STUDY THE EFFECTS OF THE MULTINITE COAT OF THE HIGH SPEED STEEL DRILL BIT IN DRILLING

Drilling is an important metal manufacturing processes. Drill bits are used in drilling to create holes. Wear of drill bits can have an adverse effect on the quality of the drilling hole. To increase the wear resistance of drill bits, surface modifications have been introduced and studied their effectiveness. Multinite coating is a candidate for surface modification techniques to increase wear resistance of the drill bits. In this study, the effect of multinite coating on the wear resistance of drill bits has been investigated. Two types of 6 mm diameters drill bits, the uncoated high speed steel, and the multinite coated high speed steel drill bits, were used to create the hole with 30 mm in depth on ASTM A36 steel. The drilling parameters were 1,100 rpm of rotation speed and 135 mm/min of the feed rate. The thrust force and the cutting torque during drilling were measured by a force sensor. Flank wear on the drill bits were measured by overlap image technique. Also, the roughness of hole surfaces were investigated. Results showed that the higher surface hardness of multinite coated high speed steel drill bit led to a lower flank wear rate at the beginning of drilling. Consequently, built-up of chip on the multinite coated high speed steel drill bit was less compared to the uncoated one. We conclude that the higher surface hardness of multinite coated high speed steel drill bit improves the wear resistance of drill bit by a decrease of wear rate at the beginning of drilling and a lesser amount of chip built-up on the cutting edge and the surface quality of hole after drilling.