US3426570A - Stretch wrapping fixture and combination thereof with drawing dies and press - Google Patents

Description

Feb. 1 I, 1969 Q J A ET AL STRETCH WRAPPING FIXTURE AND COMBINATION THEREOF WITH DRAWING DIES AND PRESS of 4 I Sheet Filed Jan. 11. 1967 W am?- W r/4 7705x05 c. J. BATH ET L STRETCH WRAPPI Feb. 1 1

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STRETCH WRAPP ING FIXTURE AND COMBINATION THEREOF WITH DRAWING DIES AND PRESS Filed Jan. 11, 1967 Sheet 4 of 4 United States Patent 3,426,570 STRETCH WRAPPING FIXTURE AND COMBINA- THEREOF WITH DRAWING DIES AND Cyril J. Bath, Chagrin Falls, and John H. Leonard, Hudson, Ohio, assignors to The Cyril Bath Company, Cleveland, Ohio, a corporation of Ohio Filed Jan. 11, 1967, Ser. No. 608,669 U.S. Cl. 72-296 Claims Int. Cl. B21d 11/02, 11/22; B21 9/18 ABSTRACT OF THE DISCLOSURE The stretch draw fixture is employed in a drawing die press, one fixture at each end of the set of drawing dies. Each fixture includes a gripping head which grips the adjacent end margin of the sheet. The heads are arranged for tensioning a sheet of metal unidimensionally into the yield range while wrapping it onto the forming face of the male die, preparatory to closure of the dies. Each head is supported by linkages which are pivotally connected at one end to the male die and at the other end to the head. The pivotal axes of each linkage define a quadrilateral with axes extending transversely of the direction of tensioning of the sheet. The linkages cause the heads to move apart for tensioning the sheet as the heads are moved by power means in the direction for laying the sheet onto the male die.

This invention relates to a stretch draw fixture and combination thereof with a drawing die press, and is an improvement on the inventions disclosed in United States Letters Patent of Cyril J. Bath, No. 3,116,780, issued Jan. 7, 1964, in the application of Robert A. Mackenzie, Ser. No. 514,219, filed Dec. 16, 1965, entitled, Prestretch Fixture and Combination Thereof With Drawing Die Press, which application was abandoned in view of the filing of an application of Robert A. Mackenzie, Ser. No. 475,487, filed Aug. 12, 1966, now US. Patent No. 3,314,269, issued Apr. 18, 1967, and in the application of Cyril J. Bath, Ser. No. 550,520, filed May 16, 1966, and entitled, Link Supported Gripping Head.

In the above-entitled patent there is disclosed a conventional draw press employing complementary drawing dies combined with stock gripping stretch heads which are operable by hydraulic piston and cylinder assemblages to tension a sheet of metal stock unidimensionally preparatory to and during drawing of the stock by and between conventional drawing dies. The stretch heads are mounted on carriers which are movably connected to elevators and support the heads for horizontal movement, relative to supporting elevators, toward and away from each other for tensioning the stock. The elevators, in turn, are mounted on a frame for vertical sliding movement and are power driven, by hydraulic piston and cylinder assemblages or other means, for lowering and raising the carriers, and thereby the heads, so as to wrap the tensioned stock about the male die preparatory to die drawing the stock to final shape. The heads are maintained in substantial parallelism with their starting position at all times. Such a structure, with tension controls, are very desirable for stretch drawing the more exotic metals and alloys wherein considerable flexibility in timing and intensity of applied forces is required from piece to piece of stock due to the nonuniformity of the stock and the closeness of yield to ultimate strength. This structure, while highly effective in such applications, is expensive, due particularly to the hydraulic piston and cylinder assemblages used for moving the heads and the elevators, and the cycling controls required.

3,426,570 Patented Feb. 11, 1969 One manner of simplifying the stretch head mountings by connecting the stretch heads to the elevators with generally upright parallelogram linkages is disclosed in the above Bath application. In that case, the elevators were retained, but the slides and guideways thereon for the head carriages were eliminated. The parallelogram linkages connected each head directly to its elevator so that the head was constrained to swing relative to its elevator substantially horizontally in a direction toward and away from the die and to remain substantially parallel with its starting position.

