US3194039A - Method and means for holding a workpiece during the explosive forming thereof - Google Patents

Description

July 13, 1965 D KRANTZ 3,194,039

METHOD AND MEANS OLDING A WORKPIEOE DURING THE EXPLOSIVE F0 NG THEREOF Filed Dec. 1961 VACUUM VACUUM INVENTOR. DONALD E. KRANTZ ATTORNEY United States Patent METHOD AND MEANS FOR HQLDENG A WGRK- PIEQE DURING THE EXPLGSIVE FGRMING THEREOF Donald E. Krantz, Canoga Park, Califi, assignor to North American Aviation, Inc. Filed Dec. 18, 1961, Ser. No. 15?,865 1 Claim. (Cl. 72-56) This invention relates to a method and means for holding a workpiece during the explosive forming thereof and more particularly relates to the locking in position of a workpiece during an explosive forming operation in order to prevent a wrinkling thereof.

Heretofore it has been common practice in the explosive forming art to secure a workpiece during an explosive forming operation by means of conventional clamp-type hold down rings and the like. Such hold down rings are generally employed to positively position said workpiece and to prevent an undue drawing thereof into the forming die cavity. Such standard hold down rings are generally cumbersome and weighty in construction thus providing for increased operational costs primarily due to the relatively large set-up and removal times involved therewith. Furthermore, such hold down rings oft-times do not function to positively prevent the outer peripheral portions of the workpiece from slipping toward the die cavity, i.e., the workpiece may slip under the hold down ring thus causing the formed workpiece to wrinkle.

The present invention has overcome many of the above mentioned inadequacies by providing a novel method and means for positively holding a workpiece during the explosive forming thereof. In accordance therewith, the present invention provides a method and means whereby a workpiece to be formed is initially positioned over a die cavity and explosive forces of predetermined magnitude are thereafter discharged onto said workpiece and towards said die cavity. The explosive forces function in a twofold manner, i.e., to positively hold peripheral portions of said workpiece and also simultaneously form said workpiece into said die cavity. The means provided to achieve the above mentioned holding function essentially com prises a groove formed around the periphery of said die cavity.

An object of this invention is to provide a method and means for positively holding a workpiece during the explosive forming thereof.

Another object of this invention is to provide a method and means for expeditiously and economically explosively forming a workpiece.

A further object of this invention is to provide an explosive forming method and means whereby workpiece forming time is substantially reduced and workpiece quality is substantially enhanced.

A still further object of this invention is to provide a method and means for explosively forming a workpiece whereby explosive forming forces function to retain outer peripheral portions of a Workpice in set position during the forming operation and also function to form the workpiece to the desired configuration.

These and other objects of this invention will become apparent from the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a top plan view illustrating the novel explosive forming concepts of this invention; and

FIG. 2 is a cross-sectional view taken on lines 2-2 in FIG. 1.

FIG. 1 is a top plan view illustrating the novel concepts of this invention. As shown, a suitable base or foundation such as a cement floor or the like is adapted to positively retain a die assembly 11 thereon. The die assembly 11 is illustrated as formed on a longitudinal axis 3,ii,39 Patented July 13, 1%65 'ice x-x and may be so fixedly retained by its own weight and/ or by standard fastening means such as bolts or the like (not shown).

The die assembly 11 is shown, for illustration purposes, as comprising a substantially rectangular shaped die member 12 having a die cavity 13 formed in first selected surface portions thereof. The die member may comprise any heavy duty steel constituent or the like which is adapted to withstand extreme explosive forces which may be imparted thereon. A groove or cutout portion 14 is formed in second selected surface portions of the die member 12 and is constructed and arranged radially of the periphery of the die cavity 13. It should be understood that the particular cross-sectional configuration of both the die cavity 13 and groove 14 are primarily a matter of choice and design depending on the particular design considerations.

A workpiece W is positioned over the die cavity 13 and is constructed and arranged to extend radially of the groove 14 by a predetermined distance a. Such a construction and arrangement provides that the downwardly facing surface portions of the workpiece W are exposed to the groove 14 by a predetermined radial dimension b. An upwardly extending ridge portion 15 abuts the surface portions of the workpiece which are defined by the radially extended distance 0. The portions of the workpiece which are subsequently stretched into and formed by means of the die cavity 13 are defined by the diameter d. It should be noted that the above described distance a, b, c, and d may also be defined in terms of the respective efiective upwardly facing surface areas of the die member 12 which are juxtaposed to the workpiece W. For reasons hereinafter more fully explained, it is preferable in most applications that the workpiece surface area which is defined by the dimension b be equal to or greater than the workpiece surface area which is exposed to the die cavity 13 and defined by the dimension (1. A continuous seal (O-ring) may be provided in member 12 around the annular area of distance a.

