US 2878561 A
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States METHOD OF FORGING A METALLIC WORKPIECE Application November 9, 1954 Serial No. 467,878
4 Claims. (Cl. 29-5522) No Drawing.
The present invention is related generally to the art of forging, and more particularly concerns itself with a new and improved forging method.
Machined parts for early production quantities of new aircraft have been heretofore almost entirely produced in steel dies carved from solid steel billet stock. As can be appreciated, such an operation is somewhat time consuming and relatively expensive, and due largely to the limited amount of die sinking capacity which is available, it has been found necessary to allow at least an average lead time of six months for the procurement of steel forging dies.
Further, should it be necessary to produce parts subsequent to the original order, and the carved die has been lost or destroyed, it is necessary to either machine the parts or fabricate a new die. In addition, certain of the forging die materials presently being used have not thus !far proven themselves completely successful with a ,diversity of forging metals in successive production runs.
It is therefore an important aim of the present invention to substantially eliminate the difiiculties above noted, and to provide a forging method that utilizes forging dies which may be cast in a relatively short period of time and which may be remelted with a resultant high rate of recovcry of virgin metal.
Another object of the invention lies in the provision of a hoteforge process which utilizes a non-ferrous material in the forging dies employed therein, which material is characterized by relatively high strength, thermal conductivity and elasticity.
Another object of the invention is to provide a method of hot-forging a metallic workpiece that utilizes a forging die material which is castable, readily formable and productive of accurate detail.
Still another object of the invention is to provide forging die materials and a hot forging method by means of which there is attained closer dimensional control, and a relatively low pouring temperature whereby foundry practice is substantially simplified.
A further object of the invention lies in the provision of a forging method wherein there may be successively produced forged parts of a number of different materials Without deleterious effects upon the die or forged parts.
Other objects and advantages will become more apparent as the description to follow proceeds.
In the co-pending application of Will L. Wheeler et al., Serial No. 456,600, filed September 15, 1954, and which is assigned to the assignee of the present application, there is disclosed a novel forging die and method of producing the same which has proven itself capable of eliminating many of the difficulties previously encountered with the heretofore used carved steel dies. A preferred die material, according to said Wheeler et al. application, is a zinc base alloy identified by its manufacturer, National Lead Company, as Kirksite A alloy. While this particular material has produced results far superior to those earlier accomplished, there exists in the art a need for a forging die possessive of increased utility for short runs of steel forgings, long runs of aluminum or magnesium forgings, and the forging of substantially larger parts in hydraulic presses having a relatively extended dwell time cycle.
Experience thus .far indicates that a forging die material capable of accomplishing many of the foregoing objectives should preferably be characterized by certain definite physical properties. Thus, in order to have sufficient ductility to adequately withstand repeated runs with hydraulic presses and forging hammers, the die material when cast and aged should have a compressive strength not substantially less than 88,000 lbs/sq. in. (B of Rockwell hardness). Further, to conserve on the stock of raw die materials maintained by the forging industry, it is of importance that the forging die metal be suitable for use with more than one forging metal. In addition, it is considered advantageous that the die material be remeltable by customary foundry techniques at relatively low temperatures without excessive loss of metal, and that said material is capable of improved hardness, tensile and compressive strength, and elongation by variations in annealing, aging, and other heat treating processes. Further, it is desirable that the metal from which the forging die is cast have a relatively low coefficient of friction whereby the use of conventional die lubricants may be eliminated or substantially reduced. Also, by essentially avoiding lubrication of the die, galling may be almost entirely eliminated.
A number of castable metallic substances, such as meehanite, cast ductile iron, certain of the cast steels, aluminum bronze, manganese bronze and aluminum silicon copper, have in some measure the properties just noted; however, certain of the copper base alloys are at this time particularly favored to accomplish the present purposes. While a number of different compositions of this general type alloy may be suitable, one which has proven itself particularly well adapted is a beryllium copper alloy designated as Berylco 20CR by its manufacturer, The Beryllium Corporation of Reading, Pa. Variations in the composition of this alloy are of course possible to render it more suitable for different forging uses; however, a composition comprising 2.00 to 2.25 percent beryllium, 0.35 to 0.65 percent cobalt, and the balance copper is particularly effective to achieve the objectives herein stated.
