US 2719500 A
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D. w. KRAYBILL 2,719,500
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FLANGE FORMING PRESS 5 Sheets-Sheet 3 mmwz zw 00L 1955 D. w. KRAYBILL 2,719,500-
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' @WWW United States PatentO FLANGE FORMING PRESS Daniel W. Kraybill, Downey, Calili, assignor to Northrop Aircraft, Inc., Hawthorne, Calif., a corporation of California Application July 28, 1950, Serial No. 176,367
1 Claim. (Cl. 113-44) In the use of the presently known rubber press, particularly for producing aircraft parts, the forming of straight flanges can be satisfactorily accomplished; but the forming of flanges around curved edges is very limited, especially in the matter of shrink flanges where the excess metal in the flange around a convex curve goes into wrinkles. This wrinkling occurs because pressure is exerted on one side, only, of the metal in the flange, there being nothing on the other side to support and draw the metal smooth. Consequently, a great deal of hand finishing is required to hammer the part into its final desired shape around dies which are in addition to those used in the initial forming operation. The additional, finishing dies must be made of sufliciently rugged material, such as hardened steel, to maintain its accurate dimensions, and the expense of this hand finishing is obvious.
Other tools, such as draw rings and plates, drop hammers, and punch presses, having companion punches and dies, have been employed to form parts not successfully produced on rubber presses, but the cost of the tooling necessary in these latter processes is substantially higher than with the rubber press apparatus. This tooling and die cost is particularly undesirable in the aircraft industry, where, in many instances, experimental and short-run contracts obviously do not result in realizing the full use of such tooling, and its abandonment constitutes an appreciable loss.
It is one object of the present invention to provide, in a forming process using a rubber press, a means and a method of completely machine forming sheet metal parts having various stretch and shrink flanges, joggles, indentations, and the like, thus eliminating costly handforming operations now required on such parts which are only partially finished in the press, and making possible the production of these parts without expensive detail tooling heretofore required to draw presses and other similar forming machinery.
Some attempts have been made to achieve better flange forming in rubber presses, by means of various partial backing members intended to keep the flange material smooth while being drawn or compressed into final shape.
However, some wrinkling or curling is still to be expected,
above with a single cycle of press operation,;to;prod11ce Patented Oct. 4, 1955 "ice 2. uniform parts by the elimination of the human element in hand finish forming, and to keep the cost of detail part tooling at approximately the same as that existing in the overall jobs using the ordinary rubber press.
It is still another object to provide a means and method of forming compound contoured stifleners, panels, and the like, on a rubber press not requiring companion die sets, and to complete this forming or drawing in one machine operation.
Further objects and advantages of my invention will be brought out in the detailed description of a preferred embodiment forming a part of this specification.
Briefly, this invention comprises a central die block, surrounded by a solid forming ring of approximately the same height as the die block, these partshaving the blank of sheet metal to be formed lying on top of them and being supported on a bolster plate which is adapted to make contact with an upper cage assembly containing. a flush rubber platen. An upper power cylinder then compresses the rubber to .the desired pressure on the die block, forming ring, and .sheet metal blank, after which the die block is raised by means of lift rods or pins coming through holes in the bolster plate, leaving the forming ring stationary, to perform the .actual bending and forming operation on the metal blank. In one embodiment, a metal ring is laid on top of the edge portion of the blank to be formed.
My invention will be more fully understood by reference to the accompanying drawings which are for illustrative purposes only, in which:
' Figure 1 is a vertical cut-away view, mostly in sectional form along the vertical center plane, of a hydraulically operated flange forming press of the present invention, showing a sheet metal blank, and die therefor, in position ready for a forming operation. p I
Figure 2 is a partial elevation view of the press in Figure 1, showing, in vertical section, the first step of the forming operation for the metal part blank.
Figures 3, 4 and 5 are views similar to Figure 2, showing progressive and final steps in the forming operation. Figure 6' is another press'view similar to Figure 2, showing the upper and lower, platens separated for removal of the finished part. i I
Figure 7 is a perspective view of a typical flanged part formed as shown in the preceding figures.
Figures 8, 9, 10 and 11 are cross sectional views of other kinds of parts made according to this invention.
