US3299689A

US3299689A - Method and apparatus for combined stretch forming and die drawing

Info

Publication number: US3299689A
Application number: US368014A
Authority: US
Inventors: Stanley M Dolney; Robert A Mackenzie
Original assignee: Cyril Bath Co
Current assignee: Cyril Bath Co
Priority date: 1964-05-18
Filing date: 1964-05-18
Publication date: 1967-01-24
Anticipated expiration: 1984-01-24

Description

1967 s. M. DOLNEY ETAL 3,299,689

METHOD AND APPARATUS FOR COMBINED STRETCH FORMING AND DIE DRAWING Filed May 18, 1964 6 Sheets-Sheet 1 L INVENTORS.

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2 1957 s. M. DOLNEY ETAL 7 3,299,689

METHOD AND APPARATUS FOR COMBINED STRETCH FORMING AND DIE DRAWING Filed May 18, 1964 6 Sheets-Sheet 2 32 IM ENTORfi.

2055B?" ,4. MAC/(E/VZ/E Jan. 24, 1967 Filed May 18, 1964 s. M. DOLNEY ETAL 3,299,689 METHOD AND APPARATUS FOR COMBINED STRETCH FORMING AND DIE DRAWING 6 Sheets-Sheet 5 l giltj -jjii:lltfi iiiii fill? I Q P 1% 2 L1: l 2 3 2 2111:: :::f\\;::: -11 :::L LI

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S. M. DOLNEY ETAL METHOD AND APPARATUS FOR COMBINED STRETCH Jan. 24, 1967 FORMING AND DIE DRAWING Filed May 18, 1964 6 Sheets-Sheet 4 IN \I'ENTORS OOO Qua

TTO/P/VEY Jan. 24, 1967 s. M. DOLNEY ETAL 3,299,689

METHOD AND APPARATUS FOR COMBINED STRETCH FORMING AND DIE DRAWING Filed May 18, 1964 6 Sheets-Sheet 5 m VENTORS. J774/\/ 5V M. .004 NE) B05587 A. MACKf/VZ/E s. M. DOLNEY ETAL 3,299,689 METHOD AND APPARATUS FOR COMBINED STRETCH Jan. 24, 1967 FORMING AND DIE DRAWING Filed May 18, 1964 6 Sheets-Sheet 6 INVENTOR5. J'TANAEV M- 004m 205527 A. M C/(A/Z/ X4 ,4 77O/Q/VA K United States Patent Ofiice 3,299,689 Patented Jan. 24, 1967 3,299,639 METHOD AND APPARATUS FOR COMBINED STRETCH FORMING AND DIE DRAWING Stanley .M. Dolney, Parana, and Robert A. Mackenzie,

Chagrin Falls, Ghio, assignors to The Cyril Bath Company, Cleveland, Ohio, a corporation of Ohio Filed May 18, 1964, Ser. No. 368,014 18 Claims. (Cl. 72297) This invention relates to a method and apparatus for combined stretch forming and die drawing of sheet material.

United States Letters Patent of Cyril 1. Bath, No. 2,961,- 028, issued November 22, 1960, and No. 3,116,780, issued January 4, 1964, disclose a method of combined stretch forming and die drawing and apparatus therefor.

As therein more fully described, sheet metal stock is formed by stretching it along one dimension into a range above its elastic limit so as to render the metal more readily formable. While the metal remains in the more readily formable condition as a result of stretching, it is drawn to final shape between conventional drawing dies. The tensioning is eifected along one dimension of the stock by gripping two opposite margins of the stock in gripping heads and then moving the heads relatively apart while leaving the other margins which extend along the tensioning dimension free to be pulled in laterally by the dies as the dies close.

In some instances, the metal is pulled in solely by the portions of the dies which draw the part of the blank that becomes the final article or part after trimming. In others, the margins of the dies surrounding such part are provided with matching beads and grooves. These beads and grooves become operative initially to gather or draw metal into the dies as the dies are closing. Near the end of the drawing operation, after the article is almost drawn to final shape, they place a yieldable restraint on the already drawn in margins so that the remainder of the metal lying within the drawn in margins is drawn to a greater degree than it would be in the absence of such restraint. This restraint, however, is imposed only by the dies themselves during their closure and not by any hold down means operable independently of the closure of the dies or prior to the drawing of the metal by the cooperation of the dies. This method, with or without the beads, has proven highly effective for large numbers of shapes.

