Method and apparatus for forming metal containers

Aug. 31, 1965 r. r. bolt etal 3,203,218

METHOD AND APPARATUS FOR FORMING METAL CONTAINERS

Filed May 22, 1961 3 Sheets-Sheet 1

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Aug. 31, 1965

R. R. BOLT ETAL

3,203,218

METHOD AND APPARATUS FOR FORMING METAL CONTAINERS

Filed May 22, 1961

Sheets-Sheet 2

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Aug. 31, 1965

R. R. BOLT ETAL

3,203,218

METHOD AND APPARATUS FOR FORMING METAL CONTAINERS

Filed May 22, 1961

Sheets-Sheet 3

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INVENTORS.

nOBE^TSOLT

DELBECBTEDMUAfO PVOBBE

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United States Patent Office Patented Aug. 31, 1965

3,203,218

METHOD AND APPARATUS FOR FORMING METAL CONTAINERS

Richard Robert Bolt, Lake Villa, and Delbert Edmund Wobbe, Cary, III., assignors to American Can Company, New York, N.Y., a corporation of New Jersey

Filed May 22,1961, Ser. No. 111,670 9 Claims. (Cl. 72—349)

The present invention relates to the production of thin walled cup-shaped containers and has particular reference to an improved method of and apparatus for forming a metal container having a sidewall and an end integral therewith from a thin flat blank in a single continuous relatively short operating stroke.

Devices and processes have already been proposed and used for forming tubular containers from a flat blank in a continuous stroke, particularly containers made from aluminum or other soft homogeneous metals. Generally, the procedure used involves drawing the blank into cup form in the usual manner after which in the same continuous stroke, the punch carries the drawn cup through an ironing die slightly smaller in diameter than the drawing die. As drawn the cup usually has bottom and side wall thicknesses essentially equal to the thickness of the blank. The ironing die thins the side wall of the drawn cup and forces the metal back thereby increasing the height of the container. Additional ironing steps may be added to achieve a desired body wall thickness and container height, generally limited, however, by the practical length of the punch stroke which can be used.

As used herein, the term “drawing” refers to the operation wherein a peripheral margin of a flat blank is turned upwardly and simultaneously smoothed by means of a drawing punch and die to form a cup having a wrinkle free side wall whose thickness is substantially equal to the thickness of the original blank. Subsequent redrawing of the cup merely turns up more of the end material into the side wall thereby elongating the side wall but resulting in a substantial reduction in the diameter of the cup.

“Ironing” refers to the operation wherein the side wall of a cup is elongated by reducing its thickness with no appreciable reduction in the diameter of the cup. It is generally accomplished by placing the cup on a closely fitting punch or mandrel and forcing the cup and mandrel through an ironing or reducing die whose diameter is slightly less than the outer diameter of the cup thereby forcing the excess metal back and producing a longer but thinner side wall.

Heretofore, the drawing and ironing method described has not been considered an economical method for the high speed production of steel containers having a large aspect or height to diameter ratio, e.g., the dimensions of the ordinary tin plate can. This is due in part to the greater difficulty of cold forming a hard, tough material such as steel resulting in a relatively small reduction per die. Since a drawing operation is generally limited to forming a blank into a cup no longer than half its diameter, the number of successive ironing operations required to thin the side wall sufficiently to produce a satisfactory container length in the same continuous operation necessitates a rather lengthy punch stroke. Because a reciprocating action is involved which creates large inertia forces in the machine parts, a lengthy punch stroke imposes severe limits on the production rate which can be achieved.

However, by the novel method and means disclosed herein, a flat steel blank may be formed using a combination drawing and ironing die into a thin-walled container having a larger height to diameter ratio than could be obtained by single die means previously used. In a more important application, the subject invention utilizes additional ironing dies positioned in close succession with the combination drawing and ironing die in a novel manner which causes the forming punch to exert a substantially uniform total force on the metal as it is being simultaneously formed in successive dies. This results in the formation of steel containers having a relatively large height to diameter ratio in a single continuous stroke with an increased efficiency and a reduced forming punch stroke as compared with procedures heretofore used.