However, in high speed production of sheet metal automobile body parts, like precision in tensioning forces applied and variation in timing and control is not necessary because of the much greater spread between the yield point and ultimate strength of the sheet steel customarily used for automobile. body stock. Instead, variability in cycling and application of precise tensioning forces becomes secondary to speed in production and dimensional precision in the length of the uutrimmed formed sheet of stock so that the uutrimmed formed sheet can be accommodated readily and properly in subsequent trimming dies and the like.

In automotive body production, substantially-all parts are asymmetrical with respect to an upright median plane extending transversely of the part at the longitudinal midportion of the sheet stock. It was found, however, as disclosed in the above Mackenzie application, that with linkages of proper lengths for the respective stretch heads and dies, and with the pivot points located in proper position relative to the dies and to the heads or their carriages, the heads could be caused to follow precise preselected paths repeatedly such that the heads would cooperate properly and consistently with asymmetrical drawing dies and duplicate both the parts and the shape and overall dimensions of the formed, but uutrimmed, sheet of stock.

The elevators for the head carriers were retained and the linkages connected the carriers to the elevators, the elevators insuring that the heads would remain substantially parallel to their starting or loading positions while moving toward and away from each other during tensioning of the stock and upwardly and downwardly during wrapping the stock about the male die. 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.

However, a problem still remained as to actuating the stretch heads extremely rapidly with hydraulic piston and cylinder assemblages when subject to the heavy inertial forces inherent in reciprocating the massive elevators and the parts carried thereby. Also, the elevators occupied a very substantial portion of the available die space of the press, and were large and expensive fabrications.

The present invention provides a structure essentially the same as that in the Mackenzie application except that the elevators are eliminated and, instead, the stretch heads are both supported and guided along precise paths and maintained in parallelism with their loading positions during the stretch drawing operation by means of head supporting parallelogram linkages of which the pivotal axes at one end of the linkages are in fixed relation to the male die and at the other are in fixed relation to the associated stretch head. As a preferred example, instead of a pair of single links, arranged one at the front and one at the rear of each head, and having common :pivotal axes, as in the Mackenzie application, one or more pairs of links are provided, each pair comprising at least two parallel links of equal length pivotally connected each at one end of the pair with their pivotal axes in fixed relation to the die and at its other end of the pair to the head with their pivotal axes in fixed position relative to the heads.

The intersections of the pivotal axes of the pair of links of a given parallelogram linkage with a plane normal to these axes, define a parallelogram, and each such an arrangement of two links is a parallelogram linkage whether the two parallel links are coplanar or are disposed in parallel planes in spaced relation to each other endwise of the pivotal axes. Such a parallelogram linkage supports the associated head and maintains it parallel to its original starting or loading position during operation and constrains the head to follow precisely to its proper predetermined path invariably. Such linkages hold the heads in the proper horizontal position for ready loading of the stock and removal of the formed sheet.

In the present invention, not only have the tensioning piston and cylinder assemblages interconnecting the stretch heads and their elevators been eliminated, but also, the elevators themselves have been eliminated, thus greatly simplifying the structure and reducing the weight and resultant inertial forces. Since tension sensing and resultant control generally are not required for such production, the carrier may be made rigid with, or an integral part of, the stretch head. If sensed tension and control thereby should be desired in a specific instance, the carrier need be merely a plate with the head interconnected with the plate by tension sensing bars and mounted on the plate for extremely limited relative movement toward and away from the dies.

Specific objects and advantages of the invention will become apparent from the following description wherein reference is made to the drawings, in which:

FIG. 1 is a front elevation of a conventional power driven drawing die press with the improved stretch wrapping fixture of the present invention combined therewith;

FIG. 2 is an enlarged fragmentary right side elevation, partly in section, of the fixture and a part of the press shown in FIG. 1, as viewed from the line 22 in FIG. 1, and showing the parallelogram linkage employed;

FIG. 3 is an enlarged fragmentary top plan view of a portion of the :press and the fixture illustrated in FIG. 2, viewed as indicated by the line 3-3 in FIG. 1.

