US2415940A

US2415940A - Metal cupping process

Info

Publication number: US2415940A
Application number: US557351A
Authority: US
Inventors: George R Eckstein
Original assignee: Remington Arms Co LLC
Current assignee: Remington Arms Co LLC
Priority date: 1944-10-05
Filing date: 1944-10-05
Publication date: 1947-02-18
Anticipated expiration: 1964-02-18

Description

Feb. 18, 1947. R. E CKSTEIN 2,415,940v

' METAL CUPPING PROCESS Filed 005. 5, 1944 I INVENTOR. GEORGE RLECKS-TE/N.

AGENT Patented Feb. .18, 1947 UNITED s ArEs fPAT'ENr orrice M TAL currm'c rnocnss George R. Eckstein, Bridgeport, Conn., assignor to Remington Arms Company, Inc., Bridgeport, Conn., a corporation of Delaware f Application October 5, 1944, Serial No. 557,351

The present invention relates, in. general, to

metal drawing, and, in particular, to an improved means and method of forming cups from steel blanks for the manufacture of small arms ammu-. nition components, as, for example,.caliber .50 steel cartridge cases,

Cartridge cases have been manufactured from time immemorial by punching a metal blank from a sheet of brass, cupping the blank and subsequently subjecting-the cup to a number of deep drawing, annealing and trimming operations to secure the properi shape and dimensions of the case. Brass has been used almost exclusively in the manufacture of cartridge cases because its j metallurgical characteristics are such as to tender a brass blank amenable to the deformations and stresses which are introduced into the metal during the shaping of the case, and to which the -finished case is subjected when fired.

The problem of manufacturing steel cartridge cases in quantity production lots has not been solved heretofore due primarily to the high modulus of elasticity of steel, its low rate of .work, hardening and its high corrodibility. Other factors such as the heterogeneous nature of steel,

the relative difficulty with which it can be worked and the tendency of workpieces to pick up or cling to the draw punches have also contributed to the problem of manufacturing steel cartridge cases on a commercially successful basis.

In view of these factors, it is not surprising to find that a steel blank reacts differently than 3 Claims. (em-148a when such cases are fired have their origin in the cup for whereas malformed brass cups are amenable to correction during subsequent drawing operations any eccentricity, asymmetry or other defects of a steel cup will not be corrected as the cup is being processed. Hence it is of paramount importance that a steel cup have the highest degree of perfectionin order to insure satisfactory cases.

Extensive experimentation has demonstrated that of the requisite characteristics of a steel cup for making .50 caliber'steel cases, its susceptibility to processing by drawing; exterior walls free from shearsurface; and a lip comprising substantially the entire shear surface of the blank and having a prescribed contour, are among the most important.

An object of 'the present invention is, therefore, the provision of a means and method of forming cups of steel which can be processed successfully to form drawn steel articles. A further object is the provision of steel cups which will yield steel small arms ammunition components equivalent to brass in substantially all respects and in'quantity production lots, A still furtherobjectis the provision of a means and method of blanking sheet steel and drawing the resulting blank to form steel cups wherein the shear surface-of the blank is confined substantially Wholly to the lip of the cup. Astill further.v object is to provide a method of drawing steel cups embodying the step of coining the lip of the cup,

These and other objects, features and advantages of the invention will be more fully described in the following specification and illustrated in the accompanying drawing, in which:

Fig.1 is a representation of a macrophotograph of asectioned wide angle steel blank showing the one hundred and fifty times that heretofore 'encounteredin the manufacture of deep drawn steel articles. As might be expected, therefore, theusual means and method of drawing steel blanks are not applicable to the manufacture of steel cartridge cases.

Moreover, it has been discovered, as a part of this invention, that a large proportion of the defects which have been found in finished steel carverted blank, but before the lip of the cup has flow lines of the metal at the tshear surface and includes a fragmentary'view of a blanking punch and die assembly.

