US2961028A - Method and apparatus for combined stretch and die forming of metal stock - Google Patents

Description

Nov. 22, 1960 c. J. BATH METHOD AND APPARATUS FOR COMBINED STRETCH AND DIE FORMING OF METAL s'rocx 7 Sheets-Sheet 1 Filed March 17, 1960 lllEk INVENTOR. MI BY i m-me/wx Nov. 22, 1960 c. J. BATH METHOD AND APPARATUS FOR COMBINED STRETCH AND DIE FORMING 0F METAL STOCK 7 Sheets-Sheet 2 Filed March 1'7, 1960 IN V EN TOR. 7%

f ATTORNEY.

Nov. 22, 1960 c; J. BATH 2,961,028

METHOD AND APPARATUS FOR COMBINED STRETCH AND DIE FORMING OF METAL STOCK Filed March 17, 1960 7 Sheets-Sheet 3 "\1 I T K I II I INVIENTOR. 6904:} M, BY

rArroeA/fx Nov. 22, 1960 c. J. BATH 2,961,028 METHOD AND APPARATUS FOR COMBINED STRETCH AND DIE FORMING OF METAL STOCK Filed March 1'7, 1960 7 Sheets-Sheet 4 INVE'IYTOR. Fig 5 W j 2 @Arm/e/ve'x I NOV. 22, 1960 c, J BATH METHOD AND APPARATUS FOR COMBINED STRETCH AND DIE. FORMING 0F METAL STOCK Filed March 1'7, 1960 7 Sheets-Sheet 5 INVENTOR. W 2 BY 1" ATTOENEK METHOD AND APPARATUS FOR COMBINED STRETCH AND DIE FORMING OF METAL STOCK Filed March 17, 1960 7 Sheets-Sheet 6 IN V EN TOR.

94 64 BY 2L Nov. 22, 1960 c. J. BATH 2,961,028

METHOD AND APPARATUS FOR COMBINED STRETCH AND DIE FORMING OF METAL STOCK Filed March 17, 1960 7 Sheets-Sheet 7 INVENTOR. M

A ATTOENEK United States Patent WIE'I'I-IOD AND APPARATUS FOR COMBINED STRETCH AND DIE FORMING 0F METAL STOCK Cyril J. Bath, Chagrin Falls, ()hio Filed Mar. 17, 1960, Ser. No. 15,588

14 Claims. (Cl. 153-35) This invention relates to a method and apparatus for forming metal stock, and particularly for forming sheet metal stock into articles between the complementary matching surfaces of drawing dies.

One of the principal objects of the present invention is to precondition metal stock, immediately prior to formation thereof between matching surfaces of drawing dies, and independently of die operation, so as to render it more readily fiowable and plastic, whereby it can be made to conform more accurately to the matching die surfaces upon closure of the dies with far less pressure than heretofore required for die forming.

Another object is thus to precondition the stock wherefore the produced articles have physical properties superior to the same articles when shaped by the conventional methods of forming in matching drawing dies.

A more specific object of the invention is to precondition the stock, immediately prior to, and independently of, closure of the matching drawing dies and the formation of the article thereby, by stretching the stock into a range above its elastic limit and below its ultimate strength, whereby it is rendered more flowable and plastic and, promptly upon its thus being rendered more flowable and plastic and before work hardening, forming it between matching surfaces of the drawing dies.

Another specific object is to effect the final formation in drawing dies, after prestretching and while the stock is thus softened, by applying the dies to the stock progressively from one end of the dies to the other so that, during forming, the metal between the dies can flow gradually from the portion instantaneously being engaged to the unengaged portion and thus accommodate itself more readily to the die surfaces line at a time while the already engaged portion remains confined, by the die surfaces, whereby wrinkles and entrapped air pockets are eliminated and better physical properties, greater accuracy in shape, less spring back, and greatly reduced power requirements as compared to the conventional practices of drawing metals into shape in matching drawing dies, are obtained.

Another specific object is to form large metal sheets into shallow spheroidal segments of large surface area, such as automobile top panels, side panels, engine and rear compartment cover panels, and the like, wherein the depth of the segment or bulge is so limited in relation to the area that the major portion of the metal stock cannot be drawn and formed effectively by conventional drawing die operations because it remains to a large ex tent in its elastic deformation range in the closed positions of the dies and hence does not take the final shape of the die surfaces but returns toward its original shape.

