Device for forming annular articles from powder material

Abstract

The present invention relates to a device for forming tubular articles from powder material including an upper pressing punch, a lower punch, a core pin and a matrix having an inner periphery corresponding to the outer periphery of the upper and lower punch, a molding cavity being defined between the upper and lower punch, the core pin and the matrix, whereby the core pin is movable in relation to the matrix. According to the invention the upper pressing punch is arranged to actuate movement of the core pin or the matrix during compacting of a powder in the molding cavity so that the pressing punch and the core pin or the matrix move together.

Description

FILED OF THE INVENTION

[0001] The present invention relates to a device for forming tubular articles from powder material. More particularly, the present invention is directed to a device comprising an upper pressing punch, a lower punch, a core pin and a matrix having an inner periphery corresponding to the outer periphery of the upper and lower punch, a molding cavity being defined between the upper and lower punch, the core pin and the matrix, whereby the core pin is movable in relation to the matrix.

BACKGROUND OF THE INVENTION

[0002] A problem encountered when making tubular articles, such as bearing rings, by compacting powdered metal located in a mold cavity having a stationary bottom wall and stationary side walls is uneven compacting of the articles, especially if the height of the tubular article is large in comparison with the wall thickness. This is due to friction between the particles in the metal powder and the walls of the molding cavity during the compacting step so that a large part of the compacting energy is consumed as frictional heat, the result being that the compacted tubular article is more compacted in the parts lying nearest the pressing punch than in other parts.

[0003] EP-A1-0 450 784 discloses a device for forming cylindrical compacts. In this device all the components except the lower punch is moved with different travelling speeds during the compacting step, which leads to a complicated and expensive construction of the device.

SUMMARY OF THE INVENTION

[0004] An object of the present invention is to provide a device in which the compacting of the tubular articles is more even than in a device having a mold cavity with a stationary bottom wall and stationary side walls, and which device is of a simple construction.

[0005] According to one aspect, the present invention provides a device for forming tubular articles from powder material comprising an upper pressing punch, a lower punch, a core pin and a matrix having an inner periphery corresponding to an outer periphery of the upper and lower punch, a molding cavity being defined between the upper and lower punch, the core pin and the matrix, whereby the core pin is movable in relation to the matrix, wherein the upper pressing punch is arranged to actuate movement of the core pin or the matrix during compacting of a powder in the molding cavity so that the pressing punch and the core pin or the matrix move together.

[0006] In a preferred embodiment, the core pin is movable between a first position in which the upper end thereof is located in line with, or above, the upper wall of the matrix, and a second position in which the upper wall of the core pin is located below the upper wall of the matrix. The core pin can advantageously be biased against the first position. Furthermore, the upper pressing punch has in a first position a part of its lower wall in contact with the upper end wall of the core pin, so that the pressing punch will force the core pin to follow downwards movement thereof from its first position, and the upper pressing punch is preferably moveable upwards from its first position in order to open up the molding cavity for insertion of powder materials. The lower punch can advantageously be upwardly moveable in order to eject a compacted article from the molding cavity.

[0007] In another embodiment the core pin is an integral part of the upper pressing punch.

[0008] It is pointed out that the term “tubular articles” includes articles having various sectional shapes such as polygonal (e.g. - rectangular), circular, etc. The sectional shape can also be an open tubular shape (i.e. - with other shapes than circular), for example a U-shaped section.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The invention will now be further described with reference to the enclosed Figures, of which;

[0010] FIG. 1 is a schematic sectional view of a device according to a preferred embodiment of the invention, showing the device immediately before the pressing step, and

[0011] FIG. 2 is a view similar to FIG. 1, showing the device in the end of the pressing step.

DESCRIPTION OF EMBODIMENTS

[0012] The device in FIGS. 1 and 2 comprises a cylindrical core pin 1 and an annular matrix 2, which has an inner diameter that is larger than the diameter of the core pin 1 so that a cylindrical space is defined between the core pin and the matrix. A lower punch 3 having the form of a hollow cylinder is dimensioned to fit into the annular space between the core pin and the matrix and the upper wall of the lower punch 3 constitutes the bottom wall of a molding cavity 4. A work piece 5 of powder metal is disposed in this cavity in FIG. 1.

