Influence of welding parameters on morphology and mechanical performance of friction spot pressure welded thin monomer cast nylon 6 sheets

In this paper, 1-mm-thickness monomer cast nylon 6 sheets were joined under the pressure and the frictional heat generated between the pinless tool and thin stainless steel plates, which was named friction spot pressure welding technology. Influences of welding parameters on spot weld diameter, morphology, and mechanical performance were investigated. Results showed that incomplete interfacial bonding was observed under insufficient plunge depth. Increased rotational speed, plunge depth, and dwell time caused severer extrusion ring and reticular cracks on the joint surface. Material overheating occurred under rotational speed of 1000 rpm and material adhesion on the back of steel plate happened under plunge depth of 0.25 mm. The weld-bonded area diameter increased with larger welding parameters, but the corresponding joint fracture loads increased and then decreased. Four failure modes including lap interface tearing (IT), upper sheet fracture (UF), outer bonding area separation (BS), and the mixed UF and BS were observed. Spot welds failed with UF possessed the maximum tensile load while joints fractured with IT showed low performance. Three different morphologies were observed on the fracture surface of the IT joints while the fracture surfaces of the joints failed with other fracture modes showed elongated strips and flocculent structures.