Manufacturing method for fluid passage forming member made of synthetic resin

A manufacturing method for manufacturing a fluid passage forming member (1, 21) made of a synthetic resin by joining at least two passage members (1a through 1c, 21a through 21c) that are formed of a thermoplastic synthetic resin and have junction surfaces (2, 2) to be joined with each other, said method comprising the steps of:

• forming fluid passages composed of apertures (3, 23) or grooves (4, 24) in communication with each other between a pair of passage members in the junction surfaces (2, 2) between said passage members, allowing for shrinkage of the passages in advance so that fluid passages having predetermined design sections may be formed by shrinkage of said fluid passages during a heating and joining process of the pair of passage members;
• and
• closely fitting said passage members in a forming mold (10) with the passage members joined with each other at junction surfaces, sealing the mold while pressing the junction surfaces to be joined to each other into contact, and heating and softening them to join them by melting at said junction surfaces thereby effecting connection at the junction surfaces of said passage members,
• wherein, in joining said passage members, deformation of the passage members in a direction orthogonal to said junction surfaces is restrained by an inner surface of the sealed forming mold, and a flow component of a material produced due to expansion of the passage members caused by heating of the passage members and contact pressing of said junction surfaces is moved along a surface parallel to the junction surfaces thereby to absorb it mainly by shrinkage of said fluid passages, and
• wherein the passage members are formed using a methacrylic resin, and a heating temperature for joining said passage members is set at 110 to 130° C.