Figure 12 is a cross sectional view of a die set-up according to the present invention, showing a pressure strip laid over the edge'of the part blank to be'formed.
I Referring first to Figure 1 for a detailed description of the illustrated apparatus, a press assembly 1 comprises a support base 2, four upright cylindrical members 3, the center portions of which are us'edas ways 4, an upper housing 5 attached to the tops of the upright members 3, a fixed cage 6 below the upper housing 5, and a lower bolster plate 7 'sildable on the ways 4 from the base part of the press. Mounted in the cage 6 is a rubber platen 8 composed of rubber laminations and a lower membrane 9 of extra tough elastic material. This rubber platen 8 is preferably of sponge rubber consistency havinga Shore hardness of from '20 to 50 'so that it will flow readily around the tooling. The rubber platen 8 is cemented together and to the lower'face of an upper piston 10 which operates in the cylindrical interior 11 of the upper housings. An upper piston down hydraulic line 12 mp pliesfluid to the space above the piston from a conventional high pressure hydraulic pump (not shown) as desired, and anvupper piston up hydraulic line 14, also coming from the external hydraulic equpiment, connects to a lower spaced below a piston flange 15 for moving the pistonu An interior surface 16 of the support base 2 is also cylindrically shaped to contain a lower piston 17 working vertically therein. A lower piston hydraulic line 19 supplies fluid for raising the lower piston 17. The lower piston has a support 'flan'ge20 which is apertured to slide over "the .ways 4, .and the lower bolster plate 7 rests on and is removablyfastened'to the support flange 20. The lower piston 17 is also Ihollowedto contain an inner .piston 21 operating vertically therein, and a flexible hydraulicline 22 supplies fluidthrough aflowerpiston passage 24 for raising the inner piston 21 within the lower piston17.
The bolster plate 7, which moves upwardly with the lower piston '17, containsa recessed space '25 on 'itslower side which permits the 'inner piston '21 to move up and occupy this space '25. A plurality of vertical, preferably cylindrical, holes 26 are provided throughout the working area of 'thebols'terplate 7, theseholes 26 carrying lift pins 27 of'the desired number and length. All pins used during the forming of any ,part .are long enough to be pushed above .the upper surface of the bolster plate 7 when the inner piston 21 is raised relative to the lower piston 17.
'The tooling which is supported on the bolster plate 7 includes a die block '3'0'having its upper and side surfaces conforming to the pattern for the finished part, and a forming ring/31 surrounding the die block 30 where the flanges are desired. The forming ring 31 is substantially the same'height as the die block 30 and is located closely adjacent to the die, although this distance is not at all critical, as will be referred to later, and the forming ring 31 does not have to conform accurately to the mold lines of the die block '30. Both the die block 30 and forming ring 31 may be of any suitable fiberboard material, such as Masonite, for example, or cast Dural, rolled alloys of zinc, aluminum, and copper (commonly known as Kirk- Site, for example), cast zinc alloys, or the like.
' A sheet metal blank 32, pretrimmed to final size, is placed on top of the'die block 30 and forming ring 31, as s'h'ownin Figure 1, where it is located in the proper position by tooling pins 34 in the .die according to conventionalprocedure. The metal part to be formed'may be of aluminum, steel or alloys of either; in fact, all types of presently used formable materials can be formed in this .machine.
'The' particular metal blank .32 used for this example is now ready for the .forming operation, from the position shown in Figure '1. Referring .to Figure 2 for the first step in the cycle, the lower piston 17 has been elevated, by pumpinghydraulic fluid .into the base 2 through lower piston'line 19, to place the bolster plate 7 in contact with the fixed cage 6. Pressure is then built up so that the lower piston 17 will not be overcome by the pressure of the other two pistons in later steps, and the pressure is then looked until the forming cycle is complete. The .die block 30, forming ring 31, andmetal blank 32 have thus been forced into the rubber platen 8 as a unit, and a certain pressure exists on these parts.
