US2332926A

US2332926A - Method and apparatus for forming sheet material

Info

Publication number: US2332926A
Application number: US462106A
Authority: US
Inventors: Kenton L May; Fred L Williamson
Original assignee: Bell Aircraft Corp
Current assignee: Bell Aircraft Corp
Priority date: 1942-10-15
Filing date: 1942-10-15
Publication date: 1943-10-26
Anticipated expiration: 1960-10-26

Description

Oct. 26, 1943. K. L. MAY ET AL 2,332,926

METHOD AND APPARATUS FOR FORMING SHEET MATERIAL Filed Oct. 15, 1942 4 Sheets-Sheet 1 Fig.1.

INVENTORS Kenton L May 6; BY Fmdhwuhamson,

MMrQMATTORNEY Oct. 26, 1943. K. L. MAY ET AL 2,332,926

METHOD AND APPARATUS FOR FORMING SHEET MATERIAL Filed Oct. 15, 1942 I 4 Sheets-Sheet 2 Fig.2.

INVENTORS Kanion L. May & BY FmdLWnhamson,

an, QM. AfToR EYs Oct 26, 1943. MAY AL 2 2,332,926

METHOD ANDJQPPARATUS FOR FORMING SHEET MATERIAL Filed Oct. 15, 1942 4 Sheets-Sheet 5 Fig. 3.

INVENTORS KanronL.May& BY FredLWflhamson,

@W,MM QW. T RNEY Oct. 26, 1943; M Y AL 2,332,926

METHOD AND APPARATUS FOR FORMING.SHEET MATERIAL Filed Oct. 15, 1942 4 Sheets-Sheet 4 54 ss 5s 5 6g &

INVENTORS Kenton LMoy & 62 BY FmdLwmiamson aw, RNEYs Patented Oct. 26, 1943 METHOD AND APPARATUS FOR FORMING I SHEET MATERIAL Kenton L. May and Fred L Williamson, Kenmore, N. Y., assignors to Bell Aircraft Corporation,

Buffalo, N. Y.

Application October 15, 1942, Serial No. 462,106

24 Claims.

This invention relates to novel methods and means for forming sheets of thermo-plastic material into various desired forms.

The invention has particular application in the production of various concavo-convex shapes, spherical, ellipsoidal, or otherwise from initially fiat sheets. According to the method of the present invention, and as now practiced in the prior art, a stock sheet of resinous material, cellulosederivative material, or other thermo-plastic material, is heated to the point where it softens, and is then stretched or drawn over a convex form complementary to the desired contour of the finally formed piece.

I have found that results very superior to those obtaining in the case of prior art methods and apparatus are achieved by continuous or to and fro relative movement between the stock sheet and the form, in planes roughly parallel to those of the form, during the period when the stock sheet is being drawn over and about the form. The choice as between continuous and to and fro relative movement is one of expedience. In the case of spherical or circular pieces, continuous rotation thereof or of the form may provide the desired continuous movement. In the case of ellipsoidal or other non-circular shapes a rocking or to and fro relative movement between the stock sheet and the form may be employed.

In the forms set forth'herein by way of example the various means suggested comprise essentially a male form, means for grasping and holding the marginal portions of a stock sheet, means for moving either the stock sheet holding means or the male form, one toward the other,

and means for rotating or oscillating either the movable or the stationary element. The nature of the desired relative rotative or oscillative movement will appear more clearly from a consideration of the various specific forms of apparatus described in detail by way of example. The effect, as between the stock sheet and the male form, may be described as ironing.

One of the fields of practical application of the present novel procedure is found in the formation of Windshields, windows, or other transparencies, wherein transparent resin or cellulose-derivative materials, or the like are to be formed into semispherical, semi-ellipsoidal, or other dished or curved forms. Such devices are now widely used in aircraft cabin and cockpit enclosures and the like. Like application is found to some extent in the field of land vehicles, but it is believed that a vastly expanding use may bemade in this field in the future.

A significiant advantage of procedure in accordance with the teachings of the present invention resides in the fact that forms produced thereby are substantially entirely free of certain thickness variations which tend to produce optical aberration effects which are attendant upon and heretofore entirely unavoidable in the pursuance of prior art methods. These prismatic efiects give to such prior art pieces very undesirable optical distortion and aberration.

