Tapping-free sintering process for internal thread of MIM product

Abstract

The invention discloses a tapping-free sintering process for an internal thread of an MIM product. The process comprises the following steps (1) preparation of a POM screw mould core: calculating thedimension of the POM screw mould core according to dimension of the internal thread of the MIM product and shrinking percentage of a POM material and manufacturing the POM screw mould core according to corresponding dimension; (2) preparation of an MIM injection molding blank: first, injecting metal powder and a binder to a cavity filled with the POM screw mould core, and then heating and meltingthe POM screw mould core to prepare the MIM injection molding blank with an internal threaded hole; (3) degreasing: degreasing the MIM injection molding blank with the internal threaded hole by usinga catalytic degreasing technology; (4) degreasing the MIM injection molding blank with the internal threaded hole by adopting a vacuum sintering technology; and (5) carrying out inspection. The process not only can solve the problems that the tapping cost is high, the service life of a screw tap is short and tapping is forgotten as the hardness of the sintered product is high thoroughly, but alsocan improve the percent of pass of the product greatly. A reworking condition is avoided.

Description

technical field [0001] The invention belongs to the technical field of powder metallurgy, and in particular relates to a tapping-free sintering process for internal threads of MIM products. Background technique [0002] MIM is a molding method that injects a plasticized mixture of metal powder and its binder into the model. The process steps are to select the metal powder and binder that meet the requirements, and then use an appropriate method at a certain temperature. The powder and binder are mixed into a uniform feed material, and then injected into a semi-finished product through a mold after granulation. The obtained semi-finished product is degreased, sintered, and then undergoes subsequent shaping, drilling and heat treatment to obtain the final product. The MIM products prepared by the above method have the advantages of uniform structure, high density, smooth product surface and high dimensional accuracy. People usually use MIM technology to make thin parts with co...

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Problems solved by technology

The MIM products prepared by the above method have the advantages of uniform structure, high density, product surface finish, and high dimensional accuracy. People usually use MIM technology to make thin parts with complex structures and small volumes.

However, it is inevitable that the products made by MIM technology will need to process threaded holes. In the existing technology, the processing of threaded holes is generally carried out after the product is sintered. When processing threaded holes in this way, due to The hardness of the product after sintering is relatively high. When taps are used for tapping, the taps are relatively easy to deform, which not only cannot guarantee the accuracy of tapping, but also results in a low pass rate of the product, and there is also the problem of missed tapping, which seriously affects the tap. Although some manufacturers also process the internal thread on the injection molded blank before degreasing and sintering, and then degrease and sinter, but due to the inability to better control and master the degreasing and sintering technology, it still leads to sintering. The deformation of the internal thread is serious, which cannot meet the needs of use, and the qualified rate of its products is low

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