Isotropic finishing removes surface asperities whilst maintaining the integrity of the residual compressive layer. The process is also designed to leave some of the valleys from the peened or machined finish for vital lubricant retention.
Improvements in surface finish allow for the lubricant film to remain coherent, thus reducing friction, lubricant temperature and ultimately resulting in reduced power loss and enhanced performance and life from the transmission.
Isotropic finishing is a technique of final machining in a controlled and gentle manner to reduce surface finish using oxalic acids and non-abrasive finishing stones to remove surface asperities. The oxalic acids oxidise the surface which causes the asperities to be more susceptible to micro honing, with the result that the most positive or peak surface areas are progressively removed.
After a predetermined time the chemical phase ceases as the final flushing and burnishing phase gradually halts the oxide formation and produces a bright mirror like smooth surface. The specially formulated chemical solution does not etch, erode the surface or attack the grain structure of the material. It does however, reduce processing time making it feasible for high production volume components.
The isotropic finishing stones are selected to span machine lay and therefore cutting of the negative (valleys) surface areas are avoided enabling beneficial lubricant retention.
Many gear designs are limited by pitting fatigue as the critical factor for load considerations. The C.A.S.E.™ superfinishing process has proved effective in improving resistance to macro-pitting and micro-pitting of gears because the improved surface finish allows contact loading to be distributed over more surface area reducing contract stress and extending pitting fatigue life.
Go to: Applications | The shot peening process
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