Mold manufacturing method

A mold manufacturing method comprising:

• kneading casting sand and a binder, filling flasks therewith, performing compression so that curing occurs in the flasks, and performing removal from the flasks, to make sand blocks;
• performing a cutting step;
• and performing a mold matching step, to manufacture a sand mold, wherein
• the mold manufacturing method is performed with
• a machining head configured to be operated by a robot to cut the sand blocks and cut upper and lower molds,
• a gripping arm configured to be operated by a robot to grip the upper mold and perform matching between mold matching surfaces, of the upper and lower molds, in which cavities are formed, and
• a coordinate measurement sensor configured to detect a coordinate through contact, with a detection piece, of at least the upper mold gripped by the gripping arm,
• side surfaces of the sand mold have such slopes as to, as opposed surfaces, get closer to each other as the side surfaces get closer to the mold matching surfaces,
• gripping surfaces of the gripping arm also have same slopes as those of the side surfaces of the sand mold,
• a Z axis for defining Z coordinates extends in an up-down direction,
• the cutting step includes
• forming, through cutting, the mold matching surfaces in the respective upper and lower molds by the machining head and
• forming, through cutting, the cavities in the respective upper and lower molds by the machining head with the mold matching surfaces being references, and
• the mold matching step includes
• measuring at least three points that are not located on a same straight line and that are located on the mold matching surface of the lower mold placed on a placement surface,
• causing recognition of Z coordinates of these respective points,
• measuring at least three points that are not located on a same straight line and that are located on the mold matching surface in the upper mold gripped by bringing the gripping surfaces of the gripping arm into contact with the side surfaces,
• causing recognition of Z coordinates of these respective points, and
• subsequently performing mold matching by the gripping arm with the mold matching surfaces of the upper and lower molds being oriented to be kept parallel to each other.