Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Making composite or hollow article
Patent
1990-11-29
1991-10-29
Lechert, Jr., Stephen J.
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Making composite or hollow article
419 10, 419 23, 419 39, 419 47, 2281736, B22F 700
Patent
active
050614398
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for the manufacture of dimensionally precise pieces which are at least in part made of a sintered material which, before the sintering, comprises a mixture of at least three pulverous constituents, of which the first is primarily of a metal of the iron group and with a maximum particle size of approx. 150 .mu.m, the second constituent contains copper and/or phosphorus, with a maximum particle size of approx. 150 .mu.m, and the third constituent contains at least copper. The invention relates in particular to the manufacture of forming tools by using at least in some phase the sintering method according to the invention
The manufacture of forming tools has traditionally been both difficult and time-consuming, and therefore they have been relatively expensive. This is due to the fact that, when such tools are manufactured in large sizes, they must be made manually with high precision, in which case the manufacture as a rule starts with one steel piece into which the required cavities and holes are machined. This steel piece will then serve as both the frame and the mold surface against which the final product's metal part to be formed, such as a sheet, is formed by pressing.
It is also known to form sheet material by making a die from some material easier to form and thereafter to introduce, by means of a rubber diaphragm or the like, fluid pressure on one side of the metal sheet while the die is on the other side, and thus to press the sheet into the form of the die, as depicted in, for example U.S. Pat. No. 3,021,803. The advantage of this method is that in this case no prefabricated upper tool is needed for forming the sheet, since the pressure automatically adapts to the shape of the die. U.S. Pat. No. 3,996,019 discloses a further development of this method, by means of which different sheets and parts can to some extent be joined or laminated. These methods have the disadvantage that, when an easily machined material is used as the die, the production runs must be relatively short and the sheet to be worked on relatively thin, since such a die does not withstand the great force required for a thick sheet and since the die wears out and/or becomes damaged when the number of items is high.
It is known that relatively strong and complex pieces have been manufactured by molten-phase sintering, in which case different pulverous constituents are mixed, whereafter the mixture is fed into a mold and compacted either by vibrating and/or compressing before the mixture is heated so that one of the constituents melts and binds the other constituents together. In this case, through the capillary effect, the melt fills the spaces between the powder particles and, when solidifying, binds them together. The sintering itself can take place either under a very high pressure or under atmospheric pressure. This manufacturing method is not at all applicable to short production runs or to the manufacture of individual products, since the compression and/or vibrating of the powder requires strong and precise molds in order that the piece can be made so dense that it can withstand its removal from the mold and its sintering treatment as a detached piece. In addition, the pieces sintered tend to shrink during the sintering, which results in that the pieces need to be given a finishing treatment.
Mainly for the manufacture of magnetic pieces, in which what is desired is dimensionally precise products without the necessity of machining them after the sintering, powder mixtures have been developed by using which the shrinkage during sintering of a piece fed into a mold and compressed into a compact state in the mold can be diminished or eliminated. Such mixtures have been disclosed, for example, in publications SE-414 191, SE-372 293, EP-11 989 and JP-57-233041. Because of the magnetic properties, the objective in these magnetic mixtures is a relatively high phosphorus content, which increases the tendency of the material to shrink. It is noted in these publications that the adding of copper incr
REFERENCES:
patent: 3779717 (1973-12-01), Gustison
patent: 3957508 (1976-05-01), Davies et al.
patent: 4838936 (1989-06-01), Akechi
patent: 4971755 (1990-11-01), Kawano et al.
Nyrhila Olli J.
Syrjala Seppo O.
Aktiebolaget Electrolux
Lechert Jr. Stephen J.
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