[1]la, 39459@025 United States Patetit Office ]Patented Aug. 5, 1969 2 properly and consistently with asymmetrical drawing dies and dliplicate repeatedly the shape and overall dimensions of the formed, but untrimme d, sheet of stock. The linka,-es connect ed the carriers to the elevator s, and the elevators and carriers insured that the heads would remain substantially parallel to their starting or loading positions. This assured that the heads could approach very closely the ends of the dies, thus reducing the length of the sheet required for a given part or group of parts. 10 Applicati on Ser. No. 608,669, d;sclose s a structur e from WI-,ich the elevator s are eliminat ed and, instead, the stretch heads are both support ed and guided along precise paths and maintain ed in paralleli sm with their loading positions during the stretch drawing operatio n by 15 means of head supporti ng parallelo gram linkages of which the pivotal axes at one end of the linkages of each head are in fixed relation to the male die and at the other are in fixed relation to the associated head. The intersections of the pivotal axes of the pairs of links of a given parallel20 ogram linkage with a plane normal to these axes, define a parallelo ,-ram. Such a parallelo gram linkage supports the associat ed bead and maintain s it parallel to its ori,-Inal startin.- or loading position during operatio n and constrai ns the head to follow precisel y its proper pre25 determi ned path invariabl y. This structu re is particu larly useful for high speed produ ction of autom obile body parts in that, among other things, it permit s the grippi ng jaws to appro ach substa ntially to the end limits of the die in the tensio ning dimen30 sion so that very little metal is wasted in trim. Howe ver, in conne ction with airplan e parts, quite often a substa ntial amoun t of metal exten ds beyon d the end limits of the die. Also, the metals used for airplan es and rocket s do not lend thems elves to abrupt bends. In such 35 cases the margin of the sheet of metal gripped between the stretch head jaws and the contiuous portion of the sheet of metal between the end of the die should be a continuous stirface free from abrupt folds and bends. 40 General ly, this requires that the gripped margin extend tangenti ally relative to the end of the fornting surface of the die at the end of the forming operatio n. It has been found that this effect can be obtain ed by use of nonparalle lo,-ram quadri lateral linkag es, as to 45 each of which the axes define a quadrilat eral at least one side of which is of a length different from the length of the side opposite to it. Thus the quadrilat eral is either a trapeziu m or a trapezoi d. Such linkages not only cause the heads to follow the general path desired for the par50 ticular forming operatio n as in the above applicati on, but they also can be selected to impose on the head controlled rockin.- movements about axes parallel to the linkage axes to various tilted positions, relative to the starting 55 posil@io n, in which 'the stock between the end of the die and also that portion of the stock gripped by the jaws of Lhe stretch head - will form a continuo us surface tangent to the forming die surface at the instantae ous point of tangenc y of the stock already in contact with the forming 60 surface of the die. Also, in some cases, it is desirabl e to bow the sheet upwardl y when loading it into the jaws, so that it assumes the shape of an arch and become s selfsupp orting against downwa rd saging. The Iiiiks can be chosen so that the position of t'he heads for loading is 65 one in which the jaw throats slope upwardl y inwardly endwise of the die toward their upper ends, and can readily be loaded with the sheet in arched condition. Also, when desired, the heads can be thus rocked to maintain the tangency at preselected portions of their paths of 70 travel and selected nontangent relations at other portions of their path. 3,459,025 STRETCHING FIXTURE WITH QUADRILATERAL LINKAGE CONTROL OF STRETCH HEAD MOVEMENTS Cyril John Bath, Chagrin Falls, Ohio, assignor to Th-Cyril Bath Company, Cleveland, Ohio, a corporation of Ohio Filed Dec. 7, 1967, Ser. No. 688,794 Int. Cl. B21d 11102; B21j 9118 U.S. Cl. 72-296 10 Claims ABSTRACT OF TI-IE DISCLOSURE The stretching fixture of this invention is used in stretching sheet metal stock in one dimension by means of stretch heads which are caused to grip two opposite mar@ins of a sheet of stock and then are moved in predetermined paths such that they stretch the sheet in said dimension and wrap it about the convex forming face of a male die. The path of each head is predetermined by a plurality of identical quadrilateral linkages which are shown as alined with each other transversely of the tensioning dimension with their pivots at their corresponding apices coax,@al. Each linkage has its pivolal axis at is inboard end in fixed position relative to the die and its pivotal axis at its outboard end in fixed position relative to the head. Each link is of fixed length. The specific improvement is that, as to each quadrilateral linka,-e of the same head, at least one link is of a different length than the link opposite it, whereby the associated head is caused to rock relative to its starting or loading position about axes parallel to said pivotal axes as it is moved along its predetermined path. The axes of each quadrilateral linkage, therefore, definc either a trapezoid or a trapezilim, as distinguished from a parallelogram. This invention relates to a stretching fixture and combination thereof with a drawing die press, and is an improvement on the inventions disclosed in the U.S. patent of Robert A. Mackenzie, No. 3,314,269, issued Apr. 18, 1967, entitled Prestretch Fixture and Combination Thereof with Drawin.