Accordingly, an object of the present invention is to provide an improved method of forming a thin-walled cup-shaped steel container which will overcome the problems hereinbefore pointed out.

Another object is to provide such a method wherein a maximum amount of working of the metal is accomplished in a minimum of operating stroke.

Another object is to provide such a method wherein the force exerted by the punch on the metal as it is being simultaneously formed in successive dies is maintained at a substantially uniform level.

A further object is to provide an apparatus for forming a cup-shaped steel container having an end thickness equal to and a side wall thickness substantially less than the thickness of the original blank.

Yet a further object is to provide such an apparatus which requires a shorter forming punch stroke as compared to procedures heretofore used.

Numerous other objects and advantages of the invention will be apparent as it is better understood from the following description, which, taken in connection with the accompanying drawings, discloses a preferred embodiment thereof.

The above objects are accomplished in the present invention by providing a flat circular blank B of thin steel such as tin plate. A blank holder H positions the blank B over an annular die A and presses a peripheral marginal portion of the blank against the die with a substantial predetermined force. The die A has a combined drawing and ironing surface comprising a rounded drawing face D merging with a uniform diameter ironing face I which forms the minimum internal diameter of the die.

A punch P forces the blank B through the die A to form the flat blank into a cup-shaped article. The blank is initially drawn as the marginal portion is pulled from beneath the blank holder H and over the drawing face D. The holding force maintained by the blank holder H on the marginal edge portion of the blank B prevents wrinkling or folding of the blank and insures that the blank is smoothly stretched as it is being drawn.

As the metal leaves the drawing face D, it moves immediately past the ironing face I where the side wall of °° the cupped portion is ironed between the ironing face and the punch P. Upon emerging from the die A, the end of the cup-shaped article formed thereby has a thickness substantially equal to the thickness of the blank B, while the side wall thickness is substantially less than the ⁶⁰ thickness of the blank.

The side wall is subsequently decreased in thickness in the same continuous stroke by forcing it through one or more ironing dies positioned below and in close succession to the drawing die A. The diameters of the ironing faces ⁶⁵ and the spacing therebetween have values which cause the cup to enter each succeeding die before completely emerging from the preceding die and which result in a substantially uniform force being exerted on the metal by the punch P during the portion of the operating cycle ‘° wherein the side wall portion is simultaneously being formed by successive dies.

3,303,218

Referring to the drawings:

FIGURE 1 is a sectional view of an apparatus embodying features of the present invention;

FIGURES 2 through 5 are fragmentary views similar to FIGURE 1 showing a blank being formed to a desired container configuration;

FIGURE 6 is an enlarged fragmentary sectional view showing the profile of the combination drawing and ironing die.

As a preferred or exemplary embodiment of the instant invention FIGURE 1 shows a hydraulic press generally designated 11 having a die carrier 12 attached to a frame 13. An annular die A having a die aperture 14 is suitably mounted in the die carrier 12. The die aperture 14 has a combined drawing and ironing surface comprising a rounded drawing face D adjacent the upper surface of the die which curves towards and becomes tangent to a constant diameter ironing face I forming the minimum diameter of the die aperture (FIGURE 6).

A cylindrical forming punch P reciprocatably mounted above the die A in axial alignment with the die aperture 14 has a lower end surface 15. The shape of the end surface 15 determines the end shape of the article to be formed and may be flat, conical, spherical, or a combination of these shapes. In the preferred embodiment shown in the drawings, a flat end surface 15 is used for producing flat ended containers.

A flat, circular blank B is inserted between the die A and an annular blank holder H disposed above the die. The blank holder H has an inner diameter slightly greater than the diameter of the punch D and a spaced series of guide holes 16 extending through the blank holder adjacent the outer edge. Studs 17 having shank portions 18 and heads 19 are threadably engaged to the die carrier 12 with the shank portions extending upwardly through the holes 16 in the blank holder H to prevent the blank holder from moving transversely relative to the die A while permitting it to move upwardly along the longitudinal axis of the die.