Another specific object is to form sheet metal stock by tensioning the stock in a range above its elastic limit unidimensionally, as distinguished from so tensioning it concurrently endwise and crosswise, prior to and independently of the operation of the drawing dies, and, while maintaining the stock thus tensioned in said range,

effecting closure of the dies progressively in the tensioning direction, as distinguished from transversely of the tensioning direction, from one stock margin which extends transversely of the tensioning direction to the opposite stock margin, while leaving those margins of the stock which extend in the tensiom'ng direction free to creep laterally between the matching faces intothe dies in a direction transversely of the tensioning direction, and while maintaining each increment of the stock confined between the matching faces from the instant that it is initially confined therebetween until the end of the die forming operation so that the major portion of the finally shaped article is disposed within the peripheral limits of the matching surfaces, in the final forming position of the dies, and in that final position is engaged over a large portion of its surface area with the entire areas of the matching faces.

Another object is to provide apparatus especially adapted to perform die steps of the methods herein disclosed.

Various other objects and advantages of the invention will become apparent from the following description, wherein reference is made to the drawings illustrating preferred embodiments of the invention, and wherein:

Fig. 1 is a perspective view illustrating a preferred embodiment of the invention;

Fig. 2 is a front elevation, partly in section, of the machine as illustrated in Fig. 1;

Fig. 3 is a right end elevation, partly in section, of the main frame, rocker arm and dies of the machine illustrated in Pig. 2, the other mechanisms being omitted;

Fig. 4 is a top plan view of one part of the stretch forming mechanism used in the present machine;

Pig. 5 is a side elevation of the apparatus illustrated in Fig. 4, part thereof being shown in section for clearness in illustration;

Fig. 6 is a top plan view of the complementary part of the stretch forming mechanism, part thereof being shown in section for clearness in illustration;

Fig. 7 is a side end elevation of the structure shown in Fig. 6;

Fig. 8 is an enlarged vertical axial sectional view of one of the sets of gripping jaws illustrated in Figs. 6 and 7;

Fig. 9 is a diagram illustrating a hydraulic circuit for operating the machine;

Fig. 10 is a perspective view illustrating a modification of the machine illustrated in Fig. 1;

Fig. 11 is a perspective view of a modified arrangement of the dies for the machines illustrated in Figs. 1 or 10; and

Fig. 12 is a front elevation of a modified form of dies illustrated in Fig. 11.

For purposes of illustration, the method and apparatus are described hereinafter as applied in the formation of present day automobile panels, such as top, side, and door panels, engine compartment covers, and rear compartment covers, as the formation of panels of this type presents special difficulties which can be overcome readily by the present method and apparatus.

Such a panel usually is a large sheet which has been formed into a very shallow spheroidal segment having a large surface area and a depth so limited in relation to the area that the major portion of the stock cannot be drawn into final shape and formed effectively by conventional drawing die operations. This is because that major portion remains below the elastic limit of the stock and, therefore, only within the elastic deformation range, throughout die closure and even in the closed position of the dies.

In the conventional drawing of these panels, the periph- 2,961,028 a i W cry of the sheet is engaged by the press hold-down or clamping means and the entire area within the peripheral limits of the dies is drawn by applying the dies, through the entire drawing operation, parallel to their final closed position. As a result, most of the stretching and drawing occurs only at a very narrow zone just inside the periphery engaged by the holddown means. Quite-often, the metal in this zone is overstretched and thinned while the more central major portion of the sheet is not permanently stretched significantly. Instead, the unstretched central portion is merely compressed and work hardened with a resultant deterioration in its physical properties.

Because of these phenomena, consistent high quality and dimensional accuracy are not often obtained and hand finishing often is necessary.

As mentioned, the present method generally comprises stretching a length of sheet metal stock, preferably unidimensionally,independently of, and prior to, the die drawing operation, into a range above its elastic limit, then promptly engaging it between the matching faces of drawing dies, while the metal is still in a plastic flowable condition due to having been previously stretched into a range above the elastic limit of the stock, and

before work hardening has resulted from the stretching operation. 7

In the case of some metals and shapes, the tensioning force may be discontinued before engagement of the sheet between the dies, if the die forming follows the stretching in the few seconds during which the plasticity due to stretching continues and before work hardening results, but preferably the tensioning force is continued by means independent of the dies, during closure.

Furthermore, it is desirable that the unidimensional tensioning into the range above the elastic limit be employed, as in the Dolney and Hein Patent No. 2,810,421, issued October 22, 1957, or in the Peter P. Matthews application Ser. No. 757,973, filed August 29, 1958, as distinguished from stretching rectangular sheets by simultaneously tensioning them endwise and laterallyby stretching devices connected to all four margins.