A compound of the above character, when cast and aged, has been found to have an ultimate tensile strength of 85,000 to 110,000 p.s.i., a yield strength (0.2% offset) of 45,000 to 60,000 p.s.i., a Rockwell hardness of B90-100, 10-25 percent elongation in 2 inches, a thermal conductivity of 0.22-0.28 cal./cm. /cm./sec./ C., and a density of 0.292 lb./ cu. in. Further, the melting range of the noted alloy composition is between 1575 to 1780 F., and said alloy has a shrinkage of only A of an inch per foot. The compressive strength (0.00l-in. set) of this alloy when solution annealed and fully aged is 165,000 to 180,000 p.s.i. I
A forging die formed of the composition earlier set forth may be produced by a number of different forging methods. However, one method which has proven itself well adapted is that disclosed in said earlier noted Wheeler et al. application, and illustrated in Figures 5 to 10 of the drawings therein. By the method as therein described, a raised pattern of the shape to be produced is preferably first formed on a mounting board and ashell-like retainer, located upon said board in surrounding relation to the shape thereon. After a plaster pattern combination is formed in the manner disclosed, a foundry flask is located thereover, sand packed compactly therein, and a made up sand mold thereafter produced. Preferably, forthe present application, the sand which is used ls that known to the art as core sand with which has been admixed a suitable binder. To assist in avoiding the formation of hydrogen bubbles during the production of thedie itself, it has been found preferable to heat the sand mold at approximately 375 F. for a period of two or three hours.
To fabricate the present forging die, a predetermined molten quantity of the beryllium copper alloy is poured at a temperature range of between 1585 and 1780 F. into the made up sand mold formed as disclosed in the Wheeler et a1. case, and the desired forging die thus cast therein. Subsequent to setting, the die is preferably processed through a suitable finishing operation whereby rough edges are removed and a substantially fiat bottom produced thereon. Thereafter, the die or die insert may be located in retainer members in the manner also disclosed in said Wheeler et al. application, and particularly shown in Figure 11 thereof. By means of the other apparatus therein described, forged parts of various mate rials may be effectively produced.
To demonstrate the ability of the present beryllium copper die to adequately withstand successive runs therein of steel, aluminum and magnesium forgings, as well as to show the effectiveness of such a die to produce various forged parts in hydraulic presses having a dwell time of generally more than fifteen seconds, a number of forgings were produced from a die formed in the manner earlier described. Set forth below is a summary of the conditions existing and results obtained:
Example I Utilizing pieces of 14S aluminum stock measuring approximately 4 inches in diameter and 12 inches long, which were each heated to a temperature between 810 and 820 R, an average of 28 blows by an 8000 pound steam hammer were struck on said pieces of stock while located in the beryllium copper die, the temperature of which during forging was between 150 and 250 F. The lubricant used was graphite in lead base oil, and the forgings when removed from the die ranged between 500 and 650 F. The forgings produced compared favorably with those made from conventional steel dies, and there were no noticeable objectionable cracks in the die.
Example 11 Substantially immediately thereafter, and employing the same die as in Example I, five pieces of 4340 steel, measuring approximately 3 inches square and 12 inches long, were successively located in the die after being heated to approximately 2120 F. An average of 19 blows were struck on each of said pieces and the forgings thus produced were considered excellent. The same lubricant as above was used, and the die maintained substantially its original dimensions. Further, there was no noticeable copper pick-up by the steel forgings.
Example Ill The same die as used in the above examples was preheated and subsequently located in a 1500 ton hydraulic press. Five pieces of 75S aluminum of the same size as in Example I were heated to 710 F. and successively located in the die while its temperature was maintained at about 550 F. Three pressings exceeding fifteen seconds were made on each piece with no noticeable deterioration of the die. The forgings were comparable to those received from steel dies, and the die size was precisely as before. Temperature measurements on the forgings when removed from the die showed them to be between 600 and 630 F.
Example IV was the same as above and said pieces were at a temperature of approximately 690 F. when located in the die,
the temperature of which was about 550 F. Two pressings were made of each piece with a 1500 ton hydraulic press and there was no sticking of the pieces to the die as has been characteristic with the use of steel dies for magnesium forgings. In fact, the surface finish of the die seemed to improve with use. The lubricant employed in this and the foregoing run was a mixture of equal amounts of Kerns die lubricant and lead base oil.
