Metal working – Method of mechanical manufacture – Utilizing transitory attached element or associated separate...
Patent
1989-01-30
1991-10-08
Gorski, Joseph M.
Metal working
Method of mechanical manufacture
Utilizing transitory attached element or associated separate...
295276, 29424, 228156, B23P 1700
Patent
active
050541846
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The process and the apparatus in accordance with the present invention concern hot shaping by plastic deformation of metal alloys by means of a pressing tool.
This process and apparatus concern in particular metal alloys which have a high level of resistance to deformation at elevated temperatures, in association with a low degree of ductility. They also concern metal alloys which have a relatively low level of resistance to deformation at the shaping temperature but which after shaping have numerous surface flaws which are harmful from the point of view of subsequent use thereof.
DESCRIPTION OF THE RELATED ART
The method of extrusion is known, which permits a large number of metals or metal alloys to be shaped by means of a pressing tool.
That method is known to consist of subjecting a billet formed by a metal or metal alloy and disposed in a container, also referred to as the pressing pot, to the thrust force of a pressing piston, with the billet having been preheated to the desired temperature. By virtue of a sufficient pushing force, the billet is extruded through a die which is connected to the end of the container. Bars are produced by the extrusion of solid billets. It is also possible to effect extrusion of hollow billets, that is to say billets which have a hole passing entirely therethrough. That situation involves using a piston provided with a needle or mandrel which engages into the hole in the billet and into the die. As in the case of a solid billet, it is possible to extrude the hollow billet which has been suitably preheated by virtue of a sufficient thrust force so as to cause flow thereof by plastic deformation between the needle or mandrel and the die, in the form of a tube.
It is also known that it is possible to effect an expansion operation prior to extrusion of a hollow billet. The aim of that expansion operation, which is also performed by hot shaping using a pressing tool, is to increase the diameter of the hole without a major loss of material prior to the extrusion operation. For that purpose the hollow billet which is preheated to a suitable temperature is disposed in a container without a die and a needle or mandrel which is of a larger diameter than the hole in the billet is pushed into the hole by the pressing piston. That results in an increase in the diameter of the hole and in most cases an increase in the length of the billet, the outside diameter of which is limited by virtue of that of the container. The billet is therefore driven back in the opposite direction to the direction of displacement of the needle or mandrel.
The extrusion operation and also the expansion operation if included are effected at temperatures which depend on the characteristics of the metals or metal alloys used. In the case of refractory or stainless steels, and other refractory alloys, the shaping temperature range exhibits a lower limit which in most cases is of the order of 900.degree. C., both in regard to extrusion and expansion. Glasses are almost exclusively used as a lubricant, the composition of the glasses being adjusted so that they present the appropriate degree of viscosity, in the temperature range in which extrusion or expansion of a given metal alloy is to be effected.
Although glass-base lubricants thus permit a very large number of metals or metal alloys to be extruded, there are however metal alloys including stainless or refractory steels which remain unsuitable for hot shaping under those conditions. They are metal alloys forming part of the category comprising at least one base component belonging to the group including Fe, Ni, Co and Mo, the hot shaping of which, under the conditions which have just been defined, remains very difficult. Among such metal alloys, mention may be made of refractory alloys and in particular those comprising substantial additions of elements such as chromium and tungsten. Any major plastic deformation of the latter alloys, by extrusion or expansion, is accompanied by the formation of cracks which are often deep an
REFERENCES:
patent: 3160951 (1964-12-01), Markert et al.
patent: 3350907 (1967-11-01), McDonald et al.
patent: 3584368 (1971-06-01), Sargent, Jr.
patent: 3657804 (1972-04-01), Krock et al.
Gorski Joseph M.
Hughes S. Thomas
Valinox
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