US2716806A - Milling and stretching integral panels - Google Patents

Description

Se t. 6 1955 M. s. REED MILLING AND STRETCHING INTEGRAL PANELS Filed July 8, 1952 R O T N E V m flamam/JJI feed ATTORNEYS Patented Sept. 6, 1955 2,716,806 MILLING AND STRETCHIN G INTEGRAL PANELS Macdonald S. Reed, Erie, Pa. Application July 8, 1952, Serial No. 297,667 6 Claims. (Cl. 29-548) This invention relates to methods of forming metal sheets, and particularly to the forming of thin sheets having integral upstanding ribs, such sheets being commonly referred to as integrally stiffened panels.

It is desirable, especially in the aircraft industry, to have sheets of relatively large surface area and quite thin provided with integral upstanding ribs or flanges formed thereon to provide stiffening whereby such sheets may be employed as a rigid skin,for the aircraft. The production of such structural sheets has heretofore been impractical by known methods since the finished sheet requirements, as relating to the thickness of the integral flanges and the heights thereof, is such as to render such shapes impractical to produce by any previously known methods. In general, it is desirable that finished sheets of a thickness of the order of magnitude of inch be provided with integral ribs or flanges of about the same thickness projecting from one surface and spaced apart from 1 /2 to 3 inches. The ribs are desirablyof a height of the general order of one inch or more. It can readily be seen that integral structural shapes of those dimensions would be extremely difiicult to produce by conventional methods.

Attempts have previously been made to economically produce integrally stiffened panels of the type described, but none of them have thus far proven successful. Applicant proposes to produce such panels by milling grooves into the opposed faces of relatively thick metal plates to define spaced parallel ribs with reversely bent corrugations between the ribs. Preferably, the corrugations extend substantially throughout the full thickness of the original plate. The corrugated sheet thus produced is thereafter stretched in a direction transverse to the ribs to flatten the corrugations, leaving the ribs themselves upstanding from a surface of the resulting panel. The finished product comprises a fiat sheet much thinner than the original plate with integral upstanding ribs thereon of a height about equal to the thickness of the original plate. The flattening of the corrugations may be accomplished by stretching the milled plate, as described, or may be accomplished by other means such as by pressing or by means of suitably shaped rollers.

By thus milling the intermediate product to a sheet of corrugated form, and later flattening the corrugations, a final product of much greater width than the original mill capacity is possible.

It is, therefore, an object of this invention to provide a method of forming integrally stiffened panels more efficiently and more economically than by methods heretofore known.

Another object of this invention is to provide a method of forming integrally stiffened panels of practical dimensions from metal plate.

It is still another object of this invention to provide a method for forming sheet material whereby pieces of greater area may be fabricated than possible with previously known methods.

A still further object of this invention is the provision of a method of forming an article with conventional apparatus and resulting in a product of greater size than the capacity of the appratus to produce directly.

It is another object of this invention to provide an intermediate structure by milling or sawing solid metal stock so that the milled intermediate product may be later processed to the desired finished shape.

Further objects and advantages will appear to those skilled in the art as the description proceeds in connection with the accompanying drawings, wherein:

Fig. 1 is an end view of a portion of a metal plate after it has been milled to the desired shape;

Fig. 2 is a fragmentary end view of the finished product produced from the structure of Fig. 1;

Fig. 3 shows a portion of the metal plate stock in full lines and indicates, by dotted lines, a possible arrangement of milling cutters and/or saws for producing the intermediate product of Fig. 1;

Figs. 4, 5, 6, and 7, illustrate alternative intermediate products that may be cut from thick plate stock to produce dilferent final products.

Referring first to Fig. 2, which is a fragmentary end view of the finished product, numeral 2 indicates the thin fiat skin previously referred to having integrally solid upstanding ribs 4 projecting from one surface thereof. Preferably, the material from which these panels are made is aluminum, aluminum alloy, or a suitable magnesium alloy for use in covering aircraft frames. Clearly, however, other metals or materials may be employed, especially if the product is to be used in other installations than aircraft.

