Analysis of size effect on flow-induced defect in micro-scaled forming process

In microforming process, flow-induced defects caused by the irrational material flow in forming process have a significant effect on the quality of micro-formed part. In design of micropart and microforming process, this type of defects needs to be analyzed and the formation mechanism identified, such that the defects can be predicted and avoided via the rational design of micro-formed parts and microforming process. To address this issue, the size effect affected flow, and deformation behaviors need to be investigated. To explore how the size effects affect the flow-induced defects, experimental studies on the influence of a few significant parameters including geometry and grain sizes on the degree of flow-induced defects in microforming process of pure copper were conducted in this research. The flow-induced defects in microforming of a designed part are investigated, and the microstructure and flow pattern in micro-scaled extrusion of the parts with complicated shape are also studied. Based on the experimental results, the formation of folding defects is mainly affected by geometry size. The folding defect-free deformation occurs in the cases with coarse grains such that the parts with coarse grains do not have flow-induced defects, but some grains are broken and become potential insecurity factor. Furthermore, the relationship between grain and geometry sizes under which the flow-induced defects and grain broken can be successfully and simultaneously avoided is identified.