented from turning and maintained in its true posture throughout the pulling operations. If in certain cases it be desirable to have the gripper free-to turnor twist, as for manually adapting it to the work, this is readily eiTected by turning the lock screw Into remove the lock tooth 69 from engagement with the operating pinion 66. By applying power to the shaft of the pinion an actual twisting action upon the gripper and work may be introduced if desired, in the nature of a torsion.

Describing next the illustrated structure of gripper G, this is shownas having a stem or shank 15 carrying a box or enclosure 16 surround ing a gripper chamber. The box proximal'wall 18, i. e. nearest the center of the press, facing the die D, has an aperture 19 to receive with snug fit the end of the bar to be gripped and stretched, its distal wall 80 being united with the gripper stem 15, shown as a'continuation of piston rod 6|, these parts and the box side walls. 8| being shown in Fig.1 and as well in Figs. 9 to 12.

The gripping means within box 16 and adjacent thereto comprises resilient opposite squeeze members 85 acting upon the workpiece or bar, preferably through rigid jaw members 83; with rigid plungers to compress the squeeze members when operated by pistons working in cylinders under hydraulic actuation. The parts are shown relaxed and the gripper released in Figs. 9 and but are gripping the work, a 'T-bar, in Fig. 11. The proximal gripper chamber wall!!! constitutes a removable cover, as indicated in Fig. 1, and it may be interchanged for different shapes of blank.

In the use of this gripper the blank or bar. to be shaped is manually inserted inthe aperture 19 and thus extended into and across the interior of the gripper box, where it is gripped and held. It is preferable to provide a pair of rigid jaw blocks 83 between which the web of the blank may be directly gripped, these blocks being of sectional shape to fill out the section of the blank into a quadrangle. To avoid having the jaw. blocks loose in the box or attached to the squeeze blocks they are suitably mounted in-a position to be ready for th gripping action. and for convenience this isherein done by attaching or formgripping action. When these parts are so assembled and the blank inserted, the latter is subject to the gripping pressure of the jaw blocks 83bearing on the blank web, while the outer sides of the bar flanges are exposed, as are the edges of its web and flanges, these parts thus being in readiness to receive high clamping pressure adapted. to prevent the bar slipping out of its gripped position.

The active gripping element of the disclosed gripper consists of the rubbery or similarly yieldable squeeze blocks 85. These blocks are located with the jaw blocks and blank between them, and are composed preferably of rubber or other flowable but preferably non-liquid material, so that normally they retain their shape as seen in Fig. 10 but are adapt-ed to b deformed for gripping purposes. Initially, when the blank is'first inserted, there may be empty spaces at both lateral sides of the bar and jaw blocks, as shown; or the squeeze blocks might be initially shaped to 00- cupy partly such spaces.

Beyond the opposite rubbery squeeze blocks 85 are shown a pair of rigid pressure blocks 86,

having a tight sliding fit in the otherwise open top and bottom of the gripper box, thereby to act as compression plungers. The walls of the opposite hydraulic cylinders extend inwardly toward the gripper box walls. with cutaway extensions 81' between which the compressing blocks may slide. toward and from each other. Beyond each of the two plunger blocks, and occupying the full section of each cylinder 11, is a piston 89 working therein and adapted to thrust the adjacent pressure block toward the center or gripping position of the device. For preventing leakage of hy draulic liquid, the outer end of each piston is shown provided with a packing cup 90 upon which bears a washer 9| attached by screw 92 to the piston.

The described assembly of the two cylinders, with gripper box between them, and various interior parts, is completed as a, unitary device by the provision of end pieces or head walls 93 into which the outer ends of the respective cylinders are set, and which end pieces have extensions or lugs to receive longitudinal tie-bolts 94 operating to unify rigidly the entire gripper device. The various fixed parts or walls may be held together by means of the clamping pressure of the end pieces, supplemented if desirable by welding or other attaching means. The perforated wall 18 however is preferably removable for example by being attached to the gripper box by machine bolts as indicated in Fig. 1; thus permitting the interchange of walls and to provide apertures and jaw blocks designed to suit the shape of blank or bartobe operated upon.

The gripper device is completed by the provision of piston operating means. There is shown a liquid chamber 95 between each piston and the adjacent end wall 93. with an entrance passage 95 through such wall having a nipple connection 97 to a supply pipe 98, these being filled with liquid L supplied from any suitable pump or source of pressure. Preferably the two pipes 98 are interconnected with each other and with a common source. so that an equal zing pressure action upon the blank is. produced Thus, the pistons and parts betwe n them may be caused to deliver a high mechanical pressure upon the workpiece, the rubbery blocks 85 gripping the bar in part directly and in part through the jaws 83. Fig. 11 shows how the rubbery masses 85 are caused to flow and become molded about the workbar and jaw blocks under their heavy compression, giving intense and secure friction hold, adapted for the purposes described. In order to permit the various necessary movements of the gripper during operation the liquid supplying pipe 98 should be a flexible connection or hose, such as a thick=walled rubber tube; and the control of the described hydraulic and gripping actions may be manual or under automatic timing.

The gripper 6 thus described is made the subject of a continuation in part, Serial No. 664,925, filed April 25, 1946.

Describing next the general hydraulic means of operation and control, particularly for the lifting and lowering of the rams or plungers 21 of the die and saddle and for the advance and retraction of the opposite grippers, the preferred principles are illustrated in the diagram of Figs. 6, '7 and 8, wherein are shown a reservoir or supply of liquid or oil L, a system of pumps for forcing the liquid around operating circuits, and controlling valves in the conduits by which the liquid advances to the controlled devices and returns to the supply. For convenience the diagram is shown in symmetrical form, with similar hydraulic elements for the operation of each of the two die operating rams and other connections for each of the two cylinder and piston devices which advance and retract the grippers toward and from the central die or templet. For simplicity the diagram omits the connections from the supply reservoir to and from the hydraulic gripper closing and releasing means and to and from the plunger and barrel device for controlling the tilting of the head 45 through which each gripper is mounted upon its traveling carriage; but these devices may. be operated or controlled by generally similar means and in the manner already described.

