Plastic mating dies and metallic holder supports therefor
US 3124092 A
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March 10, 1964 B. F. RAYNES 3,124,092
PLASTIC MATING DIES AND METALLIC HOLDER SUPPORTS THEREFOR Filed Aug. 25. 1958 :5 Sheets-Sheet 1 INVENTOR.
B.F.RAYNES ME. r v
ATTORNEY March 10, 1964 B. F. RAYNES 3,
PLASTIC MATING DIES AND METALLIC HOLDER SUPPORTS THEREFOR Filed Aug. 25, 1958 3 Sheets-Sheet 2 INVENTOR. B. F. RAYNES Mg-I2... i ATTORNEY United States Patent 3,124,092 PLASTIC MATING DIES AND METALLIC HULDER SUPPORTS THEREFOR Burt F. Raynes, Chula Vista, Califi, assignmto Rohr Corporation, a corporation of California Filed Aug. 25, 1953, Ser. No. 756,849 3 Claims. (Cl. 113-49) This invention relates to plastic mating dies having metallic holder supports for forming sheet metal to a desired shape and to a method for making such dies.
In bending large fiat metal sheets against dies having substantial curvature large forces must be applied by the dies and they must be thick and strong enough to withstand these pressures without bending. It has been the practice to make the dies of steel or special kinds of iron so that they are heavy and difiicult to raise into position in the forming press or drop hammer which effects the forming. It has also been expensive to machine the faces of such metal dies to the proper curved contours required to form the sheets. It is accordingly a purpose of my invention to provide a method for making forming dies wherein a large cost saving is effected over prior methods.
A further object is to provide mating dies, each made of two parts of which the part which contacts the metal sheet is made of non-metallic plastic material which has become rigid. The plastic die portion fits into a rigid metal holder which supports it and reecives the large stresses incident to form the sheet. Another object is to provide means for anchoring the plastic die portion to its supporting holder which permits the quick and easy attachment or detachment of the die and its holder.
A further object is to provide plastic mating dies which are much lighter in weight than the usual steel or iron mating dies and are therefore easier for the operator to put in position in the forming press or drop hammer which effects the forming.
A still'further object is to provide means for introducing pressurized fluid between the die and its holder to separate the die and thus facilitate its removal from the holder.
Further objects will become apparent as the description of a punch and die set proceeds. For a better understanding of the invention reference is made to the accompanying drawings, in which:
FIG. 1 is a front view of a master model used to shape the die;
FIG. 2 is a transverse sectional view through the die;
FIG. 3 is a transverse sectional view of a punch and die in a molding machine;
FIG. 4 is a front View showing the punch and die in a drop hammer;
FIG. 5 is an end view of the punch, die and hammer of FIG. 4; and
FIG. 6 is an isometric drawing showing half of a two stage die set embodying the invention.
Referring to FIG. 1 a model 10 is made having a central raised portion 11 whose exposed face 12 is made to the shape of the workpiece to be formed. Model 10 could be made of metal and face 12 made by a cutting tool such as a milling machine cutter. But the model is preferably made of plaster of Paris or similar material, and face 12 shaped by hand tools before the plaster has set hard. After the plaster has set, the top of the model is covered with a thin film of a parting agent such as wax (not shown) and a sheet 13 of fiberglass or canvas cloth laid on projection 11. The sheet can be thoroughly impregnated and covered on both faces with a polymerizable plastic resin either before it is placed on projection 11 or after. The sheet is pressed and worked against l the model until it is the shape of projection 11, as shown.
The model is then heated to polymerize and set the plastic or the plastic may be a resin of the epoxy or polyester type and contain a catalyst which causes it to harden at normal room temperature.
After the sheet is hard it is removed from model 10, inverted and placed on a supporting frame 14 disposed in a recess 15 in an aluminum mold 16. All the sidewalls 17 of recess 15 converge inwardly as shown and they, together with bottom wall 18, have previously been coated with a thin film of wax or other parting agent (not shown). Frame 14 has a plurality of long legs 19 which support the edge portion of sheet 13 and legs Zil (one being shown) which support its center portion. The number of supporting legs required will depend on the size of sheet 13 but in any case enough legs will be provided to prevent any appreciable bending or distortion of it. The space around and under 13 is now filled with a viscose plastic resin which hardens on polymerizing to form the plastic die 21. Any of the usual thermo-setting resins such as those of the alkyd, urea, methyl methacrylate types may be used in which case the mold 16 with the die 21 therein are placed in an oven and heated to a temperature high enough to polymerize the plastic. Or the resin may be of the polyester or epoxy types and contain a catalyst which causes it to polymerize and harden at normal room temperature of around 70 F.
