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A set of MIM gears is required to transmit the oscillating movement to the rotating bristles of an electric toothbrush. MIM allows the part to be made to a consistent high quality at a relatively low cost. The complex shape and tight specification of dimensional tolerances makes it an ideal candidate for metal injection moulding. Special requirements are: (1) corrosion resistance against the whole range of tooth pastes which have pH values ranging from 4 to 10; (2) resistance to abrasion by the polishing ingredients.
These requirements led to the choice of the austenitic stainless steel 316L (17Cr, 13Ni, 2Mo). Dimensional tolerances between ISO 9 and 10 are achieved, and a production rate equivalent to 30,000 parts per day is required.
MIM allows the part to be made to a consistent high quality at a relatively low cost.