As shown in Figure 3, the upper, piston is next forced downwardly to further compress the laminated rubber 8 above the metal blank 32 and increase the .pressure. .It will be noted that pressure .is evenly distributed'on both sides of the flat metal blank 32. By having this pressure on :both sides of the areas to be flanged, i. e., :the edges resting on the forming .ring 31, wrinkling .of the flanges will .be prevented during the subsequent bending operation. The pressure to which the upper piston 10 must be subjected to prevent this wrinkling is ascertained by trial runs, and is easily established on production'runs by means of hydraulic pressure regulators, for example, and thenlocked at this value during the nextstep.
In Figure -4, pressure is admitted to the bottom surface o'f'the inner pi-stoni21,through the passage "24, to force the inner zpiston 2-11upwardly into the bolster plate space '25. The lift pins 27 are contacted by the upper face of th'e inner piston 21 and are thus forced up under the die block 30 'to raise it into the rubber platen 8. No lift pins are installed in the plate holes 26 beneath the forming ring 31, and the ring remains on the bolster plate 7 as the die block 30 is being raised. A flange 35 is thus begun over the edges of the die block 39, with the edge portion of the metal blank 32 being pulled from between the rubber platen 8and the forming ring 31. The above described pressure on both sides of the metal blank edges constitutes a clamping force and causes'this material to be stretched or contracted, as required, to form a smooth flange 35.
Upward motion of the inner piston 21 and lift pins 27 continues to the full up position, as shown in Figure 5, where the flange 35 is completely formed aaginst the die block sides. Length of the lift pins 27, of course, determines how far the die block 30 is lifted.
In most cases it is now desired to lock the inner piston 21 in its full up position and further increase the 'pressure above the upper piston 10 to approximately the full capacity of the machine. This is to set the flange 35 tightly around the die block 30 and thus make sure the flange-touches thedie at all points.
After the flange 35 is in the completely formed condition, pressure on the upper piston 10, through the down line 12, is changed to pressure in the up.line 14 and the piston moves back to the original up position, and then lower piston 17 pressure is removed to allow it 'to return to the original down position. The press 1 thenh'as the position shown in Figure 6, where the part is removed while the die block 30 is being held in its up position on the lift pins 27. If a turned-under flange is formed on all four sides, the die block 30 is designed to be taken apart for this operation, as is well known.
After removal of the formed part, which in this case is a nose rib part '36, as shown in Figure 7, the inner piston '21 maybe lowered to its bottom position ready for another cycle as pictured in Figure 1, upon insertion of another blank.
The forming ring 31, as shown, has a flat upper surface which is used for pretrimmed blanks for parts like the nose rib '36, but in forming drawn sections such as bulkheads 37 'having clearance spaces (Figure 11), compound contoured beaded stiifeners 39 (Figure 8), metal tank ends 40 (Figure 9), and cowl flap stiffeners 41 (Figure 10), the forming rings 3111 are preferably cast and have contours 4'2 and locking beads 44 as required. In Figures 8 and '10 parts such as the cowl flap stiffener 41 and compound beaded stifii'ener 39 can be trimmed by a sharp edge 45 on the die block 30a in the same press cycle just after completion of the forming operation.
For securing deeper flanges on curved edges with smaller radii, or in operations having less working pressure than desirable, an arrangement as shown in Figure 12 may be preferred. Here, the die block 30, forming ring '31, and metal blank 32 are placed as usual upon the bolster plate '7. A pressure strip 46 is additionally employed, this strip being laid over the edge of the blank 32 'to be flanged, with a spacer 47 set between the forming ring 31 and pressure strip 46 just past the edge of the blank 32. The spacer 47 has the same thickness as the part blank '32. Upon pushing the die block 30 upwardly at the proper time in the forming operation, the action is the same as that described previously, only with a harder surface in contact with the top side of the blank edge, to prevent wrinkles from forming as a result of buckling into the softer rubber platen at this point. The flange 'will thus be formed smooth, and no scratches will occur if the pressure strip 46 has a smooth surface and a rounded corner 49.
The bolster plate '7 is shown herein as moving upwardly and downwardly only. However, it may be designed to move out from under the press, for ease of reloading blanks, onto a loading platform and then back under the-press for the forming cycle.
