Process for producing metal parts

Details Process for producing metal parts Process for producing metal parts

1989-10-04

1990-11-06

Seidel, Richard K.

Metal founding

Process

Shaping liquid metal against a forming surface

164120, B22D 1802

Patent

active

049678264

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to a process for producing metal parts in accordance with the principle of squeeze, or forge, casting approximately the amount of liquid metal required for one part being introduced into a permanent mold and being displaced therein by means of an upper die with the part to be produced being formed.
2. Prior Art
Such processes have numerous advantages because of the combination of casting and pressing, reported on by J. R. Franklin and A. A. Das in "Squeeze casting--a review of the status", British Foundryman", No. 3, 1977, 1984, pages 150 to 152. In principle, these processes provide for the liquid metal, once introduced into the usually preheated permanent mold, to undergo a slight cooling before the upper die is introduced. During this process the liquid metal is displaced, any solidification thereof in the mold being avoided until the final forming of the part is complete. The lowering-in pressure is then maintained while the liquid metal solidifies, after which the upper die is withdrawn and the part removed from the mold. Maintenance of the pressure during solidification allows good filling of the mold while avoiding shrinkage or blowholes and gas pockets. However, the structure does not differ substantially from the cast structure.


BRIEF SUMMARY OF THE INVENTION

Taking this as a starting point, the invention is based on the object of further developing the process based on this generic type such that parts having the properties of forged parts can be produced. In particular, these parts are not only to have a good dimensional stability and dense structure but at the same time are to be characterized by the transformation of the cast structure into a forged structure which is characteristic of forging. Compared with a forging process, however, the structure is to be denser and a considerable reduction in the process time is to be achieved.
This object is achieved in the invention by the process wherein a permanent mold lower die having a mold cavity and a movable upper die having a part insertable into the cavity are provided, a deformable seal is positioned on a flanged surface of the lower die surrounding the mold cavity and effectively increasing the depth thereof, liquid metal is introduced into the cavity in an amount sufficient for forming one metal part but only partially filling the mold cavity below the flange and seal, the insertable part of the upper die is inserted into the mold cavity to displace the liquid metal to fill the cavity substantially to the height of the seal, the liquid metal is allowed to at least partially solidify and pressure is applied so the upper die can deform the metal to the final shape and deform and spread the seal. Compared with a conventional forging process, in which the starting point is a cast, solidified and then re-heated workpiece, there is the advantage that a completely dense structure is arrived at. Unlike the principle of squeeze casting taken as a generic basis, there is the advantage of arriving at a structure which has a forged texture and which consequently makes possible a high degree of mechanical strength in the part produced. The dimensional stability is also improved, particularly in that the hot-plastic metal is subjected to reshaping.
The seal which is provided neither in squeeze casting nor in the conventional forging process must allow an expansion in respect of the strength of the permanent mold and of the upper die and in respect of the pressures and temperatures used, such that the structure is reliably compressed. Thus copper or a copper alloy proves particularly advantageous for this purpose. If, for example, workpieces of an aluminum forging alloy are to be produced, the material used for the permanent mold and the upper die is a known heat-resistant steel.
In accordance with this example, the metal to be processed, the permanent mold with the upper die and the seal must each be matched to one another from the point of view of their material, so that the

REFERENCES:
patent: 2233057 (1941-02-01), Luce
patent: 2716792 (1955-09-01), Kroyer

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