US2301960A

US2301960A - Method and apparatus for forming metal sheets

Info

Publication number: US2301960A
Application number: US368604A
Authority: US
Inventors: Lermont Basil; Arnold M Wolf
Original assignee: CAIRNS CORP
Current assignee: CAIRNS Corp
Priority date: 1940-12-05
Filing date: 1940-12-05
Publication date: 1942-11-17
Anticipated expiration: 1959-11-17

Description

Nov. 17, 1942. B. LERMONT ETAL 2,301,950

' METHOD AND APPARATUS FOR FORMING METAL SHEETS Filed Dec. 5. 1940 5 Sheets-Sheet 1 35 34 Basil Lermazzt 10 50 2g 28 BY flnwZdfl-W ATTORNEY Nov. 17, 1942. LERMQNT ETAL 2,301,960

METHOD AND APPARATUS FOR FORMING METAL SHEETS Filed Dec. 5, 1940 5 Sheets-Sheet 2 INVENTORS Basal 'Lermont ATTORNEY Nov. 17 1942 B. LERMONT ETALJ METHOD AND APPARATUS FOR FORMING METAL SHEETS 5 Sheets-Sheet 3 Filed Dec. 5. 1940 A Ali n. A 4 A AA AA l AzA 6 A lNV'Eb lTORS' Basil-Lamont BY .flrnold/YJ Vo.

ATTORNEY Nov. 17, 1942. B. LERMONT ETAL METHOD AND APPARATUS FOR FORMING METAL SHEETS Filed Dec. 5, 1940 5 Sheets-Sheet 4 NMN l f dw v ATTORNEY Nov. 17, 1942. B. LERMONT ET AL METHOD AND APPARATUS FOR FORMING METAL SHEETS Filed Dec. 5, 1940 5 Sheets-Sheet 5 Patented Nov. 17, 1942 METHOD AND APPARATUS roa FORMING METAL snca'rs Basil Lermon t, New York, and Arnold M. Wolf.

Brooklyn, tion, New York, N. ware N. Y., asalgnors to Cairns Oormra Y., a corporation oi Dela- Application December 5, 1940, Serial No. 368,604

22 Claim.

This invention relates to methods and devices for shaping sheets of metal into compound curved forms and relates more particularly to methods and devices for forming transversely and longitudinally curved sheets by means of a pulling or drawing operation. N

Devices of the type embodying the invention are characterized by transversely curved forming elements by means of which sheets may be stretched at their centers and edges to varying degrees to cause the sheets to bulge and thereby assume transverse and longitudinal curvatures by pulling the sheets over said forming elements. The forming elements may be moved relatively to vary the curvature of the sheet. The sheets are stretched principally in the direction of pull but at the same time stresses are set up in the sheet having components extending at angles to the direction of pull. These stresses tend to cause the-sheet to spring back or form the sheet into a coil. In addition to the mechanism described above the devices embodying the present invention may also include elements for limiting the shrinkage of or for stretching the sheet transversely to the direction of pull simultaneously with the longitudinal stretching operation in order to overcome the tendency of the sheets to form themselves into coils. The transverse stretching strains the sheet transversely in opposition to the transverse component set up by stressing sheet longitudinally and overcomes the tendency of the sheet to curl or form itself into a coil. This straining of the sheet transversely results in the accurate control and the stabilizing of the transverse curvature directly, as contrasted with the relatively uncontrolled transverse curvature imparted to the sheet as a component of the longitudinal stretch.

Devices of this type may be manually or automatically controlled to produce characteristically shaped sheets or large numbers of identical sheets of many different shapes, such as for example, aero-dynamically curved plates for use in the wings and iuselages of airplanes. Such aerodynamic forms usually are of varying curvature and must be carefully and accurately formed so that they may be joined without setting up undesirable stresses therein. The transverse stretching of the sheets together with the longitudinal stretchr' ing assures the formation of smooth sheets of accurately controlled curvature which do not tend to buckle or change shape due to unequally dis tributed stresses therein.

