GB2056327A - Making cup-shaped cylindrical shells - Google Patents

Abstract

The method for making cup- shaped cylindrical shells having thick bottom and thin wall sections which includes the insertion of a cup-shaped blank into a die cavity the bottom of which is constituted at least partially by a knock-out pin 25, introducing a punch 26 into the blank and applying pressure to the edges of the blank by means of a sleeve 27 surrounding the punch, the pressure effecting extrusion of the material to fill accurately the space between the punch and the die bottom 24 and side walls 22, 23. On a drawing operation in a second die the cylindrical side wall is drawn to its desired thickness, the bottom thickness being unchanged, and a top flange, formed during redrawing, can thereafter be removed by pinch trimming. <IMAGE>

Description

SPECIFICATION Method for making cylindrical shells This invention relates to the method for drawing and forming cup-shaped cylindrical shells wherein the material in a cup-shaped blank is extruded into the space between the bottom wall of the die and the bottom end of a punch, the extrusion being effected by the edge of a pressure sleeve moved downward along the sides of the punch, the partially formed shell then being subjected to drawing in one or more dies which form the cylindrical side wall and a top flange, without altering the thickness of the bottom. The flange or trim ring can thereafter be removed by pinch trimming, in the same machine. Under certain conditions the sleeve may be integral with the punch, the extrusion being effected by movement of the sleeved punch into the die cavity.

In the shell drawing method heretofore practiced, a preformed cup is fed into a redraw die having a set edge portion and stacked dies which act to thicken the bottom of the shell, by radial compression, at an early stage in the drawing operation, as the shell is carried downward on a first punch. The partly drawn shell is then transferred to a second die station and is carried through a second set of stacked dies to further thicken the bottom of the shell and draw the sides.

The shell has no flange, since it is drawn entirely through the bottom draw die and stripped against the edge thereof on the upward stroke of the punch. Excess length must be trimmed in a separate trimming operation to complete the shell.

Disadvantages of this method include the following: 1. The cup which is fed into the first die has to have exact specification of metal thickness in its forming operation since the thickening of the bottom is not positively controlled in the first or successive operations.

2. There is no way of controlling the thickness of the bottom of the shell in any die. That is, as the shell passes through the die angles of the stacked dies, material is pushed axially and radially toward the bottom in a free flow manner and through careful proportioning of the cup the required thickness at the bottom may be approximated.

3. Due to the drawing operations (draw and redraw) the cylindrical portion of the shell is workhardened and in order to perform subsequent working operations the shell has to be annealed prior to such additional work.

4. Since the cylindrical portion of the shell has no flange on its upper portion it can only be removed by a turning operation such as in a lathe since it has been work-hardened by passing completely through the draw and redraw dies. The metal in the upper portion is also susceptible to splitting or cracking or other flaws which may appear at the top edge of the redrawn shell.

The present invention consists in the method of forming cup-shaped shells which includes the steps of providing a closed die cavity, two open die cavities and three punches, one associated with each die cavity, the bottom of the first punch and the bottom wall of the closed die cavity being adapted to define a space corresponding to the desired form and size of the finished shell bottom, the second punch having a form and size corresponding to the desired finished interior of the shell with a flare at the top, the first open die cavity having a diameter corresponding to the desired finished exterior of the shell with a smoothly radiused flare at the top, the third punch having tapered lower portions adapted to fit in the upper portion of the shell and bounded upwardly by an annular shoulder having a diameter approximately equal to the outer diameter of the shell, and the second open die cavity terminating upwardly in a narrow annular zone having a diameter approximately equal to that of said annular shoulder, placing a cup-shaped blank in the closed die cavity, moving the first punch to a position such that the punch and the bottom wall of the cavity define the finished form and size of the bottom of the shell, extruding the blank material into the space so defined, transferring the shell blank to the first open die cavity, actuating the second punch to draw the side wall of the shell blank to its final desired internal and external diameters with a flared flange at the top, transferring the shell blank to the second open die cavity, and actuating the third punch to pinch trim the flared flange from the shell blank.

In carrying out a preferred method according to the invention the bottom thickness and contour of the shell can be positively determined and controlled. The stacked draw dies heretofore used are eliminated. Shells can be drawn to a desired depth, leaving a flange or trim ring at the mouth of the shell, and can then be trimmed and ejected.

The metal in the flange of the shell is not workhardened, thereby reducing the incidence of splits, crack or other flaws in the shoulder at the top of redrawn shells. The flange on the shell can be removed in a subsequent operation in the same machine, instead of requiring removal for a subsequent turning operation or the like. Finally, the shell is formed with minimal work-hardening so as to remain relatively ductile and adapted for further processing.

The invention will now be described, by way of example, with reference to the accompanying drawings, wherein: FIG. 1 represents an elevation, partly in section, of a cup-shaped blank to be formed into a shell, the upper portion being broken away; FIG. 2 represents a vertical section through a set of stacked dies and a shell driven therethrough by the punch, as in the prior art method; FIG. 3 represents an elevation, partly in section, of the shell formed as in Fig. 2, being trimmed, as in the prior art method; FIG. 4 represents a vertical section through the die assembly according to the invention, with a punch carrying the shell blank into the closed die cavity where the size and shape of the shell bottom are positively determined; FIG. 5 represents a vertical section through the second die station, showing the shell completely drawn;; FIG. 6 represents a vertical section through the flange trimming station; FIG. 7 represents a vertical section, parts being in elevation, showing somewhat diagrammatically the drive means for a punch and extruding sleeve for carrying out the stage of the method illustrated in Fig. 4; and FIG. 8 represents a vertical section, partly in elevation, of a modified form wherein the sleeve is integral with the punch.