The dies are preferably applied progressively, line at a time in the direction of tensioning, from one stock margin which extends transversely of the tensioning direction toward the opposite margin. The dies are drawing dies and once any surface area of the area of the metal is engaged by their matching faces, it remains so engaged until the end of the drawing operation so that the entire areas of the die faces are in engagement with the stock at the end of the drawing operation. The unidimensional tensioning into the range above the elastic limit is effected by extraneous means prior to, and in dependently of, the die closing operation, and preferably is continued from its inception until the dies are in closed position. A very brief period of dwell of the dies, after die closure, is dmirable in some instances. With unidimensional tension, the margins of the sheet extending in the tensioning direction, are left free so that the metal of the sheet can creep and be drawn inwardly transversely of that direction during closure of the dies.

As a further refinement, the tensioning may be reduced ,while the dies are closing so that the tensioning by the extraneous tensioning'means independently of the die closure, combined with the tensioning of the metal imposed by the engagement of the dies with the metal, maintain the metal above its elastic limit during die 4; to flow so as to eliminate wrinkles, air pockets, and the like.

Again, the drawing dies employed are distinguished from wipe forming shoes, either in the form of a friction shoe or a roller, disclosed in the patents; Though the forming shoe is shown therein as a type of die and engages and forms the stock progressively from one end to the other While the stock is held under extraneously applied stretch forming tension, this shoe type of die is one in which only substantially line contact is maintained with the stock at all times by the die or shoe, and each portion of the stock that is engaged is immediately released so that, at the end of the forming operation, no part of the metal, except possibly for a line of contact at the very end, is in engagement with the face of the shoe or die.

Hereinafter, whenever reference is made to the tensioning of the stock endwise, this does not necessarily 7 wise of the stock, but not both concurrently.

Again, hereinafter reference is made to forming the I sheet metal stock into an article between complementary closure. This reduces the possibility that the tension due drawing dies by forming it to the final shape desircd, but between male and female dies of which the entire forming surfaces at the completion of the drawing operation are in contact with the stock concurrently and the major portion of the formed article is within the peripheral limits of the forming surfaces. This wording is chosen primarily to distinguish from what is known as joggling in which a large article is formed onto a side face die and a small ofiset of some nature is then formed in the article. Joggling is broadly old and is disclosed in the Bath Patent No. 2,514,830, issued July 11, 1950. In such joggling practices, the joggling die and the side face die about which the stock is stressed are not the type of matching drawing dies herein referred to, which are of the type in which substantially the entire periphery of the article is within and confined within the peripheral limits of the die faces and substantially all of the stock, or at least the major portion thereof, is confined between matching surfaces of the dies at the end of the forming operation.

, Referring ,to Figs. 1 through 9, a preferred form of machine embodying the principles of the present invention is illustrated. This machine comprises a main frame 1 which, for convenience in description, is assumed to be horizontal. The frame 1 is comprised of spaced side frame membersZ and a top frame member or table 3. A compression die or drawing die 4 is supported on the table 3 in fixed position. In the illustrative example, the die 4 is shown as a male drawing die.

A complementary female die 5, having a forming face matching with the forming face of the die 4, is supported on the frame for movement into cooperative relation to the die 4 so as to form the sheet stock by engaging it between the complementary matching faces of the dies 4 and 5.

The dies 4 and 5 are of the general type customarily used for drawing in conventional presses in which a sheet 'of metal is disposed between the dies and, by means of suitable hold-down devices engaging the periphery'of the sheet, the periphery is held in fixed position while the major portion of the sheet is drawn by closure of the dies simultaneously over their entire matching forming surfaces by moving them from an open position while they are held parallel to their final closed or forming position. Because of the periphery of the sheet being held infixed position, themetal is stretchedsolely by the dies.

In the present instance, the stock is tensioned unidimensionally independently of the dies prior to, and during the drawing operation. The stock preferably is not held at the margins extending in the tensioning direction, and the die closure is such that the matching die faces engage the stock progressively from one margin to the opposite margin in the tensioning direction. Several advantages are obtained by these changes. For the purpose of supporting the die so that it can be closed relative to the die 4 progressively from one edge of the dies to the opposite edge, a rocker arm 7 is pivotally connected at one of its edges by a pivot 8 to upright posts 9 on the rigid frame 1. These upright posts are spaced laterally of the frame and the arm 7 is formed of laterally spaced plate members 19 so that ready access is afforded to the die space both from the end and sides of the machine.

In order to rock the arm about the pivot 8, piston and cylinder assemblages 12 are provided at the edge of the arm opposite from the pivot 8. Each assemblage 12 comprises a cylinder 13 in which is reciprocable a piston 14. The piston has a rod 15 which is connected by a pivot 16 to the end of the arm 7 opposite from the pivot 8. Each cylinder is connected at its lower end by a pivot 17 to the frame of the machine. Two such assemblages 12 are provided and they are spaced apart laterally of the frame of the machine at the lateral outer limits of the arm 7 so as not to obstruct access to the die space from that end of the machine. By admitting pressure fluid to the rod ends of the cylinders 13, the arm 7 can be rocked downwardly about its pivot 8 to close the dies progressively from one edge to the opposite edge. By admitting pressure fluid to the head ends of the cylinders 13, the arm can be raised to starting position.