It may thus be seen that the forging die herein disclosed fills a need which has long existed in the art. First, a beryllium copper forging die may be effectively employed with a variety of materials having different physical properties. Thus, as was shown in the examples, aluminum, steel and magnesium may be successively run in the same die without evidence of the forging adhering to the die cavity and without surface damage thereto. Heretofore this was substantially impossible to accomplish with steel dies, and although applicant is not certain as to the exact reason, beryllium copper would appear to have self-burnishing characteristics, and as compared to the forging material, a relatively low coefficient of friction.
Second, steel parts may be forged at temperatures exceeding the melting point of beryllium copper without any appreciable breakdown in the die, such as expansion or the creation of fissures or cracks therein. Apparently this is explainable by a high rate of heat transfer in the die. Third, as a result of the relative ease with which beryllium copper forging dies may be made, the prior lengthy lead time for die procurement may be substantially eliminated.
Fourth, the dies of the present invention may be remelted at relatively low temperatures (around 1800- 2000" F.) by foundry techniques with a general recovery of about 95% virgin metal. As a consequence, the dies themselves need not be stored long after the production run is completed. Instead, it is merely necessary to retain the male pattern, and should additional forged parts be subsequently needed, a new beryllium copper die may be fabricated. Particularly is this desirable in the aircraft industry since dies are frequently rendered obsolete by design changes.
It will be appreciated that it may at times be desired to employ certain of the beryllium alloys other than the Berylco 20CR material above described. As for ex-' ample, it may be preferred to use other high strength alloys such as Berylco 275CR" containing about 2.60- 2.85% beryllium, 0.35-0.65 cobalt, and the balance copper. The melting range of this alloy is approximately 1625 -17 10 F., the ultimate tensile strength after being cast and aged is 95,000-110,000 p.s.i., the yield strength (0.2% offset) 55,000 to 65,000 p.s.i., and the Rockwell hardness 390-100. The elongation, shrinkage, and density of the 275CR alloy are substantially the same as for the 20CR alloy. However, its compressive strength (0.001 set) when solution annealed and fully aged is 190,000 to 210,000 p.s.i. On the other hand, beryllium nickel alloy is also effective, having a tensile strength of approximately 200,000 lbs/sq. in., a Rockwell hardness of C52, and good corrosion resistance. This particular alloy is understood to contain nominally 2.6% beryllium and the balance nickel.
It will also be appreciated that changes in the composition and procedures herein disclosed may be practiced without departing from the spirit of the invention or the scope of the appended claims.
1. The method of forging a metallic workpiece comprising: heating said workpiece to a hot-forge temperature, placing said heated metallic workpiece in a forging die made of a composition comprising not more than 10% by weight of beryllium and not less than by weight of a metal selected from the group consisting of copper and nickel and having, after casting and aging, a compressive strength of substantially not less than 88,000
p.s.i. and a Rockwell B hardness of not less than 90, subjecting said heated workpiece to sufficient pressure to cause said workpiece to conform to a portion of said die, and thereafter removing said workpiece from contacting relation with said die.
2. The method defined in claim 1 wherein said forging die contains beryllium in an amount of from approximately 2.00% to approximately 2.85% by weight.
3. The method defined in claim 1 wherein said forging die contains beryllium in an amount of from approximately 2.00% to approximately 2.85% by weight, and further contains cobalt in an amount of from approximately 0.35% to approximately 0.65% by weight.
4. A method of forging a metallic workpiece which includes the steps of: heating said workpiece to a temperature greater than approximately 700 F., placing said heated workpiece in contacting relation with the cavity of a die fabricated substantially of copper alloyed with from approximately 2.00% to approximately 2.85% by weight of beryllium and having, after casting and aging, a compressive strength of substantially not less than 88,000 p.s.i. and a Rockwell B hardness of not less than 6 90, subjecting said heated workpiece to repeated blows to cause a surface portion thereof to develop a contour corresponding to the contour of said cavity, and thereafter removing said workpiece from contacting relation to the surface of said cavity.
References Cited in the file of this patent UNITED STATES PATENTS 1,231,323 Arthur June 26, 1917 1,875,586 Friedman Sept. 6, 1932 1,889,823 Cole Dec. 6, 1932 1,920,699 Hurley Aug. 1, 1933 2,137,281 Hensel Nov. 22, 1938 2,167,684 Sawyer Aug. 1, 1939 2,349,920 Welcome May 30, 1944 2,397,168 Touceda Mar. 26, 1946 2,494,935 Dunn Jan. 17, 1950 2,503,630 Norton Apr. 11, 1950 2,518,890 Heron Aug. 15, 1950 2,644,352 Ressegger July 7, 1953