The relationship between welding tip vibration amplitude and weld strength of 6-mm-thick and 10-mm-wide stainless steel specimens is shown in Fig. 5. The welding tip vibration amplitude is altered from 18 to 30 lm (peak-to-zero value). The static clamping pressure at the welding surface is 70 MPa and the welding time is maintained at 3.0 s. The maximum weld strength about 450 MPa is obtained under vibration amplitude 23 lm.