In order to stretch form the material, suitable tensioning means are arranged at opposite ends of the die 4 and are operable to tension the stock unidimensionally in a range above the elastic limit, and maintain it so tensioned before and during die closure. Both of these tensioning means may be the same, if desired, but for economy it is preferable that the stretch forming means at the edge of the dies adjacent the pivot 8 be a mere gripping head mounted for swinging about a horizontal fixed pivot extending parallel to the pivot 8. At the opposite edge of the dies, a gripping head employed is connected, to swing about a horizontal pivot extending parallel to the pivot 8, to a hydraulic piston and cylinder assemblage. The assemblage is arranged to yieldably urge its associated stock gripping head away from the head at the opposite edge of the dies so as to yieldably tension the stock between the heads unidimensionally as distinguished from tensioning it concurrently both endwise and crosswise.

Referring first to the stretch forming means at the end of the machine adjacent the pivot 8, this tensioning means comprises a stretch head 20 on which are detachably mounted a plurality of grippers 21. The grippers 21 are arranged in a row extending transversely of the machine. They are adjustably mounted on the head 20 so that, if desired, they can form a gripping throat which is curvilinear transversely of the machine and conforms approximately to the cross section of the convex curvilinear die 4 when such a die is used.

For this purpose, each gripper is swivelly connected by a swivel 22 to a T-head support 23 which is slidable vertically in suitable guideways 24 in the head 20. Adjusting screws 25 respective to the supports 23 are provided for adjusting the heights of the grippers 21 independently of each other. The grippers are supplied with fluid pressure through suitable manifolding, indicated generally at 26, so that all can be opened and closed simultaneously in a well known manner.

While the specific structure of the jaws does not form a part of the present invention, for a better understanding of the invention one set of jaws is illustrated in Fig. 8. Each gripper 21 is open at its forward end and is pro vided with inwardly facing cam surf-aces 27 between which are complementary gripping jaws 28. The jaws 28 have outer cam engaging surfaces so arranged that when the jaws are thrust forwardly toward the open end of their grippers 21, they are moved relatively toward each other, and when withdrawn rearwardly from the open en they separate from each other for releasing the stock. The jaws are connected to a common piston rod 29 of a piston 3t which is reciprocable in a cylinder 31 in the gripper 21. Pressure fluid can be supplied to opposite sides of the cylinders 31 through ducts 32 and 33 respectively, and vented therefrom by the ducts, so that the piston can be forced to advance or retract as desired for closing and releasing the jaws.

It sometimes happens that, due to the slight spacing of the grippers 28 from each other endwise of the row, the stock is not tensioned to as high a degree at the spaces between the grippers and consequently the stock tends to develop wrinkles extending in the tensioning direction from these spaces partway toward the opposite edge of the stock. This is often the case with other than relatively soft metals.

In such instances, a single gripper of the same type as the grippers 21, but coextensive in length, endwise of the row of grippers, with the entire group, may be employed. This assures that the gripping force is continuous for the entire length of the gripped portion of the stock and, therefore, the tensioning force is uniformly applied to each increment along the gripped portion. If desired, the gripping throat may be curved transversely of the tensioning direction so that the gripped margin of the sheet is curved transversely of the tensioning direction more nearly approximate the corresponding section of the dies prior to applying the stock to the die.

If only a few duplicate articles are to be formed, a like effect can be obtained by employing two continuous gripping jaws between the jaws 28, the continuous jaws extending unbrokenly for the full length of the gripped margin of the sheet and thus, in effect, providing a single pp The entire stretch head 20 is mounted for swinging movement about a horizontal axis by a horizontal pivot 35 by which the body is connected to suitable supports 36 on the frame of the machine. The pivot supports the head 20 for swinging upwardly and downwardly so that it can align itself and the sheet more effectively with respect to the surface of the die 4.

The complementary stretch forming means at the opposite end of the dies comprises a head 40 to which a plurality of grippers 41, similar to the grippers 21, are connected. The head 40 may be in the form of a single gripper as described in connection with the head 20. The head 40, in turn, is connected, for swinging about a horizontal axis, by a pivot 42 to a piston rod 44 of a piston and cylinder assemblage 45 having a piston 46 and a cylinder 47. The cylinder 47 is mounted on trunnions 48 for rocking about a horizontal axis. The axes of the pivot 42 and the trunnions 43 are parallel to the axis of the pivot 8.

