Effect of metallurgical parameters on the drilling and tapping characteristics of aluminum cast alloys

The present study was performed on an Al-6% Cu-0.7%Si alloy, and 319 and 356 alloys following different heat treatments. The main task was to evaluate the drilling and tapping characteristics of the Al-Cu alloy with respect to the Al-Si-based 319 and 356 alloys. The drilling work was carried out on a Huron K2X8five CNC machine at 15,000 rpm with continuous cooling to absorb the heat and to clean the holes from the chips formed during the drilling operation. The results show that the addition of Si coupled with T6 aging treatment produces the highest cutting forces (about 360 N) among the alloys studied (approximately 270 N) after 2500 holes. Considering the Al-Cu-based alloys, varying the aging treatment has practically no significant bearing on the cutting forces. Apparently, a high Cu content acts as a self-lubricant, facilitating the drilling process up to 2700 holes, with no sign of tool wear. However, due to the low level of Si in the Al-Cu-based alloy, built up edge (BUE) is more frequent, with conical chips, which would affect the precision of the size of the drilled hole. The chips are normally dull and characterized by their rough surfaces compared to those obtained from A356.0 alloy. Tapping of the drilled holes was carried out using Guhring 971 H6 M6 6HX- HSSE taps. The HT200-based alloys revealed excellent machinability with no sign of tool wearing after 2500 holes. In contrast, the tool failed after 1600 holes in the case of 356 alloy and 2160 holes for 319 alloy. Thus, it is concluded that the presence of 3.5% Cu in the 319 alloy helped in reducing the severity of wearing due to eutectic Si particles. However, the tapping forces reached 120 N prior to failure compared to about 75 N in the case of T200-based alloys.