For the better understanding of the present invention reference may be had to the accompanying drawings, in which a Fig. 1 is a'view in side elevation of a typical form of device embodying the present invention;

Fig. 2 is a view in end elevation of the device;

Fig. 3 is a view in side elevation of the forming elements of the device;

Fig. 4 is a perspective view of the cooperating curved and straight edge forming elements of the device;

Fig. 5 is a plan -view of one of the elements for transversely stretching the sheet of metal;

Fig. 6 is a view in section taken on line 6-8 of Fig. 5;

Figs. '7 and 8 are respectively side and top views of portions of the links .forming the gripping elements of the transverse stretching device;

Fig. 9 is a wiring diagram of the controls forthe transverse stretching mechanism;

Fig. 10 is a view in side elevation of a modified form of device embodying the invention; and

Fig. 11 is an end View of the device disclosed in Fig. 10.

In the form of the invention disclosed in Figs. 1 to 4 the sheet shaping mechanism is applied, for example, to a conventional metal planer. This device includes a supporting framework it upon which is slidably mounted a draw bench l l which is adapted to be moved longitudinally of the supporting frame It.

The device includes a standard l2 consisting of side elements l3 and it. connected by a cross member I 5 and having a planer crosshead it extending between the side elements l3 and it about midway of their height.

A secondary framework, which consists of supporting legs I! and having a platform l8 further supported on the standards l3 and Hi, serves as a support for the lower forming element of the device, presently to be described. The platform It also supports a second spaced platform l9 upon which the lower forming element 20 is directly supported as best shown in Figs. 3' and 4.. The lower forming element 20 consists of a flexible bar 2| of generally rectangular cross-section but having a curved leading edge 22 and downwardly projecting end portions 23 and 24 which are received in

recesses

25 and 26, respectively, in the supporting platform IS. The

recesses

25 and 26 are of substantially the same width as the end portions 24, but are of greater length in order to permit the end portions to move toward and away from each other. The end portions 23 and 24 may be secured in the slots 25 and 26' by

meansof pins

23a and 24a which pass through the end portions and are received in slots a. and 230. in the sides of the

slots

25 and 28.

The bar 2| normally is flat, but can be bowed transversely by. means of a plunger 21 which projects upwardly through the platform I! and is moved in a vertical direction by means of a tapered cam 28.

The cam 23 is slidably supported in a housing 29 which is secured to the under surface of the platform l9, said cam being movable only in a horizontal direction. The movement of the cam 23 is controlled by a rack and pinion construction 30 and 3|, the rack 30 being supported for sliding movement on a platform 32 which projects laterally from the standard l4. The rack may be moved endwise in any desired way as, for example, by, means of a crank and pinion (not shown).

-The pinion 3| is fixed to a horizontal shaft 33 and has an externally threaded inner end 34 which is received in a turn buckle 35 ,on the end of a rod 33 which is connected to the right-hand end of the cam 28. Upon endwise movement of the rack 3| the shaft 33 is rotatedthereby screwing it into or out of the turn buckle 35 and shifting the cam 23 endwise. As the cam 28 moves to the right the plunger 21 is moved upwardly causing the strip 2| of the forming element to bend upwardly. As the inclined cam 28 moves to the left the normal resiliency of the strip 2| of theforming element 20 causes it to straighten and tend to return to its initially flat form.

As best shown in Figs. 2 and 3, a second cooperating forming element is also provided for causing the sheet of material S to be stretched and worked and thereby shaped into transversely and longitudinally curved form. This forming element 31 consists of an elongated block preferably formed ofmetal to aiford strength and having a generally rectangular cross section; The lower left-hand edge of the block 31 as viewed in Fig. 3 is rounded and, if desired, may consist of a circular steel rod 38 which forms a smooth surface under which a sheet of metal S may be drawn. The block 31, as best shown in Fig. 3, is supported by a plate 39 which in turn is connected to the cross-head l6 by means of a toggle construction 40. The toggle construction consists of a plurality of pairs of links 4| joined pivotally to the under edge of the cross-head I6. The'lower ends of the links 4| are connected to the upper ends of other pairs of links 42 which in turn are pivotally connected to the upper surface of the plate 39. I

The toggle construction is collapsed and expanded by means of a lever 43 which is pivotally connected to the under surface of the crosshead IB and is provided with a horizontally extending link 44 which is connected to the shafts 45 connecting the adjacent ends of the links 4| and 42 of the toggle. Thus upon movement of the lever 43 to the left as viewed in Fig. 2 the toggle is collapsed lifting the forming element 31 and upon movement of the lever 43 to the right the forming element 31 is moved downwardly to a position below the upper surface of the formin element 20 when the latter is in its uncurved position. The intermediate adjustments of the toggle permits the relationship of the forming

elements

31 and 20 to be varied at will to control the amount that the sheet S is bent and stretched in passing between these elements.

