Micro Incremental Forming of a Herringbone Pattern for a Rotating Shaft Considering Elastic Recovery

摘要

High-precision micro-fluid dynamic bearings (FDB) are commonly used as bearings in electronic storage devices. The shape of the groove pattern of the herringbone type is a key factor in generation of pressure in a FDB. The formation of grooves in micro-fluid dynamic bearings is generally done by electrochemical micromachining involving etching or precision machining. In this paper, an incremental plastic forming technique is utilized to form radial grooves on the shaft in FDBs. Plastic forming results in high productivity and high quality of the manufactured parts with high cost efficiency as well. Because the depth of the groove is relatively low compared to the material diameter, incremental rolling is a feasible method. Issues to resolve when using the incremental forming process for micro-sized parts include spring-back of the formed material, die shape design issues, ensuring alignment between the dies, and proper process management. In this paper, the forming process for a herringbone pattern is conducted through finite element simulation and experimental verification processes. The investigated parameters in the analysis are the variation of the groove depth, the forming load, and the amount of the elastic recovery during the elasto-plastic micro-forming. The analysis results demonstrate that the groove is uniformly shaped with depth of 3 μm considering the elastic recovery while excluding the tip area. In addition, the simulation result coincides with the experimental result. This result reveals that the incremental forming process can be utilized to create herringbone patterns on bearing shafts.