For forming thin metal sheet stock, die 21 could be used in support 16 by laying a flat thin metal sheet on it and pressing the sheet against the die by a thick rubber pad as shown and described in United States Patent No. 2,190,659 to H. E. Guerin. 0r the sheet could be pressed against the die by means of hydraulic pressure contained in a rubber bag as disclosed in US. Patent No. 2,066,085 to L. V. Whistler.
Instead of using the sheet 13, the plastic die may be made entirely of plastic resin by placing the resin in recess 15 and shaping the top of it by hand tools of known type to the desired contour while the resin is still plastic. The resin is then polymerized by the action of heat, or, at room temperature, by the catalyst contained therein.
To make a punch or male die complemental in shape to die 21, two or more holes 22 (FIG. 3) are drilled in block 16 and a cylindrical guide pin 23 secured in each hole. This assembly is then placed on the base 24 of a molding machine 2.5. A wax gasket 26 is then placed on die 21 and a wax layer or film 27 applied to the top of sheet 13, the film 27 having a thickness equal to that of the metal sheet to be later formed between the mating dies. An upper mold 28 made of aluminum and having a recess 29 of the same size and shape as recess 15 of mold 16 is provided, a pair of fill and vent holes 3% terminating in recess 29. Mold 28 also has holes 31 drilled therethrough to receive the guide pins 23, as shown. With the parts described in position, as shown in FIG. 3, viscous plastic resin of any of the aforementioned types is introduced through one of the holes 36 until recess 2? is entirely filled with plastic. The ram 32 of the press is then lowered to compress the plastic against coating 27. During the compression gasket 26 keeps the plastic from escaping from between the molds 16 and 28. If the plastic is of the type which hardens at room temperature the parts are left in machine 25 until the plastic has set when it forms a male die or punch 33 of the desired shape. If the plastic is of the thermosetting type, the assembly is heated by any suitable heating source (not shown) to polymerize the plastic. With either types of plastic, filler material such as particles of gravel, broken glass, or grains of sand to the extent of percent of the mixture may be mixed in with the viscous plastic resin. After the plastic hardens the die is removed from mold 28 and the two fingers which extend into the holes 30 cut off. Also wax coating 27 is removed from die 21.
The plastic die set made in the above manner may be used to form metal sheets in a drop hammer as follows. Referring to FIGS. 4 and 5, a lower die holder 34 made of steel or Meehanite has a recess 35 cut therein the same shape and size as recess 15. A shallow circular depression 36 is cut at the center of recess 35 and a passage 37 connects this depression to the outer face of holder 34. Two or more vertical guide pins 33 have their lower ends secured in holder 34 and their upper ends are adapted to enter cylindrical holes 39 in upper die holder 40 made of steel or meehanite. Die holder 34 is secured to the anvil 41 of the drop hammer by four clamps 42 and bolts 43. Lower plastic die 21 made as above described is placed in recess 35 in which it is a close fit and held securely for forming.
Upper die holder 40 has a recess 44 therein the same shape and size as recess 29 so that male die or punch 33 fits closely in this recess. Four recesses 45 are made in the ends of punch 33 to receive the ends of screws 46 which enter threaded holes 47 provided in the end walls of holder 40. The screws may be locked by lock nuts 48. A shallow circular cut 49 is made at the top of recess 44 and a passage 50 connects this cut to the outer face of die holder 40. The holder 40 is placed against the bottom face of ram 51 of the drop hammer so that the holes 39 are in alignment with guide pins 38 and locked in place by clamps 52 and bolts 53. To form a flat thin metal sheet to the shape of the dies, the sheet is laid on die 21 and the ram 51 of the hammer released by any known means (not shown) so that it drops and causes punch 33 to press the sheet against the face of die 21 and deform it to the desired shape, as shown at 54. After a sufficient number of sheets have been formed, the end of a tube carryingcompressed air is placed against the outer end of passage 37, the air pressure lifting die 21 slightly away from holder 34 when it is removed by the operator. To remove punch 33, the operator loosens screws 46 and introduces compressed air into passage 50. This loosens punch 33 from its holder 40 and permits its removal from the drop hammer.