FIG. 4 is a hydraulic diagram showing the supply of hydraulic fluid for operating the apparatus, the timing controls being omitted because not part of this invention;

FIG. 5 is a fragmentary diagrammatic front elevation of the stretch wrapping fixture of the present invention illustrating a different positioning of links for providing parallelogram linkage for the stretch heads;

FIG. 6 is a fragmentary diagrammatic top plan view of the structure of FIG. 5;

FIG. 7 is a fragmentary diagrammatic front elevation of the stretch wrapping fixture illustrating another positioning of links for providing a parallelogram linkage;

FIG. 8 is a fragmentary diagrammatic top plan view of the structure illustrated in FIG. 7;

FIG. 9 is a diagrammatic perspective view of another form of parallelogram linkage used in the present invention; and

FIG. 10 is a diagrammatic top plan view of the structure illustrated in FIG. 9.

Referring to the drawings, a preferred form of the invention is illustrated wherein a stretch wrap fixture of the present invention is shown installed in a conventional upright hydraulic press 1 having a bed 2 with upright guide members 3 arranged at the corners and guiding a power driven ram 4 for vertical reciprocation. A male die 5 having a forming face which is convex upwardly both lengthwise and transversely is supported on the bed 2, and a companion female die 6 is mounted on the ram 4. Conventional holddown rings or devices are not employed as the stock is left free to draw in transversely of the tensioning dimension.

The invention, being particularly desirable for combined stretching and die drawing of sheet metal automotive body stock and the like into shapes which are nonsymmetrical about an upright median line extending transversely of the tensioning dimension, the male die is shown as asymmetrical endwise.

The ram is driven on its forming and return strokes by means of hydraulic piston and cylinder assemblages 7, including cylinders 8 and pistons 9, having rods 10 connected to the ram. The stretch wrapping fixture generally includes two units 11 arranged on the bed 2 at the two limits of the male die which are opposite each other in the tensioning dimension. Regardless of whether the tensioning dimension is the longer or shorter dimension of the work piece or die, it is considered the endwise dimension.

Each unit 11 comprises a stretch head 12 having a pair of jaws 13 operated for opening and closing through linkages 14 by piston and cylinder assemblages 15, thereby to grip the associated margin of the sheet of stock for applying tension thereto upon movement of the head along its predetermined path. Each head is mounted on a carrier 16 which, if desired, may be in the form of a plate rigid with the main casting or body of the head 12, or may be an integral part thereof. The head 12 is elongated forwardly and rearwardly of the press. At its forward and rearward ends, it is provided with fixed gussets or brackets .17, respectively, rigid with the head 12 and carrier 16.

For raising and lowering the heads, a plurality of hydraulic piston and cylinder assemblages 18 are provided for each head. Each assemblage comprises a cyl inder 19 carrying a piston 20 having a rod 21 pivotally connected by a pivot 22 to a suitable bracket on and rigid with, the carrier 16. The lower end of the cylinder 19 is pivotally connected by a pivot 23 to a suitable bracket 24 which is connected in fixed position relative to the bed 2 of the press.

With the structure thus far described, it is apparent that the stretch heads 12 can be moved toward and away from each other generally horizontally for tensioning a sheet of stock S and concurrently can be moved vertically by the assemblages 18. However, to apply the proper stretching forces and assure that all sheets of a lift of like sheets will be substantially identical in shape and dimension when formed and before trimming, the heads are constrained to move parallel to their loading positions, each in a fixed invariable path so as to provide concurrently the desired components of horizontal and vertical movement. In order to constrain each head 12 to move in its selected path, chosen so that the stock is always properly tensioned during the wrapping of the stock on the die, parallelogram linkages are provided.

