A mold assembly for forming a wax pattern in the shape of a golf club head includes a plurality of outer molds coupled together to defined a cavity and an inclined tunnel therein, with a plurality mold cores received in the cavity and a supporting member received in the inclined tunnel, in order to form a wax pattern which has an opening formed in an inclined front face thereof. Furthermore, both the tunnel and a parting plane between the mold cores make such a compensatory angle with horizontal surfaces of the outer molds that the opening of the wax pattern may be delimited by a peripheral wall perpendicular to a front face of the wax pattern.