In describing the diagram the several pieces of apparatus will be designated by the reference numbers li, I02 etc., while the pipes or conduits between them, from the reservoir to the ultimate instruments, the ram cylinders 30 and the gripper cylinders 45, will be designated by the letter references a, b'etc. The pipes leading from the reservoir or toward the ultimate instrument will be termed supply pipes or serving pipes, communicating as they do the operating pressures by advancing flow to such instruments, while the pipes by which the discharges of these circuits are brought back to the reservoir will be termed return pipes or conduits; in some cases the terms uptake and downtake being used, with out intention however of limiting the flow to these directions.

Referring. to the operation of the die rams, these are shown symmetrically placed with respect to the die or saddle, and symmetrical but independent hydraulic connections are preferably provided by which the two rams may be actuated either simultaneously and equally or, on the other hand, differently, for the purposes already explained. With this understanding, for each die ram there is shown a supply or serving pipe a constituting an uptake from the reservoir 55 to the inlet of a force pump IOI; the force pumps II and the other force pumps I25 being preferably continuously and positively acting hydraulic pumps of any conventional structure. From each pump IOI extends a supply pipe 12, constituting the pump outlet, and with which is associated a pressure gage I02 by the aid of which the action of the pump and other instruments may be initially adjusted. The uptake pipe b extends from the pump to a relief valve I03, being a valve which does not restrict through flow but which yields for collateral discharge of liquid either for safety prevention of excess pressure or for predetermining the intensity of pressure which may be communicated to the ram. Thus the valve I03, in the'nature of a regulated bypass, comprises the through duct I04 for normal flow, and a chamber I05 lateral thereto, with a spring pressed gate I06 for closing the passage from the duct to the chamber and an adjuster or screw I01 for predetermining the valve action and thereby the pressure at which the relief or bypassing action occurs. From the valve chamber of the relief valve extends a discharge connection q leading to a general or main return pipe 1 in the form of a downtake delivering into the supply reservoir 5!.

Continuing the hydraulic circuit, the relief valve delivers through pipe 0 to a throttle valve or similar manually adjustable or needle valve I08, of conventional character having an adjusting screw I09 by which the flow resistance can be predetermined in cooperation with the actions of the pump and the relief valve and the elements beyond the throttle valve. These elements lead by way of a supply pipe d to a flow reversing orthree-way valve I I0 which, from a suitable port III is connected with the ram cylinder 30 by a pipe e which at certain times constitutes a supply pipe conducting liquid to the ram to elevate the die,'and at other times a return pipe or downtake for the backflow of liquid and eventual discharge into the reservoir.

The various arrow heads applied to the various pipes show the direction of flow, and in certain cases, as with pipe e, appear oppositely pointing arrows thus indicating flow alternately in both directions, in view of which such pipes may be designated as supply-return pipes or conduits.

The flow-reversing valve IIO may be of known or conventional character, describable as follows. It has the outlet port I II near the right end, already mentioned, and a similar port H2 at the left. The central chamber H3 is constantlysupplied with liquid through the uptake d, and the valve contains also a righthand chamber H4 and a lefthand chamber H5, both of which discharge through ports IIB to a return pipe p leading eventually to the reservoir. The valve stem II! has tandem collars H8 near the right and H9 near the left end of the valve, with a restoring spring means I20 tending to centralize the stem and thus cut off the discharge ports at certain periodsof operation, during which the pumped liquid under pressure must escape through the relief valve I03 to the reservoir unless the pump IOI be shut down at this tir In order'to shift the valve stem rightward proximally and thereby admit pressure liquid to the ram, in the manner illustrated in Fig. 7, there is provided a solenoid I2I which, when energized,-

shifts the stem and starts the operation of lift ing the ram; while at the other end is provided a solenoid I22 tending to move leftwardly or distally the valve stem, to the extreme position shown in Fig. 8. However, since the rams are shown lowered by gravity, and therefore are not double acting, there is no need of a pipe between port H2 and the ram; but the second solenoid I 22 is used to shift leftwardly the valve stem to to prevent escape of liquid. Manifestly if the rains were not arranged for gravity return, or if it were desired to supplement gravity by hydraulic return, the described functionless parts of the valve III) could be placed in action by connecting the lefthand discharge port II2 thereof with the ram cylinder in an opposite sense to the connection of pipe e thereto.

These diagram descriptions apply especially to the parts at the left side of Fig. 6, showing the interiors of elements; but are applicable also to the righthand side if it be borne inmind that the latter is symmetrically opposite in the diagram, so that the descriptions right and left should be reversed therefor,

Referring next to the operations of the gripper advancing and retracting cylinders 45, near the two ends of the press, each having a double acting piston 60 within the cylindrical shell 51 and a piston rod 6| by which the gripper is moved axially toward and from the die and work, each piston and cylinder is shown power-operated in alternate directions by the following means. Associated with each of the two gripper cylinders is, in the first place, an uptake supply pipe I from the liquid reservoir 55 to a, force pump I25. The connections therebeyond may be substantially duplicates for the two sides, but permitting either equal or differential actions of the two cylinders, under manual or automatic control. Describing more particularly the elements at the left side of the diagram of Fig. 6, the pump I25 is connected by uptake 9 with a bypass or relief valve I21, the pipe having a gage I26 similar to the gage I02 Previously mentioned. The valve I21 contains a through duct I28 and a lateral chamber I29, as in the case of thevalve I03 already described, with a spring operated gate I30 adjusted by a screw I3I to determine the pressure at which the liquid is relieved or bypasses through a discharge pipe 11 and via a pipe m to the main return pipe or downtake r.