[0013] A pressing punch 6 having a cylindrical body with a diameter corresponding to the inner diameter of the matrix 2 is slidable within the inner cylindrical space defined by the matrix. The lower end surface 7 of the pressing punch has a central recess into which the upper end portion 8 of the core pin 1 is fitted.

[0014] According to the invention the core pin 1 is slidable within the lower punch 3 and is biased to a first position by a spring 9 disposed between the lower end surface of the core pin and an opening in the foundation. In the first position of the core pin its upper end surface is flush with the upper surface of the matrix 2 in order to facilitate removal of superfluous powder filled into the molding cavity. In FIG. 1, the core pin is disposed in its first position.

[0015] In FIG. 1 the pressing punch 6 is placed in a first position from which the step of compacting the work piece 5 takes place by pressing the punch 6 downwardly with a pressing force P. In the first position of the pressing punch, the surface of the central recess in its lower end surface 7 abuts the surface of the upper end portion 8 of the core pin and the side wall of the upper end portion 8 abuts the vertical wall of the recess in the lower end surface 7 of the pressing punch. The core pin is thus forced to follow downward movement of the pressing punch from its first position.

[0016] During the pressing step the pressing punch and the core pin will thus move together. Thereby, the friction forces created between the moving wall of the core pin and the particles in the powder material 5 disposed in the molding cavity 4 will have an opposite direction relative to the frictional forces created between the particles in the powder material and the stationary matrix wall. The friction forces created during the pressing step will thus balance each other and the powder material will be more evenly compacted throughout the height thereof.

[0017] In FIG. 2 the inventive device is shown in the end of the pressing step. The powder material in the molding cavity being compacted to an annular ring 10. The lower punch 3 is by some suitable means arranged to act as a knock-out punch after the pressure P on the pressing punch 6 has been released, so as to eject the finished ring 10 from the molding cavity. For example, hydraulic pistons disposed in the foundation under the lower punch 3 can be arranged push the lower punch 3 upwardly when actuated. Before the ring 10 is ejected the upper pressing punch 6 is moved upwards to a position above the position shown in FIG. 1 in order to facilitate removal of the ring 10 from the molding cavity 4.

[0018] It is not unusual that the device is used also for compacting powder material in the form of preshaped tubular articles or green bodies. The devices should therefore preferably be designed to facilitate insertion of such preformed articles into the molding cavity.

[0019] The described embodiment can of course be modified in several respects while remaining within the scope of the invention. For example, the pressing punch and the core pin can form an integral piece. However, such a structure makes the use of the device for preparatory or green compacts complicated and is therefore not preferred. Moreover, the pressing punch can have a totally flat lower end surface instead of the recess disclosed in the described embodiment. However, this is not preferred since the guiding of the core pin will then be decreased. Furthermore, the matrix can be arranged to move together with the pressing punch during the pressing step instead of the core pin, which in such an embodiment is stationary. The scope of invention should therefore be limited only of the wording of the enclosed patent claims.

[0020] While the present invention has been described by reference to the above-mentioned embodiments, certain modifications and variations will be evident to those of ordinary skill in the art. Therefore the present invention is to be limited only by the scope and spirit of the appended claims.

Claims

1. A device for forming tubular articles from powder material comprising an upper pressing punch, a lower punch, a core pin and a matrix having an inner periphery corresponding to an outer periphery of the upper and lower punch, a molding cavity being defined between the upper and lower punch, the core pin and the matrix, whereby the core pin is movable in relation to the matrix, wherein the upper pressing punch is arranged to actuate movement of the core pin or the matrix during compacting of a powder in the molding cavity so that the pressing punch and the core pin or the matrix move together.

2. The device according to claim 1, wherein the core pin is an integral part of the upper pressing punch.

3. The device according to claim 1, wherein the core pin is movable between a first position in which the upper end thereof is located in line with or above the upper wall of the matrix and a second position in which the upper wall of the core pin is located below the upper wall of the matrix.

4. The device according to claim 3, wherein the core pin is biased against the first position.

5. The device according to claim 3, wherein the upper pressing punch in the first position has a part of its lower wall in contact with the upper end wall of the core pin so that the pressing punch will force the core pin to follow downwards movement thereof from its first position, and that the upper pressing punch is moveable upwards from its first position in order to open the molding cavity (4) for insertion of powder material.

6. The device according to claim 1, wherein the lower punch is upwardly moveable in order to eject a compacted article from the molding cavity.