Referring specifically to the right hand unit 11 illustrated in FIG. 1, the parallelogram linkage shown for illustration comprises rigid rods or links capable of withstanding the endwise compression without buckling or distortion and arranged in pairs, preferably one pair at the front end of the head 12 and one pair at the rear end of the head 12. All of the links are of equal length and all are parallel to each other. The links of each pair are spaced from each other transversely of their pivotal axes. Each link 25 is pivotally connected at one of its ends by pivot 26 to an associated one of the brackets 17. The axes of the pivot 26 at this end of the pair extend parallel to each other and are in fixed relation to the gusset 17 and head 12. The opposite ends of the links 25 are pivotally connected by pivots 27 to a rigid supporting means which, in the form illustrated, is shown as an integral body portion of the die 5, but which may be a detachable separate bracket or the like mounted in fixed position relative to the die 5.

The pivots 27 are parallel to the pivots 26 and are arranged the same distance apart so that the intersection of the axes of the four pivots of each parallelogram linkage with a plane normal to the axes define a parallelogram. The parallelograms defined by each parallelogram linkage for a given head are identical with each other and preferably are arranged so that corresponding pivots 26 and 27 of one pair are coaxial with other pair of the same head, if any, essential.

The links form one pair of opposite sides of the parallel linkage. The other pair of opposite sides of the same linkage may be separate links, but it is convenient instead to allow the rigid portion of the die body '5 and of the gusset 17 to function as such. All the pivots 25 and 26, and all of the links 25 of all of the parallelogram linkages, if more than one linkage is used, are parallel to each other and the links are all the same length. However, the parallelogram linkages, if more than one per head is employed, need not have their corresponding pivotal axes at the same elevation or in the same position endwise of the die, so long, however, as the parallelograms themselves are identical and have their corresponding axes parallel.

'In the case of some specialized dies, a stationary gripping head may be used at one end of the male die opposite from a single head 12, but most generally two companion units are desirable and necessary.

Referring to the left hand unit in FIG. 1, it is the same in all respects as the right hand unit, except that the links 30 of each parallelogram link-age are generally of different lengths than the links 25 and the pivots 31 may be differently arranged relative to each other and to the die. Of course, in those few instances in which the die face is symmetrical about its median line, the parallelogram linkages of the two units may be identical in shape, size, and position relative to the male die. In the right hand unit, at least two parallelogram linkages are provided which are arranged so that at all times they are parallel to each other. The specific length of links 30 and positioning of the pivots 3.1 and 32 are readily selected in relation to the shape of the die between its crest and the end adjacent the particular unit.

The units 11 are arranged so that preferably, while the metal is either untensioned or lightly tensioned, the heads move down until the sheet S engages the crest of the male die. They continue moving and by the time the metal is in firm engagement with the crest, or shortly thereafter, they have moved apart from each other so as to tension the stock into a range above the elastic limit so that it reaches the yield point.

It is to be noted, for example, that this is eflected'in the case of the links 2'5, as illustrated in FIG. 1, because as the right hand head 12 moves downwardly, it moves away from the die 5, thus tensioning the stock, until the links 25 become horizontal or at dead center relative to their pivots. The head then no longer moves away from the die, but since a substantial amount of metal is being wrapped onto the forming face of the die, even though the head moves toward the die, it does not move toward the die as rapidly as the stock is foreshortened end'wise of the die 5, by being stretch wrapped about the die face.

Referring to FIG. 4, the unit and press may be operated from a pump 35 driven by a motor 36, pressure fluid being fed to the assemblages 7 of the press through'a suitable reversing and stop valve 38 so as to raise and lower the ram, selectively. Also, pressure fluid is supplied from the pump 35 through reversing valves 39 to the piston and cylinder assemblages 15, respectively, for opening and closing the jaws independently of each other. Fluid from the pump also is delivered through reversing and stop valves 40 to the piston and cylinder assemblages 18, respectively, for raising and lowering the heads independently of each other.

Thus, each piston and cylinder assemblage 18, by pulling downwardly on the associated head while the head is constrained by the parallelogram linkage to swing in an invariable fixed path and parallel to its starting or load ing position causes the linkages to apply the requisite tension to the stock. If desired, of course, instead of the assemblages 18, suitable pressure applying push rods those of every though this is not may be provided on the ram for driving the heads downwardly, as described, for example, in the application of Stanley M. Donley, Ser. No. 517,616, filed Dec. 30, 1965, and entitled, Hydraulic Push Rod for Stretch Draw Press. If push rods are used, lighter piston and cylinder assemblages, located as are the piston and cylinder assemblages 18, may be used to apply light yieldable resisting pressure to raise the heads when the ram and push rods are not forcing them downwardly.

