G1301-1-5 鉄系粉末を用いたグリーン加工(生産加工・工作機械一般)

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The powder forming process is advantageous for near net shape manufacturing when compared with metal casting and metal forming processes. However, because of an increasing demand for formed parts with more complex shapes in recent years, some material removal processes are necessary for formed parts, including sintered mechanical parts produced by powder forming, despite its superiority in near net shape manufacturing. As such, machinability is also becoming an important factor for powder forming. The metal removal process used for powder metallurgy parts is usually applied to sintered compacts. However, a removal process for the powder compact prior to sintering (referred to as "green compacts"), which is known as green machining, has been attracting attention lately. Since the mechanical strengths of green compacts are markedly lower than that of sintered parts, the cutting force required for green compacts is much lower than that required for normal sintered parts even in difficult-to-cut-materials. Furthermore, because the chips from green machining are considerably smaller than those from sintered parts, the removal of chips from the holes of the drilled parts is much easier in case of green compacts. This provides a strong advantage when producing parts containing holes, such as hydraulic components, which must be totally free of chips. On the other hand, the relatively low mechanical strengths of green compacts, compared with sintered compacts, are disadvantageous in the chucking to cutting machine of the green parts, because they are harder to clamp in place (chuck). In order for green machining to gain full acceptance, it is necessary that sintered parts produced by this method have the same mechanical strength as sintered parts produced by conventional sinter machining. In the present study, we compared the mechanical strength of a cylindrical compact formed from ferrous powder, which was drilled and then sintered, with the mechanical strength of a part that was sintered and then drilled to produce the same shape. The mechanical strength was evaluated according to the radial crushing strength test (JIS-Z-2507). The result was as follows : (1) The mechanical strength of the test piece produced by green machining and then sintered was no different from that of the test piece produced by machining after sintering (2) The torque required during the drilling process of green machining was approximately 30% of what was required for drilling after sintering, and the thrust in the same comparison was approximately 40%.