US2400004A - Means for forming sheet metal - Google Patents

Description

y 1946. H. M. JAGER 2,400,004

MEANS 'FOR' FORMING SHEET METAL Filed June 8, 1942 C V 16 16a 10'" 14 VB 10 B [I 13 12 12 1:2 I a IN VEN TOR:

HOWARD. M. JAGER A TTORNEYI Patented May 7, 1946 Howard M. lager, Oceanside, N. Y., assignor to Republic Aviation Corporation, Farmingdale, N. Y., a corporation of Delaware Application June 8, 1942, Serial No. 446,218

z Claims. (01. 113

This invention relates to means for forming sheet metal andv more particularly for flanging sheet metal blanks of irregular contoursinvolving convex or serpentine curves by means of a single piece die in a press using as acounter-tool a body'ofyieldable plastic material, such as a rubber or a composition having rubbery qualities.

In this particular field, known in the art as convex fianging, as the amount of metal around the outside edge of the blank to be flanged is greater thanthe amount of metal in the finished flange and, as the rubber is not capable of effecting directly the necessary shrinking of the metalin the flange, there is a tendency towards buckling, wrinkling. or crimping unless some means are provided'to take care of this excess of metal; either by notching the die or notching the blank along the entire width of the flange.

The drawbacks and disadvantages of both of these methods are well known: the notched die does not prevent the formation of wrinkles, but merely causes thewrinkles to be turned inside, which make it inconvenient for bucking rivets, while the notching of the blank edge is adifllcult operation in itself; requiring expensive'anddelicate tools, as it cannot be performed economically in a rubber press or by routing.

To remedy these disadvantages, it has been proposed to undulate, or "scallop" the edge of the blank with such=a wide flow that this operation can be performed by blanking or routing, the spacing between twosuccessive wave centers determining'the rivet pattern; Such a scalloped blank canthen be flanged in a rubber press if the die is provided with a suitable retainerblock to direct the now of rubber and localize the pressure where it is most needed, and,

that part of the work most likely to wrinkle, rubber strips or pads of from one to two inches thick, or to build up the die so that it extends atleast one inch higher off the platen of the press with respect to the surrounding dies, thus eilecting and localizing an overpressure over this particular area or die.

While both methods are satisfactory for forming horizontal flanges and in most cases of sheet metal-forming involving a stretching of the metal,

such asin concave flanging, the overpressure if the solid'part of the flange (exclusive of the waves or. scallops"), does not exceed a maximumrheight given by standard charts for every givengage of sheetl metal, the method is satisfactory. g

Though this last method is successful in preventing the formation of wrinkles and permits only when the curved fiangeto be formed lies substantially horizontally in the plane of the press and cannot be used when this curved flange stands vertically up and is substantially parallel to the direction of motion of the platen of the press.

It is an object of this invention to overcome all these difficulties and to produce in a rubber press, and ina singleforming operation, formed sheet metalarticles of irregular shape, involving a substantial shrinkage of the material during said forming operation, which will nonetheless be entirely free of any objectionable folds, creases. wrinkles, crimps, buckles, or the like.

More particularly, it is an object of this invention to produce in a rubber press from plain flat blanks, and in a single flanging operation, sharply-profiled aircraft 'duraluminum flat parts having substantially vertical flanges of convex or serpentine contour, these flanges; being entirely free of any objectionable folds, creases or wrinkles even if-in order to allow ample space for riveting--they are formed higher than the maximum charted for rubber work and convex flanging.

These objects are attained, according to the present invention, by drawing in a rubber press the irregular part of the sheet metal from which the desired article is formed between two rigid members contoured to the desired shape and held apart during the single forming operation at a breadth substantially equal to the thickness of said sheet.

Another feature of the method of the present invention consists in covering the convex edge of a flat blank, from which a desired flanged article is to be formed in a rubber press, with an auxiliary drawing tool, the surface of which is substantially larger than the area, of said edge.

It is also an object of my invention to provide means to carry out the method of this invention, and as will be made manifest hereinafter, the means and the method are interdependent in concept and function.