It is apparent that this arrangement, with the heads 12 in the fully raised position illustrated in FIG. 1, the margins at the ends of the sheet of stock S are gripped in the jaws 13, whereupon the ram is started on its downward stroke to lower the die 6. The assemblages 18 begin lowering the heads 12. As the heads lower, they may apply light tension or substantially no tension on the stock. The choice of length of the parallelogram linkages and location of the pivots is such that the stock engages the crest of the male die 5 before the stock is tensioned to a degree which would cause fluting or wrinkling. However, after the stock engages the crest, the heads continue downwardly and tension the stock into the yield range, above the elastic limit and then wrap the stock while thus maintained under tension, onto the male die. After the parallelogram linkages pass dead center, the heads begin moving back toward the die 5, but at a rate such that, due to the amount of the sheet stock wrapped on the die, the tension is still maintained during the inward movement. This operation continues until the stock is fully wrapped on the die 5. With the properly selected length of the sheet S, the inboard faces of the gripping jaws, adjacent to the die, move substantially to the end limits of the die. When the heads reach this relative position and the stock is thus fully wrapped, it is struck by the female die 6 which completes formation of the article, as in the conventional draw die operation.

Thus, it will be seen that the relatively large and expensive elevators, slide mountings of the heads or carriages thereon, the banks of stretch forming assemblages, and raising and lowering assemblages of the large size heretofore required are eliminated. The parts required are so few and inexpensive that each die and its stretch heads and linkages can be retained and stored as a unit without disturbing the relation between the heads and the forming surfaces of the dies. This assures: that at any time replacement parts are to be made they will be duplicates of the original car production. In this connection it might be noted that the piston and cylinder assemblages 18 may be proportioned for the particular head with which it is associated so that they have exactly the right starting and stopping points both in lifting and lowering. If so, they carrremajn attached to, and stored with the units. On the other hand, if the strokes of these assemblages are to be variable and otherwise controlled, then of course these assemblages can be detached from the associated units by detaching the pivots, such as 22 and for different dies and stretching and wrapping assemblages.

In the form illustrated, twoparallelogram linkages are provided for each head. More may be provided, or, if desired, single parallel linkage of sufficient strength may be used.

If several parallelogram linkages are used for a given head, the parallelograms defined by them have their corresponding pivots coaxial. However, this is not essential. As illustrated in FIGS. 5 and 6, for example, there are shown two identical parallelogram linkages 42 and 43. It is to be noted that while the parallelograms defined by these linkages are parallel and of the same size and shape in any given position of the associated stretch head, the axes of the four pivotal axes at corners of one linkage are not coaxial with the corresponding axes of the other, transversely of the axes therefrom.

In FIGS. 7 and 8 are shown two identical parallelogram linkages 44 arranged with the two ends of each parallelogram linkage disposed in parallel planes which are offset endwise of the pivotal axes.

Thus, identical parallelogram linkages may be arranged with the two links of each linkage in a common plane or in respective planes parallel to each other and spaced apart endwise of the axes, and with corresponding axes coaxial are offset radially from each other. Again, pairs of parallelogram linkages may be offset transversely of the axes. However, in all cases, the parallelograms defined by the axes must be identical and with their corresponding sides parallel.

FIGS, 9 and 10 illustrated a modification of the linkage in which only a single parallelogram linkage is provided for an associated stretch head. In this form a stretch head 45 is provided at its sides with supporting plates or brackets 46 between which a single rigid parallelogram linkage is disposed. The parallelogram linkage comprises an upper link 47 and a lower link 48, these links being in the form of castings or fabrications, each including a generally horizontal portion 47a and a vertical portion 47 b extending upwardly therefrom. By having the horizontal and upwardly extending portions, the links can be connected to the die by pivots 49 so as not to interfere with the die and to the head 45 by pivots 50. The links of a pair in a given parallelogram linkage may be substantially identical, and similar to the single links disclosed in the above copending application of Robert A. Mackenzie, Ser. No. 514,219, filed Dec. 16, 1965.