The trunnions 48 are mounted in suitable upright side walls of an O-frarne 49. Thus, the gripping heads 20 and 40' can be caused to grip opposite margins of the sheet. By applying pressure fluid to the rod end of the assemblage 45, the stock can be tensioned unidimensionally to the degree desired. The capacity of the assemblage 45 is such that it can raise the stock up to and beyond its elastic limit or even up to its ultimate strength. Usually the gripping head 40 is sufliciently low so that the stock can be drawn over the left margin of the die 4 by the head 20. However, the stock preferably is kept above the forming face of the die 4 in the initial stretching operation. For this reason, it is desirable that the head 40 be arranged to swing downwardly after initial tensioning and before die operation, so that the stock can be stretch formed approximately progressively on ;from the right edgeto the left edge of the dies.

the die 4 and pulled downwardly around the left margin of the die 4. For this purpose, the O-frame 49 for the piston and cylinder assemblage 45 is mounted on a rock er arm 50. The arm 50 is connected to the frame by a horizontal pivot 51 so that the arm 50, and with it the .O -frame 49, can be swung upwardly from the solid line position illustrated in Fig. 2, and downwardly therefrom at least to and below thedotted line position shown in Fig. 2. Space is allowed between the side frame members 2 of the frame so that the O-frame 49 can be swung even farther down than illustrated.

For swinging the O-frarne 49 downwardly, apiston and cylinder assemblage 52 is provided. This assemblage comprises a piston 53 having a rod 54 and being reciprocable in a cylinder 55. The piston rod is connected by a pivot 56 to the arm 50. By introducing pressure fluid into the rod end of the piston, the arm 50 can be swung downwardly, and by introducing pressure fluid to the opposite "end of the piston, the rod can be raised 'io'the desired startingposition. The assemblage 52 can be connected to the frame by means of a pivot 57 so as to align itself properly during the swinging action of the arm 50. i

For operating the machine, pressure fluid is supplied to the parts by a suitable pump P driven by an electric motor M through a line 60 to which are connected in parallel three-way valves61, 62 and 63, respectively.

The valve 61 is connected to the assemblages 12, the.

-valve 62 to the assemblage 45, and the valve 63 10 the assemblage 52.

In thepreferred operation of the machine, the piston :and cylinder assemblages 12 are operated to raise the :arm 7' to its uppermost position, thus holding the dies .4 and 5 separated for their full length. In this condition, the sheet metal stock to be formed is gripped by the grippers of the heads 20 and 40 of the stretch forming means. With the arm still in the starting position, prior Ito any operationof the 'dies, the pressure fluid is intro- :duced to the rod end of the assemblage 45 to apply tension to the stock up to and beyond its elastic limit.- This tension preferably is maintained in this range above the elastic limit throughout the entire forming operation,

either by the tensioning means alone or by the tensioning means plus the frictional pull of the dies 4 and 5, as later to be explained.

- 'While the stock is maintained at a tension above the elastic limit by the extraneous stretch forming means acting independently of die operation, the assemblages .12 are operated to lower the arm 7. Since the arm must swing about. the pivot 8, the dies 4 and 5 are first closed at the right edge adjacent the pivot 8 and engage both faces of the stock between their complementary matching faces. While the tension is being held, the dies are progressively closed from the edge adjacent the pivot S toward the opposite edge adjacent, the head 41;

The die 4 is preferably upwardly convex and curvilinear both in longitudinal and transversesection, and the die 5 is correspondingly downwardly concave. -However, as-in many drawing dies the central portion of the forming face of the die 5 may be-omitted, unless some critical area need be formed thereby. Ordinarily, due to the drawing effect of the peripheral portions of the die faces and the central portion of the male die face, -it is not necessary to have a female matchingportion -at the central portion of the female die as the stoclcwill be stretched and formed adequately over this central portion ofthe male die so as to'take the form thereof.

Due to the gradual closure 'of the-dies progressively from one edge to the other edge in the tensioning or 'stretchforming dimension, combined with the maintenance'of the'stock in plastic condition due to tensioning .it into a range above itselastic limit, the metal tends to flow in the direction of closure, which, inFig. 2, Ais t strained and unconfined by any extraneous holding means at these edges of the dies which extend in the tensiondirection. Since the metal can creep into the dies freely transversely of the tensioning direction and can flow in the tensioning direction as urged'so to do by the die faces and extraneous tensioning means, the metal readily takes the form of the matching faces of the die. All wrinkles and entrapped air and lubricants and the like are ironed ou in the direction of closure and eliminated. The normal tendency of the sheet metal to contract transversely of the tensioning direction assists the flow of metal inwardly of the dies transversely of that direction and the conformance of the metal to the matching die faces. It is to be noted that once any increment of the metal is initially engaged between the matching faces of the dies, it remains so confined therebetween throughout the remainder of the die closing operation, so that, at the end of the die closing operation, the article, or the major portion of the article, is within the peripheral limits of the dies. Furthermore, due to this combined stretching and die forming, the metal article when formed retains its shape under severe variations in conditions, such as heating to high temperatures and the like. Instead of warping and oil canning under temperature changes or when subjected to extraneous stresses applied normal to its faces, it holds, or returns to, its

original shape.