Essentially, these means comprise, in combination with a matrix or form-block, a movable rigid auxiliary drawing-tool, engageable by the rubber of the press and engaging that part of the sheet metal which is expected to shrink during the single forming-operation, viz: that portion of the blank overlying a convexed portion of the form block and means to guide said tool along the forming face of said matrix or form-block.

These means may also comprise a countertool associated with said drawing tool so as to form a bi-partite flange-holder, and means allowing the maintenance of an adjustable and constant holding-pressure between the jaws of the flangeholder thus formed.

The invention further includes the novel details of construction shown, described, and particularly pointed out in the claims.

In the accompanying drawing, which illustrates, by way of exempliflcation only, three embodiments of the invention:

Figure 1 is a plan view of an embodiment, showing a die of irregular contour according to the invention for forming on one side of the die, a flange of serpentine curve;

Figures 2 and 3 are enlarged cross-sections through a tool embodying the present invention where the flange overlying the convexed part of the form block i to be bent at an angle of 90 and showing the auxiliary tool in operative position between the flowing pad and the fixed bolster or form block of a hydraulic press of the rubber type, respectively at the start and at the end of a fianging operation;

Figures 4 and 5 are enlarged cross-sections along line 55 of Figure 1, showing a die of irregular contour in operative position in the same rubber press respectively at the start, and the end, of a hanging operation whereby the flange is positioned at an angle of 95; and

Figure 6 is a plan view of an embodiment of tools according to the invention for forming convex vertical fiange around corners of a rectangular flanging die of known design, the cooperation of the several elements being that shown in Figs. 2 and 3.

The present invention comprises a flanging die or form block In having at least part of its edge convexed and, in upper face having a relatively wide and deep annular channel ll, so as to form a plug or matrix [2 and an outer upstanding retaining flange I3, projecting a certain distance above the top surface of the matrix l2.

In the channel H is yieldably mounted, on vertical springs H, a floating plate l5, having a sliding fit into the retaining flange [3. This floating plate I5 is normally kept substantially flush with the top surface of the matrix l2 by these springs The workpiece, or blank, A, previously formed from flat sheet stock to the desired flat contour, is laid flat on this top surface of the matrix I! with its peripheral or edge portion, to be flanged, overlapping the floating plate l5 and bridging a narrow annular gap or clearance provided between the inner edge of said ring 15 and the convexed flanging face of the matrix i2. The width of this gap is preferably equal to twice the thickness, or gage, of the metal of the blank A. It is to be noted that the members l5 and I6, as Well as the member lia, to be described, comprise relatively flat sections of metal curved laterally to correspond to the convex curve of the face of the matrix l2.

An auxiliary drawing tool I6 is then inserted into the retaining flange l3 above the floating plate l5 and the outer portion to be flanged of the blank A. Outwardly, this auxiliary drawing tool has a close sliding fit into the retaining flange l3, while inwardly, its drawing face comprises a concaved portion l6a, which overhangs the center line of the annular gap between l2 and I5, and a rounded edge lib, which cooperates with the usual rounded edge of the matrix H so as to progressively bend the work around this latter edge during the downward stroke of the press. The height of this auxiliary drawing tool I6 is preferably such that its upper surface lies normally flush with the top surface of the retaining flange i3. (See Figure 2).

If the article to be formed is such that a small hole may be cut in the blank A, a centering pin 11, fitting exactly into this hole, is used to locate and center the blank A on top of the matrix I2 and to prevent any lateral shift of the blank during the flanging operation. Otherwise, a recess (not shown) into which the blank flts or nests exactly is formed either in the top of the floating plate 15, or in the bottom of the auxiliary drawing tool H5, or a washer (not shown) made of the same stock as the blank A, is used to fill the flat annular gap left between the plate l5, and the auxiliary drawing tool l6 and between the blank A and the retaining flange l3.

Whether or not a centering pin I1 is used, the use of this recess (or this washer) is recommended when a constant determined pressure, i. e. an uniform pressure, is desired on the edge of the blank A, confined between the plate [5, and the auxiliary drawing tool I6 as this edge is drawn into the desired flange. As is well known in the art, this pressure becomes one of the important factors to be considered in all forming process as soon as a drawing operation enters into this forming. This pressure should be just enough to keep the metal flat and smooth at all stages of the flanging operation, while allowing for its progressive slipping from between the jaws of the flange-holder constituted by the plate l5, and the auxiliary drawing tool I6. If the pressure is too light wrinkles of such a size are apt to form between the jaws of said flange-holder that they will stop the auxiliar drawing tool 16 in its downward stroke before it has reached the normal end of this stroke, with the result that these wrinkles will be uncompletely flattened by this drawing. 0n the other hand, if this pressure is too great, the metal is prevented from slipping on time, and is thereby unduly strained around the edge Nib and tearing may occur before the actual drawing starts.

