Grain size effect on the assembly quality of micro-scaled barrel formed by microforming

Abstract

In this research, a method employing micro-extrusion was designed to produce the micro-scaled barrel-shaped parts with complex geometrical features to study the feasibility of the proposed microforming method and its grain size effect on the formability of the complicated internal features in terms of deformation behavior, material evolution, accuracy of dimensions and final components quality. The results reveal that the deformation behavior is highly affected by grain size and becomes unpredictable with increased grain size. In addition, assembly parameters including feature dimension, tolerance and coaxiality also vary with grain size, and the variation of grain size needs to be accommodated by different assembly types, viz., clearance fit or transition fit. From the microstructural evolution aspect, it was identified there were two dead zones and four shear bands, and the formation of these deformation zones was barely affected by the variation in grain size. Though bulges, cracks, and fracture induced voids were observed on the surface of the final components, tailoring the microstructure of the working material with finer grains could significantly avoid these defects. This study advances the understanding of forming microparts by extrusion processes and provides guidance for microforming of similar microparts.

Keywords

Microformed part / Size effect / Extrusion / Microstructural evolution / Dimensions / Assembly accuracy

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Funding

National Natural Science Foundation of China http://dx.doi.org/10.13039/501100001809(51835011); The Hong Kong Polytechnic University(ZE1W); General Research Fund of Hong Kong Government(15223520)