By repeating the above process but using a model 11 whose contoured face 12 is of different size and shape, a second plastic die set can be made in which the female die will fit in recess 35 of holder 34 and the punch will fit in recess 44 of holder 40. When these plastic dies are placed in the hammer, they are properly aligned without any further adjustments to form a thin metal sheet between them when the ram is dropped. A large number of die sets can thus be made, each having a forming face of different size and shape to form a number of metal sheets to a variety of different shapes. The dies of each set fit snugly in the die holders 34 and 40 and since they are made of polymerized plastic, they weigh only about /6 of what similar steel dies would weigh so that it is much easier for the operator to put them in the drop hammer and remove them.
In certain cases it is necessary to press a metal sheet twice to form it to a desired shape. Under my invention this may be done by providing two female die faces 56, 56 (FIG. 6) in plastic die 21' and two complemental shaped punches 57, 58 on upper plastic die 33'. The dies 21 and 33 fit in the recesses 35 and 44 and are secured in the drop hammer in the manner above described. The fiat sheet to be formed is placed on the first stage die 55 and the ram 51 allowed to fall. The ram is raised and the partly formed sheet removed from die 55 and placed over die 56. Upon allowing the hammer to again fall, punch 58 presses the partly formed sheet against second stage die 56 and completes the forming. By making the two stage die of only two pieces of plastie, the die cost is kept at a minimum.
This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment of the invention is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.
Having thus describedmy invention, what I claim as new and useful and desire to secure by Letters Patent is:
1. Light weight composite drop hammer dies for applying large forces for bending a workpiece in the form of a large thin flat sheet of metal to a predetermined shape of substantial curvature comprising a pair of meta llic holders respectively attachable to the anvil and ram of a drop hammer and having confronting faces, said faces respectively having substantial and deep recesses with sidewalls which converge substantially away from said faces, a pair of insertable and detachable blocks of rigid molded polymerized plastic resin, said blocks having tapered portions, respectively seated interfittingly within said recesses and wholly supported therein and against the sidewalls thereof, said blocks having interfitting and matching male and female surface portions for engaging and forming the workpiece therebetween and conforming to said predetermined shape of the workpiece, said blocks having light weight relative to said metallic holders and having sufiicient strength per se to withstand and transmit to said holders the stresses developed by the drop hammer on the workpiece, said blocks respectively having smooth molded surfaces which close-1y match and interfitwith the surfaces of said recesses whereby said stresses incident to the drop hammer operation are transmitted to and absorbed by said holders, said holders having sufficient strength to receive and absorb said stresses transmitted thereto through said blocks and to withstand said stresses without bending, said holders having complementary means for aligning the same as the ram moves toward the anvil thereby to assure a mutually aligned relationship of said recesses and of said conforming surfaces of the blocks seated interfittingly within the recesses, said holders and blocks being forced into mutually tightly interfitting relationship by said stresses incident to the forming of the workpiece, said holders respectively having means for introducing pressurized gas between said closely interfitting surfaces of the blocks and their respective holders to release the blocks therefrom, at least one of said blocks and its holder having complementary means for releasably anchoring the block in seated position in the holder.
2. Drop hammer dies as in claim 1, one of said matching and conforming surfaces of said molded blocks having a plastic impregnated fiberglass surface layer.
3. Drop hammer dies as in claim 1, said blocks having discrete particles of rigid material embedded therein.
References Cited in the tile of this patent UNITED STATES PATENTS 429,349 Hobson et a1. June 3, 1890 469,741 Judd Mar. 1, 1892 673,822 Sagendorph May 7, 1901 779,096 Nazel Jan. 3, 1905 875,940 Mason Jan. 7, 1908 999,303 Falk Aug. 1, 1911 1,351,048 Lockwood Aug. 31, 1920 1,956,875 Paradise May 1, 1934 1,989,646 Tuttle Ian. 29, 1935 2,492,131 Burger et al Dec. 27, 1940 2,305,866 Graf Dec. 22, 1942 2,350,004 Whistler et a1 May 30, 1944 2,478,171 Macpherson Aug. 9, 1949 2,836,530 Rees May 27, 1958 2,965,383 Steiner et al Dec. 20, 1960 FOREIGN PATENTS 21,170 Norway Feb. 20, 1911