By suitable adjustment of the height of this recess (or of this bracing washer) with respect to the gage of the blank A, this holding pressure may be adjusted and made independent of the increase in pressure resulting from the compression of the springs it during the downward stroke of the plate l5, and the auxiliary drawing tool l6, as these latter are positively held a fixed distance apart during this entire stroke.

In the case of a recess made in the top surface of the floating plate IS, the blank A is simply dropped and nested therein before insertion of the auxiliary drawing tool l6, while, if a recess made in the bottom surface of the auxiliary drawing tool I is employed, the drawing rounded-edge lib must be shifted accordingly and the blank A is made to fit so tightly in the recess, that it will not drop therefrom when inserting the auxiliary drawing tool l6 into the retaining flange Hi. When using a washer, the blank and the washer are first arranged concentrically on the levelled matrix [2 and plate I5 and the auxiliary drawing tool It is then dropped above them.

The dielll is now ready to be placed between the bolster B and the moving platen containing the flowing rubber pad C of a hydraulic press of the rubber type, for instance, by means of the usual transfer-table or gangplate shuttled on and off the bolster B and on which the die III is merely laid on, together with other dies and formblocks. During the downward stroke of the press, the rubber first contacts simultaneously the ,top surfaces of both the retaining flange l3 and the auxiliary drawing tool l5 (position shown in Figure 2) and thereafter, due to the resistance to bending of the overlapping edge of the blank and to the springs l4, there occurs for awhile but a nominal bending of the flange, as the annular portion of the pad Copposite the flange l3, and

the auxiliary drawing tool IE, is locally compressed and some rubber flows, on the one side, around the upper outer edge of the flange l3 and, on the other side, around the upper inner edge of the auxiliary drawing tool l6. This latter flow of rubber then fills the empty space above the matrix l2. Thus, when the real bending operation starts, a continuously increasing pressure is applied by the rubber respectively on the central part of the blank, to keepit flat on the top of the fixed matrix, and on the fixed flan e l3, to force the rubber tofiow inside the channel ll,

while the pressure acting simultaneously on the yielding tool 16 is constantly limited by the amount of yield of the springs ll.

Thereby, near the end of the downward stroke of the press, there is no excessive gripping of the work between the plate l5, and the auxiliary drawing tool l6, which would otherwise prevent the slipping of the work from between the jaws of the flange holder thus formed and create thus a liability of cracking or tearing the work at the bend around the edge llib. Simultaneously, the relatively small wrinkles that may eventually form in the work between. the plate l5, and the auxiliary drawing tool It, due to this yielding of the springs ll, are subsequently smoothed out between the drawing face Ilia and the periphery of the matrix as the gap between these two cylindricaLsurfaces corresponds exactly to the gage of the work, i. e., as the work is exactly confined between these two drawing surfaces. Though thus limited by the action of the springs II, the amount of pressure applied on the auxiliary drawing tool l8 can easily be adjusted, by increasing either the areaof the auxiliary drawing tool IE or the depth of the channel ll, so as to give a pressure sufficient to affect a perfect drawing operation.

At the end of this downward stroke (Figure 3), the lower edge a of the flange snaps out of the flange holder formed by the plate l5, and the auxiliary drawing tool l6 and seats around the convexed edge or face lib of the matrix l2.

Later on, this uncompletely flanged edge a, which is mostly made of the excess material drawn from the body of the flange, is trimmed in any suitable way. All surfaces between which the drawing of the flange takes place are kept very clean and smooth, especially the face lia and the edge lBb.

