In this study a CNC controlled three axis vertical machining centre with maximum spindle speed of 12000 rpm has been utilized for welding purpose and the welding is performed on Aluminium 2024 alloy plate in butt joint configuration. The size of aluminium 2024 alloy plate utilized for welding is 4 mm thickness, 100 mm length and 60 mm width and its chemical composition is given in Table 1. In order to fabricate welding tool, H13 tool steel, hardened to 60HRC through heat treatment process, is used. Welding tool consists of a shoulder with 6 concave profile and a straight cylindrical pin with threads engraved over it. Welding tools have been fabricated by varying size of shoulder diameter and pin diameter to study its effects on surface defect formation. Fig. 1(a) demonstrates the welding tool fabricated with different shoulder diameter and pin diameter. Along with tool geometry, tool rotation speed and welding speed are varied accordingly to investigate their effects on defect formation. Table 2 shows the input parameters and their values considered for conducting experiments. For considered parameters, number of experiments to be conducted is large; hence to reduce number of experimental trials, design of experiment technique is adopted. Taguchi L27 orthogonal array has been constructed which is given in Table 3 and experiments are conducted according to it.