In the accompanying drawings:

Fig. 1 is a somewhat schematic elevational view, partly in cross-section, of apparatus for forming sheets according to my invention by the rotational method;

Fig. 2 is an elevational view of apparatus for forming sheets by oscillatory movement of the male form;

Fig. 3 is an elevational view of the apparatus of Fig. 2 taken at right anglesthereto;

Fig. 4 is a somewhat schematic view showing an intermediate phase of the work sheet forming operation in the case of a form likethat contemplated in Figs. 2 and 3;

Fig. 5 is a view similar to Fig. 4 but taken at right angles thereto; and

Fig. 6 is a vertical cross-sectional view of apparatus for interchangeably forming sheets according to my invention by either the rotational or to and fro methods.

Throughout the several figures of the drawings 'like characters of reference denote like parts.

Fig. 1 depicts, somewhat schematically, means for producing dished members of circular form. In

Fig. 1 the numeral l0 designates a convex mold.

or form which conforms identically with the desired interior contour of the part to be produced. The form I 0 is mounted for rotation about its axis by means of a shaft ll secured rigidly and coaxially therewith and having journal portions i2 and I3 for mounting in suitable bearings (not shown). In Fig. 1 the numeral I4 designates a pulley secured to the shaft H which may be enaged by a belt or the like for rotation of the form Ill. The approximate order of the speed of rotation is from twenty to sixty revolutions per minute but this may be varied to suit variations in operating requirements, such as the diameter of the piece being drawn, the depth of draw, the thickness of the work piece, etc.

In Fig. 1 the numeral l5 denotes a vertically movable cage or frame structure which supports a pair of frame-like clamping elements l6 and I! which may be removably associated with the marginal portions of a work sheet It by means of screw connections or the like (not shown). Any convenient means may be employed for moving the cage structure downwardly over the male form ID to bring the clamp portions l6 and I! to the final position illustrated in Fig. 1. In this position the work piece |8 has been brought to final desired shape over the male form In.

Rotation of the male form ID in the manner set forth in the foregoing is found to eliminate from the final product the optical defects and aberrational effects which have previously been considered a necessary evil in the deep drawing of thermoplastic sheets. It appears that the ironing action of the male form against the interior surface of the work sheet is responsible for the accurate optical surface produced when th instant method and apparatus are employed.

When surfaces other than circular surfaces are to be drawn, as for instance when the desired contour is semi-ellipsoidal or the like, rotation of the male form in the foregoing manner is obviously not feasible. The desired results may, however, be closely approximated by to and fro ironing action, as distinguished from the continuous rotation of the male form ll] of Fig. 1. Figs. 2 and 3 show side and end elevational views, respectively, of apparatus for oscillating a longitudinally extending convex mold about an axis extending lengthwise of the mold or form and, in the illustrated instance, approximately in the plane of the bottom surface of the mold or form.

.In'Figs. 2 and 3 the numeral l9 designates a bed plate and designates leg elements which ris above the bed plate IQ for supporting superstructure to be hereinafter described. In Figs. 2 and 3 the numeral 2| designates an elongate upwardly convex male form which is mounted for oscillation about an axis lengthwise thereof and adjacent its bottom portion by means of a shaft 22, j-ournalled in

bearings

23 and 24 and having a crank arm 25 for oscillation thereof.

As shown in Fig. 3, oscillation of the crank arm 25 is effected by means of a motor 26 whose shaft is provided at one of its ends with a sheave portion 21 which receives an eccentric'pin 28 carried by one end of a pitman or connecting rod 29. It is desired that oscillation of the form 2| be yieldable or restrainable, particularly during the latter phases of a forming operation. To this end the connection between the connecting rod 29 and the crank arm 25 is resilient. This resiliency may be accomplished b slotting the end of the connecting rod 29 adjacent the crank arm 25 and interposing therein a pair of compression coil springs 3| and 32. The end of the crank arm 25 carries a pin 33 which extends between the springs 3|- and 32 and may in fact be fixed to the adjacent ends thereof. It is clear from the foregoing that reciprocation of the connecting rod 29 by the motor 26 will result in a varying amplitude of oscillation of the form 2|,

' depending upon the resistance to oscillation which the form'oifers. If the resistance to oscillation exceeds a predetermined amount all of the reciprocatory movement of the connecting rod 29 will b absorbed by the springs 3| and 32 and the crank arm 25 and the form 2| will be stationary.

In this way the male form 2| may be forcibly held against-movement even though the motor 26 is operating. In Figs. 2 and 3 the numeral 34 designates a downwardly opening cage structure which is supported for guided vertical movement by pins 35 secured thereto and having axial sliding bearing in bearing formations 36 associated with superstructure in th nature of a crosshead A clamping rail 40 is associated with the bottom of the cage 34 to secure a work sheet 4| marginally thereagainst. Clamping screws 42 are provided for securing the clamping frame 40 to the bottom of the cage 34 with the margins of the work sheet 4| firmly ecured therebetween.

