US2726973A - Method of and apparatus for forming and quenching metal - Google Patents

Description

Dec. 13,

Filed May 24, 1952 J. S. CORRAL METHOD OF AND APPARATUS FOR FORMING AND QUENCHING METAL 2 Sheets-Sheet l FIG. I

2| /4 he Q 19; flfl[ 9 24 7 l8 l7 I? J I) 23 ,zz INVENTOR.

RESEFWR JOSEPH s. CORRAL FIG.4 BY

wzzam [K ATTORNEY Dec. 13, 1955 s, CQRRAL 2,726,973

M OD A PP TUS FOR F ING AND NC G METAL 2 Sheets-Sheet 2 Filed May 24, 1952 FIG. 9

INVENTOR.

JOSEPH S. GORRAL Wow/ ATTORNEY United States Patent METHOD OF AND APPARATUS FOR FORMING AND QUENCHlNG METAL Joseph S. Corral, Los Angeles, Calif., assignmto North American Aviation, Inc.

Application May 24, 1952, Serial No. 289,915

6 Claims. (Cl. 148-115) This invention relates to a method and means for forming and quenching, and more particularly to a method and means for forming, quenching and stress relieving sheet metal parts having recessed portions.

it has become a matter of increasing importance in present day industry to provide sheet metal parts with integral stitfeners. Such parts obviate the necessity of attaching stiffening elements by means of rivets, bolts or other methods and result in parts that are stronger, lighter and have a smoother exterior than sheet metal parts to which stifieners are subsequently attached. Such parts may have their thinner portions of varying thicknesses, or with cutouts therein, and it may be necessary to form these parts to various contours. Great difficulty has been encountered in the past in forming such parts. This is because it is necessary to provide a means for forming in the recessed portions of the parts (i. e., between the stiffeners) as well as the marginal and stiffening element portions of the parts. There has been no known method or means that would introduce varying degrees of work into the metal as required to accurately form the portions of the part having varying thicknesses. Several methods were unsuccessfully tried in an attempt to accomplish this. For example, it was attempted to form such parts by dies of a contour corresponding exactly to the desired contour of the finished part, including die portions for projecting into the recessed portions of the part between the stiffening elements. However, despite great care exercised in making such dies their use was not satisfactory. The variations in thickness of such sheet metal parts due to normal manufacturing tolerances meant that in some cases the projecting portions of the die would contact the thinner portions of the part prior to contact at the thicker stiifening portions, and as a result the part would shear oft at the recessed portions instead of being properly formed. in other instances the stiffener portions would be contacted first which would'mean that the material within the recessed portions was not properly formed. Further difiiculties were encountered in springback in the part after being formed, and difficulty in obtaining maximum strength properties of the finished parts. Forming at room temperature produced diifering degrees of springback in the parts due to the variance in residual stresses in the several parts. It was also found in prior forming efiorts that the greater forces required in bending the heavier stilfening portions of the metal would cause the thinner portions of the metal to fail as the part was formed.

Therefore, it is an object of this invention to provide a method and means for forming sheet metal parts having integral stiffening elements.

Another object of this invention is to provide a method and means for forming sheet metal parts without damage to the parts.

An additional object of this invention is to provide a method and means for simultaneously forming and quenching sheet metal parts.

Still another object of this invention is to provide a method and means for forming sheet metal parts by utilizing a fluid pressure.

Yet another object of this invention is to provide a method and means for rorming sheet metal parts that does not require expensive machining operations.

A still further object of this invention is to provide a method and means for forming sheet metal parts that will give the part maximum stren th properties.

These and other objects will become apparent from the following detailed description taken in connection with the accompanying drawings in which Fig. 1 is an elevation, partly in section, of a workpiece in a press prior to forming,

Fig. 2 is a bottom plan view of a workpiece prior to forming,

Fig. 3 formed,

Fig. 4 is an elevation, partly in section, of a workpiece being formed according to a modification of this inven; tion,

Fig. 5 is a fragmentary sectional view showing the use of filler blocks,

Fig. 6 is a fragmentary sectional view illustrating the use of low melting point metal as a fo.ming medium,

Fig. 7 is a fragmentary se onal view showing a method of sealing around a workpiece,

Fig. 8 is a fragmentary sectional view illustrating a modified means of sealing around the workpiece,

Fig. 9 is a fragmentary sectional view of an arrangement for forming a workpiece having no marginal stiffening elements, and

Fig. 10 is a sectional view along line ltl1tl of Fig. 9.

