The surfaces of the steels which are used in the sheet metal forming moulds produced for the automotive industry and which include carbon in a low amount up to 0.35% by ratio can be hardened manually through induction surface hardening method. The effects of heat treatment parameters on surface hardness in the hardening of the surfaces of workpieces made of 1.2333 cast tool steel often used in the production of sheet metal bending moulds and EN-JS 2070 spheroidal graphite cast iron using a robot-controlled induction system developed were investigated in this study. Workpiece material, heat treatment/hardening temperature, and feed rate were selected as the control factors and experiments were conducted according to L18 Taguchi orthogonal array. As a result of the experimental study, the most effective parameters on surface hardness were the interaction between workpiece material and treatment heat (36.193%), feed rate (33.92%) and treatment heat (12.655%) respectively. Under all heat treatment conditions, the surface hardness of the 1.2333 (G59CrMoV185) material was obtained higher. By reducing the feed rate it has been concluded that surface hardness of both materials are increased. Depending on increasing application temperature while surface hardness value decreased for EN-JS 2070 material, increased for 1.2333 material. Moreover, a predictive quadratic equation was developed to predict the surface hardness values under the selected conditions and the correlation coefficient of this equation was calculated as R-2=0.81.