The demand for micro-end-milling for products in fields such as the medical, optical, and electronics industry is increasing. However, when machining with a small diameter end-mill (micro-end-mill) with diameters such as 0.5 mm, the rigidity of the tool itself is low; hence, the cutting conditions must be set to low values to achieve stable machining. Therefore, we examined various cutting phenomena that occur during actual machining processes to achieve high machining accuracy, high finished-surface quality, and long tool life. Some studies on micromachining achieved high accuracy, high-grade machining by considering the cutting phenomena. In previous papers, we dealt with the side-cutting phenomena in micro-end-milling of hardened die steels using a high-speed air-turbine spindle with rolling bearing. Cutting experiments were carried out by measuring the cutting force and flank wear of a cutting tool to investigate the difference in cutting phenomena caused by cutting direction in high-speed micro-end-milling. Observation of the machined surface and measurement of the profile of the cutting edge and machined surface were demonstrated. It was revealed that machining quality in high-speed up-cut milling was better than that in down-cut milling. Shoulder cutting, in which both peripheral and bottom cutting edges act simultaneously on the workpiece, was also investigated. A novel small diameter end-mill with left-hand helical tool with right-hand cut was developed to avoid damaging the cutting edge in the initial cutting stage. In the present study, high-quality shoulder cutting of a vertical wall using the new tool was proposed and demonstrated.

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