Figs. 4 and 5 show, respectively, schematic longitudinal and transverse elevational views, partly in cross-section,'with the work sheet in an intermediate stage of the drawing operation. The dot and dash line showing indicates the final form to which the sheet will be drawn.

Fig. 6 is a vertical cross-sectional view of apparatus which may be used alternatively in drawing either circular or non-circular forms. In Fig. 6 the apparatus is set up for the production of elongate shells similar to those contemplated in Figs. 2 through 5. When the apparatus of Fig. 6 is set up in this manner the mold or male form is given a wobbling movement during the drawing operation, as distinguished from the oscillation of Figs. 2 through 5. This movement of the form may be termed nutation.

In Fig. 6 the male form is designated 50 and is positioned upon a ball journal 5| by means of a socket bearing 52. The ball journal 5| is rigidly associated with a turntable 53 which is rotatably disposed at the upper end'of a tube 54 through the intervention of an annular axialthrust ball bearing 55.

The tube 54 has a number of tracks 56, in the present instance four, spaced about its outer periphery. The tracks 56 are engaged by rollers 51 carried in channels 58 which are-rigidly associated with building frame-work or the like. In this way the tube 54 and the elements carried by it are guided for vertical axial movement.

In the present instance the apparatus is shown associated with an intermediate floor 60 of a building and the channels 56 are secured thereto by means of gussets 6|. In Fig. 6 the bottom ends of the channels 58 are joined and braced by a base plate 62 which also supports a pneumatic cylinder 65 having therein a piston (not shown). A piston rod 66 projects from the cylinder 65 and engages a plate 61 which is rigidly secured within the tube 54. The parts are shown in Fig. 6 in.

their upper position where the work piece is finally formed and movement of the tube 54 and parts carried thereby to this position from a lower beginning position is effected by the application of fluid pressure to the under side of the piston in the cylinder 65.

The turntable 53 is arranged to be rotated upon the tube 54 by means of a motor 10 which may be actuated electrically, pneumatically, hydraulically, or otherwise,

When forming non-circular pieces it is desired that the form 50 be held against rotation with the turntable 53 and to this end the form 56 has resilient connection with brackets 12 fixed to the upper end of the non-rotative tube 54. Connection in the present instance is by means of springs 13 which permit limited resilient oscillation of the form 50.

For wobbling the form 50 during the drawing operation it is provided at its under side with a ring 15 which has an eccentric or cam shaped opening which is engageable by a freely rotattrio opening in the ring 15imparts pivotal movements to the form 50 about its universal pivot mounting 52. This is by reason of the fact that the opening is eccentric, while the orbit of the roller 11 is concentric with respect to the axis of the turntable 53. This movement, proceeding progressively about the vertical axis of the form 50, results in a wobbling movement of the form during the drawing operation. The motor 16 is arranged to be variably controllable as to speed down to zero whereby wobbling of the form may be retarded at will as final form is approached.

For supporting a work sheet, designated 88, in a predetermined elevated position during upward forming movement of the form 50, upper and lower clamping rings 8| and 82 are provided. These clamping rings clamp the marginal portions of the work sheet 80; In the illustrated instance the lower clamp 82 is secured rigidly to a ring 84 which is removably associated with a plurality of vertical supporting posts 85. The posts 85 have square or rectangular base flanges 86 for engagement in ways 81 secured to the floor 60. The ,several Ways 8'! extend radially with respect to the axis of the tube 54 whereby the various posts 85 may be radially adjusted to accommodate different clamp assemblies. To the same end, the clamp supporting ring 84 is removable from the posts 85,,to be replaced by a clamp supporting ring of another form.

The upper clamping ring 8| is releasable and engageable by means of a cam or toggle lock mechanism 88 whose details are not important to a proper consideration of the present invention. Any conventional form of cam or toggle clamping means may be resorted to.

When circular forms are to be produced continuous rotation of the form is most desirable, as has been stated above. Accordingly, for circular work pieces the form is secured directly and fixedly to the turntable 53 for rotation there-- with. Under these circumstances the ball journal 5| and the wobble roller 11 may be removed unless the circular form is suffciently hollowed out so as not to be interfered with by these elements.

