Die

Abstract

A die for magnetically forming impressions in a tubular metal workpiece. The die comprises a rigid hollow body having at least one aperture therein for introducing a workpiece and an induction coil and a tubular elastically deformable casing mounting at least one impression in intaglio or in relief. One end of the casing is fixed in said at least one aperture so as to define an annular, hermetically sealed chamber between itself and the inner wall of the hollow body. A conduit is provided for the introduction or removal of a fluid into or from said chamber to permit the forming and subsequent removal of a formed workpiece respectively.

Description

The present invention relates to a die.

The magnetic forming of impressions on a tubular metal workpiece is known (for example from German Patent No. 1,122,188). This is achieved by disposing the tubular metal workpiece between a coil and a die, and discharging a capacitor in the coil to produce induced current in the metal workpiece. The interaction between the magnetic field of the coil and the induced field has the effect of causing an expansion force to act on the metal work-piece. The resulting expansion is limited by a die, so that the metal workpiece deforms according to the relief of the die.

Dies used hitherto (French Patent No. 1,512,119 and U.S. Pat. No. 3,540,250) are constructed in the manner of moulds and comprise two rigid shells which are separated in order to position a workpiece to be formed within them and are then re-assembled in order to close the die. As in the case of moulds, the interface of the shells of the die leaves a mark on the magnetically formed object which even great operating precision does not completely eliminate. Also the extraction of the magnetically formed workpiece from the die may be difficult, or even impossible, as the separation of two semi-cylindrical shells is complicated if the die has impressions which terminate adjacent the interface. In such cases it is necessary to divide the shells and to separate them radially, which considerably complicates the manufacture of the die and leaves the marks of at least a second interface.

The object of the present invention is to provide a die for magnetically forming impressions on a tubular metal workpiece which obviates or mitigates the aforementioned drawbacks. According to the present invention, there is provided a die for magnetically forming impressions in a tubular metal workpiece, the die comprising a rigid hollow body having at least one aperture therein for introducing the workpiece and an induction coil, a tubular, elastically deformable casing, mounting at least one impression in intaglio or in relief and being fixed by its ends to the hollow body, one end being fixed in said at least one aperture so as to define an annular, hermetically sealed chamber between itself and the inner wall of the hollow body, and a conduit to provide for the introduction or removal or a fluid into or from said chamber respectively.

The accompanying drawings illustrate by way of example, embodiments of the present invention.

FIG. 1 is an axial sectional view of a die according to the present invention;

FIG. 2 is a sectional view through the FIG. 1 embodiment when provided with a first reinforcement means;

FIG. 3 is a sectional view through the FIG. 1 embodiment when provided with second reinforcement means, and

FIG. 4 is a sectional view through the FIG. 1 embodiment when provided with a third reinforcement means.

The die illustrated in FIG. 1 comprises a rigid cylindrical hollow body 1 of for example metal or a synthetic material such as nylon. The body 1 has two opposed circular apertures 2 and 3. Flexible means including a tubular casing 4 of elastically deformable material has the two ends thereof fixed at the apertures 2 and 3. The casing 4 can comprise for example rubber having a hardness of 75.degree. to 80.degree. Shore A, and its inner or working surface is provided with impressions 5 in the form of annular grooves. The ends of the casing 4 are secured to the body 1 by means of two rings 6 and 7 which are expanded mechanically or by magnetic forming in order to grip the edge of the casing 4 between the body 1.

Means for selectively effecting contraction and expansion of the casing 4 comprise the casing 4 and the cylindrical shell of the body 1 which define an annular chamber 8 which is hermetically closed and may be connected by a conduit 9 to a source of fluid, for example oil under pressure.

A magnetic forming coil 10, into which capacitors (not shown) discharge, is disposed so as to be co-axial to the cylindrical body 1 and the casing 4. The object to be formed is constituted in this case by a tubular metal blank 11 which is introduced axially into the die between the coil 10 and the casing 4 in the direction indicated by the arrow F.

Once the blank 11 is in position, the oil under pressure is introduced into the chamber 8, the pressure having the effect of applying the casing 4 against the blank 11 as illustrated at 4'. The discharge current is then passed through the coil 10 and the blank 11 deforms due to radial expansion, thus following the relief 5 of the die.