The position of the forming element 31 may be controlled by a cam 46 having cam track 41 -in a bushing 50 connected to tlie'housin'g 29 while the opposite end is pivotally connected to a link 5|which is, in turn, pivotally connected to a lever 52 pivotally mounted on the upright l3. The upper end of the lever 52 is connected by means of a link 53 to the lever 43 whereby endwise movement of the rod 49 under the control of the cam track 41 will move the lever 43 to the left or right and thereby raise or lower the forming element 31, as described above.

The relationship between the forming

elements

31 and 20 and the curvature of the upper surface of the forming element 20 determine to a large extent the transverse and longitudinal curvature imparted to the sheet S. It will be understood that inasmuch as the sheet S is bent more at its center by passing beneath the forming element 31 and over the curved upper edge of the forming element 22 than it is at its edges, the center of the sheet when drawn between these elements will be stretched to @a greater extent than its edges. These added increments of length tend to cause the sheet to curve longitudinally and transversely. By moving the forming element 31 upwardly and downwardly the longitudina curvature can be varied and by bending the forming element 20 to a greater or lesser extent both the longitudinal and transverse curvatures can be varied. Thus by gradually changing the curvature of the forming element 20 and by gradually moving the forming element 31 relative to the forming element 20 the curvature of the sheet can be varied throughout its'length.

Preferably the sheet is drawn between these forming elements by means of the draw bench H which, as illustrated in Fig. 1, is provided with a standard 54 having rearwardly projecting gripping jaws 55 thereon. The gripping .Iaws may consist of a pair of

plates

55 and 51 which have roughened insert portions, such as for example, file-like teeth for seizing the end of the sheet S. The

plates

56 and 51 may be clamped together by means of bolts 58 and nuts 59.

In accordance with the present invention means are also provided for preventing wrinkling of the sheets, which is sometimes caused by flow of the metal from the edges to the center of the sheet as the center of the sheet is stretched and also for eliminating undesirable stresses at an angle to the direction of pull of the sheet which would tend to cause the sheet to curl up. As shown in Figs. 1 and 2 devices 60 are provided for gripping the edges of the sheet outwardly of the ends of the forming

elements

20 and 31. As best shown in Figs. 5 to 9 the elements 60 include pairs of chains 6| and 62 which are mirror images and are inclined with'relation to each other so as to be brought into engagement with the edges of the sheet S on the side adjacent the forming element and separated on the side re- 64 and at the other end a groove 65 for receiving the tongue 64 on the next adjacent link. The

' links are connected by means of pins 33 which therein which is supported by the draw bench pass through the tongue 64 and the portions of I the links defining the groove 65. The ends of the links 88 may be suitably curved and recessed in order to permit relative pivotal movement.

The chains 8| and 82 are supported in a suitable framework which may consist of a housing and guide element, which is generally c-shaped in cross-section, formed of an upper section 01 and a lower section 88. The lower section 88 is -links 83 is such that the gripping faces 14 of the links are disposed horizontally on the pass adjacent the edge of the sheet S. The upper chain 8| is similarly anti-frictionally supported by an insert and roller construction in the upper section 81 identical with that supporting the lower chain 82.

Outward movement of the links of the chains 8| and 82 is provided by means of

rollers

18 and 18 supported by the upper section 61 and the lower section 88, respectively, which engage the outermost edges of the chains. The rearward pass of the chain BI is supported by rollers 11 in the lower section 88 and the rearward pass of the upper chain BI is supported by rollers 18 in the upper section 81 so that the proper inclination of the chains without buckling or binding is assured.

The outer curved ends of the chains may be covered by suitable semi-circular housings 18 supported on opposite ends of the

blocks

81 and 68.

The

sections

81 and 68 may be separated in order to facilitate repair and to permit the edge of the sheet S to be initially inserted therebetween. This is accomplished by means of the threaded pins 88 which pass through both of the

sections

61 and 88 and thus upon rotation by means of the handles 88a permit the

sections

81 and 68 to be moved together or separated. Springs 8| may be interposed between the

sections

61 and 88 to facilitate their separation.