However, in some instances in which abrupt changes of contour or so-called sharp character lines are required for decoration or utility, improved results can be obtained by controlling the movement of the stock inwardly of the dies in a direction transversely of the tensioning dimension. This control can be effected by means which can be operated independently of the die movement and thereby initiate the restraint prior to any drawing by the coaction of the dies, or at any stage of die closure.

In accordance with the present invention, the metal stock is first prestretched in one dimension into a range above the elastic limit so as to render the metal more readily formable by the dies, as described in the above patents. Then, preferably before drawing the metal by the coaction of the dies but while the stock is in the more readily forma-ble condition, the margins of the stock extending along the tensioning dimension are engaged by hold down means which restrain and control the movement of the margins inward-1y transversely of the tensioning dimension during the closure of the dies. The hold down means are operable for gripping the margins independently of the die closure so that, if desired, the restraint can be initiated not only prior to any drawing by die closure, but also at any stage of drawing by the dies, and continued until the dies are fully closed.

For brevity in description, the dimension in which the sheet metal stock is stretched by the stretch forming units preparatory to die'closure are referred to hereinafter in the description and claims as endwise, the margins gripped by the units are referred to as end margins, and the margins extending along the tensioning dimension are referred to as lateral margins. These terms are used whether the stock is longer or shorterin the dimension of tensioning than transversely thereof. t

For carrying out the present method a conventional double action press is employed, as distinguished from the single action press disclosed in the above patent. The stretch forming units may be carried by the press directly, or by fastening them on one of the drawingdies, as illustrated.

Generally it is preferable to maintain tensioning by the stretch forming units during die closure. In such a case, only the lateral margins of the stock are controlled by the hold down means, and the stretch units are used to control the pull in of the end margins gripped by the stretch units. In this instance, stretch units which app-1y yieldable tensioning force to the stock are employed, as they can be drawn inwardly endwise by the stock with controlled yieldable resistance during die drawing.

On the other hand, in some instances, it is unnecessary to maintain the tension by the units during drawing. This is because once the metal is tensioned above the elastic limit to render it more readily deformable, it remains in the more readily deformable condition for an instant. Accordingly, as soon as the metal is thus tensioned, its entire peripheral margin may be gripped immediately by the hold down means, and the dies operated immediately to draw the metal While this more readily deformable condition obtains and before work hardening. In such an instance, the stretch forming units may be released from the metal before or after' gripping of the peripheral margin of the stock by the hold down means. This is possible because the press operation is sutliciently rapid so that the more readily deformable condition of the stock exists at the time of die closure whether the gripping beads are maintained in gripping relation thereto or not.

The restraint imposed on the lateral margins of the sheet is not usually a total restraint, but instead a controlled restraint obtained by affording some slippage of the stock margin gripped by the hold down means. This slippage is selected in accordance with requirements im posed by the shape of the particular article being formed, Only in usual circumstances are the gripped lateral margins completely locked against slippage and resultant movement inwardly of the die.

As mentioned, the stock is first stretched endwise by the stretch forming units before it is drawn by coaction of the dies, but it may be stretched by the units partially over the male die only, and then subsequently restrained at the margins by the hold down means.

In either event, after the stock is thus rendered more readily deformable prior to coaction of the dies, the press is operated to cause the hold down means to engage the selected margins of the stock under predetermined pres sure while the stock remains, or is maintained, in the more readily deformable condition.

Various 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 the combined die drawing and stretch forming press embodying the principles of the present invention;

FIG. 2 is a bottom plan view of the male die and the hold down means showing their relation in the press;

FIG. 3 is a top plan view of the female die with the stretch forming units of the present invention in assembled 3 relation therewith as viewed from line 3-3 in FIG. 4, but with the male die lifted clear of the female die;

FIG. 4 is an enlarged fragmentary front elevation of the stretch forming units and female die illustrated in FIG. 1, part of one of the stretch forming units being shown in vertical section for clearness in illustration;

FIG. 5 is an enlarged right end elevation of the female die and one of the stretch units mounted thereon;

