Failure mode analysis of micro machine gears and the limitation of micronization

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The reliability of the gearing for micro machine becomes quite low, when its design is worked out according to the conventional method load carrying capacity of gears. To clarify the cause of this phenomena, the reliability test of gears of module 0.1 to 1.0 mm and the theoretical investigation for that have been carried out and the following results are revealed :1.The influence of manufacturing error and alignment error on the gear reliability becomes considerably stronger, when the module of gears becomes small. The unavoidable misalignment of gear mounting in the device is main cause of it. The method of evaluation of that effect is proposed.2.Contaminants that exist in the lubricating oil of micro-gears damage tooth flanks by meshing-in. For microgears, the increase of tooth roof fillet stress is very large in comparison with the state for gears of moderate module. The damage of tooth flank itself does not so strongly increase the state of contact stress of tooth flank of micro-gear as the case of root stress.3.The probable meshing-in of contaminants between tooth crest and mating back tooth flank and that between back side tooth flanks at the beginning of tooth meshing induces sufficiently strong increase of tooth bending stress.4.Chemical compound layr such as white layr by nitriding or oxidized layr by quenching will be separated-off from the tooth flank during the operation. This will deteriorate the tooth flank form of micro-gears badly to reduce the load capacity of gears. The separation of such layr is a big cause of existence of contaminants in lubricant that has also bad influence to reduce the load capacity of gears as mentioned above.