The lower .surface of the blank holder H has a circular recessed portion 20 of substantially the same diameter as that of the blank B and a depth which is slightly less than the thickness of the blank, the recessed portion serving to position the blank in axial alignment with the . die aperture 14. As thus positioned, a marginal edge portion 23 of the blank B is gripped between the die A and the blank holder H with a substantial predetermined force due to the action of compressed springs 24 disposed on the stud shanks 18 between the blank holder and stud heads 19.

The upper end of the punch P is attached to the piston rod 26 of a hydraulic actuating cylinder 27, the cylinder being secured to the frame 13 of the machine and having upper and lower ports. 28 and 29 respectively. The admission of pressurized hydraulic fluid from a suitable source (not shown) to the cylinder 27 through the upper port 28 moves the punch P downwardly bringing the lower end surface 15 of the punch into contact with the blank B.

The punch P continuing to move downwardly progressively pulls the marginal edge portion 23 of the blank B from beneath the blank holder H and forces it into contact with the drawing face D of the die A. The marginal edge portion 23 is thus drawn across the drawing face D and is stretched and shaped into a tubular configuration to form a side wall portion 30 of a cupshaped article having an end 33 (FIGURE 2). The side wall portion 30 as well as the end 33 of the drawn article have thicknesses substantially equal to the thickness of the blank B.

Concurrently with the formation of the drawn side wall portion 30 by the drawing face D, the part of the drawn side wall leaving the drawing face is immediately moved past the adjacent ironing face I of the combination die A.

⁴

The ironing face I reduces the thickness of the side wall and correspondingly increases its length.

During this combination drawing and ironing operation, the force with which the marginal edge portion 23 of the blank B is gripped between the blank holder H and die A is maintained at a level sufficient to insure that the blank is plastically stretched rather than being wrinkled or folded as the marginal portion is withdrawn from beneath the blank holder but is not so great as to result in tearing or cracking of the metal. The metal is thus simultaneously subjected to three types of loading in the combination drawing and ironing operation, i.e., a compressive loading on the marginal edge portion 23 of the blank B due to the holding force, a tension or stretching load on the metal adjacent the drawing face D as the metal is drawn from the flat to the tubular form, and a compressive type loading on the metal adjacent the ironing face I as the side wall is ironed and reduced in thickness. By working the metal in this manner, it has been found that the amount of ironing of the drawn side wall portion 30 which can be accomplished by the ironing face I is greater than could be achieved by first completely drawing a cup and thereafter ironing the side wall of the drawn cup.

While not wishing to be bound by any particular theory, it is believed that this result is due to a high back stress in the metal as it enters the ironing face I. This apparently permits the greater deformation of the metal without creating an excessively high die pressure at the ironing face which would tend to cause tearing and rupturing of the metal.

Generally, the holding force used will be determined by the particular forming operation. For example, in the combined drawing and ironing of a 6^]/a x .019 thick soft steel blank into a %e diameter cup having an .014 side wall thickness, a holding force equivalent to approximately 10,000 lbs. on the marginal edge portion of the blank is preferred.

While still engaged by the ironing face I, the cupshaped article enters an annular ironing die 34 mounted in the die holder 12 below the combination die A (FIGURE 3). The ironing die 34 has an ironing face 35 which is smaller than and axially aligned with the ironing face I of the combination die A. A spacer plate 36 is disposed between the combination die A and ironing die 34 to produce a predetermined spacing between the respective ironing faces I and 35 of the dies. The downward movement of the punch P forces the side wall portion of the cup-shaped article past the ironing face 35 reducing the thickness of and thereby elongating the side wall portion.

A second ironing die 37 having an ironing face 38 is similarly mounted in the die holder 12 below the ironing die 34. A spacer 39 disposed between the ironing dies 34 and 37 produces a predetermined spacing between the respective ironing faces 35 and 38 thereof. As the punch P continues downwardly, it carries the cup-shaped article into the ironing face 38 while the side wall is still engaged by the ironing face 35 of the first ironing die 34. Depending upon the spacings between the respective ironing faces required to produce a substantially uniform punch force, as more fully discussed hereinafter, the side wall may also still be engaged by the ironing face I of the combination die A when it initially enters the ironing face 38 of the second ironing die 37 (FIGURE 4). As it is moved downwardly, the side wall is then disengaged from the ironing face I while still engaged by the ironing faces 35 and 38 of the ironing dies 34 and 37 respectively (FIGURE 5).