- Die Press, and in the application of Cyril J. Bath et al., Ser. No. 608,669, fil-.d Jan. 11, 1967, and entitled Stretch 'vvrapping Fixture and Combination Thereof with Drawing Dies and Press. In the above-entitled patent there in disclosed a conventional draw press employing complemer@tary drawing dies combined with stock grippin- stretch heads. The stretch heads are moi-,nted on carriers which are movably connected to elevators and which support the heads for horizontal movement, relative to supporting elevators, toward and away from each other for tensionirg the stock. The elevators, in tum, are mou-@ited on a frame for vertical sliding movement and are power driven by hydraulic piston and cylinder assemb'a,es or other means for lowcring and raising the carriers, and thereby the heads. The heads are moved relative to the elevators, during lowering of theelevators, by rigid links so as to tension the stock to its yield point. The combined action of the links and elevators causes tlie heads to wrap the tensioned stock about the male die for stretch forming, or preparatory to stretch drawin, the stock to final shape, as the case may be. The head @ s are maintained in substantiil pa rallelism with their starting position at all times. With the pivot points of the links located in proper position relative to the dies and to the heads of their carriages, the heads can be caused to follow precise preselected paths r--peatedly such that the heads cooperate
[2]3 3,459,025 4 Specific objects @and advantages of the invention will become apparent from the following description wherein reference is made to the &awings, in which: FIG. 1 is a front elevation of a stretch head and die combination which may be used for stretch forming or stretch drawing between companion male and female drawing dies in a stretch press, and embodyin@ the quadrilaterat linkage of the present invention for controlling the paths of the stretch heads, respectively; FIG. 2 is a top plan view of the structure illustrated in FIG. 1; FIG. 3 is a diagrammatic illustration on a reduced scale showing the location and rocked position of the lefthand stretch head in FIG. 1 at the beginning and end of the forming operation; FIG. 4 is a side elevation of a structure similar to FIG. I showing a modified quadrilateral linkage for controlling the path and tilted position of the stretch head; FIG. 5 is a diagrammatic illustration on a reduced scale showing the location and rocked position of the lefthand head in FIG. 4 at the beginning and end of the drawing operations; and FIG. 6 is a @diagrammatic illustration showing two stretching fixtures installed in a drawing die press for stretch drawing. Referring to the drawings, the structure is shown as mounted on a horizontal bolster I of which at least the longitudinal central portion is adapted to rest on the bed of a conventional power driven draw die press. Supported on the bolster 1, through the medium of a plurality of rigid spacer blocks 2, is a drawing die 3. In the form illustrated, the die is a male die having an upwardly convex forming face. The die is assumed to be one for forming airplane parts in which a considerable amount of the metal stock S in the finished shape will extend considerably beyond the ends of the forming face of the die 3, the amount depending upon the particular part being formed. In order to stretch the stock about the die 3, either for stretch forming or preparation to stretch-drawing it between companion drawing dies, suitable stretch heads 4 are provided, and are spaced from the ends of the die, one at each end of the die in the drawing direction. Each head comprises a stationary jaw 5 and a movable jaw 6 connected together by a pivot 7 for rocking into stock gripping and releasing positions. The jaws are operated by suitable linkages 8 driven by a piston and cylinder assemblage 4 which may be of the air or hydraulic fluid type. The head 9 is supported on a carrier 10 having brackets 11 at its ends to which are pivotally connected, by pfvots 12, pistons rods 13 of reversible piston and cylinder assemblages 14 which preferably are of the hydraulic type controlled by a conventional reversing valve. In order to constrain the head to move along a preselected path and to rock about axes extending forwardly and rear-wardly of the heads and bolster block 1, the quadrilateral linkage means of the present invention are provided. In the form illustrated, the linkage means for the heads comprise linkages at the front and rear of the beads, respectively, as illustrated in FIG. 2. Each linkage of the left-hand head in FIG. 1 includes an upper side link 15 and a lower side link 16. Each of the links 15 and 16 is fixed in length and each is pivoted at one end so as to rock about an axis which is in fixed position relative