Critical Feed/Tooth Value Providing Finest Machined Roughness by Peripheral Cutting with Micro Endmills

Abstract

This study concerns the rational determination of machining conditions for micro endmills that are less than 1.0mm in diameter. The characteristics of machined surface roughness are measured according to machining conditions, especially the feed per tooth Sz. The machined surfaces conditions are also observed with SEM. From the experiments, the following are made clear: (1) The feed per tooth Sz at the critical value Szc makes machined surface roughness the finest. (2) The conditions of Sz larger than Szc make cutting marks regular, that is, stable cutting can be done under those conditions, and then, the roughness improves according to decreasing Sz. (3) The conditions of Sz smaller than Szc cause irregular machined surfaces including pileups and diggings, that is, cutting becomes unstable conditions. The excessively thin chip-thickness prevents from stably engaging edge on workpiece surface. (4) Although the values of Szc are independent from the type of machine tools and cutting speeds, the values decrease according to decrease in tool diameter. (5) The value of Szc increases when tool has worn over its limit. Therefore, in order to determine machining conditions rationally, the changing behavior of Szc should be understood according to tool wear.