The oil pressure in the chamber 8 is then reduced and the casing 4 re-assumes its initial position due to its elasticity. This expansion of the casing 4 has the effect of automatically releasing the magnetically formed blank from the relief of the die, thus facilitating its axial extraction in the direction of arrow F'. In the case of deep impressions, it may occur that the return of the casing 4 to its initial position is not sufficient to completely release the blank. In such circumstances, a vacuum can be created in the chamber 8 in order to bring the casing into the position 4" for the period necessary to extract the blank 11.

This die has the following advantages, which are apparent from the drawings:

The absence of any interface which might leave a mark on the magnetically formed blank;

The automatic release of the object formed, facilitating easy extraction;

The automatic centering of the object to be formed with respect to the axis of the die and of the coil during the compression of the die;

The complete and automatic adjustment of the object to be formed in the die;

Simplicity of manufacture;

Automation can be readily achieved with conventional means;

The die may be cooled by means of the compression fluid, thus making it possible to achieve high operating speeds without any danger of damaging the die or the induction coil.

During the magnetic impulse, the casing 4 undergoes a very violent shock. It may be advantageous to reinforce this casing by means able to assist it in withstanding this shock. FIGS. 2, 3 and 4 show three possible solutions.

In the embodiment illustrated in FIG. 2, the casing 4 is surrounded by a tubular steel sheath 12 which is split along a generatrix 13 to form a spring.

In the embodiment illustrated in FIG. 3, the casing 4 is surrounded by four arcuate members 14, 15, 16 and 17 which are spaced apart and held against the casing 4 by a number of coil springs 18.

In the embodiment illustrated in FIG. 4, the casing 4 is reinforced by means of metal wires 19 provided in the body thereof and extending either parallel to the generatrices of the casing 4 or in the form of helixes.

As an alternative to the embodiment illustrated in FIG. 1, the casing 4 could occupy when in the stationary position, the position 4', the die being opened, i.e. brought into the position 4 or 4" by creating a vacuum in the chamber 8.

Since the die is formed in one piece and since the resultant of the forces of expansion is, as a rule, zero, it does not need to be secured in a rigid manner to its support, i.e. to the frame of the machine, but may be mounted on a moving arm and introduced, with the workpiece to be formed, on to the coil. In this case, it is thus possible to eliminate the aperture 2.

Claims

What is claimed is:

1. In an electromagnetic forming apparatus, a die for magnetically forming a selected impression in a tubular metal workpiece, the die comprising a rigid hollow body having at least one aperture therein for introducing the workpiece and an induction coil inserted therein, a tubular, elastically deformable casing having an inner surface corresponding to a selected impression and fixed by its ends to the hollow body, one end being fixed in said at least one aperture so as to define an annular, hermetically sealed chamber between said casing and the inner wall of the hollow body, and a conduit to provide for the introduction or removal of a fluid into or from said chamber respectively to effect deformation of said casing.

2. A die according to claim 1, further comprising rigid members distributed around said casing surrounding same to conform with its surface, and springs surrounding the rigid members.

3. A die according to claim 1, further comprising a steel tube split along one generatrix and surrounding said casing to reinforce same.

4. In an electromagnetic forming apparatus of the type having an electromatnetic coil insertable into a tubular workpiece and expandable when energized to effect forming of a selected impression on the workpiece: flexible means having a working surface having a relief impression corresponding to the selected impression and configured to receive therein both the workpiece and the inserted electromagnetic coil for contracting to closely fit said working surface about the workpiece and for expanding to define a clearance between said working surface and the workpiece; and means for selectively effecting the contraction of said flexible means to enable the electromagnetic coil when energized to impress the selected pattern on the workpiece and for selectively effecting the expansion of said flexible means when the electromagnetic coil is deenergized to enable both insertion and removal of the workpiece.

5. In an apparatus according to claim 4, wherein said flexible means comprises an elastically deformable cylindrical die having an inner surface corresponding to said working surface; and wherein said means for selectively effecting the contraction and expansion of said flexible means comprises means defining a fluidtight fluid chamber one wall of which comprising said elastically deformable cylindrical die and receptive of pressurized fluid into and out of said chamber to effect movement of the deformable die.

6. In an apparatus according to claim 5, wherein said flexible means further comprises reinforcing means for reinforcing said deformable die.

7. In an apparatus according to claim 6, wherein said reinforcing means comprises rigid members disposed on the outer surface of said deformable die and springs surrounding said members.

8. In an apparatus according to claim 6, wherein said reinforcing means comprises a rigid tube disposed about said deformable die and having means defining a slot along the whole length thereof.

9. In an apparatus according to claim 6, wherein said reinforcing means comprises metal wire disposed in the body of said deformable die.