to the head 4 and at the other end so as to rock about an axis which is fixed in position relative -to the die 3. Foi example, a pivot 17 at the outboard end of the link 15 is in fixed position relative to the head 4 and a pivot ;18 at the inboard end of the link 15 is in fixed position relative to the die. Correspondingly, a pivot 19 at the outboard end of the link 16 is in fixed position relative to the head and the pivot 20 at the inboard end of the link 16 is in fixed position relative to the die. The end links are provided, respectively, by the portion of the carrier 10 to which the pivots 17 and 19 are connected, and by the portion of a fixed supported 21 to which the pivots 18 and 20 are connected. The supports 20 are secured in fixed position relative to the die 3. The axes of all of these pivots are parallel to each other and define in a plane normal to the axes a quadrilateral which is either a trapezium, as illustrated in FIG. 1, or a trapezoid, as illustrated in FIG. 4. Starting with the head 4 in a loading position, the 10 throat of the jaws 5 and 6 are horizontal and extend forwardly and rearwardly of the bolster I or press in which the bolster is supported. Thus the throat is at a height to receive the sheet edgewise for supporting it out of contact with the face of the die 3. As the heads are 15 swung downwardly by operation of the assemblages 14, they are constrained by the links 15 and 16 to move outwardly, or in some cases outwardly and then back inwardly, as the heads move downwardly. By this action the stock is wrapped abotit the die 3 while tensioned into 20 its yield range. At the same time, since the axes of the linkages do not form parallelo.-rams, the head 4 is caused to rock about axes parallel to the axes of the links. Generally the lengths of the links 15 and 16 are chosen so that the left-hand head in FIG. 1 rocks counterclockwise 25 to a degree such that at the end of the stretching operation the jaws slope upwardly toward the die so that the gripped edge of the stock, indicated at 22, and the portion of the stock between the gripped margin 22 and the end of the die forming face indicated at 23, are lineal and 30 are both tangent to the forming face of the die at 23. While, as illustrated in FIG. 3, the head 4 is shown as horizontal above the die in loading position, in some cases for loading it might be tilted slightly upwardly to the ri,@ht so that the stock is arched and convex upwardly 35 during loading as such arching prevents sagging of the stock and causes the stock to retain its initial loading position more effectively. At the end of the forming operation the head is tilted so as to be tangent to the male die 3. 40 However, it may be that a female die is to be used which will force the metal downwardly further around the end of the die 3, in which case the final position of the head in FIG. 3 might be a tilted position in which the stock gripped by the head and the portion of the stock 45 between the head and die would be tangent to the end of the forming surface of the female die. Again, different degrees of tilt of the head at different positions of the head along its path of travel can be obtained, as desired. The right-hand stretch head and its accompanying links 50 are the same in general as the left-hand head and its links, except, of course, since the pieces to be formed may be asymmetrical, the axes of the links at the righthand will form a different quadrilateral pattern than the axes of the links at the lefthand end. 55 In FIG. 4 there is illustrated a modification of the structure illustrated in FIG. 1, in which the quadrilateral linkages of the head 4a each comprises upper and lower links 15a and 16a. These links are arranged so that their pivoted axes at their outboard ends are secured to the heads in 60 fixed position relative to each other and the axes at their inboard ends are secured to a suitable support 23a arranged in fixed position at the outboard end of the forming die 3a. These axes define a trapezoid, as distinguished from a trapezium, but not a parallelogram. 65 The press and its operation, and control of the stretch units, may in all other respects be such as described in the above-identified patent, or, as mentioned, the stretching and die assemblage may be used separately for stretch 70 forming, as distinguished from stretch drawing bet@veen companion dies. For stretch drawing, one or two of the stretching fixtures may be mounted in a drawing press 25 having a ram 26 which may be driven in any conventional manner; for 75 example, by reversible hydraulic piston and cylinder as-
[3]5 semblages 27. Hydraulic fluid is supplied to the assemblages 27 through a control valve 28 from a pump 29 driven by a motor 30. The assemblages 14 of the fixtures are driven independently of each other by hydraulic fluid supplied by a pump 31 driven by a motor 32. The assemblages for each head are connected in parallel with the pump through th@eir common control valve 33. Conventional air or hydraulic pressure may beused to open and close the jaws. Generally two stretch heads are employed and are located one at each end of the die, as illustrated. In some cases, however, one of the heads may be stationary and in fixed position relative to the die. Having thus described my invention, I