The construction described above, if fixedly connected to the platform l9, would prevent inward shrinkage of the metal while passing between the forming elements. In many instances a mere retention of the initial width of the sheet by means of these gripping elements is sufficient to prevent the ceiling of the sheets, but when working with other types of materials and when different degrees of curvature are to be imparted to the sheet it is often desired to support the gripping elements 68 in such a manner that they may stretch the sheet transversely.

A mechanism for so moving the gripping and stretching elements 88 is shown in Fig. 5. This construction consists of a lug member 88 which may be rigidly connected to one of the members 88 or 6'! and is connected to a boss 83 by means of a pivot pin 84. The boss 83 is bolted firmly to the platform I8. The gripping and stretching member 88 therefore may be moved about the pivot pin 84 by the preferred mechanism illustrated in Fig. 5, or by the simpler mechanism shown in Fig. 2, in order to control the amount of stretch to be imparted to the sheet. In the mechanism disclosed in Fig. 5 the stretching element 88 is moved about the pivot pin 84 by means of a shaft 88 having its right-hand end, as viewed in Fig. 5, sildingly pivotally connected to the element 88 by means of a pivot pin 88. The opposite end of the shaft is threaded and is received in a threaded bore in a worm gear 81. The shaft 85 is supported in a boss 88 and a thrust bearing 88 is interposed between the boss 88 and the worm gear 81. The worm 81 is mounted on a shaft 88 which is supported in a journal 8| and is driven through bevelled gearing 82 by means ofa motor 88. The bevelled gearing is driven by a transverse shaft 84 which in a similar manner to that described above is attached to the gripping and stretching element 88 at the opposite side of the machine. Thus upon operation of the motor 88 in one direction or the other the gripping and transverse stretching elements 88 are swung around the pivot pins 84 inwardly or outwardly. Inasmuch as the sheet will be gripped firmly by the chains GI and 62, the sheet will be stretched as it moves along while retained by the gripping element, if the chains in opposite gripping and separating elements diverge. Preferably the shaft 85 which controls movement of the forming elements is substantially in axial alignment with the forming

elements

28 and 81 and accordingly will impart the great-v est amount of stretch to the sheet at the time it is being stretched longitudinally.

The amount of transverse stretch imparted to the sheets is extremely small per inch of width of the sheet under most conditions. this stretch is sumcient to interpose stresses transversely of the sheet which tend to neutralize the stresses extending longitudinally of the sheetand thereby produce a .stable form of curved sheet having no tendency to curl or coil up. In,

The control of the transverse stretch to be imparted to the sheet may be accomplished manually. However, for large scale production and when it is desired to duplicate the curvature of a large number of sheets it is preferable to control the movement of the elements 58 automatically. A 'circuitfor controlling the forming elements is shown diagrammatically in Fig. 9. The mechanism for controlling the forming elements 68, as described above, includes a motor 83 for driving a shaft 98 and by means of the bevelled gearing 82 and the worm and worm gear, controls the movement of the forming elements 58. The power circuit for the motor 93, which may be a conventional three phase sixty-cycle. reversing motor, includes a main control switch having the contacts 95a, 95b and 950 thereof connected to the service lines. The opposite contacts 95!), 95c and 95f are connected by suitable lines 96 to the input contacts 91a, 81b and 810 of a relay switch having solenoid relay actuating coil 81d. The blades of the relay switch 91 are connected by suitable wiring 98 to the input contacts 98a, 89b and 980 of a reversing relay double throw switch including the actuating solenoid 98d. The

However,

solenoid coil IOI which controls the operation of conventional solenoid control spring brake I02 which operates to stop the shaft 90 immediately when energlzation of the motor ceases. When the motor 93 is energized, thesclenoid IN is likewise energized and the brake I02 is released thereby permitting the motor to operate.

The control circuit for actuating the relay switch 91 and the reversing relay double throw switch 99 which is normally biased to cause the motor 93 to rotate in one direction will now be described. The direction and amount of operation of the motor may, as illustrated, be controlled by a suitable cam I03 which is supported by the draw bench II and movable therewith.

upon rotation of the shaft 94 the threaded block I will move to the right or left along the threaded "shaft I01 which is suitably supported .by journal blocks H0 and III. The ratios of these gears may be such that a relatively large traverse of the block I00 takes place for a small' shifting movement of the stretching elements 60. The upper end of the lever I is provided with a finger II2 which engages between a pair of fingers II 3 on an upwardly projecting plate Ht which is likewise pivotally connected to the block I00. Thus upon rocking of the lever I05 in one direction the plate II4 will rock in the opposite direction. This movement of the plate I I0 is utilized to control the operation of a pair of mercury switches H5 and H0 which are provided with suitable contacts II5a and II5b and Ba and IIBb.

