A laser welding has been used for manufacturing a composite product which comprises a plurality of resin parts.
JP-2002-248688A shows that one resin part with a convex portion is welded to the other resin part by a laser beam, while the convex portion is pressed to the other resin part. JP-2003-19752A shows that one resin part is press-inserted to the other resin part receiving a laser beam so that two resin parts are welded together.
However, in JP-2002-248688A, since an end surface of the convex portion and a contacting surface of the other resin part have surface roughness, some clearances are not avoidable therebetween. Due to these clearances, the resin parts are not well welded to generate voids in a welded contacting portion, so that the strength and air-tightness of the welded contacting surface are deteriorated.
In JP-2003-19752A, when the resin part has a complicated shape or when the insert amount is small, some clearances are generated between contacting surfaces of two resin parts, whereby the resin parts are not well welded to generate voids in a welded contacting surface, so that the strength and air-tightness of the welded contacting surface are deteriorated. Even if the shape of the resin parts is simplified and the insert amount is made large, some cracks may be arisen in the resin parts.