The side wall is further ironed by the ironing face 38 to reduce its thickness and increase its length. The drawn and ironed container 40 finally formed has the end 33 of substantially the same thickness as that of the blank B and a side wall 43 whose thickness is substantially less than that of the blank. It is to be understood

3,203,218 that, while the drawings show only two ironing dies, additional ironing dies may be used to produce any desired side wall thickness and container height.

It has been found by extensive testing that the reduction in the thickness of the side wall of a steel cupshaped article in a series of successively aligned ironing dies is accomplished at a greater efficiency and a shorter stroke when the punch exerts a substantially uniform force on the metal as it is being formed as compared to the case where the punch exerts a fluctuating force on the metal, e.g., where the cup is forced through the dies in separate successive operating steps. Also, that a uniform punch force can be achieved by using a predetermined combination of ironing face sizes and spacings whereby the metal is simultaneously engaged and being worked by successive ironing faces. For a particular desired container configuration, various combinations of these parameters may be used to accomplish the same total working of the metal, e.g., a large number of closely spaced ironing faces with a small reduction in thickness per ironing face as compared to a lesser number of more widely spaced ironing faces with a large reduction in side wall thickness by each ironing face. Generally, it is preferable to have each ironing face spaced from the preceding ironing face a distance no greater than 75% of the length of the side wall which is formed by the preceding ironing face.

The continuous downward movement of the punch P carries the formed container through a conventional stripper disposed below the die A. The stripper consists of a segmented flat annular ring 44 having a series of segments 45 adapted to slide radially within a recessed portion 46 in the lower surface of the die holder 12. The segments 45 are urged radially inwardly by springs 47 and are retained within the recessed portion 46 by an annular flat retaining ring 48 secured to the die holder 12 by screws 49. At the extreme inwardly position of the segments 45, the segmented ring 44 has a substantially cylindrical inner surface 50 whose diameter is slightly less than the diameter of the punch P with a smoothly rounded upper edge 53 and a sharp lower edge 54.

As the formed container 40 is conveyed toward the stripper by the punch P, it contacts the rounded upper edge 53 of the segmented ring 44 forcing the segments 45 outwardly to allow the punch and container to pass through the ring. After the container has passed through the ring 44, the springs 47 move the segments 45 inwardly against the punch P. By suitable valving means (not shown), the flow of pressurized hydraulic fluid is then directed to the lower port 29, whereupon the punch P is moved upwardly by the actuating cylinder 27. During the upward movement of the punch P, the upper edge of the formed container engages the sharp lower edge 54 of the segmented ring 44 which prevents any further upward movement of the container thereby stripping it from the punch.

By the use of the apparatus described, which also exemplifies the method steps required for consummating the process of the invention, it is possible to form in a single continuous operation a cup-shaped steel container at a higher efficiency and using a shorter punch stroke than heretofore required. The container thus formed may have a relatively short side wall height by employing a single combination drawing and ironing operation, or the side wall may be relatively long as compared to the diameter of the container by using additional ironing steps. Since by the subject method the deforming force exerted by the punch on the metal is maintained at a maximum value during the greatest portion of its stroke, resulting in the maximum working of the metal for a given punch stroke, containers having a relatively high length to diameter ratio can be produced in the minimum space and time. Consequently, the process is particularly suited for production at higher rates of speed than can be presently achieved.

While the foregoing description is particularly directed to the forming of steel containers because this metal is difficult to form economically and at high speeds, it is to be understood that the general method described is ₅ also applicable and has advantages in the forming of other metals such as aluminum and copper alloys. In any case, the more uniform working of the metal during the .punch stroke which is achieved by the subject method results in a shorter -punch stroke for a given total work.

₁₀ It is thought that the invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction, and arrangement of the parts and -that changes may be made in the steps 15 of the method described and their order of accomplishment without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely a preferred embodiment thereof.