The effects of spin friction pressure and time on the friction welding between parts of the same material and different materials are discussed. The heat-affected zone is divided into three regions: the plasticized region (Zpl), the partly plasticized region (Zpd), and the undeformed region (Zud). The tensile fracture morphology has three sections: the non-plasticized central section (Fud), the plasticized peripheral section (Fpl), and the partly plasticized section between Fud and Fpl (Fpd). Friction pressure (spinning timing): 0.784 Mpa (6 seconds), 0.981 MPa (8 seconds and 10 seconds) in PMMA-PMMA welding, 0.588 Mpa (10 seconds) in PVC-PVC welding, and 15.7 MPa (15 seconds) in PMMA-PVC welding attains better bonding strength, because these parts have larger Fpd and Fpl regions, which have no Fud in the central part.