This study deals with shoulder cutting phenomena in micro-end-milling of hardened die steel. Demand for micro-end-milling for products in the medical, optical, and electronics industry is increasing. However, in machining with a small diameter end mill that has diameter of e.g., 0.5 mm, the rigidity of the tool itself is low; therefore, cutting conditions must be set to low values to achieve stable machining. We revealed that cutting phenomena became unstable because the end cutting edge was damaged early in shoulder cutting. Therefore, we experimentally prepared a left hand helical tool with a right hand cut to perform complete processing by improving the strength of the end cutting edge. Cutting experiments were carried out while measuring cutting force and observing cutting phenomena, end cutting edge, and machined surface via scanning electron microscopy (SEM). We determined the effects of such tools on fundamental phenomena in shoulder cutting with a small diameter end mill. The rake angle of the tool was improved based on experimental analysis of the damage mechanism of the cutting edge in the shoulder cutting. A result of the examination to investigate the influence of the difference in rake angle on chip evacuation showed that the chip discharge direction was affected by the rake angle; when the angle is blunt, the chips were discharged upward, and the chip discharge performance improved.

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