While a number of applications of the principles of the present invention are shown and described in the foregoing, it is to be understood that the spirit and scope of the invention is not to be considered as limited, otherwise than as defined in the appended claims,

What is claimed is:

1. The method of imparting accurately predetermined dish form to a thermoplastic stock sheet comprising heating the same to soft condition, fixing the margins thereof'against relative movement, drawing the stock sheet over a male form with the margins so fixed, and simultaneously imparting substantially continuous relative surface movement between the inale form and the stock sheet in addition to the incidental relative surface movement resulting from stretching of the stock sheet.

2. The method of imparting accurately predetermined circular dish form to a thermoplastic stock sheet comprising heating the same to soft condition, fixing the margins thereof against relative movement, drawing the stock sheet over a male form with the margins so fixed, and simultaneously imparting substantially continuous rotative relative surface movement between the male form and the stock sheet.

3. The method of imparting accurately predetermined dish form to a thermoplastic stock sheet comprising heating the same to soft condition, fixing the margins thereof against relative movement, drawing the stock sheet over a male form with the margins so fixed, and simultaneously imparting substantially continuous oscillating relative surface movement between the male form and the stock sheet.

4. The method of imparting accurately predetermined elongate dish form to a thermoplastic stock sheet comprising heating the same to soft condition, fixing the margins thereof against relative movement, drawing the stock sheet over a male form with the margins so fixed, and simultaneously imparting substantially continuous relative surface movement between the male form and the stock sheet by oscillation about an axis longitudinal with respect to said elongate dish form.

5. The method of imparting accurately predetermined dish form to a thermoplastic stock sheet comprising heating the same to soft condition, fixing the margins thereof against relative movement, drawing the stock sheet over a male form With-the margins so fixed, and simultaneously imparting substantially continuous relative surface movement between the male form and the stock sheet by continuously wobbling one of said elements during said drawing.

6. The method of imparting accurately predetermined dish form to a thermoplastic stock sheet comprising heating the same to soft condition, fixing the margins thereof against relative movement, drawing the stock sheet over a male form with the margins so fixed, simultaneously imparting substantially continuous relative surface movement between the male form and the stock sheet by relative oscillation thereof, and progressively diminishing the amplitude of said oscillation as final form is approached in drawing the stock sheet.

7. The method of imparting accurately predetermined dish form to a thermoplastic stock sheet comprising heating the same to soft condition, drawing the stock sheet over a male form, and simultaneously imparting substantially continuous relative surface movement between the male form and the stock sheet in addition to the incidentalrelative surface movement resulting from stretching of the stock sheet.

8. The method of imparting accurately predetermined dish form to a thermoplastic stock sheet comprising heating the same to soft condition, gripping the margins thereof by means of a holding device, drawing the stock sheet over a male form by moving said holding device relative to the form to press the stock sheet against the form, and simultaneously imparting substantially continuous relative surface movement between the male form and the stock sheet in addition to the incidental relative surface movement resulting from stretching of the stock sheet.

9. Apparatus for forming softened plastic stock sheets into dished shape comprising a convex male form, means for supporting a stock sheet in a position opposed to said form, means for moving one of said elements toward the other to draw the stock sheet about the male form, and means'for moving one of said elements transversely with respect to the first mentioned movement to efiect relative surface movement between the male form and the stock sheet during the drawing of the latter.

10. Apparatus for forming softened plastic stock sheets into circular dished shape comprising a convex male form, means-for supporting a stock sheet in a position opposed to said form, means for moving one of said elements toward the other to draw the stock sheet about the male form, and means for rotating one of said elements about an axis coincident with the axis of the convex male form to effect relative surface movement between the male form and the stock sheet during the drawing of the latter.

11. Apparatus for forming softened plastic stock sheets into circular dished shape comprising a convex male form, means for supporting a stock sheet in a position opposed to said form, means for moving one of said elements toward the other to draw the stock sheet about the male form, and means for simultaneously rotating said convex male form on its axis to effect relative surface movement between the male form and the stock sheet during the drawing of the latter.

12. Apparatus for forming softened plastic stock sheets into dished shape comprising a convex male form, means for supporting a stock sheet in a position opposed to said form, means for moving one of said elements toward the other to draw the stock sheet about the male form and means for oscillating one of said elements on an axis transverse with respect to the first mentioned movement to eifect relative surface movement between the male form and the stock sheet during the drawing of the latter.