The panel of Fig. 2 was produced from the intermediate product shown in Fig. 1. As shown in Fig. l, the the intermediate product consists of spaced ribs 4 but the skin 2 of the finished ,panel is arranged in the form of a corrugation 6 extending upwardly between the ribs 4. After the intermediate product of Fig. 1 is produced, tension may be applied to the ends of the skin, as indicated at A. The application of such tension results in the flattening of the corrugation 6 to the form shown in Fig. 2. After the corrugation assumes a flat condition, the sheet is further stretched to slightly exceed the elastic limit of the metal and permanently setthe panel in the flat condition to which it is drawn. As will be obvious, the stretching of the sheet in the manner indicated has no elfect on the ribs 4 other than to move them apart. As is clearly evident from the drawings, the ribs 4 are quite close together in the intermediate product of Fig. l, but spaced apart a considerably greater distance in the finished product of Fig. 2.

Fig. 3 shows at 8 a solid line representation of a portion of a relatively thick metal plate constituting the stock material of the present invention.

Referring again to Fig. 1, the intermediate product consists of a thick plate having grooves 10 cut into one surface thereof and grooves 11 cut into the opposite surface. Saws or cutters 12 of Fig. 3 may be arranged on a mandrel 14 to cut the grooves 10 while the saws or milling cutters 16 may be arranged on a second mandrel 18 to cut the grooves 11. The saws 12 may be spaced apart the required distance by means of spacers 20 and auxiliary milling cutters 22. The auxiliary cutters 22 are for the purpose of forming the curved upper surface 24 of the corrugation 6. Preferably, the saws or cutters 12 and 16 are rounded at their peripheries to form round bottomed grooves. The mandrel 18 may also be provided with auxiliary cutters 26 adjacent the cutter 16 for the purpose of forming the curved surfaces 28 at the bottoms of the corrugation 6. Spacers 30 may be employed to separate adjacent groups of cutters 26 and their associated saw or cutter 16.

As is clearly evident from the drawings, the grooves 10 extend downwardly such a distance that their bottoms are spaced from the bottom surface of the original plate a distance substantially equal to the spacing between grooves 10 and 11, and since the bottoms of the groove and the shoulders at the entrances of the grooves are all rounded, the material remaining between ribs 4 may be described as a thin plate arranged as a corrugation between the ribs. The spacing between grooves 10 and 11 determines the thickness of the skin 2 shown in Fig. -2.

The saw and/ or cutter arrangement of Fig. 3 is merely illustrative of one possible arrangement. Many other forms of conventional milling cutters or saws could clearly be employed to produce the intermediate product of Fig. 1. Fig. 3 also suggests the simultaneous cutting of the grooves in opposite sides of the plate 8 but clearly the grooves cut by the cutters on mandrel 14 could constitute one operation and the cutting of the grooves 11 could be a subsequent and separate operation, if desired.

Fig. 4 illustrates a modified intermediate product wherein the ribs 4' are considerably thicker than those shown in Figs. 1 and 2 whereas the skin is of substantially the same thickness. The apparatus suggested in Fig. 3 may be readily adjusted for the production of the Fig. 4 product by merely increasing the thickness of the spacers 2t) and 30, the remainder of the set-up remaining the same.

Fig. 5 illustrates a still further modified form of intermediate product wherein the corrugation 6 is formed to extend a substantial distance above the tops of the ribs 4.

Such an intermediate product results in a final product similar to that of Fig. 2 but wherein the ribs 4 are spaced apart a materially greater distance since the length of sheet material comprising the corrugation 6' is greater than the length of material comprising the corrugation 6 of Fig. 1.

Fig. 6 shows a still further modified form of intermediate product comprisnig the spaced ribs 4 but wherein a pair of corrugations 32 and 34 are formed between adjacent ribs. Fig. 5 was described as a method of increasing the spacing between the ribs 4 but it is clear that that method has limitations since it involves the waste of a greater amount of material than the method of Fig. 1. All of the material above the ribs 4 must be removed and is lost. When it is desired to produce a final product having the rib spacing substantially greater than is possible with the method of Figs. 1 or 5, the intermediate product of Fig. 6 may readily be produced. It will be evident that when the intermediate product of Pig. 6 is stretched to its final form, the spacing between ribs 4 will be substantially twice that shown in Fig. 2 while the thickness of the skin 2 and the height and thickness of ribs 4 remains the same.

The intermediate product of Fig. 6 may also be readily produced by a mere addition of cutters of Fig. 3, it being only necessary to add additional saws and auxiliary cutters between the saws 12 that define the sides of the ribs 4 and the addition of an additional cutter 16 and auxiliary cutters 26 on mandrel 18. The cutters 12, 22, 16, and 26 may all be identical and of standard proportions.