Fig. '2 is a representation of a macrophotograph of a sectioned steel cup formed from an inverted blank showing the formation of the fracture line in the outer wall of the cup.

g. 3 is a representation of a macroph tograph of a sectioned steel cup formed from a noninbeen coined. v

Fig. 4 is a fragmentary side elevation in section of the improved cupping punch and die assembly of this invention.

Fig.5 is a representation of a macrophotograph tridge cases as heretofore made or which occur of a sectioned steel cup having a planar bevelled ing punch and die assembly comprises a cylindrical member ID, the diameter of which is substantially 1.443 inches and 0.110 inch less than the diameter of the blanking die aperture ll. Due to the difference in diameter of the blanking punch and blanking die aperture, the angle of the shear surface l2 of the blanked disc B is relatively wide being of the order of 15 which is conducive of a clean cut shear surface. Moreover, the shear surface of the blank hereinafter termed a wide angle blank is necked down or pinched during the blanking operation, as shown by the flow lines in Fig. 1, .so that the area of the shear surface is reduced. This effect minimizes the tendency of the shear surface to wrinkle during the subsequent cupping operation, which tendency has been found to induce incipient cavities in the lip of the cup and to propagate cold shuts during subsequent drawing operations. Although a blanking punch'die clearance of 0.110 inch is preferred, satisfactory wide angle blanks have been formed with a blanking punch and die clearance as small as 0.083 inch.

Heretofore, efforts were made to cup steel blanks in the so called inverted position, that is to say, the blank was turned over before cupping so that its top or surface of small diameter seated inthe cupping die, a noninverted cup being one whose blank has been seated bottom down in the cupping die.

Fig. 2 shows an inverted cup or cup formed from an inverted blank. It has been found as a part of this invention that inverted steel cups invariably develop a. fracture line in the outer wall which carries through into the completed cartridge case which may result in case breakoifs during final drawing, ruptures on firing and localized necking. Moreover, this fracture line was found to coincide invariably with the bottom edge II! of the shear surface l2 of the blank which, as shown by the metal flow lines in Fig. 2, doesnot form the lip of the cup as might be expected but, due to a nonuniform flow of metal at the top and bottom of the inverted blank, is drawn down over into the outside wall of the cup.

The present invention relates in part to a method and means of eliminating the fracture line in steel cups based upon the concept that by confining the shear surface of the blank to the lip of the cup, the shear surface and fracture line, if such should occur, may be completely eliminated from the drawn case at least by the second cut-off and without a prohibitive waste of material. a

It was discovered that an important factor contributing to the confinement of the shear surface of a wide angle blank to the lip of a cup was the concept of seating the blank bottom down or in a noninverted position in the cupping die.

Fig. 3 illustrates a cup formed from a noninverted blank. It will be noted that the shear surface i2 of the noninverted blank has been held substantially to the lip of the cup and that the nature of the flow lines of the metal is such that the bottom edge 13 of the shear surface has not been turned outwardly into the outer wall of the cup as occurs in the inverted cup shown in Fig. 2. This characteristic metal flow of the noninverted blank is due in part to the fact that the larger by the coining amount of metal in the bottom of the blank en- .ables the metal to stretch sufliciently before becoming work hardened to permit the lower edge l3 of the shear surface of the blank to gain the lip of the cup. It will be noted that the flow lines of the metal of a noninverted cup run out completely into the lip and that these flow lines are substantially parallel to the inside and outside walls of the cup.

Other factors, however, are influential in shaping the lip of the cup. It will be noted that the lip i2 of the cup shown in Fig. 3 is somewhat concave and during subsequent drawing operations this condition tends to be aggravated resulting in the formation of cold shuts in the mouth of a drawn case. The concave contour of the lip may be due in part to that effect known in the art as pull up, wherein the outside edge of the lip of the cup is pulled up higher than the inside edge. As a part of this invention, it has been found that the amount of pull up increases with an increase in size of the ledge or shelf of the cupping die hereinafter described, and, on the other hand, a shelf of appreciable size is essential to the stability of the blank which in turn is an important factor in securing wall concentricity. Accordingly, a cupping die was developed as shown at M in Fig. 4 which embodies a minimum ledge or shelf l5 comprising a compound curve, the upper portion of which has a radius R1 of substantially 0.100 inch adapted to blend into the lower portion of the curve, the radius R: of which is substantially 0.234 inch.