13. Apparatus for forming softened plastic stock sheets into dished shape comprising a convex male form, means for supporting a stock sheet in a position opposed to said form, means for moving one of said elements toward the other to draw the stock sheet about the male form, and means for oscillating one of said elements transversely with respect to the first mentioned movement to effect relative surface movement between the male form and the stock sheet during the drawing of the latter.

14. Apparatus for forming softened plastic stock sheets into dished shape comprising a convex male form, means for supporting a stock sheet in a position opposed to said form, means for moving said supporting means toward the male form to draw the stock sheet about the male form, and means for simultaneously moving said male form transversely with respect to the first mentioned movement to eifect relative surface movement between the male form and the stock sheet during the drawing of the latter.

15. Apparatus for forming softened plastic stock sheets into dished shape comprising a convex male form, means for supporting a stock sheet in a position opposed to said form, means for moving supporting means toward the male form'to draw the stock sheet about the male form, and means for simultaneously imparting a and the stock sheet during the drawing of the latter.

1'7. Apparatus for forming softened plastic stock sheets into elongate dished shape comprising an elongate convex male. form, means for supporting a stock sheet in a position opposed to said form, means for moving one of said elements toward the other to draw the stock sheet about the male form, and means mounting said male form for oscillation about an axis transverse with respect to the first mentioned movement and longitudinal with respect to said elongate male form to effect relative surface movement between the male form and the stock sheet with a minimum of bodily displacement therebetween during the drawing of the latter.

18. Apparatus for forming softened plastic stock sheets into dished shape comprising a convex male form, means for supporting a stock sheet in a position opposed to said form, means for moving one of said elements toward the other to draw the stock sheet about the male form, and means for moving said male form independently of the first mentioned movement toeffect relative surface movement between the male form and the stock sheet during the drawing of the latter, said means comprising a universal support for said male form and cam means for wobbling said male form simultaneously with the drawing of the stock sheet thereabout.

19. Apparatus for forming plastic stock sheets comprising a stationary clamping frame for releas'ably gripping the margins of stock sheets, a turntable and means for rotating the same on an axis substantially normal to the gripped stock sheet, a universal pivot bearing on said turntable and a convex form supported by said pivot hearing for universal pivotal movement about a point, means for moving said form against the gripped stock sheet to form the latter, means restraining said form against rotation with said turntable, and cam means acting between said turntable and said form for nutating the latter during forming movement of the form against the stock sheet.

20. Apparatus for forming plastic stock sheets comprising a stationary clamping frame for releasahly gripping the margins of stock sheets, a turntable and means for rotating the same on an axis substantially normal to the gripped stock sheet, a universal pivot bearing on said turntable and a convex form supported by said pivot bearing for universal pivotal movement about a point, means for moving said form against the gripped stock sheet to form the, latter, means restraining said form against rotation with said turntable and cam means acting between said turntable and said form for nutating the latter during forming movement of the form against the stock sheet, said form and its pivot bearing and said cam means being removable for replacement by a circular convex fixed coaxially to said turntable.

21. Apparatus for forming plastic stock sheets comprising a stationary clamping frame for releasably gripping the margins of stock sheets,

supporting means guided for longitudinal movement toward and away from said clamping frame, a turntable on said supporting means and motor means for rotating the same on an axis substantially normal to the gripped stock sheet, a

universal pivot bearing on said turntable and av form against rotation with said turntable and cam means acting between sato'. turntable and stock sheet to form the latter, means resiliently restraining said form against rotation with said turntable and means acting between said turntable and said form for wobbling the axis of the latter during forming movement of the form against the stock sheet.

23. The method of forming a heat-softened stock sheet into curved sectional shape comprising providing relative movement toward each 20 other of said stock sheet and a form device curved substantially complementary to the desired iinalcontour of the stock sheet whereby to draw the stock sheet into confo ty with said curved surface of the form device, while simul- 25 o taneously providing relative surface movement between the stock sheet and said form device in addition to the incidental relative surface movement resulting from such drawing of the stock sheet into conformity with the shape of said form device.

24. The method of forming a heat-softened stock sheet into curved sectional shape, comprising gripping said stock sheet at marginal portions thereof and then providing relative movement betweeen said heat-softened stock sheet and a form device having a stock sheet contact ing surface portion thereof curved substantially complementary to the prescribed curved shape to which the stock sheet is to be formed whereby to draw the stock sheet into conformity with said curved surface portion of the. form device,- and providing relative surface movement between the stock sheet and said form device in addition to the incidental relative surface movement resulting from such drawing of the stock sheet into conformity with the shape of said form device.

KENTON L. MAY. FRED L. WILLIAMSON.