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

按齿轮承载能力的常规方法设计微机械齿轮传动时，其可靠性很低。为了弄清产生这一现象的原因，对0.1 ~ 1.0 mm模数齿轮进行了可靠性试验并进行了理论研究，得出以下结论：齿轮模数越小，加工误差和对中误差对齿轮可靠性的影响越大。装置中不可避免的齿轮安装不对中是其产生的主要原因。提出了评价这种效应的方法。微齿轮润滑油中存在的污染物通过啮合破坏齿侧。对于微型齿轮，齿顶圆角应力的增加比中等模数齿轮的状态大得多。齿面本身的损伤对微齿轮齿面接触应力状态的增加不像齿根应力那样强烈。3 .齿顶与配合后齿翼之间以及齿侧后齿翼之间的污染物在齿啮合开始时可能的啮合导致了足够强的齿弯应力增加。在操作过程中，会从齿面分离出化学化合物层，如氮化后的白层或淬火后的氧化层。这将严重恶化微齿轮的齿面形态，降低齿轮的承载能力。这一层的分离是润滑油中污染物存在的一个重要原因，也对上述齿轮的承载能力降低有不良影响。

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.