Experimental study of different cooling conditions in drilling magnesium alloy

Magnesium alloy is a lightweight material with high strength to weight ratio, making it great potential as a structural material in automation industries. Magnesium alloys are generally characterized as having good machinability, but the risk of chip ignition and build-up edges (BUE) formation still prevents it from being alternative to conventional materials. Several machining conditions are selected to investigate its machining performance in order to overcome this drawback. Thus, MQL condition using pure castor oil and chill air condition using vortex tube are selected to study drilling performance of magnesium alloy AZ91 which is then compared with dry machining. The drilling process is conducted at a cutting speed of 70 m/min and feed rate of 0.3 mm/rev. The drilling performance is evaluated based on the tool wear by measuring the flank wear using Stereo Microscopy Image Analyzer and surface roughness, Ra is measured using Accretech Handysurf E-35 as well as Coordinate Measuring Machine (CMM) for the dimensional accuracy. The result shows that chill air condition produced the best results by obtaining the lowest tool wear at 0.075 mm and the lowest surface roughness, Ra of 0.62393 µm compared to other machining conditions. As for hole diameter, MQL condition has produced the lowest dimensional deviation of 0.282 mm for the nominal diameter of 6mm. Overall, chill air condition is recommended as the most suitable machining condition in drilling of magnesium due to the reduced BUE formation to produce better hole and tool life.