Referring to Fig. 4, the diameter of the bottom of the blank is shown as substantially equal to the diameter of the cylindrical mouth ll of the cupping die I4 which in the embodiment shown is substantially 1.555 inches diameter and inch deep. The portion of the cupping die aperture between the lower end of the shelf [5 and the upper edge of the die land shown at I8 is known as the approach surface and comprises a conical surface [9 which makes an angle of substantially 12 with the longitudinal axis of the die. The lower end of the approach surface 19 is blended into the land 10 by a radius R3 of substantially 1; of an inch. The diameter of the land is substantially 1.177 inches, its depth being substantially 0.090 inch. As is the usual practice, the lower edge 20 of the land is square and sharp to facilitate stripping, a counterbore 22 being provided on the underside of the cupping die id to maintain the sharp edge 20 of the land. It will be understood, however, that an independent stripper die may be used.

The particular cupping die contour defined by the shelf [5, the conical approach surface I9 and the radius R: which blends the latter into the land i8 has the effect of forming a cup lip which is substantially free from pull up, fringe and cavities, the shelf IS, in particular, insuring sufficient blank stability to guarantee cups having concentric walls and bottoms symmetrical with respect to the walls.

bility. The punch may be guided in its reciprocable movement with respect to the die 14 by means of a guide sleeve 24 which, in the usual practice, is resiliently mounted and adapted to enter the mouth I! of the cupping die slightly in advance of the cupping punch. The means for actuating the cupping punch 23 and its guide of substantially 56 with respect to 24 are conventional and well known in the art I and hence has not been shown. The lower end of the punch is reduced to provide a slightly tapered nose 25 which is substantially 0.837 inch in diameter at its lower end and 0.400 inch long.

In the present embodiment, the radius R4 of the end of the nose is substantially of an inch.

The upper end of the nose 25 is substantially 0.847 inch in diameter andis joined'to the lower end of the shank 23 by an integral conical shoulder 26, the slope of its surface making an angle tudinal axis of the punch. I

The conical shoulder 26 of the cupping punch I invariably produces a defective piece for drawing.

As pointed out above, anoninverted blank cupped in'a die having the contour specified above has its shear surface held to the lip of the cup, the walls of the cup being concentric and the base of the cup substantially symmetrical with respect to the walls. Moreover, .the lip of the cup is free from such defects at pull up, fringe and cavities.

It has been found, however, that the lip does not invariably have the prescribed contour for insuring optimum results in subsequent drawing operations.

Generally, the lip will comprise a surface sloping from the outer edge of the cup inwardly and downwardly, the profile of the surface being slightly concave adjacent the inner edge of the cup, as shown atl in Fig.6. As a part of the present invention, it was conceived that by providing a suitable shoulder on the cupping punch, the concave portion of the lip could be ironed out so as to make true the'optimum lip profile. To this end, the intersection of the conical shoulder 26 of the cupping punch with itssllght- 1y tapered nose portion comprises a relatively sharp corner; 21.

Referring to Fig. 6, it will be seen that when this sharp corner strikes the inner edge of the lip of the cup, the metal atthis section ofthe lip will be, flattened and simultaneously displaced outwardly toward the outer edge of the cup by the coining action of the bevelled shoulder 26.. In this manner, the concave portion I20 of the surface of the lip is eliminated and a substantially planar bevelled surface on the lipwill be made true. I

The sharpness of the corner 21 and the location, on the punch of the shoulder 26,- which is hereinafter termed a coining shoulder, has been arrived at byextensive experimentation and constitute features which are essential to the formation ofthe optimum profile. It has also been ascertained that the coining shoulder resists a tendency of the shear surface of the lip of the cup to move down-into the inside wall thereof and that by maintaining a coining shoulder of substantially the dimensions and configuration described, blank thicknesses varying as' much as 0.010 inch may be cupped successfully 75 the longielled surface thereon.

