Assessment of ignition risk in dry helical hole milling of AZ31 magnesium alloy considering the machining temperature and chip morphology

The helical hole milling process is gaining importance due to its capability to generate lower cutting forces and produce quality holes compared to the mechanical drilling process. However, high machining temperature coupled with the production of discontinuous particulate chips can amplify the risk of chip ignition and combustion. Therefore, the work addresses the risk of ignition during dry helical hole milling of AZ31 magnesium alloy by evaluating the machining temperature and chip morphology. The results showed that cutting speed highly influenced the machining temperature. In contrast, the rise in the machining temperature with tangential feed and the helical pitch was moderate. Lower machining temperatures can be accomplished by maintaining the cutting speed at 30 m/min, tangential feed at 0.02 mm/z, and axial pitch at 0.1 mm/rev. The investigation also revealed a high degree of dominance of helical milling variables on the chip morphology. The discontinuous cut at the peripheral edge produced short comma-shaped chips, while the chips were characterized as fragmented arc-shaped, conical, and ribbon-type chips at the front cutting edge. The free surface of the chips was marked by the presence of lamellar structures whose thickness increased with the chip size. Nevertheless, no burn marks were noted on the chip surface, even at higher machining temperatures. The results demonstrate that the risk of chip ignition resulting in fire hazards is relatively low, and the helical hole milling can be a sustainable alternative to the dry drilling process.