The most economical and desirable intermediate prod net is of the type shown in Figs. 1, 4, and 6, wherein the crests of the corrugations lie in the same plane as the tips of ribs 4, that plane being the original upper face of the stock plate 8. Thus, the least amount of material need be removed to produce the intermediate product.

Fig. 7 shows another modified form of intermediate product comprising spaced ribs 4 and an upstanding corrugation 40 of less height than the ribs 4. The corrugation 40 is provided, on its crest, with a rib or projection 42. Obviously, this intermediate product may be readily produced by the same operations described in connection with the previous embodiments and when stretched or flattened to a shape comparable to that of Fig. 2 the rib or projection 40 will remain as an upstanding rib in the finished product located centrally between ribs 4 but of much less height. Clearly, the auxiliary or shortened ribs 42 may also be provided on such structures as illustrated in Fig. 6, wherein more than one corrugation is formed between the major or principal ribs 4.

While applicant has referred herein to milling cutters and saws, it is to be understood that the term is intended to include any and all cutting tools capable of producing the shapes described or other obvious or equivalent shapes and might conceivably even be shaper cutters, and mills, or the like.

While a single specific method has been shown and de-- scribed herein, it is to be understood that the same is merely illustrative of the invention and not intended as a limitation. Many modifications and changes may be resorted to which fall fairly within the scope of the appended claims.

I claim:

l. A method of forming an integrally stiffened panel, comprising the steps of: milling opposite faces of a relatively thick metal plate to provide spaced integral ribs on one side and at least one corrugation between said ribs, and thereafter flattening said corrugations to pro duce a wider and substantially flat panel of less thickness than said plate having spaced parallel solid integral ribs upstanding from one surface thereof.

2. A method as defined in claim 1, wherein said corrugations are flattened by stretching said milled sheet in a direction transverse to said ribs.

3. A method of forming an integrally stiffened panel, comprising the steps of: milling a first set of spaced grooves in one face of a relatively thick metal plate; milling a second set of spaced grooves in the opposite face of said plate, the grooves of said second set extending between certain but less than all of the grooves of said first set whereby to provide spaced solid ribs ex tending to said one face, and at least one corrugation between adjacent ribs, and thereafter flattening said corrugations to produce a wider and substantially flat panel of less thickness than said plate having spaced solid integral ribs upstanding from one surface thereof.

4. The method defined in claim 3, wherein said flattening step is performed by placing said milled plate under sufficient tension, in a direction transverse to said ribs, to flatten said corrugations and thereafter to stretch said fiat panel slightly beyond its elastic limit.

5. A method of forming an integrally stiffened panel, comprising the steps of: milling a first set of spaced pairs of parallel grooves in one face of a relatively thick metal plate; milling a second set of spaced parallel grooves in the other face of said plate, each of the grooves of said second set being milled to extend between the grooves of said pair of grooves in said one face, the material be tween said pairs of grooves defining ribs extending toward said one face, each of said grooves being milled to a depth sufficient to space their bottoms from the opposite face of said plate a distance substantially equal to the spacing between adjacent grooves; and defining corrugations between said ribs, thereafter flattening said corrugations by placing said milled plate under sufficient tension, in a direction transverse to said ribs, to flatten said corrugations and thereafter to stretch said flat panel slightly beyond its elastic limit.

6. A method of forming an integrally stiffened panel, comprising the steps of: cutting a first set of spaced pairs of grooves in one face of a relatively thick metal plate; cutting a second set of spaced grooves in the other face of said plate, each of the grooves of said second set being parallel to and cut to extend between the grooves of said pair of grooves in said one face, the material between said pairs of grooves defining solid ribs extend ing toward said one face, each of said grooves being cut to a depth to space their bottoms a substantial distance from the opposite face of said plate; and defining corrugations between sail ribs, thereafter flattening said corrugations by placing said cut plate under sufficient tension, in a direction transverse to said ribs, to flatten said corrugations and thereafter to stretch said panel slightly beyond its elastic limit.

References Cited in the file of this patent UNITED STATES PATENTS 1,623,273 Rendleman Apr. 5, 1927 2,018,085 Otte Oct. 22, 1935 2,263,425 McKee Nov. 18, 1941 2,615,234 Dumbleton Oct. 28, 1952 2,617,179 Burke Nov. 11, 1952

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