Apparatus for deforming sheet metal blanks by fluid pressure

Abstract

A sheet metal blank is clamped between opposed annular members and deformed in its central area by fluid pressure applied thereto. The clamping members are urged together by the same fluid pressure; and to this end, one of the clamping members is mushroom-shaped with the head of the mushroom comprising a piston urged in a clamping direction by fluid pressure applied by an annular cylinder chamber that communicates with a central chamber whose fluid deforms the blank. In this way, the annular marginal portions of the blank are tightly gripped and only the central exposed portion of the blank is deformed.

Description

The present invention relates to deforming sheet metal blanks under fluid pressure, both for the production of formed workpieces and also for laboratory testing.

One such method of laboratory testing is to apply hydraulic pressure to a test blank to cause a circular or elliptical central portion thereof to bulge. However, the hydraulic pressure machines designed for this purpose heretofore have suffered from the disadvantage that portions of the blank outside the central test area may also be drawn radially inwardly, thereby invalidating the results of the test. The same problem of course is detrimental to the production of workpieces.

Accordingly, it is an object of the present invention to provide apparatus for deforming sheet metal blanks under fluid pressure, in which only the exposed central portion of the blank is deformed.

Another object of the present invention is the provision of such apparatus, in which the peripheral portions of the blank are gripped with a pressure that varies as the pressure with which the central portion of the blank is deformed.

Finally, it is an object of the present invention to provide such apparatus, which will be relatively simple and inexpensive to manufacture, easy to operate, maintain and repair, and rugged and durable in use.

Other objects, features and advantages of the present invention will become apparent from a consideration of the following description, taken in connection with the accompanying drawing, which is a cross-sectional view of apparatus according to the present invention.

Referring now to the drawing in greater detail, there is shown apparatus according to the present invention, comprising an outer body 1 which is a figure of revolution and is generally cylindrical or cup-shaped. A blank holder 2, which is also a figure of revolution, is axially slidably disposed within body 1. Piston 3 slides coaxially with a fluidtight fit within blank holder 2. An annular holding die 4, which is also a figure of revolution, is disposed within body 1 in coaxial superposed relation with holder 2 and piston 3, and has an outwardly directed peripheral flange 4' which is received beneath an inwardly directed annular flange 1' at the upper extremity of body 1, and a central opening 4". Die 4 is releasable from the engaged relationship with body 1 which is shown in the drawing, by means of a bayonnet lock or detachable interengaging portions, or other conventional means (not shown). In this way, the assembly can be opened for the insertion and removal of workpieces.

Holder 2 has a flat annular surface confronting die 4, which is faced with a gasket 5 of a material softer than either holder 2 or the metal sheet to be deformed.

At least one opening 6 extends through the cylindrical axially-extending stem of holder 2 to convey to the radially outer side of holder 2 the same fluid pressure that acts on the radially inner side of holder 2 and on the circular blank 7. To this end, holder 2 is provided with an axially extending passageway 8; and the radially inner end of the hole or holes 6 communicates with the passageway 8, while the radially outer end of hole or holes 6 communicates with an annular cylinder chamber 9 defined between body 1 and holder 2.

Body 1 is bolted to a support (not shown) by bolts or other fasteners (not shown) that pass through a flange 10 thereon.

The cavity of body 1 in which the head 11 of holder 2 is disposed is cup-shaped and of a depth greater than the depth of the head of holder 2. Seals 12 provide slidably sealed contact between piston 3 and the supporting side walls of passageway 8, and between holder 2 and body 1 on opposite sides of chamber 9.

In operation, with the die 4 removed, a sheet metal blank in the form of a circular workpiece 7 is placed on gasket 5 and die 4 is returned to the position shown in the drawing. Holder 2 can then be urged against the workpiece by any desired means (not shown), after which piston 3 is advanced upwardly as seen in the drawing. Passageway 8 and chamber 9 are filled with hydraulic fluid such as oil, whose pressure is increased by the upward movement of piston 3. This upward movement has two effects: The pressure imparted to the hydraulic fluid causes workpiece 7 to deform and bulge upwardly into opening 4", as seen in the drawing; and also the pressure of the hydraulic fluid transmitted through hole or holes 6 to chamber 9, causes holder 2 to advance in the manner of a piston, thereby more tightly clamping the annular peripheral portions of the workpiece against radially inward movement. To this end, it is preferred that the area of chamber 9, measured in a plane perpendicular to the axis of the apparatus, should be larger than the area of workpiece 7 that is exposed to the fluid by passageway 8, the broad range of ratios of these two areas being 1:1 to 10:1.

The higher the pressure against the exposed central portion of the workpiece, the greater will be the force with which holder 2 clamps the peripheral portions of the workpiece; and in this way, the tendency of the workpiece to be drawn radially inwardly toward its center, upon deformation of the central portion in an axial direction, is effectively countered. At the same time, it has not been necessary to provide the clamping surfaces of holder 2 and die 4 with ridges or deformations or other asperities that would themselves change the shape of the workpiece.

To release the formed workpiece, or to discontinue the test in the case of testing apparatus, it is necessary only to back off the piston 3, whereupon the fluid pressure is relieved and die 4 can be removed upwardly, after which the formed workpiece or the tested specimen can be removed and replaced with an undeformed or untested piece.

From a consideration of the foregoing disclosure, therefore, it will be evident that all of the initially recited objects of the present invention have been achieved.

Although the present invention has been described and illustrated in connection with a preferred embodiment, it is to be understood that modifications and variations may be resorted to without departing from the spirit of the invention, as those skilled in this art will readily understand. Such modifications and variations are considered to be within the purview and scope of the present invention as defined by the appended claims.

Claims

Having described my invention, I claim:

1. Apparatus for deforming only a central portion of sheet material by fluid pressure, comprising means to clamp a peripherial portion of said material entirely about said central portion while leaving said central portion exposed, means mounting said clamping means for free and unimpeded movement toward said material, means to apply the pressure of a fluid under pressure to said exposed central portion of said material to deform only said central portion of said material, and means to apply said pressure also to said clamping means so that the force with which said peripheral portion is clamped by said clamping means varies directly as said pressure over the entire range of said pressure thereby to maintain said peripheral portion against substantial radially inward movement over said entire range of pressure.

2. Apparatus as claimed in claim 1, said clamping means comprising an annular member, means mounting said annular member for movement toward and away from the material to be clamped, and means for applying said fluid to said material centrally of said annular member.

3. Apparatus as claimed in claim 2, and an annular die on the side of said material opposite said clamping member, said annular die having a central opening for receiving material deformed by said pressure.

4. Apparatus as claimed in claim 1, and a hollow body within which said clamping means is mounted for sliding movement toward and away from said material, said clamping means and said hollow body defining between them an annular cylinder chamber, and means for applying said pressure within said cylinder chamber to urge said clamping means in the direction of said material.

5. Apparatus as claimed in claim 4, said clamping means having a central opening through which said fluid is applied to said material, said applying means comprising at least one opening through said clamping means communicating between said annular chamber and said central opening.

6. Apparatus as claimed in claim 4, the area of said annular cylinder chamber in a plane perpendicular to the axis thereof being greater than the area of said material exposed to said pressure.

7. Apparatus as claimed in claim 4, said clamping member having a head thereon that defines said annular chamber between said head and the bottom of a cup-shaped recess within said body.