If desired, the head 49 can be lowered so that the entire sheet is stretch formed approximately across the convex die 4 before initiation of the closure of the female die 5. On the other hand, if desired, the head 40 may be arranged so that the stock is not fully laid on the die 4 during stretch forming before initiating the closure of the die 5. The stretch forming and the'closure of the die 5 may progress together so that the stock is, in effect, suspended between the two dies by the stretch forming heads 20 and 419 from theinstantaneous point of closure to the left and thus is less restrained by frictional drag against either die during die closure. After the part is formed in the manner described, the heads 20 and 40 are released from the stock and thereupon the dies 4 and 5 are opened and the article removed. I V

The method and apparatus are particularly suitable for forming the panels described and, when so formed, they are free from what is' commonly known as oil canning, a condition in which, if any pressure is applied from the convex side of the bulge, the panel tends to snap past dead center in the direction of the applied pressure and presents an outwardly concave area at the face to which the force is applied. T V

In cold forming the articles in accordance with the present invention, as herein described, the stock is given its final shape by the action of the drawing dies, but while it is in the more plastic or flowable condition caused by stretching: it into the range above its elastic limit immediately before and during closure of the drawing dies.

As heretofore mentioned, it is possible to stretch the metal above the elastic limit so as to render it plastic and, within a very few seconds and before it work hardens, form it in the compression dies. This is because the metal, when once stretched beyond its'elastic limit, remains for a period of some few seconds in the plastic or fiowable condition so that it can be more readily formed. Therefore, it can be moved from the stretchforming means and placed in a separate press die and formed while in this condition with some advantages. While certain advantages over conventional'die drawing can 9 multidimensionally, then it cannot flow as readily into the dies transversely of the tensioning direction, and air is entrapped, wrinkles formed, and the resultant article does not hold its shape as well. The lateral tensioning of the stock in the present instance is that imposed by the drawing action of the ies.

Preferably, the tensioning is maintai ned above the elastic limit until the dies are fully closed, as mentioned. In many instances, while the dies are held closed on the article, the stock may be given an additional restretch by suddenly increasing pressure in the stretch forming or tensioning piston and cylinder assemblage. If such restretching is desired along both ends of the stock, the head 24 can be operated by a like stretch forming assemblage as that of the head 49, so that with the dies closed, the end margins of the stock can be stretched in opposite directions while the mid-position of the stock is held frictionally in fixed position by the dies. This restretch tends to set the material around the margins.

In the form illustrated, there is a relatively shallow bulge over the entire article and the closure of the dies does not greatly increase the tension on the stock. However, in some instances, the dies themselves during closure do impart a considerable amount of tension. The combined effect may result in tensioning the stock both laterally and longitudinally. If this die imposed tensioning is appreciable in the direction of independently applied tension, it can be allowed for in the tensioning of the stock by the extraneous tensioning means, such as the heads 20 and 40. When this is done, the tension to raise the stock above the elastic limits is determined and generally is provided by the heads 20 and 49. However, if the closure of the dies adds an appreciable tension, which might raise the stock up to its ultimate strength or too high in the range above the elastic limit, then the initial tensioning is reduced during closure of the dies so that the tension applied by the heads 20 and 40, plus the tension imparted by the dies themselves during closure, maintains the stock above the elastic limit but below its ultimate.

Referring next to Figs. 10 through 12, a modified form of the machine is illustrated, this machine functioning in essentially the same manner as that heretofore described. The modified machine comprises a rigid frame 7% on which is mounted a male die 71 and a complementary female die 72, these dies being of compression drawing type. The dies may be mounted on carriers as illustrated. They are arranged so that the extraneous tensioning is in the direction of their short dimension, and they are closed progressively in the same direction. However, they are connected together at one edge by a pivot 73 so that they can swing from open to closed position the same as the dies 4 and 5 heretofore described. Mounted at opposite edges of the dies, respectively, are the extraneous stretch forming means which can tension the stock into a range above its elastic limit independently of operation of the dies. Each stretch unit of these stretching means is the same in form and function, so only the one at the left end of the machine will be described specifically.