It is to be noted that in the above-entitled application, Ser. No. 550,520, parallelogram linkage means constrain the head to movement which is approximately horizontal relative to an elevator which is the supporting means to which are connected the ends of the links opposite to the ends connected to the head. This elevator provides essentially all vertical components of movement for wrapping the stock about a die while the links provide the horizontal components of movement of the head relative to the elevator. Thus, the pivotal axes of the ends of the links opposite from the head are in fixed relation to the elevator, but are not in fixed relation to the path of movement of the head, which path includes both components of horizontal movement due to the links and of vertical movement due to the elevator.

In the present structure, however, the parallelogram linkage means is so arranged that the pivotal axes of the ends of the links which are opposite from the head are in fixed position relative to the die and press, as distinguished from a fixed position relative to an elevator which moves relatively to the die and press. Consequently, these axes at the opposite ends of the links from the head remain at all times in fixed position relative to the path of the head, because both vertical and horizontal components of movement of the head are dictated entirely by the parallelogram linkage means.

Having thus described our invention, we claim:

1. A stretch wrapping unit comprising a stretch head arranged to grip a margin of a sheet of stock and to apply tensioning force along one dimension thereof for stretching the stock and wrapping the stock while holding the stock under tension over a male die when the head is moved along a predetermined fixed invariable path;

quadrilateral linkage means for the head;

means connecting one end of the linkage means to the head with the pivotal axes of the linkage means at said one end parallel and in fixed position relative to the head;

supporting means connected to the other end of the linkage means and supporting said other end with the pivotal axes at said other end in fixed position relative to each other and to said path;

all of the axes of the linkage means being parallel to each other; and

said linkage means constraining the loading face of the head to a predetermined position with respect to the adjacent end of the die at the end of the forming operation wherein the loading face has very closely approached said adjacent end.

2. The structure according to claim 1 wherein each quadrilateral linkage means comprises a plurality of quadrilateral linkages, and the quadrilaterals defined by the four pivotal axes at the comers, respectively, of the respective quadrilateral linkages being substantial duplicates of each other.

3. The structure according to claim 2 wherein the linkages are positioned so that corresponding corners have common pivotal axes, respectively.

4. The structure according to claim 1 wherein a male die having a convex forming face is provided and the supporting means are in fixed position relative thereto and maintain said other end of the quadrilateral linkage means with the pivotal axes at said other end in fixed position relative to the die.

5. The structure according to claim 1 wherein the sole support of the head is by the said supporting means and linkage means.

6. The structure according to claim 4 wherein the die has a first portion body integral with a portion having the forming face, said first body portion is the supporting means, and the pivotal connections of the quadrilateral linkage means with the first body portion are spaced from the surface of the face and extend generally transversely relative to said surface and die.

7. The structure according to claim 1 wherein power means are provided for moving the head along said path.

8. The structure according to claim 1 wherein two opposite sides of the quadrilateral linkage means are compression resisting links, each link is pivotally connected at one of its ends to the head and at the other of its ends to the supporting means;

and the other two sides of each quadrilateral linkage means are rigid portions of the head and of the supporting means, respectively.

9. The structure according to claim 1 wherein the head is elongated in the direction of said linkage axes, the linkage means includes at least two quadrilateral linkages which are connected to the head at the opposite ends of the head, respectively.

10. The structure according to claim 1 wherein a second stretch head is provided and is disposed in spaced relation to the first mentioned head;

quadrilateral linkage means are connected to the second head and to the supporting means for constraining the second head to movement along a second predetermined fixed invariable path in a direction generally toward and away from the first mentioned head; and the length of the last mentioned quadrilateral linkage means is different from the length of the first mentioned linkage means.

References Cited UNITED STATES PATENTS 9/1956 Oeckl 72297 4/1967 Mackenzie 72--450 US. Cl. X.R.

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