' Movement of the block I05 along thethreaded shaft I0I is limited by means of other mercury switches I I1 and II8 which are pivotally mounted on the journal blocks III and H0, respec;- tively. The mercury switches III and H0 are provided with suitable abutments which upon engagement by the block I06 rock the switches into their open position, these switches normally being closed. Movement of the various mercury switches H5, H0, H1 and H0 control the operation of the motor, 93. I

The contacts H51) and H017 of the mercury switches H5 and H6 are connected to a common lead II9 which is connected in turn to the contact I20a of a change-over relay double throw switch I20. The contacts 511 and Ba are connectedby leads Ba and II 9b, respectively, to the contacts I20!) and I200 of the switch M0.

The contact I20a of the switch is connected through the switch blade I20f, lead I2I to one side of a transformer I22 which is energized from the service lines and placed into operas tion by. the main switch 95. The blades I20d,

the contact 99c through the solenoid 99d to one end 9Ie of the solenoid 91d and thence through the conductor I2Ia to the opposite side of the transformer. The lead I24b is connected to the switch blade 99 of the switch 99 and through the blade 99f to the contact 9'Ie of the solenoid coil 91d of the switch 91.

Assuming that the curvature of the cam I03 is such as to move the roller I04 to the right slightly, the lever I05 will swing counterclockwiseand the plate H4 will swing clockwise, thus closing the'mercury switch I I6 and allowing current to flow from the transformer I22 through the blade I20f of the switch I20 to the contact I20a, through lead II9, through the switch IIB, through the lead 91), the contact I 20b to the blade I20d, through the lead I23a, mercury switch H8, through lead ma, through the solenoid 99d, the blade 99), energizing the solenoid 91d and thence through the lead I2Ia, to the transformer I22, thereby causing the motor 93 to be energized by closing of the switch 91 and moving the switch from its normally biased position to reverse the motor and rotate the shaft I07 in such a direction as to move the block I00 to the right. When the block I06 is moved into such a, position that the lever I05 is verti-- cal, the solenoid switch IIS will be opened, deenergizing the solenoid coils 99d and 91d and opening the circuit ,to the motor and thereby deenergizing the motor 93 and causing the solenoid brake to stop rotation of the shaft 94; This movement to the right can continue until the block I00 trips the solenoid switch H8 which opens the circuit and prevents further movement of the block to the right.

If the cam I03 has a curvature such that the lever I05 is rocked clockwise the plate H4 is rocked counterclockwise, thereby closing the mercury switch II5. Closingof this switch permits current flow from transformer through lead I2I to blade I20 to contact IISb of mercury switch,

the contact .II5a, through leadv H911 to contact I20c of the relay switch I20, to blade I20e. through lead I23b, through the solenoid switch III through lead I24b to blade 99; of the relay switch 99, to contact 9'Ie of the solenoid 91d and through the lead I2Ia to the transformer I22 thereby energizing the motor 93 by closing the switch 91 causing the motor 93 to rotate'in the opposite direction and moving the block I00 to the left. The switch 99 is normally biased to a position for causing the motor to drive the block to the left. The limit mercury switch I" in this instance will open if there is a tendency for the block to overrun the left-hand end of the threaded shaft I01.

In order to permit manual control ofthe devices' instead of automatic control a manual switch I 25 may be provided which is connected to a solenoid coil I 20g of the change-over relay switch I20. The contact I25a of the switch I25 and I20eare normally connected to the contacts of I20!) and I 200 respectively, and are connected by means of leads I23a and I 23b to one contact of each of the mercury switches H0 and Ill, respectively. The other contacts of the switches H8 and III are connected by means of leads I2la and I2"; to the solenoid control circuit for the switches 91 and 99.-v The lead is connected to the lead I2I, the contact I25b is connected to one end of the solenoid coil I20g while the opposite end of the coil I 20g is connected to the lead I2I a. When the contacts I25?) and I25a are connected by closing the switch I25 the solenoid I20g is energized and the blades I 20d, I20e swing into engagement with the contacts I20i and I20h at the same time moving out of engagement with contacts I20b and I200.