FIG. 6 is a fragmentary enlarged cross sectional view taken on line 66 in FIG. 1 and showing the hold down means and its manner of cooperation with the female die;

FIG. 7 is a view similar to FIG. 2, showing a modification of the hold down means thereof;

FIG. 8 is a view similar to FIG. 3. illustrating a modified form of hold down surface on the female die;

FIG. 9 is a diagrammatic illustration of the hydraulic and electrical control circuitry of the apparatus adapted for performing the method of the present invention automatically;

FIG. 10 is a fragmentary front elevation of the press such as illustrated in FIG. 1 with a modified form of the stretch unit incorporated therein;

FIG. 11 is a fragmentary top plan view of the female die and one of the stretch forming units illustrate-d in FIG. 10; and

-FIG. 12 is a fragmentary right end elevation of the press and one of the stretch forming units thereon.

Referring to the drawings, the present invention is shown as embodied in a conventional double action mechanical press-of the toggle operated type, its use with other types of mechanical presses'and hydraulic presses being readily apparent from the illustrative example.

Referring first to FIG. 1, the press, indicated generally at 1, comprises abed 2 with upright frame members 3 disposed at opposite ends of the bed. The members 3 are connected at the top to a suitable crown 4 which supports the driving mechanism of the rams of the press.

Mounted in suitable guideways 5 on the frame members 3 for reciprocation vertically is an outer or a hold down ram 6 generally in the form of a rigid box-like frame which is open at the top and bottom. The peripheral bottom edge 7 is adapted to support a conventional hold down ring, as will later be described.

Mounted within the ram 6 is a die carrying ram 10. The ram 10 has suitable extensions 11 which operate in guideways 12 on the members 3 and support the ram 10 for vertical movement relative to the ram 6. The die carrying ram 10 and hold down ram 6 are thus mounted for movement in parallel vertical paths independently of each other.

For driving the hold down ram 6 and die carrying ram 10, a suitable motor 11 is mounted on the crown 4 and drives a flywheel 12. The flywheel 12 carries a coaxial pinion 13 which, in turn, drives a gear 14.- The gear 14 carries a coaxial pinion 15. The pinion 15 directly drives one of two main driving gears 16 and, through an'idler gear 17, the other of the two main driving gears 16. The main driving gears 16 carry coaxial pinions18, respectively, one of which drives one oftwo driving gears 19 and the other of which drives the other of the two driving gears 19. The gears 19 carry eccentric crank pins 20 which are connected by links 21, respectively, to the ram 10. Carried on the shafts of the gears 16, for rotation relative thereto, are cranks 22a of conventional linkages 22, indicated in dotted lines The linkages are driven by eccentrics 22b on the gears 19, and through cranks 22a and links 23, drive the ram 6 with conventional dwell at the bottom of its stroke.

In operation of the press, the hold down ram 6 first moves to a bottom or seated position and there dwells. During the dwell, the ram 10 continues moving downwardly so that its die engages and draws the stock to final shape, after which the hold down ram 6 retracts.

Adjustment devices 24 are provided between the links 21 and the hold down ram 6, and-adjustment devices are provided between the links 23 and the ram 10. The adjustment devices 24 and 25 are for adjusting the vertical starting positions of the hold down ram 6 relative to the die ram 10 so that the seating of the hold down ring on' the ram 6 and the movement of the die to final position by the ram 10 can be adjusted with relation to each other, depending upon the requirements of the particular work to be formed.

The outer ram or hold down ram 6 carries at its lower end a hold down ring 30 having an under surface for cooperation with suitable holding surfaces on the female die. In the form illustrated, the ram 10 carries a male die 31. The press frame carries a bolster block 32 which, in turn, supports a female die 33. Generally, suitable elongated beads are provided on the under side of the ring 30 for cooperation with suitable grooves in the upwardly facing margin of the female die for gripping and controlling the pull in of the metal inwardly of the dies during the drawing operation.

The structure thus far described is a conventional press which may be purchased on the market, and of itself does not embody the present invention.

As described in the above patent, the metal is left free to be drawn in transversely of the dies except for such control as might be afforded by configuration in the cooperating faces or margins of the dies themselves. There is no hold down means operable independently of the dies themselves for holding the lateral margins ofthe stock and controlling the degree to which the metal is permitted to be pulled in laterally by closure of the dies.

