A method for producing moulds or cores for foundry purposes by means of adapting the specific electrical resistance of the material of the tool insert to the specific electrical resistance of a mixture of at least one moulding material, in particular, foundry sand, and at least one water-containing inorganic binder that can be cured by means of heat and that has an electrical conductivity of at least 5 · 10 -3 S/m, - at least one tool insert made of an electrically conductive material for holding the mixture being introduced into an electrically non-conductive housing, the electrical conductivity of the material at an operating temperature between 150 and 180 °C at least approximately corresponding to the specific electrical conductivity of the mixture at a temperature between approximately 100 °C and 130 °C, - electrical energy and thus heat being supplied to the tool insert via electrodes that are arranged in parallel in/on the housing, which leads to the curing of the mixture, - the housing being made of at least two housing parts (4, 5), which are moved together or apart from each other at the beginning and upon completion of the cycle process of the mould or core production and forming a direct contact surface, - holes for ejection pins in the tool, at least one electrode, as well as at least at least a part (4, 5) of the housing being provided for removing the sand core, - both the tool and the electrodes as well as at least a part of the housing (4, 5) being porous and/or ventilation slits being provided, and - the mould(s) or the core(s) (2, 2') being pressed out of the tool and removed by means of ejection pins after the curing of the mixture and once the housing parts (4, 5) have been moved apart from each other, characterised in that a material for tool inserts is used, which has the following characteristics: - it is a sintered solid body which - has a Mohs hardness of more than 4, - the specific electrical resistance of the material being between 0.5 ohmmeters and 200 ohmmeters at an operating temperature of 150 °C to 180 °C, and - the heat conductivity being at least 0.56 W/(m*K). - at least one tool insert made of an electrically conductive material for holding the mixture being introduced into an electrically non-conductive housing, the electrical conductivity of the material at an operating temperature between 150 and 180 °C at least approximately corresponding to the specific electrical conductivity of the mixture at a temperature between approximately 100 °C and 130 °C, - electrical energy and thus heat being supplied to the tool insert via electrodes that are arranged in parallel in/on the housing, which leads to the curing of the mixture, - the housing being made of at least two housing parts (4, 5), which are moved together or apart from each other at the beginning and upon completion of the cycle process of the mould or core production and forming a direct contact surface, - holes for ejection pins in the tool, at least one electrode, as well as at least at least a part (4, 5) of the housing being provided for removing the sand core, - both the tool and the electrodes as well as at least a part of the housing (4, 5) being porous and/or ventilation slits being provided, and - the mould(s) or the core(s) (2, 2') being pressed out of the tool and removed by means of ejection pins after the curing of the mixture and once the housing parts (4, 5) have been moved apart from each other, - it is a sintered solid body which - has a Mohs hardness of more than 4, - the specific electrical resistance of the material being between 0.5 ohmmeters and 200 ohmmeters at an operating temperature of 150 °C to 180 °C, and - the heat conductivity being at least 0.56 W/(m*K).