Investigation of dimensional accuracy and chip formation on peck drilling of mild steel

Abstract

Drilling process is the most important machining process in the manufacturing industries. Almost all mild steel industries and production are based on drilling process. However, the difficulty of the mild steel machining process is due to the high ductility resulting excessive heat generation at high cutting temperature. A higher cutting temperature was attributed to the high cutting velocity such as feed and depth which affected dimensional accuracy, surface finish and the tool life. In this study, AISI 1018 mild steel had been drilled using 6 mm uncoated high speed steel (HSS) under various cutting speed at a constant feedrate. The dimensional accuracy and chip formation were analysed under the selected cutting speed at constant feedrate of 0.15 mm/min and depth of cut of 30 mm. In this study, the lowest cutting speed of 7.54 m/min imparted the highest dimensional accuracy meanwhile the highest cutting speed of 9.42 m/min resulted in lowest dimensional accuracy. At medium cutting speed of 8.48 m/min, a better dimensional accuracy was observed than highest cutting speed. As a result, diameter errors increase as the increasing of cutting speed due to the higher vibration, affecting the diameter error. Furthermore, the chip formation in new tool produce the spiral shape while worn tool produces excessive string chips during drilling process at cutting speed of 9.42 m/min. According to the results, the best dimensional accuracy occur at the lowest cutting speed and better chip formation are produced on new tool.