The switch I25 is also provided with contacts I25c and I25d which are connected in parallel with 124a is connected to the solenoid coil 99d and 7a the contact I25a. The contacts I252 and I25] aeoaoeo tor lsdriven in the opposite direction. In this way movement of the gripping and stretching mechanisms 50 may be controlled manually while at the same time, causing movement of the block I along the threaded shaft III'I following movement of the motor. If desired, under these circumstances the lever I05 may be provided with a stylus which permits it to trace its path on a suitable surface, thereby providing secondary means for preparing a cam to automatically impart the same movements to the gripping and stretching elements if duplicate sheets are to be made.

The control mechanism described above can be applied readily to the device disclosed in Figs. 1 to 4. However, other forms of control mechanisms can be used if desired. For example, as shown diagrammatically in Fig. 2 the gripping elements 60 may be moved about their pivots by means of levers I30 which are pivotally supported on the platform I9 and have their upper ends engaging between the lugs I 3I on the ends of the elements 60. The levers are moved by means of a shaft I32 having oppositely threaded portions I33 and I34 thereon. The shaft I32 is driven by a motor I35, by means of suitable reduction gearing I36. The motor'control system may be the same as that disclosed in Fig. 9 and is indicated only diagrammatically as C.

The transverse stretching mechanism may be applied with equal facility to the type of device disclosed for example in the Cairns Patent No. 1,828,489, dated October 20, 1931, as shown in Figs.'10 and 11. In this form of device a pair of complementally curved concave and convex forming rolls I50 and I5I are supported for rotation in a frame I52 which is supported on a suitable pivot I53 for rocking movements'relatively to a supporting base I54. Associated with this frame is a draw bench I55 upon which is mounted a carriage I56 adapted to grip the end of a sheet of metal S and draw it between the rolls. During movement of the sheet between the rolls the frame I5? is rocked by means of a motor I57 through suitable shafting and gearing in order to impart the desired longitudinal transverse curvature to the sheet. In this construction the transverse stretching elements 60 may be supported on suitable platforms I59 fixed to the frame I52. The motor 93 for moving the forming elements may be supported likewise on the frame and is controlled by the cam I03 which is connected at one end to the carriage I55 and moves therewith. The operation of this device is similar to that described above.

Devices embodying the present invention, as will be understood from the foregoing description, will impart a controlled smooth and stablelongitudinal and transverse curvature to a sheet thereby rendering such sheets usable for many purposes and permitting the production of sheets of such curvatures as would be impractical to produce by the known methods of die stamping.

It will be understood that the above described embodiments of the invention are susceptible to considerable variation, such as for example in size, shape, proportion and the manner in 1. In a device for forming longitudinally and transversely curved sheets, the combination of a substantially straight member engageable with one surface of a sheet, a forming element having a curved portion engageable with the opposite surface of said sheet, means for pulling a sheet between said member and said element at anangle to cause said sheet to bend thereover and cooperative with said forming elements to stretch said sheet longitudinally-to varying degrees from its center to its edges, and means for gripping the edges of said sheet at opposite ends of said forming elements to transversely stress said sheet as it passes over said member and said element.

2. In a device for forming longitudinally and transversely curved sheets, the combination of a' pair of opposed forming elements, at least one of which has a longitudinally curved surface, means for pulling a sheet between said' forming elements over said curved surface to bend and stretch said sheet transversely and longitudinally and thereby impart a longitudinal and transverse curvature to said sheet, and means for gripping the lateral edges of said sheet at opposite ends of the ends of said forming elements to stress said sheet transversely as it passes over said curved surface.

3. In a device for forming longitudinally and transversely curved sheets, the combination of a member engageable with one surface of a metal sheet to retain it in a substantially flat condition, a curved forming element engageable with the opposite surface of a sheet and offset with respect to said member to flex said sheet transversely and bend said sheet on a line ex'- 7 ment offset with respect to said plane engageable with the opposite surface of said sheet, means to pull said sheet between said forming elements and cooperating with said forming elements to bend, flex and stretch said sheet to impart a transverse and longitudinal curvature to said sheet, and means for gripping the iongitudinal edges of the sheet and movable therewith throughout a zone extending from in front of said forming element at least into alignment with the ends of said forming element to stress said sheet transversely during its passage over said forming element.

