Grinding

Grinding of P/M parts can be very complex, especially when materials are low in density because in many cases preservation of surface integrity is essential. Usually, surface porosity decreases during grinding. A large amount of the generated powder chips is forced into pores, and many chips are welded due to the high temperature at the wheel/workpiece interface. When grinding is necessary to achieve dimensional functionality of a part, and surface porosity needs to be preserved, special processes such as ultrasonic or solvent cleaning are applied immediately after grinding. For rough applications, a downfeed of 0.025 to 0.075 mm (0.0010 to 0.003 in.) is recommended, while for finish passes, a maximum of 0.013 mm (0.0005 in.) should be used.

Stock removal rates should be either the same as or less than those used in finish turning of cast iron; wheels should be similar. It is important to keep a plentiful supply of coolant (containing an inhibitor) directed onto the wheel and the work to maintain a clean grinding wheel contact.

Grinding of P/M Tool Steels. The relative grindability of several conventional and P/M high-speed tool steels is illustrated in Fig. 11. The grinding ratio (volume of metal removal to the volume of wheel worn, as explained in the article "Principles of Grinding" in Machining, Volume 16, ASM Handbook) is clearly superior for the P/M tool steels. As expected, the grinding ratios generally decrease for both the conventional and the P/M tool steels as their alloy and carbon contents increase. The grinding conditions suggested for the CPM tool steels are similar to those recommended for conventional tool steels in the article "Machining of Tool Steels" in Machining, Volume 16, ASM Handbook. Some specific conditions for grinding CPM 10V are given in Table 3.

Table 3 Grinding recommendations for CPM 10V cold-work tool steel

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