A vacuum pump, generally shown at 16, is operatively connected to the die cavity 13 and groove 14 by means of a conduit arrangement or passages 1'7. The conduit arrangement 17 is shown somewhat enlarged relative to the associated portions of the die assembly for the sake of clarity. The vacuum pump 16 may be op eratively connected to the die member 12 to cooperate with conduit passages 17 by standard securing means, shown in the form of a circumferentially extending weld bead 18.

It should be understood that the use of the vacuum pump 16 is preferred in many work applications in order to more positively position the workpiece W onto the platen of the die member 12 prior to the explosive forming thereof. Such a vacuum pump is particularly useful when used in connection with relatively lightweight workpieces which are apt to move unless positive retained on the die member prior to the forming thereof. The vacuum utilized may comprise, for example, a pressure of minus 14.7 p.s.i. It should be further understood that although separate conduits are shown as connected to both the die cavity 13 and groove 14, that a single conduit from the vacuum pump to either one thereof may be sufiicient in many applications to impress a vacuum in both. Such is primarily true due to the non-sealing type passage 19 which is inherently formed in many applications between the ridge portion 15 and workpiece W. However, to readily assure that the vacuum desired is expeditiously realized by the die cavity 13 and groove 14-, particularly where a partial or complete sealing function is alforded at passage 19, separate conduits are preferably utilized.

the explosive charge 20 may comprise dynamite, pentaery thritol tetranitrate (PETN), trinitrotoluene (TNT), cyclonite (RDX), or any other suitable standard explosive.

Example and method of operation Referring to FIG. 1, subsequent tothe proper positioning of a 321 stainless steel workpiece W having a thickis selectively constructed 7 ness of .032 inch and diameter of 12 inches over the die I cavity 13, a substantial vacuum comprising a pressure p of approximately minus 14.5 p.s.i. was drawn thereunder to effect a preholding step. As .hereinbefore, briefly explained, the workpiece surface area defined by the radial distance b was maintained equal to or greater than the workpiece surface area which was exposed to-the die cavity 13 and defined by the diameter d. Such a construction and arrangement assured that the relatively thin workpiece did not draw into the die cavity 13 since the total force pulling on the workpiece in groove 14 was greater than the force pulling on the workpiece from die cavity 13.

In this particular example, the formed die cavity com-.- prised a diameter (d in FIG, 2) of 6 inches andthe depth thereof along the longitudinal axis x--x was 1 inch. The b dimension of the groove comprised 0.625 inch with the outermostdiameter thereof comprising 11 inches. The groove was formed 0.25 inch deep.

The explosive charge comprised/15 grams of trinitrotoluene (TNT) arranged at a.6-inch standofi distance from the workpiece'W. The charge was then ig- Although this invention has been described and illustrated in detail, it is to be understood that the same is 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: V A method of explosively forming a workpiece comprising:

positioning an inner portion of a workpiece to be formed over a die member arranged on a longitudinal axis and having a surface thereon which is constructed and arranged substantially perpendicular to said axis,- providing a die cavity on a first selected portion of the surface of said die member, forming a substantially circularly shaped groove on second selected portions of the surface of said die member, said groove constructed and arranged adjacent to and spaced radially'outward of said die cavity relative to said axis, arranging said die cavity and said groove so that the workpiece surface 'area exposed to'said groove is at least equal to the workpiece surface area exposed to said die cavity, r V impressing a vacuum in said die cavity and said groove, whereby peripheral portions of said workpiece are preheld to prevent a drawing of said portions into said die cavity, discharging an explosive force onto said workpiece and toward said die cavity, indenting said peripheral portions of said workpiece with said discharged explosive force to prevent movement of said portions toward said die cavity, and simultaneously forming said inner portion of said workpiece in conformance with said die cavity with said discharged explosive force. a

7 References Cited by the Examiner UNITED STATES PATENTS 7 2,935,038 5/60 Chatten 11344 -2,969,758 1/61 Howlett et al. 113-44 3,036,373 5/62 Drexelius 29-421 3,045,339 7/62 Callahan 29421 CHARLES w. LANHAM, Primary Examiner.

NEDWIN BERGER, Examiner.

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