5. In a device for forming longitudinally and transversely curved sheets, the combination of a pair of relatively offset forming elements hav' 6. In a device for forming longitudinally and transversely curved sheets, the combination of a pair of relatively oflset forming'elements having sheet engaging surface portions of different curvatures for bending a sheet on a line extending transversely of the sheet and simultaneously flexing said sheet transversely, means for drawing a sheet through said forming elements at an angle thereto to cause said sheet to engage said forming elements and to stretch the sheet longitudinally to different degrees from its center to its edges and impart a longitudinal and transverse curvature to said sheet, and means for gripping the lateral edges of the sheet throughout zones overlapping said forming elements and stretching said sheet transversely as it passes through said forming elements,

'Z. In a device for forming longitudinally and 7 transversely curved sheets, the combination of a pair of relatively offset forming elements having sheet engaging surface portions of different curvatures for bending a sheet on a line extending transversely of the sheet and simultaneously flexing said sheet transversely, means for drawing a sheet thro h said forming elements at an angle thereto to cause said sheet to engage said forming elements and to stretch the sheet longitudinally to different degrees from its center to its edges and impart a longitudinal and transverse curvature to said sheet, and elements extending throughout zones overlapping each end of said forming elements for gripping the edges of said sheet and movable with the latter for stressing said sheet'transversely during its passage through said forming elements.

8. In a device for forming longitudinally and transversely curved sheets, the combination or a pair of relatively offset forming elements having sheet engaging surface portions of different curvatures for bending a sheet on a line extending transversely of the sheet and simultaneously flexing said sheet transversely, means for drawing a sheet through said forming elements at an angle thereto to cause said sheet to engage said forming elements and to stretch the sheet longitudinally to different degrees from its center to its edges and impart a longitudinal and transverse curvature to said sheet, and elements extending throughout zones overlapping each end of said forming elements for gripping the edges of said sheet, means for restraining said gripping elements against inward movement and means with said flexible forming element and means for drawing a sheet of metal successively over said straight forming surface and said flexible forming element at such an angle as to cause said sheet to engage said surface and said element and be bent and stretched thereby to impart a Longitudinal and transverse curvature to said set.

it. In a device for forming longitudinally and transversely curved sheets, the combination of an elongated flexible forming element, means for flexing said forming element into a longitudinally bowed form, a second substantially straight elongated iorming element adjacent to said flexible forming element, means for moving said forming elements relatively into and out of over.-

lapping relationship .and means for drawing a sheet of metal successively over said forming elements at substantially right angles to the iongitudinal axes thereof and at such an angle as to cause said sheet to engage said forming elements and be bent and stretched thereby.

11. The device set forth in claim 10 in which the means for flemng the flexible'forming ele-' ment comprises a cam and the means for moving said forming elements relatively comprises a tog- Gle.

12. In a device for forming longitudinally and transversely curved sheets, the combination of an elongated flexible forming element, means for flexingsaid forming element into a longitudinally bowed form, a second substantially straight elongated forming element adjacent to said flexible an elongated flexible forming element, means for flexing said forming element into a longitudinally bowed form, a second elongated substantially straight forming element adjacent to said flexfor varying the angular relationship between said gripping elements and the longitudinal axis of said sheet to stretch the sheet transversely dur- -ing its passage through said forming elements.

flexing said forming element into a longitudinally bowed form, a second forming element having a straight forming surface adiacent to said flexible forming element, means for moving said second lapping relationship, means for drawing a sheet of metal over said second forming element toward and over said flexible forming element at substantially right angles to the longitudinal axes thereof, means for gripping the edges and movable with said sheet throughout a zone extending from in alignment with said forming elements to in front of said forming elements, to stress said sheet during passage of the latter between said forming elements, and means for varying the angle between said means for gripping said sheet to vary the amount said sheet is stressed.

14. In a device for forming longitudinally and transversely curved sheets, the combination of an elongated flexible forming element, means for flexing said forming element into a longitudinally bowed form, a second elongated forming element adjacent to said flexible forming element, means for moving said forming elements relatively into and out of overlapping relationship, means for drawing a sheet of metal over said second forming element toward and over said flexible forming element at substantially right angles to the longitudinal axes thereof, a pair of chain memforming element into overlapping relationship bers adjacent each end 'of said forming means for receiving the edges of said sheets, means for forcing portions of said pairs of chain members together to grip the edges of said sheets and means for varying the angles between said pairs of chain members.

