Metal founding – Process – With measuring – testing – inspecting – or condition determination
Patent
1995-08-14
1997-05-20
Batten, Jr., J. Reed
Metal founding
Process
With measuring, testing, inspecting, or condition determination
164 711, 164113, 164900, B22D 1708, B22D 1732, B22D 2300
Patent
active
056304668
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a process for shaping metal materials in a semi-solid state by means of pressure die casting or forging.
DESCRIPTION OF RELATED ART
The shaping of thixotropic metal products, particularly alloys containing iron, copper or aluminum, in a semi-solid state has been known for about twenty years. French Patent 2141979, corresponding to U.S. Pat. No. 3,948,650 to MIT, was the first to describe a process for casting thixotropic metal, the process consisting of raising the temperature of the alloy until it attained a liquid state, cooling to bring about partial solidification, and vigorously agitating the liquid-solid mixture in order to break up the dendrites and transform them into roughly spherical globules in at least 2/3 of the initial composition.
Thixotropic metal reheated to a semi-solid state handles like a solid during its reheating and its transfer to the shaping machine, but behaves like a homogeneous viscous liquid during shaping.
The processes for manufacturing articles in a semi-solid state have advantages over the standard processes: lower shaping energy and faster cooling, which results in reduced shrinkage, higher rates of production, and less wear and tear on tools and dies. These processes generally include the following steps: primary phase of partially or totally globular structure, by means of mechanical or electromagnetic stirring. production cycle in making the articles; corresponds to the desired viscosity. This reheating can be achieved by means of radiation or induction; pressure die casting machine); critical points of the process. If the metal has a viscosity which is too high, it does not flow like a homogeneous liquid during the shaping, and the articles produced have internal defects. If, on the contrary, the viscosity is too low, the blank can no longer be handled like a solid, part of the metal runs off and is lost, and the feeding of the shaping machine is disturbed. structure gets to the ideal globular structure in which all the dendrites have degenerated into perfectly spherical globules, the more the viscosity decreases; the more the viscosity decreases; increased, the more the viscosity decreases. geometry of the article, so that the desired viscosity must be obtained by means of an adequate combination of the degree of globularity and the liquid fraction.
On the other hand, this viscosity must be reproducible from one shaping cycle to the next, so as to guarantee the reproducibility of the article itself, and thus its quality.
The reheating of the blank plays a decisive role in this reproducibility insofar as it conditions both the liquid fraction proportion and the degree of globularity of the solid fraction during the maintenance of the semi-solid state, as shown in the thesis by W. Loue, entitled "Evolution microstructurale et comportement rheologique d'alliages aluminium-silicium a l'etat semi-solide"["Microstructural evolution and rheological properties of aluminum-silicon alloys in a semi-solid state"], National Polytechnic Institute of Grenoble, October, 1992.
The problem posed thus consists of finding a simple and reliable means to permanently assure a constant viscosity for the reheated blank, which will be introduced into the injection molding machine or forging press, by affecting the regulation of the reheating.
Various solutions have been proposed to assure this regulation. Casting in Semi Liquid State," published in Die Casting World, October 1992, R. Moschini describes a process which consists of directly measuring the temperature of the blank for the few seconds during which it is transferred from the reheating furnace to the injection molding machine with the aid of a fast-reading thermocouple connected to a manipulator. If the temperature measured is outside a pre-established range, the blank is rerouted in order to prevent its entering the machine at an inadequate temperature.
This method has various drawbacks, both in principle and in its practical application. On one hand, a constant temperature does n
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patent: 4569218 (1986-02-01), Baker et al.
patent: 5040589 (1991-08-01), Bradley et al.
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Patent Abstracts of Japan vol. 18, No. 23 (M-1541) 14. Jan. 1994 & JP 5-261 503 (Honda Motor Co. Ltd) Published Oct 12, 1993.
Renzo Moschini "Manufacture of Automotive Components by Semi-Liquid Process", Metallurgical Science and Technology, vol. 9 (3), Dec. 1996.
Garat Michel
Loue Willem
Aluminium Pechiney
Batten, Jr. J. Reed
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