Performance evaluation method for cutting fluids using cutting force in micro-feed end milling

A simplified evaluation method for cutting fluids has not been established to accurately estimate cutting performance. In this study, the friction coefficients of cutting fluids were calculated from the cutting force in micro feed end milling, defined as mu-MFM for the cutting performance index. For cutting conditions in which the finished surface roughness exceeded a largely theoretical value and the feed marks were hardly recognized, there was a high correlation between mu-MFM and the finished surface roughness in end milling of AISI 1045 compared with results from conventional friction tests. Moreover, the finished surface roughness in turning AISI 1045 and AISI 440C also increased with mu-MFM. The finished surface roughness in turning AISI 1045 and AISI 440C showed nearly theoretical values regardless of the cutting fluids when the cutting speed exceeded a certain speed. However, even if the cutting speed was high, the cutting edge transcription error on the finished surface in low-feed turning conditions increased with decreasing mu-MFM. It was possible that the difference in cutting edge biting performance for work material in cutting fluids had a substantial influence on the cutting edge transcription error for small uncut chip thicknesses on the finished surface formation area, such as the low-feed rate in turning. Therefore, cutting edge biting performance was evaluated using the cutting force instability rate CFIR, which was the quantitative value of the drifting cutting force in one end milling cutting with the feed rate based on the maximum uncut chip thickness on the finished surface formation area of the low-feed turning. As a result, the cutting edge transcription error in turning of AISI 1045 and AISI 440C under low-feed cutting conditions increased with CFIR. Therefore, there was a correlation between the CFIR and the cutting edge transcription error in turning at low-feed conditions.