In the present invention, the stretch forming units 34 are arranged at opposite ends of the die 33 on the bolster 32. These units may be the same as the units described in the above Patent No. 3,116,780 of January 7, 1964. However, it is advantageous to mount them on the upright end walls of the female die 33 by suitable means, such as the bolts 35.

7 Each unit 34 comprises a supporting body 36 in which is provided a reversible hydraulic piston and cylinder assemblage 37 comprising a row of cylinders 38 in which are pistons 39 having piston rods 40. The ends of the rods 40 are secured to a fixed end plate 41 of the body 36 through which the bolts 35 extend and secure the unit to the female die 33. The cylinders 38 preferably are formed in a common block, which is connected by spacers 42 to a stretch forming head 43. The stretch forming head 43 is supported on the top of a body 36 in suitable guideways 44 for movement transversely of the die path endwise of the stock. The head 43 is shown as having complementary gripping jaws 45 and cooperable wedges 46 so arranged that when the stock is gripped between the jaws and tension is applied, the jaws are drawn more firmly into gripping position. The jaws are moved to open and closed positions by means of a reversible piston and cylinder assemblage 47, the piston rod 48 of which is connected to the jaws.

The two units may be identical with each other. They are operable independently of each other. The manner of operation is illustrated in the schematic diagram of FIG. 9.

The stretch heads 43 may be, if desired, arranged on elevators as in the above Patent No. 3,116,780, particularly if the male die is carried on the bolster. This is so that the metal can be first stretched about the male die by the stretch heads if desired, though this is not essential. When the female die is carried on the bolster and the male die on the ram as illustrated, the elevators are unnecessary.

The specific details of the structure of the units 34, other than their connection to the die, are not a part of the present invention.

The stretch units 34 thus are adapted to grip opposite end margins of a length of stock and stretch it into a range above its elastic limit preparatory to closure of the dies and, if desired, during closure of the dies.

Preferably the units are arranged with the throats of the heads 43 close to the plane of the upper faces of the margins of the female die so that the heads will not have to be moved vertically during the forming operation and can be made a part of the die itself. Thus each die being provided with its own stretch units particularly adapted for its use in high production and used in such double action press is available.

Referring next to FIG. 2, the hold down ring 30 is in the form of a frame having lateral margins 50 extending in the direction of tensioning and end margins 51 extending transversely of the direction of tensioning. In the form illustrated in FIG. 2, the under faces of the lateral margins 50 are provided with raised beads 52. Such beads are conventional and, as best illustrated in FIG. 6, are in the form of solid rods 53 held in place by suitable screws, not shown. These beads are thus replaceable and may be ground off for obtaining the amount of hold down pressure required on the margins of the sheet at different portions therealong. Thus by adjusting the hold down pressure applied on the hold down ring 30 by the conventional press adjustment devices 24 of the outer or hold down ram 6 and by modifying the beads 52 by grinding, filing, shimming, or the like, preselected frictional resistance to the drawing or pulling in of the sheet margins gripped beneath the ring 36 can be provided.

Correspondingly, the margins about the cavity of the female die are provided with upwardly open grooves 57 which cooperate withthe bead 52 so that the stock can be drawn thereinto by the beads and held fixedly or with controlled slippage, as desired.

In the form illustrated in FIGS. 1 through 4, it is assumed that the stretch heads 43 will be maintained operable to provide yieldable tensioning force on the stock endwise of the stock preparatory to and during die closure. For this reason, the end margins 51 of the ring 38 are ground back slightly so they do not exert any pressure on the stock at the ends aligned with the gripping heads 43. Thus the gripping heads take over the maintenance of yieldable resistance to draw in of the stock endwise. The amount of draw in endwise can be controlled by controlling the hydraulic pressure supplied to the stretch heads. In operation, the stretch units 34 are operated to stretch the stock into a range above its elastic limit. The rams are started on their cycle, the hold down ram 6 first applying the hold down ring 30 to the margins of the stock while the stock is held under tension by the stretch units. Due to the lazy link power transmitting connections to the rams 6 and 10, the ring 30 can dwell in gripping position as the ram descends to final position. Further downward movement of the ram 10 applies the drawing die 31 to the stock to force it into the female die and draw it to final shape.