In the gripper hydraulic cylinder connections a throttle valve is unnecessary, but from the relief valve I21 extends an uptake pipe h leading to a reversing or three-way valve I32 similar to the valve IIO already described, but utilizing all three perative valve positions as shown in Figs. 6, 7 and 8. Thus, each reversing valve I32 is formed with a righthand port I33, leading by pipe 7' to the proximalend of the cylinder 45 so that the flow of liquid thereto causes retraction of the piston and gripper, A similar lefthand port I34 is connected by pipe k with the distal end of the cylinder 45 for causing advancing movement of the piston and gripper. The valve has a central chamber I35, righthand chamber I36 and lefthand chamber I31; the two end chambers having I discharge orts I38 leading to discharge pipe m extended to the main return pipe 1'. The valve stem I39 carries righthand and lefthand collars i40 and MI normally closing the passages between the valve chambers. Centralizing springs I42 tend to restore the valve to its neutral position, a solenoid I43 being shown as an actuating means to shift rightwardly the valve stem and thereby supply pressure liquid to the proximal end of the cylinder 45; while at the other end of the stem is shown a solenoid I44 arranged to 12 cause leftward shift of stem and collars thereby to supply pressure liquid to the distal end of the cylinder 45.

The electrical system may bebriefiy described as comprising circuits extending from a suitable current source to the respective solenoids and motors. Thus, referring to Fig. 6, the solenoid I2I at the left end of the machine, by which the valve I I0 is operated to bring about the rise of the lefthand die ram 21, may be energized by a circuit S, while the corresponding solenoid I2I for the righthand ram may be energized by circuit '1. The solenoids I22 which cause gravity return of the rams are energized respectivelyby circuits S for the left ram and T' for the righthand ram. Coming to the gripper controlling valves I32, the solenoid I43 at the left end, by which each valve I32 is operated to cause the retracting movement of the lefthand gripper G may be energized by circuit U, while the corresponding solenoid I43 for the righthand gripper is energized by a circuit W. The solenoids I44 through which the advancing gripper movements are effected, at th left and right ends of the machine, may be energized respectively by circuits V and X. Referring to Fig. l the iefthand motor 40 for shifting the carriage 3I' rightward and leftward may be energized by a circuit Y and the corresponding motor 42 at the other end by a circuit Z;'it being understood that each of these circuits contains means for causing reverse directions of motor rotation for the purposes already explained. All of these control actions may be effected manually or semi-automatically from the control panel or switchboard 20, through switches or the like, indicated but not shown in detail; it being understood that any given movement, as the elevation of a ram, may be under further or limiting control, as by means of limit devices arranged to break the corresponding circuits at predetermined positions of the controlled elements, as at a desired degree of elevation of a ram. The presetting of the apparatus, as of the relief pressures of the valves I21, may determine the extent of motions, such as the amount of elastic and permanent stretch of the bar being shaped.

As thus far described the pull upon the work is relied upon for the uptilting of the gripper supporting head or cylinder, but this may be obviated by an independent tilting means, such as that shown in Figs. 19 and 20. This consists of a rod I50, or an opposite pair thereof, adjacent to the position of the bar to be shaped, projecting rigidly from each group of tilting parts and adapted to bear and rest down upon the top surface of the die, with the under side of the tilting member or rod approximately in the transverse plane of the axis of the gripper stem and piston rod; or, more exactly, with the rod underside in the same plane with the part or flange of the bar which corresponds with the top surface of the die when the bar is applied to the die. For example each tilter rod is shown fixed upon the removable proximal wall 18 of the gripper box I6. It rides upon the die and as the die rises the rod slides around upon a tangency point which progresses with the progress of the curving of the bar, the rod keeping parallel with the non-curved portions of the bar and meanwhile acting, to tilt up positively the gripper and cylinder in a manner to maintain the axis thereof approximately in line with said point of tangency, and parallel with the uncurved part of the bar held in the gripper.

A typical general operation of the described press may be described as follows. Initially the parts may be as shown in Fig. 13, the blank metal sheet or bar being positioned wholly over the lowered die D, and slightly elevated above its later die-engaging position; and the rams being in their gravity-lowered position. The tilting heads 45 and the grippers rest initially horizontal in the longitudinal sense, and the latter tipped or oscillated to a lateral angle (usually zero) to conform with the position or shape of the particular workpiece or bar. gripper G is preferably in a. given intermediate longitudinal position, that is, with the piston 60 between the ends. of the cylinder 51, as seen in Fig. 6, the controlling valve I32 locking the piston and gripper in this position by reason of the valve being in its middle adjustment. As a part of the previous loading operation the carriages 3|, 32 may have been shifted to present the grippers to the edges or ends of the work, and these ends thus fed into engagement between the jaws of the grippers. and hydraulic pressure then applied through the flexible tubes 98 to cause the closing of the grippers upon the work, in which position the gripper closing parts are then hydraulically locked. The carriages may have been then slightly retracted if this appears necessary to take up any slack in the blank or bar to be stretched or the gripping thereof. This loaded condition of the press is indicated in Fig. 13.

In describing the rising of the die between the grippers as providing the shaping action, this is to be understood as a relative motion since, to less advantage the gripper system could be lowered to the same effect and result.

The blank shaping operation may now be commenced in different ways, as one instance by the elevation of the rams and die against gravity, accomplished by the energizing of the circuits S and T of the valves I IO of the respective rams, bringing about hydraulic pressure and flow through the valves. The commencement of this operation brings the die up into full engagement with the bar, and then starts the bending, an early position being indicated in Fig. 6 and its approximate conclusion in Fig. 14, the stoppage of die elevation being brought about preferably by an automatic limiting device, acting torestore the valve, rather than relying upon manual action and judgment. During the die elevating stage both shaping and longitudinal stretching of the blank occur, as the tilting heads 45 and grippers swing upwardly, thus keeping in proper line with the end portions of the bar being shaped. This stretching may be not merely elastic but beyond the yield point, giving a permanent extension of length as the blank takes its curved shape.