Referring to the drawings, it may be desired to form a workpiece 1, illustrated in section in Pig. 1 and shown in bottom plan in Fig. 2, to a curved contour. Workpiece 1 may be, for example, milled from a sheet of aluminum or other suitable material and include stifiening portions 2 and thinner sheet metal portions 3. The thinner sheet metal portions will not necessarily all be of the same thickness and may include cutout portions 4. The stiffener elements and thinner sections of the workpiece thus cooperate to define one or more recessed portions 5 in the workpiece. A pair of matching dies such as female die 6 and male 7 are provided, having the desired contour of the exterior of the finished part. However, it should be observed that these dies do not include any portions designed to project into the recessed portions of workpiece 1 for forming the metal within the recesses. These d s may be mounted in a press, such as that illustrated l, in which female die 6 is secured to and carried by movable ram 8 and male die 7 is supported on bolst r plate 9. The bolster plate in turn rests upon stationary bed it") of the press so that male die 7 is then thereby positioned against movement. Die 7 and bolster plate 9 are provided with apertures 11 and 12 respectively which are align-able and of the same diameter. There is at least one set of apertures 11 and 12 provided for each recess 5 of the workpiece and apertures 11 communicate with the recesses when the workpiece is within the dies. Within each set of apertures is a plunger 13 which is reciprocable relative to die 7 and bolster plate 9. The bottom ends of these plungers rest upon cushion which is of the movable type familiar to those skilled in the art. In the position illustrated in Fig. l, where the workpiece is resting on die 7 prior to forming, cushion is in its lowered position and ram 8 is, of course, in its raised position. Within apertures 11 above plungers 13 there is a quantity of fluid 15 which may be water, oil, or other desired fluid. Fluid 15 is sealed above the pistons by suitable means such as ring seal elements l6 around the upper portion of the plungers. In operation of the press in carrying is a fragmentary view of the workpiece being out this invention ram 8 is forced downwardly sothat die 45 engages the top of workpiece 1 and forces the workpiece to assume the contour of matching dies 6 and 7 as illustrated in Fig. 3. As soon as this is accomplished, movable cushion 14 is forced upwardly which displaces fluid 15 into recesses 5 of the workpiece. This fluid is given high pressure which will serve to force the metal of the thinner sections 3 of the workpiece into engagement with upper die 6. In this manner all portions of the workpiece are properly formed.

- It is normally contemplated, of course, that the workpiece will be heated before it is placed within the dies for the operation just described above in carrying out this invention. The heating should be such that the workpiece will be formed while in the recommended heat treating range for the particular metal involved. Of course the heating causes some expansion of the workpiece. This heating assures that the forming can take place readily and allows the dies and the fluid within the recess to quench the part while it is held within the dies so that the part will attain maximum strength properties and will be relieved of residual stresses. For example, a workpiece of 75-8 Alclad material may be heated to around 920 F. in any suitable oven and then quickly transferred to the dies before it loses much of its heat. The ram of the press is thereupon'forced rapidly down upon the workpiece and the plungers quickly shifted upwardly so that the forming operation takes place before the. temperature of the part falls below the heat treating rahge of the metal. Pressure of the dies and of the fluid should be maintained on the part until it is thoroughly quenched in order that the maximum strength properties of the material will be achieved, and so that the part will not spring back when released. The pressure should be suflicient to prevent the part from contracting along the faces of the dies as it cools. Thus for certain parts having approximately 120 square inches of area of? the stiffening portions contacting the lower die a pressure of around 2,000 tons has been found to be satisfactory to hold the part in the dies so as to preclude its creeping or contracting along the die faces as it cools. Fluid pressure of around 9,000 pounds per square inch may be provided in the recessed portions. As the part isheld and quenched it will lose its heat to the faces of the dies and to the fluid in the recesses. The fluid and the dies will prevent contraction of the workpiece around the recessed portion and the dies prevent contraction of the stiffening portions. The fluid and the dies thus cooperate to both form and quench the part. By forming at an elevated temperature and restraining the part as it is cooled the residual stresses are removed, springback is eliminated and all finished parts are uniform in dimensions and in strength characteristics.

After the forming operation is complete the cushion 14 is again shifted downwardly allowing the fluid to return to the top portion of apertures 11 as illustrated in Fig. l. The press ram is raised and the apparatus is again ready for a forming operation.