With this arrangement, the forming of some shapes which, due to so-called sharp character lines or abrupt changes in surface contour cannot be readily formed by prior methods and apparatus to the sharpness required, can be formed readily.

Usually, as mentioned, the hold down beads 52 and the grooves 57 of the die are such that the metal stock is not completely locked at the lateral edges but can slip and move in if the increase in tension due to die closure exceeds a predetermined amount. By grinding off the heads at different places along their length, the amount of resistance to draw in at diiferent positions along the sheet relative to other portions can be controlled.

It sometimes happens, however, that severe draw-in may be present at the ends of the stock and it is desired not to maintain this draw-in by the stretch heads. In such case, a ring 58 may be substituted for the ring 30. The ring 58 has lateral margins 59 and end margins 69. The only difference between the rings and 58 gage and grip the end margins of the stock. The margins 60 may be provided with beads 61 for engagement with the corresponding grooves in the female die. Accordingly, the female die, indicated at 62, is modified to provide grooves 63 complementary to the end beads 61. The lateral margins of the ring 58 contain heads, the same as the lateral margins of the ring 30.

In some cases, it is not necessary to provide beads since the clamping pressure of the fiat under surface of the ring 58 at the end margins, or lateral margins may be sufiicient. The use of beads, however, gives better control.

When using the form of hold down ring illustrated in FIGS. 7 and 8, there is no need to maintain the tensioning pressure on the gripping heads 43 after the hold down ring 58 is in seated position. Accordingly, if desired, after the hold down ring 53 is firmly seated on the stock, the pressure in the units 34 may be released. However, it can be used to supplement the holding effect of beads 61, so that finer variations in slippage can be obtained by varying the pressure if fluid supplied to the stretch units.

In some cases, for high speed production, it is desirable that the operations be controlled automatically and for this purpose, control of the stretch units relative to the cycling of the press can be obtained by circuitry such as illustrated in FIG. 9. As there illustrated, the circuitry for each unit 34 may be the same so that one only is described in detail.

Each circuit includes a pump P driven by a motor M. The pressure side of the pump is connected to a solenoid operated cut-off and reversing valve 64 which, in turn, is connected to the piston and cylinder assemblage 47 for jaw operation. When the valve is shifted to one position it admits fluid pressure to the assemblage 47 so as to close the jaws and when moved to another position it admits fluid pressure so as to open the jaws. The valve may be spring restored to a neutral position or to an open jaw position, if desired, but, as shown, is operated by solenoids 64a and 64b.

The pressure side of the pump is connected also to a suitable solenoid operated cut-off and reversing valve 65 which is connected to the stretch forming assemblage 37. It is so operated that it can lock the assemblage 37 in any selected position, or can admit pressure fluid for tensioning the stock and, in turn, release the fluid pressure for driving the heads relatively toward each other for releasing the stock. The valve 65 is operated by suitable solenoids 65a and 65b.

While not shown, the usual pressure regulators and like devices may be provided between the outlet of the pump and the valve 65, for example, as indicated in the above Letters Patent 3,116,780. Details of such specific control elements form no part of the invention.

The solenoid 64a is operated by a limit switch 640 and the solenoid 6412 by a limit switch 64d. The solenoid 65a is operated or controlled by a limit switch 650 and the solenoid 65b by a limit switch 65d. Corresponding limit switches control corresponding solenoids for the circuit of the other unit 34 which bears in the diagram the same numbers as the one described.

In order to operate the limit switches in relation to the position of the hold down ram 6 and die ram 10, they may be operated by a suitable rotatable drum 67 controller driven by a pulley 68 which may be connected to one of the driving gears of the press.

The drum control 67 is a conventional type in which sockets 67a are provided and receive suitable pins 69 which are detaichably inserted in the proper sockets in the drum for tripping the switches in selected relation to the positions of the rams. These pins are operative to trip the switches mechanically as the pins pass preselected locations.

Various other means of operating the switches in sequence may be employed if desired, or the sequence may be effected by manual manipulation of the limit switches.

In some instances, it is desirable for high speed production that all of the operations be performed mechanically. For this purpose, the modification shown in FIG. 10 is employed.