Simultaneously with the tensioning and stretching of the bar as caused by the elevation of the die, or shortly after these actions, the grippers may be caused to retract for further or supplemental stretching and final and positive shaping of the blank to the die. This may be done in different ways, for example by energizing the circuits U and W to admit, through the valves I32, liquid to the proximal ends of the gripper-moving cylinders 45, thus powerfully pulling the grippers from each other and creating the stress necessary to stretch further the bar while shaping it effectively to the die; during which action the distal ends of the cylinders 45 are allowed to discharge their contained liquid through the pipes k, valves I32 and return pipes m and 1'. On the other hand such stretching op- Initially each" eration may be effected by energizing the circuits Y and Z in a manner to retract the carriages upon which are supported the tilting cylinders 45 and grippers; or both of these gripper retracting actions may be performed in the same operation, either simultaneously or successively, and beguneither before or after the completion of the elevation of the die. To minimize frictiona1 obstruction to bar stretching after die elevation-these may be lubricated. In any case the die rams, when they have reached their full predetermined elevation. may each be there stopped by the deenergizing of its two solenoids or the otherwise caused restoration of valve H0 to the central position shown in Fig. 6, which hydraulically locks the ram. This permits any desired supplemental gripper or carriage operations before the valve H0 is reversed for the release and descent of the die. Indeed the die rams may be partly elevated as in Fig. 6 shown and there locked, and thereafter further elevated, in case of operation with two stages of die lift.

After the completion of the stretch-shaping operations-described, or others to be described, the work may be released and removed as follows. The grippers are first relaxed by releasing the hydraulic pressure supplied by the flexible tubes 98, upon which the tilting heads 45 and the grippers may commence to swing back down to initial position, but at a slow rate due to the dashpot action of the connected plunger 50 as already described. By backtracking the carriages through the circuits Y and Z'and permitting the slow gravity descent of the die by reversing the switches III] the completed work is made readily accessible for removal from the press. If the tilter rods I 50 are used, as seen in Figs. 19 and 20, the down-swing of the gripper heads will accompany the descent of the dies unless the carriages be retracted, in which case the dashpots 50, 5| function. Before opening the grippers to let go of the blank, it is best first to reverse the valves I32 and so relax the existing pull and tension.

A desirable special method of stretch-shaping certain forms of blank, including elongated bars such as shown in the drawing, can be by the disclosed press carried out as follows. After loading the press as shown in full lines in Fig. 13, the workpiece B is first not merely tensioned but permanently stretched and kept under high gripper pull while yet substantially straight or horizontal, as shown in dotted lines, this stress being somewhat beyond the yield point of the bar, and its degree being dependent upon the shape and properties of the bar and the radius of curvature it is to receive; following which the die is lifted against the so-stretched bar while the latter is maintained under the pulling stress by which it was stretched; the bar thus nicely taking its curvature by increments while under a pull which elongates its convex side inch by inch without allowing compressing or wrinkling of its concave side. As the straight bar is progressively rolled or curved around the convexity of the die these actions progress, gradually from the center toward the ends, with a coordination that necessarily results in a perfectly shaped product, of substantially its original section at every point, but slightly attenuated at its tension or upper side, and unweakened by any wrinkled or crumpled result at any portion. The continuous pumping action described is necessary to ensure maintaining the high pulling stress in the workpiece during bending to overcome the pos- 15 sibility of pressure loss by leakage through valves, joints and packings.

This special method under description is therefore a two-stage one in that preliminary stretching or extension is first performed while the blank is substantially straight, and then the curving of the blank, while yet under the high stress, around the convexity of the die as the latter rises. In the second stage the central rams force the saddle and die to ascend to a predetermined elevation and stop there, this causing the upswinging of the tilting heads 45 and grippers, the carriages 3| and 32 being preferably stationary at this time. Thus, while the bar becomes curved generally to the shape shown in Fig. 14 it is maintained under its intense longitudinal stress, which has already caused substantial stretching; this pull being beyond the yield point but short of the ultimate stress point ofthe bar, whatever the metal may be, aluminum alloy or steel, of which it is composed. By this second-stage action there is provided an effective additional stretching substantially limited to the convex or tension side of the blank, that is, along its top portion, above its neutral axis; while on the other hand the maintained pull precludes the possibility of there being any substantial compressive stress, that is, in the lower portion 'or zone of the bar, wherefore the often encountered difficulty of wrinkling and buckling of a shape being bent is wholly obviated.

For the special operation being described the parts initially are set with the gripper-moving piston 60 well retracted toward, but not to, the outer or distal end of the cylinder 45, at each side, as seen in Fig. 6. Now in the first stage, as the full hydraulic pressure is admitted to the cylinders 45, the grippers retract and create tensile pull, the plan being to place the blank under a strain intensity substantially between the yield stress and the ultimate stress of the material of the blank, but preferably nearer to and slightly beyond its yield point, and to maintain throughout both stages of the shaping operation substantially this predetermined tensile stress, thus overcoming the elastic resistance and causing a degree of permanent'bodily stretching of the blank.

This method can be brought about by means of the apparatus disclosed, including the elements shown in the diagram of Fig. 6. For the first stage or step, the stretching of the straight blank from the full line to the dotted position of of Fig. 13, the valves I32 are thrown to their second position shown in Fig. 7 wherein the liquid pressure from the pumps I25 has access through the valves to the proximal ends of the grippermoving cylinders. This liquid pressure tends to retract the'pistons and grippers, and the stress so produced is suificient to exceed the yield point and to stretch and extend the blank. Moreover, this hydaulic pull upon the grippers continues and furnishes the needed resistance to maintain the prerequisite tension during the second stage or shaping operation by the lift of the die, and thereby, in the manner already stated, permits a differential deformation with stretching at the outer or upper zone of the bar while obviating the tendency to compression and wrinkling of the metal at the lower zone of the bar.

