Patent ID: 7303714

Claim:
A manufacturing method of a cross member, which is configured to extend in a width direction of a vehicle body and which is configured to have both ends connected to side framework structures of the vehicle body, the method comprising the steps of: forming, from a material, a base frame extending in the width direction of the vehicle body by means of resinous molding, the base frame being formed to have a substantially circular or oval cross-section; forming a plurality of bosses on an outer circumferential surface of the base frame in different positions in an axial direction of the base frame within a limited range of the base frame and arranged so that each of the bosses is located in a different cross-section perpendicular to the axial direction of the base frame; forming a plurality of ribs on the outer circumferential surface of the base frame wherein each of the ribs is arranged so as to connect each of the bosses, and each of the ribs has a height lower than the bosses; accommodating the limited range of the base frame in a molding die wherein the bosses each having a height capable of contacting with the inner surface of the molding die when the molding die is closed; and forming reinforcing frame parts on the limited range of the base frame by means of insert-molding, by filling up a cavity between the outer circumferential surface of the base frame and the inner surface of the molding die with molten resin which is resinous material belonging to a same material system as the material of the base frame in a manner such that the molten resin flows between each of the plurality of bosses in the cavity and such that the molten resin flows along each of the plurality of ribs and the molten resin surmounts each of the ribs, thereby forming reinforcing frame parts integral with the base frame, the reinforcing frame parts being molded to have substantially circular or oval cross-sections whereby the base frame is covered with the reinforcing frame parts.