Positioning welding method and positioning welding clamp for precise multi-joint four-way pipe

The invention discloses a positioning welding method and a positioning welding clamp for a precise multi-joint four-way pipe. The positioning welding clamp comprises a bottom plate, fixing blocks, pressing blocks, guide positioning pins, pressing screws, first screws, positioning pins and second screws. The fixing blocks are installed on the bottom plate through the second screws and the positioning pins, a machined long pipe fitting is horizontally installed in round holes which are formed by third semicircular grooves and first semicircular grooves and have the inner diameter of phi D, and one ends of short pipe fittings are vertically installed in a through hole which is formed in the long pipe fitting and has the inner diameter of phi D1. The positions with the outer diameter of phi D2 of the short pipe fittings are arranged in round holes which have the inner diameter of phi D2 and are formed by fourth semicircular grooves and second semicircular grooves, and welding can be conducted by aligning the fixi