Micro-screws can be defined by their outer diameter of generally less than 1 mm. They are manufactured by head forging and thread rolling processes. In this study, the thread rolling process was numerically analyzed for a micro-screw with a diameter and pitch of 0.8 and 0.2 mm, respectively. Through finite element (FE) analysis, the effects of two design parameters (die gap and chamfer height) on the dimensional accuracy were investigated. Three combinations of chamfer heights were chosen first and the corresponding die gap candidates selected by geometric calculation. FE analyses were performed for each combination and their results indicated that the concave chamfer height should be less than 0.3 mm, while a 10 ?m difference in the die gap might cause degeneration in dimensional accuracy. These results conclude that ultra-high accuracy is required in die fabrication and assemblies to ensure dimensional accuracy in micro-screw manufacturing.

Recent trends to reduce the size of mobile electronics products have driven miniaturization of various components, including screw parts for assembling components. Considering that the size reduction of screws may degenerate their joining capabilities, the size reduction should not be limited to the thread region but should be extended to its head region. The screw head is usually manufactured by forging in which a profiled punch presses a billet so that plastic deformation occurs to form the desired shape. In this study, finite element (FE) analysis was performed to simulate the forging process of a subminiature screw; a screw head of 1.7 mm diameter is formed out of a 0.82 mm diameter billet. The FE analysis result indicates that this severe forging condition leads to a generation of folding defects. FE analyses were further performed to find appropriate punch design parameters that minimize the amount of folding defects.