1994-03-01

Enhanced Machinability of P/M Parts Through Microstructure Control 940357

As the geometric complexity and tolerance requirements of powder metal parts become more demanding added machining operations are required as a necessary step in the manufacturing process. Likewise, a better understanding of the effects powder metal materials and processes have on the machinability of P/M components is needed.
An investigation into the effects of post-sintering cooling rate on the microstructure, machinability and tensile properties of an FC-0208 copper steel was conducted. Machinability was measured using a drill test on a high volume production component. Three cooling rates (9, 17 and 40 ° C/minute) were used to generate the variation in microstructure. Machinability analysis was performed using box-and-whisker plots and includes drill motor load, hole size on drill entry and exit, and microfinish. Metallography and tensile properties and a discussion of their relationship with machinability are included.
Results indicate that the above mentioned cooling rates can produce a measurable difference in microstructure, machinability and tensile performance. A slow cooling rate can be employed to improve the machinability of this material. However, a substantial decrease in tensile properties results. Therefore, care must be taken to properly control the microstructure to optimize both machinability and mechanical properties for the application of interest.

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