Each stretch unit comprises a gripping head 75 which may correspond to the heads 20 and 40 heretofore described. Each head 75 is pivotally connected by a pivot 76 to a rock lever 77 which is rockable about a horizontal axis. For rocking the lever, a piston and cylinder assemblage 78, including apiston 79 and a rod 80, is provided. The rod 80 is pivotally connected by a pivot 81 to the arm 77 and pivotally connected by a pivot 82 to the frame of the machine. Thus the stock can be gripped, stretched, and swung downwardly at its gripped margins so that it is stretch formed to conform approximately to the upper face of the die 71.

In order to close the dies, suitable piston and cylinder assemblages 83 are provided for lifting the dies to open position for permitting insertion of the stock. The as- 10 semblages may be air operated and subject to control to ofier a slight yieldable resistance to closure of the dies.

In order to close the dies, an upright support is mounted on the frame and carries a pressure roll 86. which is urged downwardly under heavy pressure by a piston and cylinder assemblage 87. The roll is mounted in vertical slides 38 which are slidable vertically in guide-' ways 89 in the support 85. The support 85 itself is mounted on suitable longitudinal guideways 89 on the frame 70 for movement lengthwise of the dies 71 and 72. For moving the support 85 lengthwise of the dies, a cylinder 90 is connected to the support 35. A double end piston 91, with rods 92 which are secured at their ends to the frame of the machine, is reciprocable in the cylinder 90. Thus by introducing pressure to opposite sides of the pistons, selectively, the support 85 can be reciprocated endw-ise of the machine. Concurrently with this reciprocation, pressure fluid can be introduced into the cylinders 87 for forcing the roll 86 downwardly to apply the required pressure to the top of the die 72.

These operations are begun with the roller at the right edge of the dies adjacent the pivot 73 and are continued with the roller yieldably pressed against the top of the die 72 as the support 85 is moved to the left edge of the dies. This provides the desired progressive closure of the dies and application of forming or drawing pressure.

After the roll 86 has reached the left edge of the dies 72, the pressure in the assemblages 7% is increased if restretch is desired, and, if not, is reduced. In any event, it is finally relieved, the gripping heads 75 are then released, and thereupon the roll 86 is lifted and moved to the right end of the dies and the dies are opened and the article removed.

As illustrated in Fig. 12, it sometimes happens that it is desirable to form the piece in dies which are the reverse of those indicated in Fig. 11 in that a concave female die 94 is carried on the bed of the machine and the pivoted male die 95 is moved by the pressure applying means into engagement. In suchcase, the stock is stretched above its elastic limit,'across thecavity of the female die, and thereupon thedie 95 is lowered, all in the manner hereto fore described.

Having thus described my invention, I claim:

1. The method of cold forming sheet metal stock into an article between complementary matching male and female drawing dies of which the forming surfaces are curvilinear in both longitudinal and transverse cross section and together define a concavo-convex pattern for the article, and comprising tensioning the stock along only one dimension into a range above its elastic limit to place it in more readily deformable condition, preparatory and prior to,a nd independently of, the initiation of the drawing of the stock by the dies, th reafter, while maintaining the stock in said condition, drawing the stock both longitudinally and transversely to final shape by and between said dies, and maintaining each surface portion of the stock, after said surface portion is initially engaged by the dies, so engaged until the end of the drawing operation so that the surfaces of the dies in their entirety, at the completion of the drawing operation, are in contact with the stock concurrently, and the major portion of the resultant formed article lies within the peripheral limits of the forming surfaces.

2. The method according to claim 1 wherein the independent tens'ioning along said one dimension of the stock is effected by gripping opposite margins of the stock, and the drawing by the dies is effected progressively along said dimension from one of said margins to the other.

3. The method according to claim 1 wherein during the independent tensioning along said one dimension of the stock and the maintenance of the stock in said condition and the drawing of the stock by the dies, the lateral margins of the stock extending along said dimension are left free to be pulled in transversely of that dimension by the d e rawin pe o by the dies is progressive from the margin of one set to the opposite margin of the same set.

5. The method according to claim gl wherein, after the stock is partially drawn by the dies, the independent tensioning is reduced so that the tensioning imposed by drawing by the dies combined with the reduced independent tensioning, maintain the stock within said range and below its ultimate strength during the remainder of the drawing operation. 7

6. The method according to claim 1 wherein the independent tensioning along said one dimension of the sheet stock is effected by gripping opposite margins of the stock, and after the stock is partially drawn by the dies, the independent tensioning is reduced to a degree below said range, but suflicient to constrain the stock from being pulled into the dies from the outside of, the dies in a direction from' one of said margins toward the other during the remainder of the drawing operation.