Minor changes in construction and design may be made without departing from the spirit and scope hereof. For instance, the floating plate l5, instead of having a larger inner diameter than the drawing tool l6, could have a sliding fit around the matrix, i. e. have a slightly smaller inner diameter than that of the auxiliary tool ring IS, in order to act as a stripper which will elect the flanged article up out of the matrix when the auxiliary drawing tool I6 is withdrawn by hand from the channel ll. Also, the springs ll could be replaced by a rubber ring filling only partly the bottom of the channel ll, in order to give enough room for the lateral expansion of this ring when its height is reduced, or by a pair of spiral springs concentrically arranged in two circular grooves cut inthe lower face of the plate l5.

Figures 4 and. 5 show by way of example, a single-piece fianging die of irregular contour for producing a structural part of the aircraft, for

example, having, on one side, a flange of serpentine curve bent through, an angle of about 95? and, on the opposite side, a straight vertical flange. with a narrow re-entrant edge. As the formation of this straight flange in a rubber press does not present any problem, the method according to the invention, in this embodiment, is applied only for the formation of the slanting flange along the serpentine side of the die. This die comprises a die-bed l0, mounted on a die-plate I! carried by the bolster B and a. matrix l2, rigidly flxed on the plate l0 and having a slanting flanging face ll, of serpentine curve and an opposed vertical straight flanging face 22.

According to the invention, a straight rubber, retaining flange l3, slanting at the same angle as the fianging face ll, is mounted on the diebed l0 opposite the ,convexed face ll of the matrix and rigidly held up by means of three buttresses 24. In the gap left between this flange l3 and the face ll of the matrix I! is yieldably mounted on springs II, a floating plate l5a, vertically guided in'said gap by means of plungers 25, slidably mounted in cylindrical holes in the die-bed l0 and in'the die-plate l9. These plungers' 25 are hollow and house the springs l4.

On the plate l5a. is freely mounted an assembly comprising a lower plate IS, an auxiliary drawing-tool l6 and connecting pins 29, frictionally held in blind holes in the plate l5 and having a. tight sliding fit in holes in the tool l6. These pins 29 slant at the sameangle as the flanging face ll of the matrix l2, in order that blanks of different gages may be accommodated between the plates l5 and tool IS without affecting the relative position of said plate and tool withrespect to the flange l3. The straight longitudinal edges of both plate l5 and tool ii are also cut at an angle of so as to have a sliding springs I4 is such that the closed lips thus formed lie at the level of the top surface of the matrix I2.

The blank A is first laid down flat on the top of this matrix I2 and its serpentine edge is pushed sidewise between these lips until the usual locating holes register, then it is fixed in position with respect to the matrix by means of two locating pins II (Figure 1) fitting tightly into these holes. The two usual pillars or guidepins are designated by reference numeral 30.

In Figs. 4 and 5, not only are the drawing surfaces kept clean and smooth, but also the top surface of the floating plate I51; and the undersurface of the plate I5, as the assembly I 5-16, 29 must be able to slide laterally as a whole toward the matrix when guided down by the slanting flange I3.

Except for this sliding side motion, the operation of this die (Figs. 4 and 5) corresponds exactly to the operation of the die shown in Figs. 2 and 3, so that all variations and changes that could be incorporated in the former within the scope of the invention and can be employed in the latter without departing from the scope of this invention. Furthermore in Figs. 4 and 5, the die-bed I and the die-plate I9 can be made in one piece, or the form block I2 can be integral with its bed I0. In some cases, it is more practical to have the guiding plungers 25 entirely independent of the springs I4.

For relatively thick blanks and in other severe cases of flanging, or when there is insufficient space under the floating plate I5a to accommodate springs I4 of suflicient length and force to minimize the formation of wrinkles in the edge portion of the blank A confined between the plate I5 and the tool I6, it may be advantageous to make the plate I5 and the tool IS in a single solid piece, recessed along its concaved side to nest with the convexed face or side of the blank to be flanged or to fasten the plate I5 and the tool I6 together after insertion of the edge portion of the blank therebetween. In that case, the springs I4 may be made much shorter or may be dispensed with altogether. This fastening may be effected by any suitable means such as screws or bolts, which can be tightened more or less in order to produce the desired holding pressure,

When it is desired to form or flange an article of relatively large size, in which only certain localized convexed parts of the work present the problem that the method and tool of the present invention solve, it would be uneconomical to build a special die according to the invention, such as shown in Figures 1 to 5. In that case, an ordinary die or form-block is used for forming or flanging all the parts of the work for which there arises no specialdiificulty such as concaved or straight flanges and the invention is embodied in the form of attachments which are associated only with the convexed portions of the flnished blank.