To explain further this action, the hydraulic pulling pressure is furnished by the pumps I 25 only in cooperation with the relief or bypass valves I21 which, as explained, are pressure limiting or predetermining valves, initially adjustable by the screws I3I to any predetermined pres sure. These valves I21 being set to release liquid and relieve pressure only at a certain high point of pressure, they will determine the resistance of the hydraulic connections to the pulling inward or toward each other of the pistons 60 due to the second stage stress caused by the rise of the die. As the parts pass from the Fig. 13 dotted position to the Fig. 14 position the grippers therefore are drawn inwardly, toward each other, and away from their cylinders 45, as comparison of these figures shows, and this action is permitted because as the pistons 60 so yield they are able to force the liquid back through the pipes 7' and through valves I32, set to the Fig. 7 position, and thence through pipes h to the relief valves I21, the gates of which open slightly but sufliciently to bypass some liquid out from the valves through the discharge pipes n and m to the general return pipe 1' which leadsback to the liquid reservoir; while liquid rising frompumps I25 is discharged by the sam route, In this way the grippers at the two ends of the machine may yield axially during the longitudinal pulling of the bar caused by the rise of the die, whereas the high degree of resistance determined by the adjustment of the relief valves works in cooperation with the rise of the die, as described, to govern the second-stage stretching and shaping action and prevent wrinkling or other undesired distortion of the bar. The liquid in each cylinder 45 beyond the piston causes no interfering resistance since in the second or Fig. '7 position of valve I32 this space is in open communication through pipe 70, valve chamber I31 and pipes m and 1 with the oil tank 55.

By the method thus described the entire stretch-shaping of the blank may sometimes be performed by reason of the initial straight stretching by the grippers followed by the power lifting of the die in coordination with the hydraulic resistance and yield of the grippers, such resistance predetermining the degree of tensile pull on the blank, and the extent of the lift determining the extent of blank stretching and shaping. However it is sometimes advantageous, after halting the die lift at a predetermined point, to perform a supplemental stretching and shaping through the action of the gripper mountings or of the carriages or both.

Describing in further detail the special method, the conditions and actions may be predetermined on the following principles. Assuming the use of a given strong aluminum alloy the properties of this metal will be known, particularly its tensile yield point and ultimate tensile strength, and its elongation, at the yield point; as well as its compressive properties. Also will be known the sectional dimensions, shape and area of the blank or bar and its length between grippers. From these factors the optimum adjustments and stresses may be calculated.

Thus, from the sectional area may be obtained by multiplication the total stress corresponding to the yield point and that corresponding to the ultimate strength of the bar; and therefrom is calculable in pounds th force or pull needed to produce a total stress suitably between these, preferably nearer to the yield point stress. Knowing the effective area in square inches of each piston 60 at its rod or proximal side, the desired liquid pressure in'pounds per square inch is obtained by simple division. Each pump I25 must be capable of delivering and maintaining with continuous flow a pressure in excess of such predetermined pressure; while the bypass or reper-thrusting or resisting liquid pressure to a' predetermined pressure corresponding with a pulling stress somewhat above the yield point but well below the ultimate strength or rupture point of the blank or bar. These principles being thus explained it is deemed unnecessary to give a specific example by figures based on the particular alloy used and blank to be shaped.

Having thus set the regulating or relief valves I21 for the desired resisting pressure, and the 3-position valves I32 being in first or mid-position, with ports closed, the pumps I25 may be started in operation; their delivered pressure being that determined by the pressure regulating valves I21, as set by the adjuster screws [3! beating upon the ball or gate I30. Now, through circuits U and W the solenoids I43 may be energized to shift each of the valves I32 to its second or Fig. 7 position, which allows the preset liquid pressure to reach the proximal or rod side of each piston 60, tending to retract the piston; while at the same time allowing outflow of liquid from the cylinder 45 at the other or distal side of the piston back to the liquid reservoir, or, depending upon the piston movements, allowing inflow to the cylinder by suction produced by a yielding I advance of the piston. In this stage the blank in its initial position of Fig. 13 is put under symmetrical pull at its ends, thus coming under full tension and being straightened and then appreciably stretched, the stretch being limited to that which corresponds to the intensity of the tensile stress, for example, to the dotted position of Fig. 13.

Next is caused the power lift of the die or templet D by its rams through the action of the valves H0, shifted to their second or Fig. 7 positions by solenoids I2i energized by circuits S and T; the speed of rise being desirably slowed by the restricting action of the flow regulating or needle valves I08. The die rise, from the initial to the Fig. 14 position, is to a predetermined distance, causing the blank while under its high existing tension to be convexly stretched and shaped or wrapped around the contour of the die. As the gripper-moving cylinders 45 tilt' upwardly during this action their pistons are pulled toward the die, yielding to a substantial extent, as shown by Fig. 14, while remaining under the full predetermined liquid pressure; the displaced liquid flowing back through the valves i 32 and out by the escape valves 121 and back to the reservoir.

By these actions, as the die lifts, it extends and curves the blank, while the high resisting pull of the hydraulic cylinders 45 causes a substantial stretching of the upper, convex or tension side of the blank sufllcient to obviate appreciable compressing or wrinkling of the lower, concave or compression side. An attempt to curve the blank to the shape of the die without such control tends not only to tension and stretch the convex, but to compress and wrinkle the concave, side or zone of the blank; whereas by utilizing the described high continuous pull during the curving action this serves to accentuate the stretching of the tension portion while neutralizing or offsetting the compressing of the compression'portion of the bar or blank. In other words, by applying the longitudinal pulling or stretching factor during the lateral curving or 18 shaping action, aproduct is afforded of uniform freedom from the weaknesses of wrinkling or similar deformations. In effect, the strong pull of the grippers, preferably but not always necessarily above the yield point of the shape being curved, shiftsthe neutral axis or plane of the blank toward or nearlyto the compressionor lower 'face; so that the transverse deformation ,or bending is accompanied by unobjectionable longitudinal deformation or extension at the convex or tension side, with a slight reduction of sectional area, but is free of objectionable compression side.

force determined by the pressure-limiting valves I21 be suflicient bodily to elongate somewhat the press'ive deformation at the concave or. com- As explained, is preferred that the pulling bar, as when in its straight condition of Fig. 13. tensioning itbeyond the elastic limit of the material and beyond the yield point to afford permanent setting thereof. An. important feature lies in the permanent deformationror setting of the tension side only, during the operation of the die. This maybe attained by predetermining a pulling force approximately at and not appreciably exceeding the yield point, being therefore through the grippers, insuflicient to stretch the entire area of theblank, but sufllcient during the curving action to stretch the tension side thereof.

