The formation mechanism of the weld metal is divided into several strands through the split hole and reassembled in the weld chamber. Due to the existence of the diverter bridge, the rigid bottom of the metal flow is inevitably formed at the bottom of the bridge, so that the metal atom diffusion and binding speed is relatively slow. Tissue density decreased. Therefore, the use of split-flow composite die extrusion will inevitably exist; but a good weld can make the profile after surface treatment to avoid such phenomena as black belt. To ensure the quality of the weld, the metal in the weld of the weld chamber must be fully diffused and bonded. Otherwise, loose, coarse particles and other parts of the structure will be uneven. Therefore, the degree of deformation must be larger, especially the welding room The amount of metal deformation is large to form a large hydrostatic pressure.