As there illustrated, the press structure is essentially the same as the pressure structure heretofore described except for the mechanical means for operation of the stretch forming units. The press is shown as provided with a bolster 70' corresponding to the bolster 32. The bolster supports the female die 73 having a peripheral margin 74. Bolted to opposite ends of the die 73 are stretch units 75. Each unit includes a stretch head 76, such as heretofore described. The stretch head 76 is carried on an elevator 77 which has limited vertical movement to assure proper bottoming of the hold down ring, as is later described. The elevator 77 is urged upwardly and yieldably retained in its uppermost position by means of air or yieldable fluid pressure piston and cylinder assemblages 78, arranged at the front and rear of the press. Each head is mounted on a carriage 79 which is movable along horizontal guideways on the top of its elevator toward and away from the path of the dies. At the ends of the head are upwardly open sockets 80 which have cam surfaces 81. Mounted on the hold down ram are rigid depending members 82 carrying at their lower ends suitable cam members 83 which can enter the sockets 80. The members 83 have cam surfaces 84 complementary to the cam surfaces 81 of the sockets 80. The cam surfaces are arranged so that as the members 83 are lowered by the outer or hold down ram, they cooperate to force the stretch heads 76 relatively apart for stretching the stock. Themembers 8-2 have bottoming shoulders 85 which, when the stretch heads have been moved their maximum distance apart, engage suitable shoulders 86 on the upper ends of the heads 76. These shoulders are arranged so that the heads are in the outermost stretching or tensioning position selected at the time of bottoming of the shoulders. The outer ram 87 carries a hold down ring 88 illustrated in FIG. 10. The ring 88 may have beads 88a which, if desired, may extend about substantially the entire periphery of the lower end of the ring. These surfaces cooperate with surfaces on the upper margin of the female die which may be provided with grooves 88b extending about the entire periphery of the upwardly facing margin of the female die for cooperation with beads 88a when such beads are provided. Upon lowering of the ram 87, the heads 76 are first moved apart to stretch the stock, after which the

shoulders

85 and 86 engage and move the heads 76 and their elevators 77 downwardly against the resistance of the restoring cylinder assemblages 78. The members 82 are mounted in the ram 87 for vertical sliding movement relative thereto to extended and retracted positions and are yieldably held in extended positions by springs 89. This arrangmen-t provides a lost motion connection such that when the shoulders 85 force the stretch heads 76 to their lower-most position against stops 90, the outer or hold down ram 87 can continue to descend. The stops 90 are positioned so that when the heads 76 bottom, the stock is substantially in the plane of the upper faces of the margins of the die 73. This action brings the stock down substantially to the level of the upwardly facing upper margins of the female die 73, preferably disposing the stock against the margins while it is held stretched. This is followed by engagement and dwell of the hold down ring 88.

Since the stretch heads 76 are not urged yieldably apart and are not permitted to be drawn toward each other by the stock under yieldable resistance as the dies close, the jaws of the head 76 usually are released after the ring 88 seats and before die drawing occurs. This may be done by any suitable limit switch arrangement operated in timed relation to the operation of the outer ram of the press, .or manually. The inner ram, indicated at 91, carries a male die 92 cooperable with the female die.

In operation upon lowering of the two rams 87 and 91 concurrently, the outer ram, through the

members

82 and 83, moves the heads 76 relatively apart and stretches the material. This movement continues until the shoulders and 86' engage, whereupon they move downwardly and move the heads 76 downwardly with the outer ram while the heads remain in stretching position. This operation continues until the hold down ring 88 seats. Thereupon the gripping jaws of the stretch heads 76 are released. Continued operation of the press causes the ring 88 to dwell in gripping position and the die a2 to cooperate with the female die 73 to draw the stock promptly while it is still in more readily deformable condition as a result of its immediately preceding stretching above its elastic limit.

The releasing of the jaws of the stretch units in relation to the operation of the outer ram 87 is not shown, but it may be by conventional limit switches operated by a drum moved in timed relation to the driving of the outer ram, as hereinbefore described in connection with FIGS. 1 through 9.

In order to restore the heads to their innermost positions for inserting the stock as they are released by the members 83, suitable air operated piston and cylinder assemblages 93 are connected to the carriage of the heads, the air therein being compressed by movement of the units relatively apart, so that upon release of the units, the air re-expands and drives the heads inwardly toward their original loading or starting position. If desired, compression springs may be used in the assemblages 93 instead of air for this purpose.