, If supplemental stretching is desired after the bending thiscan be done by now tightening the relief valve I21 to provide a higher liquid pressure for the purpose; for example, after the die has risen to its Fig. 14 position, a final or supplemental stretch can-be produced by the more forcible gripper pull upon the ends of the bar, limited for example to the lineal extent shown in Fig. 15, sometimes tending better to set the shaped blank. Such a bodily-stretching increased gri per pull could be applied'before the die-lift,

or during'it; with due provision, as by pressure limit or lineal limit, to prevent undue attenuation or approach to rupture of the shape. The described apparatus, readilyprovides these vari- Sometimes, as with greater. convexity of final shape of blank, when its two ends are to be brought approximately to right angles, to each other, or to a sharper angle, special provisions or steps may benecessary; obviously witha very convex die the steps as shown in Figs. 13 to 15 would have to be modified. Thus, if the die has to be raised considerably further than as described, or the pistons 60 become pulled to the limits of their movements within the cylinders 45, it may be impossible to shape the blank completely to the die without bodily shifting the gripper mountings, including the carriages 3| and 32, toward each other. The series ofdiagrams Figs. 16, 1,7 and 18 illustrate the nature of these conditions, the die being extremely rounded and thus having to'be raised unusually high from the initial position of Fig. 16 to the later positionof Fig. 17, at which the blank has not yet been conformed to the entire length of the die curvature. At about this stage therefore the traveling carriages are brought into action as by energizing their circuits Y and Z, their motors 40 and 42 operating through screws 39 and H to cause the inward movements of the carriages and carried parts, including the tilting cylinders l5 and grippers G, toward the center of the press,

for example to a position corresponding to that indicated in Fig. 18. This operation is readily performed by the described press by reason of the retractible mounting of the grippers on the tiltable heads or cylinders 45; so that between the positions of Figs. 1'7 and 18, as the carriages and mountings are moved toward the center, the grippers may be correspondingly retracted, while under the full resisting or pulling pressure of the liquid, so that control of the shaping operation, and prevention of wrinkling are maintained throughout the shaping about such a convex die. While the action shown in Figs. 16 to 18 is thus described as the completing of the lift of the die before the inward shifting of the grippers and mountings, manifestly such inward shifting might be commenced before the die has reached its topmost position, and in that case the carriages, the tilting cylinders, the grippers and the die may all be functioning actively at the same time.

Referring further to the lifting of the die, which may be either with a parallel or with a tipping movement, the introduction of the pressure regulating valves I 03 may function more for the protection of the pumps and other parts of apparatus than in the actual lifting, these valves limiting the liquid pressure while the valves I08 limit the rate of liquid flow, thereby to afford gradual and slow rate of rise of the rams and die, as is desirable. The valves )8 actas adjustable orifices, slowing down the liquid flow from the pumps, the surplus being bypassed through the valves I03. For the return descent of the die the solenoid I22 may be energized by the circuits 8' and T, thus causing the I valve stems to shift completely leftward, to the Fig. 8 position, permitting downflow of liquid through pipe e, valve H0. and pipes p and r to the reservoir 55.

It should be stated that the pulling cylinders 45 may be operated in different ways relatively to each other, to retract the respective grippers either simultaneously or successively as might be desirable with certain assymetrical shapes of die or blank; and relatively different operations of the two die rams 21 may be cooperatively employed for a similar purpose. In case there is a tendency of the blank to shift longitudinally under any unbalance in the strengths of pull at its opposite edges, this in some cases may be unobiectionable; but in other cases can be prevented by frictional holding or clamping of the blank near the die center; or the steady positioning Of the opposite gripper devices can be assured by a simple arrangement of feelers therefor, acting through the hydraulic or mechanical trains to offset and restore any displacement tendency. In some instances the two carriages 3i and 32 may desirably be differently operated; and each may have a mechanically controlled limit switch to predetermine its extent of motion and point of stoppage; and when either carriage motor is stopped this effects locking of the carriage since its driving nut 31 is incapable of turning its driving worm or feed screw 39 or 4|.

There have thus been described, in several modifications, methods of stretch-shaping metal blanks or the like and power machines or presses therefor, embodying the principles and attaining the objects and advantages of the invention; and since various matters of combination, arrangement, construction and action may be variously modified without departing from such principles it is not intended to limit the invention to such matters except to the extent set forth in the claims.

What is claimed is:

1. A stretch-shaping power press for curving a substantially straight metal bar by conforming it to a given convex die, comprising opposite gripper devices adapted to grasp the opposite ends of the bar and having power means for actuating the gripper devices to impose tension on the blank during stretching and shaping operations, mountings for each gripper device including a tiltable' head mounted to tilt up and down to vary the position of the gripper device, and a gripper stem siidable longitudinally with the gripper on the head; and power actuating means for applying to the stern and gripper a pulling force to tension and stretch the blank; there being a guiding bracket rotatable on the head and adapted to guide the gripper in its shifting movements while permitting it to turn bodily for adapting itself to or performing a twisting operation upon the bar.

2. A stretch-shaping press for shaping or curving a metal blank or bar by conforming it to a given convex die, comprising, in combination with a saddle supporting the die and fitted for rising and return movements and having power means for actuation thereof; blank gripping means including opposite grippers adapted to grasp the opposite extremities of the blank and having power means for actuating the gripper devices to impose tension on the blank during stretching and shaping operations, supports for said opposite blank gripper devices, mountings for each gripper device on its support, including a tiltable head mounted to tilt up and down to vary tlie position of the gripper device relatively to the die and blank, thereby to aline the gripper device to the blank, and a control connection other than the blank itself and operated by the relative rise of the die acting to tilt up the head and gripper and maintain such alinement.

3. A press as in claim 2 and wherein the control connection consists of a rod extension from the head resting upon the die.

4. A stretch-shaping press for shaping or curving a metal blank or bar by conforming it to a given convex die, comprising, in combination with a saddle supporting the die and fitted for rising and return movements and having power means for actuation thereof; blank gripping means including opposite grippers adapted to grasp th opposite extremities of the blank and having power means for actuating the gripper devices to impose tension on the blank during stretching and shaping operations, supports for said opposite blank gripper devices, mountings for each gripper device on its support, including a tlitable head mounted to tilt up and down to vary the position of the gripper device relatively to the die and blank, the head being trunnioned on its carriage to tilt up and down, and having a segment and rack connection, with cushion means, to prevent abrupt descent of head and gripper.