Such an arrangement is shown in Fig. 6 wherein the locally positioned tools are substantial duplicates of those shown in Figs. 1 to 5. Here I2 indicates a form-block of known design adapted to form rectangular articles or frames flanged outwardly and inwardly at itsedges. As the formation in a rubber press of the straight portions of these flanges and of the concave corners of the inner flange does not present any problem, the invention is locally applied to the formation of the four convex corners of the outer flange in the form of four comer attachments consisting essentially each of an auxiliary drawing tool IS, a retaining upright l3 and a guiding device comprising two vertical pillars 30. To obviate the problem of locating these uprights and pillars on the platen with respect to the form-block I2 in a constant relationship, all these fixed parts are permanently mounted on a. rectangular die-bed I9 substantially larger than the form-block I2, This latter has an outside flanging face H and an inside flanging face 22.

In this case also, the blank A may be located and held on the form-block I2 against lateral shifting without pins, by being exactly nested between four washers (not shown) yieldingly held up against the under surface of the drawing tools I6 and filling the flat spaces between the uprights I3 and the rounded corners of the blank A overlapping under these tools I6.

It is to be noted that the use of an auxiliary drawing tool such as the member I6 would not be sufficient in itself to prevent the formation of wrinkles and to allow for the production of higher flanges, were it not for the concomitant essential feature of the invention that a much greater volume of flowing material, such as rubber, is effectively utilized for the forming operation than in any known prior method, i. e. that both the area and the depth of the portion of the plastic pad utilized for a given forming operation are substantially larger than in all known prior methods.

This result is accomplished, on the one hand, by providing between the retaining block and the matrix a relatively wide gap, preferably equal in width to four times the depth of the work to be formed and, on the other hand, by using a matrix having at least more than twice the height of this work or flange, and by adding to this height of the matrix, the superimposed thickness of the drawing tool in determining the effective vertical stroke of compression and penetration of the flowing material. In known flanging dies, this effective stroke of the rubber is limited to the flange depth plus of an inch as otherwise creepage of the rubber under the flange would occur near the end of the stroke and mar the work.

When using the method of the present invention, such creepage can never take place, as the rubber that flows into the channel II can never reach the lower edge of the flange formed around the auxiliary matrix, due to the fact that the drawing tool is stopped at least when its top surface reaches midway of this formed flange (see Fig. 3); or, at the most, when this top surface reaches the trim line along which the edge a is subsequently trimmed from the final flange (see Fig. 5). If the convex flange to be formed according to present invention is bent at 90, the cost and trouble of machining the upright I3 and welding it on the die-bed I9 can be avoided in certain cases by arranging on a single die-bed What is claimed is:

1. The combination with a sheet metal forming Dress comprising a bolster and a head carrying a rubber forming pad movable toward and from the bolster, of a forming die "resting upon the bolster and having a working edge including con- -"vexed and non-convexed portions, a channel having opposed side walls and located laterally contiguous to the convexed working edge of said die, a rigid i'orm block yieldingly supported and vertically reciprocable within said channel, said die adapted to support a sheet metal blank with the margins of the blank and the margins of the rubber pad extending beyond the working edges of said die and a rigid drawing tool overlying the form block for clamping the margin of said blank thereagainst, said drawing tool having a concave working edge coextensive in length with and complementary in curvature to the convexed working edge only of the die and providing with said die a clearance not substantially exceeding the thickness of the sheet metal blank, whereby said rubber pad in its movement into engagement with the die exerts a compressive force against the margin of the blank to directly bend the blank against the non-convened portion of the working edge 01' the die and exerts a compressive force against the drawing tool to depress the drawing tool to draw the metal of the margin 01' the blank about the convexed working edge of the die.

2. The combination as set forth in claim 1, including a ilange projecting above the plane of the forming die for modifying the pressure of the rubber pad. said flange being positioned adiacent that side wall of the die located remote from the working edge of the die.

HOWARD M. JAGER.

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