Secondary Operations

Secondary operations, discussed in more detail elsewhere in this Volume, must also be considered in process planning and control. Their relation with quality process control are briefly discussed below.

Heat Treat. As with sintering, baseline heat treating parameters are generally established based on the part material and the end use. Parameters are established during the initial sampling procedure, and adjustments from these settings are kept to a minimum to ensure consistent material properties.

Restrike. Whether the part is being re-pressed (densified), coined, or sized, the primary factor to producing good parts is the tool design. As with the design of compacting tools, the sizes may have to be factored to take into account subsequent processing that may change dimensions.

Plating. With powdered metal parts, virtually any of the commonly applied platings can be utilized. The primary difference between plating noncopper-infiltrated P/M versus wrought materials is that typically the parts first must be resin impregnated to fill the porosity before the application of the plating. Copper infiltration generally fills enough of the porosity to eliminate the need for resin impregnation.

Machining. A great many powdered metal alloys are readily machinable. The primary difference between P/M versus wrought is that P/M machining is actually a series of interrupted cuts, due to its inherent porosity. Speeds, feeds, and coolant parameters are different, but overall throughput and process control philosophy is similar to the machining of non-P/M metals.

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