5. A power press for stretch-shaping m'etal blanks or bars comprisin opposite blank engaging grippers each mounted shiftably upon a head and such head comprising a hydraulic cylinder with piston the stem of which carries the gripper, adapted to apply pulling force upon the gripper and blank; and a hydraulic system comprising a liquid reservoir with supply conduits extending therefrom to said cylinders, high-pressure pumpmeans adapted to be run continuously to force liquid through such conduits, a presettable relief valve adapted by release and bypassing of excess pumped liquid to maintain a predetermined pressure in each conduit during operation on'the its support to tilt upwardly with the gripper durs ing shaping, said head comprising a hydraulic cylinder with piston the stem of which carries the gripper, adapted to apply pulling force upon the gripper and blank; and a hydraulic system comprising a liquid reservoir with supply conduits extending therefrom to said cylinders, high-pressure pump-means adapted to be run continuously to force liquid througheach of such conduits, having presettable relief valves adapted by disvcharge of excess pumped liquid to maintain a predetermined pressure in each conduit, and for each cylinder a reversible main valve between the relief valve and cylinder for directing the liquid to or from the cylinder at suitable times; whereby the gripped blank may be placed under a predetermined tension and maintained thereunder while the grippers tilt and yield toward each other during the shaping of the blank by the thrust of the die.

7. A press as in claim 6 with connections for control of valves from a control point comprising actuating solenoids for the valves, electric circuits and control switches; whereby theorder and timing of operations may be determined for the die and grippers.

8. A power press for stretch-shaping metal blanks-or bars to a predetermined pattern of the kind having opposite blank engaging grippers and between them a shaping die mounted to be lifted and thrust against the blank; said press comprising a hydraulic ram for lifting the die to shape the gripped blank; and a hydraulic system comprising a liquid reservoir with supply conduit.

extending therefrom to said ram, a high-pressure force pump adapted to force liquid through such conduit, the conduit having a relief valve adapted by discharge of excess pumped liquid to maintain a predetermined pressure in the conduit, a reversible main valve between the relief valve and ram adapted for directing the liquid to or cutting it off from the ram, and throttle means between the relief valve and ram adapted to predetermine the liquid flow rate and thereby the speed of lift of the die. r

9. A. power press for stretch-shaping metal blanks or bars to a predetermined pattern of the kind having opposite blank engaging grippers and between them a shaping die mounted to be relatively lifted and thrust against the blank; at least one of said grippers being shiftably supported and operated by a hydraulic device or cylinder and piston the movable member of which carries the gripper and adapted to apply pulling force upon the gripper and blank; and a hydraulic actuating system comprising a'conduit extending from a liquid supply to said cylinder, a continuously operable pump adapted to force liquid in said conduit toward the cylinder, a main valve between the pump and cylinder adapted to direct the pumped liquid to the cylinder or cut 22. it ofi'therefrom, according to the operations to be performed; and a relief valvebetween the pump and main valve adapted by releasing and bypassing excess pumped liquid to maintain a preadjusted predetermined liquid pressure in the conduit and.cylinder; whereby the gripped blank may be maintained under a predetermined pulling and resisting tension during the shaping of the -blank by the relative thrust of the die.

-10. A press'as in claim 9 and wherein from ports of the main valve extend two flexible con- -duitsto the respective ends of the cylinder, and

the valve has two operating positions, in the first of which pressure liquid is supplied to the proximal end of the cylinder to produce pull on the gripper stem while the liquid in the distal end flows back through the valve, and in the second of which the liquid is-supplied to the distal end while the liquid in the proximal end flows back.

11. A press as in claim 9 and wherein the main valve has a locking position and at least one displaced operating position, with yielding spring means to restore it normally to locking position wherein the cylinder and piston are locked against shift; and an electrically operable device adapted to displace the valve when energized, with a revance mote control switch for such device.

12. A stretch-shaping power press for curving a metal blank or bar to conform to the shape of a convex die, comprising, in combination with a frame and a movable support for the die mounted on the frame for rising and return die movements; opposite carriages longitudinally movable on the frame relatively toward and from each other with the die support positioned between them; a gripper-carrying head mounted on each carriage to tilt upwardly and downwardly for variation of theangular relation of the head and carried gripper device to the die and blank during operation of the die; longitudinally opposite gripper devices adapted to grip the opposite edges of. the'blank to take part in pulling upon and tensioning the blank, each of said gripper devices having a gripper stem which is mounted on the'tilting head'to retract and adlongitudinally thereon; die actuating means power operable to lift said support to thrust the die against the blank to take part in shaping the blank while edge-held between said gripper devices, and power operable gripper actuating means separate from the die actuating means and including an actuating device on each of said heads adapted to apply pulling force upon the gripper stem thereby to actuate the gripper device and apply stretching tension to the blank;

said separate die actuatinglmeans and gripper actuating means being independently power operable for selectively predetermined relative actuation, of the die and the gripper devices to cooperate'in the stretch-shaping of the blank.

13. A stretch-shaping press as in claim 12 and wherein each head is trunnioned on its carriageto tilt upwardly freely with the rising of the die to maintain alignment of the gripper and blank during stretch-shaping; and the actuating device on each head is a hydraulic motor'or cylinder and piston and operable to pull the stem and gripper and tension the blank. 14. A stretch-shaping press as in claim 12 and wherein the gripper actuating means is provided with a yielding element adapted to slip above a predetermined resistance and blank tension, and tomaintain such predetermined resistance 'andtension thereby to maintain a pre- 23 determined stretching stress in the blank during shaping thereof.