A modification of the invention is illustrated in Fig. 4 wherein the fluid pressure within recess 5 is provided in a different manner from that described above. Here the bottom die rests on bolster plate 9 as before and the upper die is carried by movable ram 8. In this case one or more apertures 17 communicate with the exterior of die 7 at a location corresponding to each recessed portion of the workpiece and these apertures may be connected with a common opening 18. A suitable source of fluid provide the fluid pressure it is preferred to employ a pump 20 which will charge a suitable accumulator 21. Pump 20 is connected with a reservoir 22 which contains a quantity of the fluid to be used which may be oil, water or other desired fluid. The reservoir 22 is connected through line 23 and three-way valve 24 to line 19. When pressure is desired for forming the workpiece, valve '24 may be turned so that pressurized fluid valve is opened.

. against the workpiece.

pressure is connected through inlet 19 to opening 18 so from the accumulator flows into the recesses to supply the pressure. It is preferred to use an accumulator as well as pump 20 in order that pressurized fluid will be admitted to the recess as quickly as possible after the It is possible, however, to use pump 20 alone without an accumulator. Valve 24 may be turned so as to drain fluid from line 19 into reservoir 22 after the forming operation is complete.

In Fig. 5 there is illustrated a means whereby the quantity of fluid necessary to be supplied in the recesses may be decreased. Providing the smallest possible volume of fluid within recess 5 to achieve the forming operation is desirable because it facilitates rapid application of fluid pressure after the dies have applied a forming pressure This decrease in volume is achieved by means of filler blocks 25 which are suitably attached to the upper surface of die 7. These filler blocks fit closely within the confines of recesses 5, but are of such a-dimensionthat under no circumstances will the top of the filler blocks engage the bottom of thinner section 3 of the workpiece. These filler blocks simply act to fill up a large part of the volume within the recesses which means that there is less volume that must be filled up by These filler the fluid as it is forced into the recesses. blocks are equally applicable to the embodiment employing the use of plungers or the embodiment using the auxiliary source of fluid pressure. As illustrated in Fig. 5 a plurality of small openings 26 are provided in the filler blocks and communicate with the pressurized fluid inlet. These openings 26 radiate outward in several directions and will assist in rapid uniform distribution of the pressur'ized fluid as it is admitted to the recess. Openings 26 are also disposed so as to admit fluid along the surface of die 7 so that the pressurized fluid will be admitted in a substantially horizontal direction rather than impinging directly upon thinner portions 3 of the workpiece. Thus there is no tendency to force the workpiece upwardly due to impact pressure of the fluid. Such pressure might decrease the seal between the thicker stiffening elements of the workpiece and the lower die.

Normally the workpiece will be adequately sealed against the lower die solely by means of the pressure of the ram acting through upper die 6 so that no fluid will leak out from the recesses between die 7 and stiffening elements 2 of the workpiece. However in some instances sealing around the margins of the workpiece may become a problem where very high fluid pressure is required and relatively low ram pressure is provided. The sealing problem may be corrected in several different ways, one of which is illustrated in Fig. 6. Here a plug of low melting point metal 27 is provided for each recess of the workpiece. This metal may be, for example, lead, which has a melting point of 621 F., or certain alloys of lead, hismuth, cadmium and tin such as described on page 1707 of Machinerys Handbook. An alloy containing 50% bismuth, 25% lead, 12.5% tin and 12.5% cadmium has a melting point of 149 F. Plug 27 may be made of dimensions closely corresponding to those of the recess but slightly smaller. When the ram of the press is forced downwardly and the dies are brought into engagement with the workpiece, plunger 13 or other means of pres sure may be brought to bear against the plug forcing it into engagement with the portions of the workpiece within the recess. Because the plug has an extremely low melting point it will quickly assume a molten state and will thereupon act as any other fluid in forming and quenching the workpiece. However, this fluid metal will have a higher viscosity than oil or water and therefore will have less tendency to break the seal between the stiffener elements and die 7. After the forming operation is complete plug 27 may be permitted to solidify whereupon it may be used over again for the next part to be formed, or it may be removed and a new plug inserted for use with the next workpiece.

As another method of sealing around the workpiece a head 28 may be provided on lower die 7 around the marginal areas of the workpiece. This head will be forced against the workpiece with a very high unit pressure and will assure that there is no leakage between the workpiece and the die. It is preferable to locate the bead near the periphery of the workpiece so that it contacts the portion of the workpiece that is normally trimmed oif after the forming operation in the event that the bead makes an indentation into the workpiece.