and considerable latitude may be enjoyed 'in the cupping die profile. Fig. 5 shows the effectiveness with which the coining shoulder 26 and the sharp corner 21 of the cupping punch have held the shear-surface l2 of the cupped blank from moving down intothe wall of the cup while simultaneously coining a substantially flat bevel 111130 on the cup It will be understood that the resistance sufficient to effect a swaging or coining action is provided by the radial pressure acting between the walls of the cup and the walls of the die aperture during the drawing operation.-

During subsequent draws, the .lip of the cup mouth of the case free from shear surface metal or fracture line defects.

The method of blanking and cupping is believed to be clear butmay be briefly described as follows: A strip of steel Mis fed across the aperturell of the blanking die whereupon the blanking punch I0 is driven down onto themetal strip. The blanking punch, blanks out'a disk B having a sharp clean shear surface l2 which makes an and hence the shear surface tend to pull down inangle of substantially 15 with respect to the top and bottom surfaces of the blank and which is slightly necked as described above. The blank B is removed from the blanking die and may be cleaned and covered with a suitable lubricant or thin copper plating. The blank is then seated bottom down, that is to say, in a noninverted position on the shelf I5 of the cupping die It. When the cupping punch 23 is driven down onto the topof the blank, the latter, will be forced down'through theconical approach surface l9 of the cupping dieand into the cylindrical land Hi. During this interval, the coining shoulder or lip 26 of the cupping punch coins the shear surface |2 of the cupped blank, as indicated in Fig. 6, so as to iron out its profile and make true a planar inwardly and downwardly inclined bev- On completion of the downward stroke of the cupping punch, the

punch is withdrawn from the cupping die. The

cup having expanded radially slightlyafter passing through the land 3 now engages the sharp 60 edge 20 of the land which strips the cup from the'cupping punch in theusual manner.

The method and means described for forming a steel cup contemplates the use of separate machines for blanking the disk and cupping the blanked disk and'in view of the relatively high such as used extensively in blankingand cupping brass may be used for forming steel cups.

It will be understood that the dimensions, proportions, angles and radii given in the foregoing description are those which have been found. optimum for making a steel cup to be further processed into a caliber .50 cartridge case and are illustrations of and not limitations upon the invention.

What is' claimed is:

piece having concentric walls which are free from shear surface comprising the steps of punching a frusto-conical blank from a sheet, insertingsaid 1. A method of making a-cup-shaped draw the mid-portion thereof into a reduced diameter portion of said die, and then forcing the cup through and out of the reduced diameter portion of the die while applying to the lip thereof a pressure which induces an outward radial flow of the metal adjacent said lip.

2. A method of making a cup-shaped draw piece having concentric walls which are free from shear surface comprising the steps of punching a frusto-conical blank from a sheet, insertingsaid frusto-conical blank wide base foremost in a draw die, cupping said blank by engaging and forcin the mid-portion thereof into a reduced diameter portion of said die, forcing all of the shear surface of said blank into the lip of the drawn cup, and then forcing the cup through and out of the reduced diameter portion of the die while applying to the lip thereof a pressure which induces an outward radial flow of the metal adjacent said lip.

3. A method of forming a cup-shaped draw piece having concentric walls which are free from shear surface comprising the steps of providing a flat circular blank having a sheared edge portion of frusto-conical conformation, supporting said blank in a cupping die with its frusto-conical sheared edge flaring outwardly in a direction facing the die land, cupping said blank by engaging and forcing same through said cupping die with a cupping punch, and simultaneously shaping the sheared edge to define an inwardlybeveled lip by engagement with said sheared edge with an inverted frusto-conical shoulder formed on said punch.

GEORGE R. ECKSTEIN.

REFERENCES CITED The following references are of record in the file of this patent: