mould where the cast material is allowed or caused to harden into a casting whose form is defined by the form of the mould cavity which is enclosed in the mould the casting operation may be put into effect such that a clear and sharp interface between the different casting materials is achieved or alternatively the casting operation may be put into effect so that a certain intermingling of the two casting materials takes place in an interface zone in the casting operation so that a sharply defined interface occurs the first cast part of the tool is allowed to harden so far that no intermingling of the casting materials occurs alternatively use may be made of a tool part which is cast in a separate process or which has been recovered and recycled from at old obsolete tool and which in the heated state 600 750 u00b0 c is inserted in a mould where an additional tool part is cast or in the casting so that an interface zone is formed between the tool parts the hardening and cooling of the first cast tool part is allowed to continued only so far that a limited intermingling of the cast materials can take place or that a certain remelt of the already cast tool part can take place the positive.