15. A stretch-shaping power press adapted for curving a metal blank to conform to a convex die, comprising, in combination with a frame and a, central die support mounted thereon for relatively rising and return die movements; opposite carriage members mounted for longitudinal shift along the frame relatively toward and from each other with the die support located between them; a gripper-carrying head member mounted on each carriage member to tilt upwardly and downwardly for adaptation of the tilt of the carried gripper device to the die and blank during operation; longitudinally opposite gripper devices adapted to grip the opposite edges of the blank and actuable to take part in the stretching and shaping thereof, each thereof having a stem which is mounted on the tiltable head member to retract and advance longitudinally; and for each gripper device, means associated with one of said carriage or head members to exert stretching tension through such gripper device to the blank; and die actuating means power operable independently of the actuation of the gripper devices to lift said support to thrust the die against the blank to take part in stretching and shaping the blank while edge-held between said gripper devices.

16. A stretch-shaping power press adapted for curving a metal blank to conform to a convex die, comprising, in combination with a frame and a central die support mounted thereon forrelatively rising and return die movements; opposite carriage members mounted for longitudinal shift along the frame relatively toward and from each other with the die support located between them; a gripper-carrying head member mounted on'each carriage member to tilt upwardly and downwardly for adaptation of the tilt of the carried gripper device to the die and blank during operation; longitudinally opposite gripper devices adapted to grip the opposite edges of the blank and to take part in the stretching and shaping thereof, each thereof having a stern which is mounted on the tiltable head member to retract and advance longitudinally; and for each gripper device a hydraulic cylinder and piston associated with one of said members to exert stretching tension through such gripper device to the blank, together with self-acting means to control and maintain a steady or predetermined tension and stress in the blank during shaping comprising a slipping element associated with said cylinder and piston and adapted to yield under excess stress to permit relative approach of the heads and grippers and vice versa; and die actuating means power operable independently of the actuation of the gripper devices to lift said support to thrust the die against the blank to take part in stretching and shaping the blank while edge-held between said gripper devices.

17. A stretch-shaping power press adapted for curving a metal blank to conform to a convex die, comprising, in combination with a frame and a central die support mounted thereon for relatively rising and return die movements; opposite carriage members mounted for longitudinal shift along the frame relatively toward and from each other with the die support located between them; a gripper-carrying head member mounted on each carriage member to tilt upwardly and clownwardly for adaptation of the tilt of the carried gripper device to the die and blank during opereration; longitudinally opposite gripper devices adapted to grip the opposite edges of the blank to take part in the stretching and shaping thereof, each thereof having astem which is mounted on the tiltable head member to retract and advance longitudinally, the stem, the head member and the carriage member being in train; and

for each gripper device a hydraulic actuating means including a hydraulic couple associated with one of the members in said train to exert stretching tension through such gripper device to the blank; together with a self-acting control means to limit the stress to a predetermined tension in the blank comprising a hydraulic relief element in said hydraulic actuating means adapted to release liquid with excess pressure produced by excess tension and so relieve such pressure and stress; and die actuating means power operable independently of the actuation of the gripper devices to lift said support to thrust the die against the blank to take part in stretching and shaping the blank while edgeheld between said gripper devices.

18. A power press for stretch-shaping metal blanks or bars comprising opposite blank engaging grippers each mounted shiftably upon a head and such head comprising a tiltable hydraulic cylinder with piston the stem of which carries the gripper, adapted to exert pulling force upon the gripper and blank; and a presettable relief valve in communication with said cylinder of the kind adapted by automatic release and bypassing of liquid at and above the preset pressure to maintain a predetermined pressure and stretching pull during operation on the blank.

19. A power press for stretch-shaping metal blanks or bars to a predetermined pattern of the kind having opposite blank engaging grippers and between them a shaping die mounted to be lifted and thrust against the blank; said press comprising a hydraulic cylinder with piston for lifting the die to shape the gripped blank; at least one of said gripper being mounted shiftably upon a head and such head being mounted upon its support to tilt upwardly with the gripper during shaping, said head comprising a hydraulic cylinder with piston the stem of which carries the gripper, adapted to exert pulling force upon the gripper and blank; and a hydraulic system comprising presettable relief valves each adapted by discharge of excess liquid to maintain a predetermined pressure; whereby the gripped blank may be placed under a predetermined tension and maintained thereunder while the grippers tilt and yield toward each other during the shaping of the blank by the thrust of the die.

20. A power press for stretch-shaping metal blanks or bars to a predetermined pattern of the kind having opposite blank engaging grippers and between them a shaping die mounted to be relatively lifted and thrust against the blank: at least one of said grippers being operated by a hydraulic cylinder and piston the movable member of which is adapted during the stretching operation to exert tensioning force upon the gripper and blank; and a hydraulic actuating system comprising a conduit extending from a liquid supply to said cylinder, 0. pump adapted to force liquid at high pressure in saidiconduit toward the cylinder, a main valve between the pump and cylinder adapted to direct the pumped liquid to the cylinder or cut it off therefrom, ac cording to the operations to be performed. and a self-acting relief valve in communication with the cylinder of the kind adapted by releasing REFERENCES CITED The following references are of record in the tile of this patent:

UNITED STATES PATENTS Number Name Date 2,269,549 Oeckl Jan. 13, 1942 2,279,964 Berliner Apr. 14, 1942 2,327,440 Maize Aug. 24, 1943 2,357,027 Seifrled Aug. 29, 1944 2,301,960 Lermont et a1. Nov. 17, 1942 2,326,470 Lermont et al Aug. 10, 1943 1,461,471 Bancroft July 10, 1923 Number Name Date Kellogg Apr. 23, 1929 Bailey July 31, 1934 Longren July 2, 1935 Kuhner Sept. 13, 1938 McMillin et a1. July 14, 1942 Summers Feb. 22, 1944 Flowers Apr. 11, 1944 Seifried Mar. 13, 1945 Lermont et a1 June 19, 1945 Wright Mar. 7, 1876 Atwood Apr. 19, 1904 Oeckl July 12, 1938 Quensenbery Aug. 3, 1915 Fawcett June 6, 1916 Cole May 17, 1932 Baxendaie Oct. 21, 1941 McNeil June 9, 1936 Montuori Feb. 24, 1931 Robertson Nov. 18, 1913 Salzmann June 17, 1941 Artz Sept. 16, 1919 Brooks et a1. Oct. 22, 1940 Amiot Aug. 11, 1942

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