It is apparent that, in accordance with the present invention, the stock is first tensioned into a range above its elastic limit preparatory to its being formed by cooperation of the companion drawing dies, and preferably while it is out of contact with either die. While thus stretched, it is engaged by the hold down ring, in the first instance, at its lateral margins while held under yieldable tension at its end margins by the stretch heads, the lateral margins being thus constrained, to the degree selected, from inward movement by the hold down and the end margins by the stretch heads. While still in this readily deformable condition and so controlled, the dies are closed drawing the piece into a finished article. The usual knock-out pins and the like may be provided in the female die for releasing the article therefrom. Such are conventional and form no part of the present invention.

In both forms of the structure, as mentioned, the stock may be held at all margins by the hold down ring after once stretched, the jaws of the stretch heads being released after seating of the ring so that thereafter all control of the inward movement of the margins of the stock is by virtue of the hold down ring.

Having thus described our. invention, we claim:

1. In a combined stretch forming and die drawing apparatus,

a ram member,

a bed member,

power means for moving the members relatively toward and away from each other,

complementary male and female drawing dies carried by the members, respectively, for movement thereby to closed and open positions, for drawing sheet metal stock therebetween upon closure,

power operated stretch forming means including stock gripping heads at two opposite sides of the path of the dies for gripping two opposite margins of the stock and for stretching the stock endwise prior to movement of the dies to closed position,

power driven restraining means at the other two opposite limits of the die path and operable, independently of the dies and stretch forming means, after the stretching operation and prior to said movement of the dies to closed position for gripping opposite faces of the stock at the lateral margins and for holding the margins gripped with predetermined holding pressure, during movement of the dies to closed position, for controlling the lateral draw in of the stock by the dies during die closure.

2. An apparatus according to claim 1 wherein the restraining means include power means operable to cause the restraining means to engage the stock with sufiicient force to hold the margins fixedly in the position in which gripped.

3. An apparatus according to claim 1 wherein additional power operated restraining means are provided at the said two margins gripped by the stretch forming means, and are operable, after stretching of the stock by the stretch forming means, to engage the stock and resist draw in of the stock endwise by the dies.

4. An apparatus according to claim 1 wherein means are provided for releasing the stretch forming means after the additional power operated restraining means are rendered operative.

5. An apparatus according to claim 1 wherein the stretch forming means are operable to apply yieldable tensioning force to the stock endwise of the stock while the power operated restraining means are operative.

6. An apparatus according to claim 1 wherein the stretch forming means are carried on one of the dies.

7. An apparatus according to claim 1 wherein the stretch forming means are carried by one of the members, and means connect the other member to the stretch forming means so as to move the stretch forming heads relatively apart as the members move toward each other.

8. An apparatus according to claim 1 wherein the stretch forming means are arranged to suspend the stock between, and out of contact, with the dies, and to stretch the stock, while the dies are open, and the restraining means are operable to engage margins of the stock while the stock is so suspended.

9. The method of combined stretch and draw die forming of sheet metal stock, and comprising applying yieldable stretching force to two end margins of a length of stock to stretch the stock endwise and thereby render it more readily formable while leaving the lateral margins of the stock free to draw inwardly of the stock transversely of the stock, then after stretching the stock and while it is thus more readily formable, gripping at least the lateral margins of the stock and thereby resisting draw in of the lateral margins toward each other, and, while thus resisting lateral draw in, promptly drawing the stock between matching drawing dies.

10. The method according to claim 9 wherein the forces resisting draw in of the stock by the dies is applied to all margins of the stock prior to drawing by cooperation of the dies and said forces are maintained during the drawing of the stock by coaction of the dies.

11. The method of drawing sheet metal stock comprising applying stretching force to the opposite end margins of a length of stock to stretch the stock endwise and thereby render it more readily formable while leaving the lateral margins of the stock free to draw inwardly of the stock transversely of the stock, then after stretching the stock, and while maintaining the application of said stretching force, gripping the lateral margins of the stock, thereby causing forces resisting draw in of the lateral margins toward each other, and while the stock is thus in more readily deformable condition, drawing the stock within said margins between matching drawing dies while all of said margins are subjected to their said associated ones of said forces.