Still another sealing arrangement is illustrated in Fig. 8. In this case lower die 7 is provided with a groove at a location corresponding to the margin of the workpiece. A sealing element such as O-ring 29 of suitable heat resistant material is placed within the groove and provides a seal between the workpiece and the die when the workpiece is forced against the die.

it is sometimes necessary to form a sheet metal part wherein there are integral stiffener elements in the central portion of the workpiece, but there are no stiifener elements around the margin of the workpiece. Such a part may be, for example, an aircraft skin such as shown in Figs. 9 and 10. For such a workpiece stiffener element 2 will form integral stringers for the skin and define recessed portions 5 between the stringers. The recesses at the outer edges of the workpiece will have no stiffener element on the outer side because of the nature of the workpiece. In addition these stringers normally run in only one direction which means that both ends of all of the recesses will be open. Such a workpiece naturally involves a problem of sealing fluid pressure within the recess as the part is formed. One method of accomplishing this is to provide the workpiece with marginal elements which will engage the lower die while the part is formed and which may be machined off at a later time. To eliminate the necessity of this machining operation it is possible, as illustrated in Figs. 9 and 10, to provide lower die 7 with upwardly projecting portions 36 which extend around the margin of the workpiece. These elements 30 will correspond in thickness to the thickness of the stiffening elements so that the thinner portion 3 of the workpiece may engage projecting portions 34] of the die around the margin of the workpiece and form a seal therewith for closing off the outer recess. On the ends of such a workpiece, as best illustrated in Fig. 10, the stiffening elements may be cut back slightly so that marginal projecting portion 30 can engage the thinner section of the workpiece on all four sides and thus seal off all of the recesses. It may be observed that the workpiece of Figs. 9 and 10 has enlarged portions 31 on the bottom of stilfening elements 2 which serve to increase the rigidity and strength of the finished part. The use of fluid pressure Within the recess is particularly desirable where such portions are provided for the stiffening elements because even greater difiiculty than in the ordinary case would be encountered in attempting to place such a part within a mating die member complementary to the recessed portions of the workpiece.

Although the invention has been described in detail it should be clearly understood that this is given by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of this invention being limited only by the terms of the appended claims.

I claim:

1. The method of providing an integrally stiifened formed part from a metal workpiece having at least one recess comprising the steps of heating said workpiece to a heat treatable temperature; urging forming means into engagement with all portions of said workpiece remote from said recess to thereby force said workpiece to assume a predetermined contour; introducing pressurized fluid into said recess to urge the surface of said workpiece opposite from said recess into engagement with said forming means; and maintaining said workpiece so engaged to permit transfer of heat from said workpiece to said fluid and to said forming means to quench said workpiece, said engagement being maintained with a force sufficient to preclude contraction of said workpiece during said quenching whereby said workpiece is uniformly worked and stress-relieved.

2. The method of providing an integrally stiffened formed part from a sheet metal workpiece having recesses therein comprising the steps of heating the workpiece to a heat-treatable temperature to expand the workpiece; engaging the workpiece by die means having matching contours complementary to the exterior contour of the part to be formed; exerting a force on said workpiece by the die means; simultaneously exerting an additional force by introducing pressurized fluid into said recesses to conform the exterior of the workpiece remote from the recesses to the contour of the die means and the remaining exterior portions of the workpiece to the contour of the die means; and maintaining the workpiece so engaged while applying forces of suflicient magnitude to preclude contraction of the workpiece during the quenching by the transfer of heat to the die means and the fluid, whereby the workpiece is formed, uniformly worked and relieved of internal stresses.

3. A device for forming, quenching and stress relieving a workpiece having at least one recess therein comprising a fixed work-supporting bed means; a ram means reciprocal relative to said bed means on one side thereof; a cushion means reciprocal with respect to said bed means on the opposite side thereof; a set of matching dies for engaging opposite exterior surfaces of a workpiece supported on said bed means, said set of dies including an upper die carried by said ram means and a lower die supported on said bed means, said lower die and said bed means having alignable apertures therethrough corresponding to the recess in said workpiece; piston means in said apertures; fluid in said apertures adjacent said lower die, said pistons being supported by said cushion means whereby movement of said ram means toward said bed means forces said dies into forming engagement with the exterior surfaces of a workpiece supported thereby, and movement of said cushion means toward said bed means forces fluid into said recesses for urging the portions of said workpiece remote from said recesses into engagement with said upper die means, said die means and said fluid thereby providing a quenching medium for transmitting heat from a heated workpiece, said ram means and said cushion means being operative to exert sutficient force against such a workpiece for precluding substantially all contraction thereof during such forming and quenching.