Referring to the drawings, the blank 10 shown in Fig. 1 is of the conventional type. In the method used heretofore the amount of material in the bottom portion 11 must be carefully calculated so that it will form a properly dimensioned bottom of the completed shell, within reasonable tolerances.

Fig. 2 shows a set of stacked dies 12, having graduated diameters, through which the blank is carried on a tapered punch 13, the dies acting to deform the material 11 in the bottom of the blank both radially and axially to the dimensions indicated at 11' while the side wall 14 is elongated and its diameter reduced. The halfformed blank in the prior method is then placed on another punch, somewhat more square-ended, and redrawn through a second series of stacked dies where the bottom material is worked to the form shown at 11" in Fig. 3 and the side wall taper is reduced as shown at 14'. At this stage the shell has an upper edge of irregular form which must be trimmed off, as by means of a knife 1 5 (Fig. 3).

It will be apparent that the metal throughout the shell, formed as just described, has been workhardened by the drastic drawing and redrawing operations so that an annealing step is required if any further working is to be effected. The shell is passed completely through each set of stacked dies, requiring removal from each punch and transfer by suitable mechanism to the succeeding one.

In the method according to the invention, a blank generally similar to the blank 10 is placed in the cavity of a die block 21 the cavity having a cylindrical portion 22, and a frusto-conic portion 23 and the bottom wall 24 being constituted by the somewhat concave upper end of a knock-out pin 25. A punch 26 is moved downward to a position such that its spacing from the cavity walls 23, 24 defines exactly the quantity of material desired in the completed shell bottom and the form thereof, and a sleeve 27, slidable on the punch, is driven down against the upper edge of the blank to compress the blank material and cause it to flow into the space defined by the punch and the cavity walls, this being in the nature of an extrusion operation.

The partially formed shell 29, is then transferred into a second die 31, a punch 30 is profiled to correspond with the final size and shape of the shell cavity, and this punch carries the shell 29 through the die 31 which tapers slightly outward below the working zone 32 and is flared above said zone to form a flange 33 at the upper end of the shell. Depending upon the desired final dimensions of the cylindrical portions of the shell, more than one forming operation (as just described) may be required. However, at no time does the shell pass completely through the die thereby leaving flange 33 in a soft unworked condition.

The completely formed, but untrimmed, shell is transferred to a trimming punch 35 and the flange is pinch trimmed in the die 36 by the action of the edge 37 on the punch and the complementary edge 38 of the die. It is only in the trimming operation that the shell passes completely through the die.

The operations described can be effected in a machine of the multiple plunger power press type, such as Waterbury Farrel cam eyelet machines, suitably modified. In Fig. 7 there are shown the plunger 40 carrying the punch 26, a die block 21 and the knock-out pin 25, corresponding to the parts shown in Fig. 4. The sleeve 27 constitutes the lower end of a slider 41 actuated through the rocker arm 42 by a cam 43 suitably synchronized with the cams operating the plunger and punch. In a preferred sequence of operation, the cup or blank is inserted in the die, the pressure sleeve is brought into contact with the shoulder of the cup and the punch is inserted in the cup and moved down to force the cup against the die angle 23.

The pressure sleeve 27 then moves relative to the punch and forces the metal into the cavity bounded by the punch, knock-out pin and angular walls of the die.

It should be noted that the cup or blank which is fed into the first die does not have to be exact in its dimensions, as in the old method, since the thickening of the shell bottom is effected in a controlled manner in an enclosed space.

While the separately slidable sleeve described above is preferred for most shell-forming operations for its adaptability, comparable results can be obtained, with the use of uniformly sized cups or blanks, by mounting a sleeve 50 on the punch 51, as shown in Fig. 8, so that they will move together intothe cavity of the die 52, extruding the cup material into the same precise configuration as shown in Fig. 4. The cup so formed is drawn to the desired shell form and trimmed in the same manner as described above with reference to Figs. 5 and 6.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in carrying out the above process and in the constructions set forth without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims (4)

1. The method of forming cup-shaped shells which includes the steps of providing a closed die cavity, two open die cavities and three punches, one associated with each die cavity, the bottom of the first punch and the bottom wall of the closed die cavity being adapted to define a space corresponding to the desidred form and size of the finished shell bottom, the second punch having a form and size corresponding to the desired finished interior of the shell with a flare at the top, the first open die cavity having a diameter corresponding to the desired finished exterior of the shell with a smoothly radiused flare at the top, the third punch having tapered lower portions adapted to fit in the upper portion of the shell and bounded upwardly by an annular shoulder having a diameter approximately equal to the outer diameter of the shell, and the second open die cavity terminating upwardly in a narrow annular zone having a diameter approximately equal to that of said annular shoulder, placing a cupshaped blank in the closed die cavity, moving the first punch to a position such that the punch and the bottom wall of the cavity define the finished form and size of the bottom of the shell, extruding the blank material into the space so defined, transferring the shell blank to the first open die cavity, actuating the second punch to draw the side wall of the shell blank to its final desired internal and external diameters with a flared flange at the top, transferring the shell blank to the second open die cavity, and actuating the third punch to pinch trim the flared flange from the shell blank.

2. The method according to claim 1 which includes the steps of providing an element adjacent to the punch and movable against the blank, and moving said element toward the blank to extrude the blank material.

3. The method according to claim 2 wherein the element is a sleeve surrounding the punch.

4. The method of forming cup-shaped shells substantially as hereinbefore described with reference to, and as illustrated in, Figures 4 to 8 of the accompanying drawings.