US2847957A - Apparatus for rapidly forming deep draws in metal sheets - Google Patents

Description

ORS H21.

M. WATTER EIAL APPARATUS FOR RAPIDLY FORMING DEEP DRAWS IN METAL SHEETS Filed Dec. 20. 1955 INVENT MLChCL-Ql Wcl (Ta reR D. Pag 4 ATTORNEY i0 i, FIG.2

Aug. 19, 1958 United States Patent APPARATUS FOR RAPIDLY FORMING DEEP DRAWS 1N METAL SHEETS Michael Watter, Philadelphia, and Garrett D. Pagon,

Ambler, Pa., assignors to The Budd Company, Philadelphia, Pa., a corporation of Pennsylvania Application December 20, 1955, Serial No. 554,165

3 Claims. (Cl. 1 l3-44) This invention relates to apparatus for rapidly forming deep draws in metal sheets and has for an object the provision of improvements in this art.

The method commonly used to produce deep draws in sheets includes the steps of rigidly gripping the edges of the sheet by jaws and striking the sheet by mechanically operated dies. The impact tends to rupture the metal so that only a small amount of work can be done at one operation. This requires many operations for deep draws, is very expensive, and usually requires heat treatment between operations. The expense is greatly increased because a different die set must be used for each operation. Besides, the metal tends to buckle near the gripped edges and when these buckles or wrinkles are started they are hard to remove. Further than this, considerable metal is lost in the gripped edges which must be cut off.

According to the present invention very deep draws can be made at a single operation. There are no sudden blows and the likelihood of metal rupture is greatly minimized or eliminated.

The method comprises the guiding of a sheet at its edges around its circumference and applying fluid pressure radially inwardly to the edges of the sheet completely around its periphery. The edges are disposed between circumferential confining and sealing members which prevent escape of fluid inward but which permit the edges to move inward under pressure as the intermediate part bulges axially. The metal tends to flow axially interiorly of the space where the edges are guided because there is less opposite to flow in this direction than elsewhere, within certain limits. As an aid to axial movement, an axial pressure is applied. The radial pressure acts upon a much smaller exposed surface than the normal or axial pressure and is usually many times as great per unit area as the normal pressure. sure'forces could be applied by mechanical means, but for simplicity and controlled application it is preferable to use fluid pressure.

The detailed objects of the invention are: To make deep draws without rupture; to use as much of the original sheet stock as possible; to reduce the number of operations to attain a given depth of draw; toreduce the die cost to a minimum; and in other ways to provide an improved method and apparatus for making deep drawn sheets.

The above and other objects and certain advantages of the invention will be apparent from the following description of an illustrative embodiment, reference being made to the accompanying drawings, wherein:

Fig. l is a central axial section, partly diagrammatic in nature, showing the die apparatus used in the invention; and

Figs. 2, 3, 4 and 5 are perspective views of a conical article at different stages of formation according to the present invention.

As shown in Fig. 1, a blank or workpiece W, which is to be formed into a cone, is placed in mating dies and The axial pres- 2,847,957 Patented Aug. 19, 1958 11 which closely confine the edges of the blank in an annular zone around the circumference to keep it from buckling. Sealing means, such as rubber O-rings 13 in V-shaped grooves located at a radial distance within the outer periphery of the annular zone, insure the sealing of the edge around its circumference for the full range of action on the blank, that is for the full inward movement of its outer periphery. The die surfaces are preferably ground smooth for easy slippage of the blank edge between them.

One die part, such as 10 here, is formed with a cavity 14 into which the metal may expand and to give it form; and the other die part 11 is formed with means to receive the pressure fluid, as from a channel 16 and pipe 17.

Outside the sealing rings 13, at the radial distance left for blank contraction and at the outer periphery of the die 10, or die 11, whichever moves axially, or both, the die parts are formed with a circumferential cavity 18 to receive pressure fluid, as from a channel 19 and a pipe 20.

The die parts 10, 11 shown herein are formed as separate parts, selective as to shape, which are secured in a case 22, as by a screw retainer 23, sealing rings 24 being used on each side of the channel 18.

The pressure fluid may be provided in various ways, as by an explosive or by pumps with accumulators and sudden release means, by pumps alone, or the like. As stated, the radial pressure is greater per unit area than the axial or normal pressure, say about ten times as great. For example, for sheet material of /s" thickness an axial pressure of 5,000 lbs/sq. in. and a radial pressure of 50,000 lbs/sq. in. has been used successfully. The disk diameter at the start was about 7 /2".

The dies may be held together by any suitable means, such, for example, as the threaded assembly illustrated, by bolts, by placing in a press, or the like.

Figs. 2, 3, 4 and 5 show successive stages in the formation of the article. Preferably, though not necessarily, the blank W, Fig. 2, is preliminarily formed with a starting bulge, as W1. This may be formed on a mechanical press. It seems to aid in initiating the metal movement to some extent. The shapes shown in Figs. 3, 4 and 5 may represent various forms made on successive die sets or may represent transition stages in a single die set.

As an illustrative example, a blank of 7 /2" diameter and A5 thickness was drawn into a cone 3" deep. The final diameter over the flange was about 5". The flange gradually narrowed as the conical protuberance was formed and increased in thickness somewhat as the conical pa rt became thinner.

If a source of fluid of sutficiently high pressure is steadily available, the full draw may be made in one step, but if the pressure drops after application, it may be necessary to work in several stages. With steady expansion without sudden impact, the metal will flow properly without tearing whether the full action is affected in one step or several.

The dies illustrated have a curved throat which aids in directing the metal flow, but it has been found that the metal will flow axially from the radial edges even when a curved throat is not provided. Neither is it necessary to give the blank an initial cupped shape.

it has been found that articles drawn according to the present method and with the present apparatus have no abrupt thinning or incipient tearing and use a greater proportion of the blank stock than other known methods.

It is thus seen that the invention provides an improved process and apparatus and provides an improved product.

While one embodiment of the invention has been disclosed for purposes of illustration, it is to be understood that there may be various embodiments within the general scope of the invention.

What is claimed is:

1. Apparatus for forming deep-drawn sheet metal parts from generally flat sheet metal blanks, comprising in combination, mating axially convergent dies formed and arranged to clamp a blank in an annular outer zone, leaving the inner zone unclamped with space to expand axially, means in said dies forming an annular fluid chamber outside said annular zone, means to admit fluid under pressure to said annular fluid chamber to apply uniform pressure radially inwardly on the blank around its entire outer periphery, means sealing the space outside said annular chamber against the leakage of fluid therefrom, means at a distance radially within the outer periphery of the annular zone providing a seal against inward leakage of fluid between the blank and dies, and means for separately and independently applying axial pressure on the blank in the inner unclamped zone while fluid pressure is being applied to the outer periphery of the blank in the clamped zone to form an axial projection in the inner unclamped zone.

2. Apparatus as set forth in claim 1, wherein one of said dies fits in the bore of a surrounding case member with its outer periphery forming the outer border of said annular clamping zone at said annular fluid chamber, and in which outer fluid sealing means are provided between said case member and the die therein.

3. Apparatus as set forth in claim 1, wherein said means for separately and independently applying axial pressure comprises fluid pressure means which is controlled separately and independently of the radially acting fluid pressure means.

References Cited in the file of this patent UNITED STATES PATENTS 1,530,000 Kauflman Mar. 17, 1925 2,203,868 Gray et al June 11, 1940 2,331,430 Shoemaker Oct. 12, 1943 2,615,411 Clevenger et al. Oct. 28, 1952 20 2,649,067 Kranenberg Aug. 18, 1953

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