12. The method according to claim 11 wherein resisting forces are applied to all margins while said stretch forming forces are still being applied but subsequent to the stretching, the stretch forming forces are then released and the resisting forces maintained, after which the stock is drawn.

13. The method according to claim 11 wherein the stretching force is a yieldable force, and the end margins ?re restrained from draw in by the yieldable stretching orce.

14. The method according to claim 11 wherein additional force resisting draw in is applied at the end margins while the stretching force is maintained, and upon ap-- plication of the additional force, the stretching force is released.

15. The method of forming sheet metal stock comprising, applying stretching force to opposite end margins of a sheet of stock to stretch it endwise sufiicient to render it more readily drawable while leaving the lateral margins of the stock free to draw inwardly transversely of the stock, then releasing the stretching force, and promptly, while the stock remains in the more readily drawable condition, first applying to the stock margins, in a direction generally normal to their faces, restraining forces for frictionally resisting draw in of the stock by the dies, and then drawing the stock by the dies.

16. The method of combined stretch and draw die forming of sheet metal stock, comprising applying stretching force to two opposite end margins of a length of stock and thereby stretching the stock endwise beyond its elastic limit to render it more readily formable while leaving the lateral margins of the stock free to draw inwardly transversely of the stock and while the stock is clear of the article forming surfaces of matching drawing dies by which it is to be drawn, then, after thus stretching the stock and while it is in a more readily formable position, gripping at least portions of the lateral margins of the stock and thereby resisting the draw-in of the lateral margins toward each other and, while thus resisting lateral graw-in, promptly drawing the stock by closure of the res.

17. An apparatus according to claim 1 wherein the stretch forming means are arranged to suspend the stock between, and out of contact, with the dies, and to stretch the stock, while the dies are open, and the restraining means are operable to engage margins of the stock and apply holding force thereto prior to drawing of the stock by cooperation of the dies with the stock.

18. An apparatus according to claim 1 wherein the stretch forming means are arranged to suspend the stock between, and out of contact, with the dies, and to stretch the stock, while the dies are open, and the restraining means are operable to engage margins of the stock and apply holding force thereto prior to the dies becoming fully closed.

References Cited by the Examiner UNITED STATES PATENTS 2,002,097 5/ 1935 Peterson 72297 2,302,953 11/1942 Pocock 72-302 3,113,607 12/1963 Maize 72296 CHARLES W. LANHAM, Primary Examiner. R. IQ. GREFE, Assistant Examiner.

Claims

1. IN A COMBINED STRETCH FORMING AND DIE DRAWING APPARATUS, A RAM MEMBER, A BED MEMBER, POWER MEANS FOR MOVING THE MEMBERS RELATIVELY TOWARD AND AWAY FROM EACH OTHER, COMPLEMENTARY MALE AND FEMALE DRAWING DIES CARRIED BY THE MEMBERS, RESPECTIVELY, FOR MOVEMENT THEREBY TO CLOSED AND OPEN POSITIONS, FOR DRAWING SHEET METAL STOCK THEREBETWEEN UPON CLOSURE, POWER OPERATED STRETCH FORMING MEANS INCLUDING STOCK GRIPPING HEADS AT TWO OPPOSITE SIDES OF THE PATH OF THE DIES FOR GRIPPING TWO OPPOSITE MARGINS OF THE STOCK AND FOR STRETCHING THE STOCK ENDWISE PRIOR TO MOVEMENT OF THE DIES TO CLOSED POSITION, POWER DRIVEN RESTRAINING MEANS AT THE OTHER TWO OPPOSITE LIMITS OF THE DIE PATH AND OPERABLE, INDEPENDENTLY OF THE DIES AND STRETCH FORMING MEANS, AFTER THE STRETCHING OPERATION AND PRIOR TO SAID MOVEMENT OF THE DIES TO CLOSED POSITION FOR GRIPPING OPPOSITE FACES OF THE STOCK AT THE LATERAL MARGINS AND FOR HOLDING THE MARGINS GRIPPED WITH PREDETERMINED HOLDING PRESSURE, DURING MOVEMENT OF THE DIES TO CLOSED POSITION, FOR CONTROLLING THE LATERAL DRAW IN OF THE STOCK BY THE DIES DURING DIE CLOSURE.