An important new feature of this invention, as described above, is the provision for applying as much pressure as desired to both sides of the metal blank 32 before starting to form the flange 35. This is accomplished by sealing the space between the platens at the solid abutment between the bolster plate 7 and fixed cage 6, and then increasing the pressure on the flat pattern to any selected value by means of the hydraulically controlled upper piston 10.
Another feature which will be noted is that the die block 30 need not be developed for springback, as is required in commonly used rubber presses, and the cost and time is thereby lessened for this phase of the present invention. In addition, the die block 30 and forming ring 31 can be made very cheaply because of their materials, as mentioned previously, and the fact that the forming ring 31 is not required to be accurately shaped. I believe that the additional time necessary to build the forming ring 31 for this apparatus would be equivalent to the time saved in not having to develop the die block 30 for springback, and, therefore, the cost of tools for this machine is substantially the same as for the presently used rubber press. Consequently, the overall cost of manufacturing such detail parts which previously required other machinery is reduced because the hand finishing is eliminated.
Further, in most all cases, aluminum alloy parts made in accordance with this invention can be formed in the SW condition, rather than in the softer SO condition usually required, and they will not require a re-run operation to remove warpage due to subsequent heat treatment.
Thus it is seen that the present invention provides a cheaper way of forming many types of sheet metal parts. The replaceable lift pins 27 render the same machine usable for any sized part within the capacity of the bolster plate 7. This machine can also be used for forming compound mold-line contoured skins, and the like, since the material is gripped on all four sides rather than only two as normally done on sheet stretching machines.
From the above description it will be apparent that there is thus provided a device of the character described possessing the particular features of advantage before enumerated as desirable, but which obviously is susceptible of modification in its form, proportions, detail construction and arrangement of parts without departing from the principle involved or sacrificing any of its advantages.
While in order to comply with the statute, the invention has been described in language more or less specific as to structural features, it is to be understood that the invention is not limited to the specific features shown, but that the means and construction herein disclosed comprise the preferred form of several modes of putting the invention into effect, and the invention is, therefore,
6 claimed in any of its forms or modifications within the legitimate and valid scope of the appended claim.
What is claimed is:
Means for forming a sheet of metal into a compound contoured article, comprising a stationary base, vertical support means extending upwardly from said base, a lower bolster plate slidable along said vertical support means, a lower piston fitting into said base for moving said lower bolster plate upwardly under power, an upper housing fixed on said vertical support means above said lower platen, a fixed cage mounted on said vertical support means below said upper housing and having a central opening therein, an upper piston carried in said upper housing and operable up and down therein under power, an upper platen of conformable material having the general characteristics of rubber mounted in'the opening in said cage and having an exposed lower surface in the major central portion of said fixed cage and normally flush with the bottom surface thereof, the top surface of said bolster plate and the bottom surface of said upper platen being adapted to meet in solid abutting relationship when said lower bolster plate is raised, a die block supported by said lower bolster plate and having the desired contour to form said sheet and sides beyond which all edge portions of said sheet are to extend, rigid means supported on said lower bolster plate and abutting said die block and adapted to support edge portions of said sheet extending beyond the die block and having an upper face for positively supporting said edge portions when said lower bolster plate is raised and said upper piston is moved down to further compress said upper platen above said sheet, and die moving means carried within said lower bolster plate for pushing said die block upwardly under power relative to said lower bolster plate and said sheet edge support member, to form said sheet according to said die block.
References Cited in the file of this patent UNITED STATES PATENTS 2,233,164 Glasner Feb. 25, 1941 2,308,998 Misfeldt Ian. 19, 1943 2,317,869 Walton Apr. 27, 1943 2,345,353 Misfeldt Mar. 28, 1944 2,377,664 Berger June 5, 1945 2,400,004 Jager May 7, 1946 2,410,676 Nielson Nov. 5, 1946 2,422,883 Bruderlin June 24, 1947 2,434,375 Van Saun Jan. 13, 1948 FOREIGN PATENTS 564,552 Great Britain Oct. 3, 1944 OTHER REFERENCES Rubber Press Pads, The Goodyear Tire & Rubber Co., Akron, Ohio, March 1941, page 3.