4. The method of providin an integrally stiffened formed part from a metal workpiece having at least one recess therein comprising the steps of heating said workpiece to a heat treatable temperature thereby causing expansion of said workpiece; engaging opposite exterior surfaces of said workpiece with die means; urging against said workpiece in said recessed portion a quantity of metal having a melting point below that of said workpiece for permitting said quantity of metal to be melted by said workpiece and provide a fluid force against said workpiece in said recessed portion; and maintaining said workpiece so engaged with suflicient forces to conform said exterior portions of said workpiece to the contour of said die means, quenching said workpiece by transfer of heat to said die means and metal in said recess, and precluding said workpiece from substantially any contraction during said quenching, whereby said workpiece is formed, uniformly worked and relieved of internal stresses.

5. The method of providing an integrally stiffened formed part from a metal workpiece having at least one recess therein comprising the steps of heating said workpiece to a heatttreatable temperature thereby causing expansion of said workpiece; engaging opposite exterior surfaces of said workpiece with die means; exerting an additional force by introducing pressurized fluid into said recesses; and maintaining said workpiece so engaged with sufficient forces to conform said exterior portions of said workpiece to the contour of said die means, quenching said workpiece by transfer of heat to said die means and said fluid, and precluding said workpiece from substantially any contraction during said quenching, whereby said workpiece is formed, uniformly worked and relieved of internal stresses. 7

6. The method of providing an integrally reinforced metal member comprising the steps of recessing portions of a piece of metal thereby providing a workpiece having reinforced portions remote from said recesses and unreinforced portions of said piece of metal at said recesses; heating said workpiece to a heat treatable temperature thereby expanding the same; engaging opposite sides of said workpiece with die means having contours corresponding to the exterior contour of a part to be formed; applying during the time of such engagement fluid pressure to the recessed portions of said workpiece for urging the portions of said workpiece opposite said recessed portions into intimate contact with a die means; and maintaining said References Cited in the file of this patent UNITED STATES PATENTS 506,247 Moor-field Oct. 10, 1893 1,204,096 Waller Nov. 7, 1916 1,234,586 Wacker July 24, 1917 1,268,360 Kimball June 4, 1918 1,636,111 Rode July 19, 1927 1,793,054 Carnes Feb. 17, 1931 1,921,188 Ireland Aug. 8, 1933' 2,111,695 Seeber et a1 Mar. 22, 1938 2,156,886 Wiley May 2, 1939 2,344,779 Kolderman et al. Mar. 21, 1944 2,490,695 Leutheuser Dec. 6, 1949 2,615,411 Clevenger et al. Oct. 28, 1952 FOREIGN PATENTS 430,321 Great Britain 1935

Claims (1)

1. THE METHOD OF PROVIDING AN INTEGRALLY STIFFENED FORMED PART FROM A METAL WORKPIECE HAVING AT LEAST ONE RECESS COMPRISING THE STEPS OF HEATING SAID WORKPIECE TO A HEAT TREATABLE TEMPERATURE; URGING FORMING MEANS INTO ENGAGEMENT WITH ALL PORTIONS OF SAID WORKPIECE REMOTE FROM SAID RECESS TO THEREBY FORCE SAID WORKPIECE TO ASSUME A PREDETERMINED CONTOUR; INTRODUCING PRESSURIZED FLUID INTO SAID RECESS TO URGE THE SURFACE OF SAID WORKPIECE OPPOSITE, FROM SAID RECESS INTO ENGAGEMENT WITH SAID FORMING MEANS; AND MAINTAINING SAID WORKPIECE TO SAID TO PERMIT TRANSFER OF HEAT FROM SAID WORKPIECE TO SAID FLUID AND TO SAID FORMING MEANS TO QUENCH SAID WORKPIECE, SAID ENGAGEMENT BEING MAINTAINED WITH A FORCE SUFFICIENT TO PRECLUDE CONTRACTION OF SAID WORKPIECE DURING SAID QUENCHING WHEREBY SAID WORKPIECE IS UNIFORMLY WORKED AND STRESS-RELIEVED.

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