A molding tool assembly, in particular for producing rotor blades of wind power plants, having a first mold shell (20) and a second mold shell (22) each for receiving one workpiece part, wherein the two mold shells in a proximal position face one another but do not bear on one another, having securing means for holding a workpiece part in at least one of the mold shells and having centering means for mutually centering the two mold shells in the proximal position or during convergence of the mold shells. The centering means and the securing means are mechanically intercoupled.