In order to execute computer calculations with temperature dependent physical parameters: λ, cp, ρ, a and pulsed heat input q(t), the algebraic expression will be transformed. For this purpose we will use calculations in Mathcad programme [1]. This application is very useful for modelling and simulation of welding thermal process. Finally, the specifications of sub-procedures: Stab_time, last, calculation of roots ri, λ(T), a(T) and q(t) are presented.