Friction drilling of cast metals

This study investigates the friction drilling process, a nontraditional hole-making technique, for cast metals. In friction drilling, a rotating conical tool is applied to penetrate work-material and create a bushing in a single step without generating chip. The cast aluminum and magnesium alloys, two materials studied, are brittle compared to the ductile metal workpiece material used in previous friction drilling research. The technical challenge is to generate a cylindrical shaped bushing without significant radial fracture or petal formation. Two ideas of pre-heating the workpiece and high speed friction drilling are proposed. Effects of workpiece temperature, spindle speed, and feed rate on experimentally measured thrust force, torque, and bushing shape were analyzed. The thrust force and torque decreased and the bushing shape was improved with increased workpiece temperature. Varying spindle speed shows mixed results in bushing formation of two different work-materials. The energy, average power, and peak power required for friction drilling were calculated and analyzed to demonstrate quantitatively the benefits of workpiece pre-heating and high spindle speed in friction drilling.