15. In a device for forming. longitudinally and transversely curved sheets, the sub-combination of two pairs of traveling chain members for receiving the edges of said sheets, means for forcing portions of said pairs of chain members together to grip the edges of said sheets and means for varying the angular relationship of said pairs of chain members on opposite sides of said sheet with respect to each other to vary the stress imparted transversely to said sheet comprising a reversible motor for moving adjacent ends of said pairs of chain members toward and away from each other, an elongated cam member movable with said sheet, a cam follower movable by said cam, switching means controlled by said cam follower, a circuit including switches for controlling the direction of operation of said motor, and a second circuit for controlling said switches responsive to opera- .tion of said switching means for controlling the Y direction and amount of operation of said motor.

16. In a device for forming longitudinally and transversely curved sheets, the sub-combination of two pairs of traveling chain members for receiving the edges of said sheets, means for forcing portions of said pairs of chain members together to grip the edges of said sheets and means for varying the angular relationship of said pairs of chain members on opposite sides of said sheet with respect to each other to vary the stress imparted transversely to said sheet comprising a reversible motor for moving adjacent ends of said pairs of chain members toward and away from each other, an elongated cam member movable with said sheet, a cam follower movable by said cam switching means controlled by said cam follower, a circuit including switches for controlling the direction of operation of said motor, and a second circuit for controlling said switches responsive to operation of said switching means for controlling the direction and amount of operation of said motor.

17. In a device for forming longitudinally and transversely curved sheets, the sub-combination of means for gripping portions of the edges of a sheet and traveling with said sheet, means pivotally supporting said gripping means, and means for varying the angular relationship of the gripping means on opposite sides of said sheet with respect to each other to vary the stress imparted to said sheet comprising a reversing motor, a circuit including switches for controlling the operation and direction of operation of said motor, a threaded shaft operated by and movable in opposite directions therealong by said motor, an elongated cam movable with said sheet, a cam follower pivotally supported on said threaded member and movable by said cam,

switching means actuated by movement of said follower, and a. circuit including said switching means for controlling said switches to render the said motor responsive to the contour of said cam.

18. A method of forming transversely and longitudinally curved sheets comprising pulling an initially flat sheet of metal over at least one forming element curved transversely to the direction of movement of said sheet, changing the angle at which said sheet is pulled over said forming element to impart a varying longitudinaland transverse curvature to said sheet, and stressing said sheet-transversely during passage of said sheet over said forming element to neutralize the longitudinal stresses therein and preventthe formation of wrinkles in said-sheet.

19. A method of forming longitudinally and transversely curved sheets comprising drawing a sheet of metal over a substantially straight element while bending said sheet on a transverse line, drawing and bending said sheet over another forming element having a curvature transversely of said sheet to stretch said sheet longitudinally to varying degrees from its center to its edges and stressing said sheet transversely as it is drawn over said forming elements.

20. A method of forming longitudinally and transversely curved sheets comprising drawing a sheet of metal over a substantially flat member while bending said sheet on 'a transverse line, drawing and bending said sheet over a forming element offset at least partially out of the plane of said member having a curvature transversely of said sheet to stretch said sheet longitudinally to varying degrees from its center to its edges and stretching said sheet transversely as it is drawn over said forming element.

21. An apparatus for forming curved sheets which comprises means for gripping portions of the opposite edges of a sheet of metal and exerting a tension thereon tending to hold said sheet flat, means for varying the spacing of said gripping means to vary the tension exerted on said sheet, a curved forming member engageable with said sheet between said gripping means to bend said sheet into transversely curved form, means for adjusting said forming member to vary the curvature of said sheet, and means for said motor, a threaded member on said shaft pulling the sheet over said forming member and through said gripping means.

22. In a device for forming longitudinally and transversely curved sheets, the subcombination of two pairs of endless traveling chain members positioned on opposite sides of a traveling sheet, each pair serving to grip one longitudinal edge of said sheet, means for forcing portions of said pairs of chain members together to grip the edges of said sheet and means for variably positioning said chain members with respect to ear-h other for varying their relative angular relationship and thereby varying the lateral pull of said members on the sheet gripped thereby.

BASIL LERMONT. ARNOLD M. WOLF.