' 7. The method of cold forming sheet metal stock into an article between complementary matching male and female'drawing dies of'which the forming surfaces, are curvilinear in both longitudinal and transverse cross section and together define a concavo-convex pattern for the article, comprising tensioning the stock along only one dimension into a range above its elastic limit'to place it more readily deformable condition, preparatory and prior to and independently of the initiation of the draw ing of the stock by the dies, and thereafter while maintaining the stock in said condition and allowing it to be 7 pulled inwardly of the dies transversely of said one dimension, drawing the 'stoclrboth longitudinally and transverse ly partially into final shape by and between said dies, then discontinuing the independent tensioning, and drawing the stock to final shape in the absence of said independent tensioning, and maintaining each surface portion of the stock, after said surface portion is initially engaged by the dies, so engaged until the end of the drawing operation, so that the surfaces of the dies in their entirety, at the completion of the drawing operation, are in contact with the stock concurrently, and the major portion of the resultant formed article lies Within the peripheral limits of the forming surfaces.

8. The method according to claim lwherein, after the completion of the drawing operation and while the stock is fully enclosed in'the dies, the independent tensioning in the range above the elastic limit of the stock is temporarily increased.

9. The method of cold forming sheet metal stock hava ing two'sets of opposite margins into an article between condition, preparatory and prior to, and independently 0f, the initiation of the drawing of the stock by the dies,

thereafter, while maintaining the stock in said condition, stretch forming the stock over the male die partially into q'fin-al shape of the article while allowing the 'margins of the other set, which extend along said dimension, to be pulled freely inwardly transversely'of said dimension, then, while maintaining the tensioning and allowing said margins of said'other set to be pulled in freely, drawing the'stock both longitudinally and transversely into final :shape by and between said dies, and maintaining each surface portion of the stock, after said surface portion ;is 'initiallyiengaged by the dies, so engaged until the end of the drawing operation so that the surfaces of the dies in their entirety at the cornpletionfof the drawing operation are in contact with the stock concurrently, and

the major portion of the resultant formed article lies within the peripheral limits of the forming surfaces.

10. The method according to claim 9 wherein the drawing by the dies is effected progressively along said dimension from one margin of said one set to the other margin of said one set. V

11. :In a sheet metal forming apparatus, a frame, complementary male and female drawing dies carried thereby and having matched forming surfaces which are curvilinear in both longitudinal and transverse cross section and together define a concavo-convex pattern for the article, and which are adapted to engage opposite faces of sheet metal stock which has two sets of opposite margins and to form it into an article the shape of the pattern so that the major portion of the article is within the outermost peripheral limits of the forming surfaces, and the surfaces in their entirety are in contact with the stock concurrently when the dies are. fully closed, means supporting the dies on the frame for movement to open .and closed positions so as to maintain each surface portion of the stock, after said portion is initially engaged by the dies,.so engaged until the end of the die forming operation, power means operable to close the dies, stretch forming means, including grippers at opposite margins of one set connectable to said last mentioned margins so as to apply tension to the stock for tensioning the stock, in only the dimension extending from one margin of said one set to the other margin of said one set, into a range above its elastic limit while the stock is between the dies and the dies are open, and for maintaining the stock tensioned in said range during closure of the dies,-and said apparatus being free from means which can restrain the margins of the other set from being pulled freely in transversely of the dies by the dies as the dies are closed.

' 12. The apparatus according to claim 11 wherein means are provided which constrain the dies to close progressively in a direction from one margin of said one set to the other margin of the said one set.

13. The apparatus, according to claim 12 wherein said dies are pivotally connected together at the margins of the dies adjacent to one of the margins of said one set for rocking from open to closed position to effect said progressive closure.

14. The method of cold forming sheet metal stock into an article between complementary matching male and female drawing dies of which the forming surfaces are curvilinear in both longitudinal and transverse cross section and together define a concave-convex pattern for the article of a depth-to-area ratio too shallow to permanently deform the metal to final shape by closure of the dies, and comprising tensioning the sheet stock along only one dimension into a range above its elastic limit to place it in more readily deformable condition preparatory and prior to, and independently of, the initiation of the drawing of the stock by the dies, thereafter, while maintaining the stock in said condition, drawing the stock'both longitudinally and transversely by and between saiddies into a final shape wherein its depth is so :shallow relative to its area that, in the absence of the independent stretching, it-would remain'in the elastic range and not permanently deform into said final shape, and maintaining each surface portion of the stock, after said surface portion is initially engaged by the dies, soengaged until the end of the drawing operation, so that the surface of the dies in their entirety, at the completion of the drawing operation, are in contact with the stock concurrently, and the major portion of the resultantformed article lies within the peripheral limits of the forming surfaces.

References Cited in the file of this patent V UNITED STATES PATENTS 2,619,149. .Self. Names, 1952 2,858,070 Castleton et al Sept. 2, 1958 2,850,071

Kraybill Sept. 2, 1958

Images