Stability of the friction stir welding process in presence of workpiece mating variations

This paper explores common process variations encountered in friction stir welding (FSW) and the limits to which acceptable joint strength is maintained while welding with a robotic FSW system. Part fit-up and mating variations are common in manufacturing, yet the limits to which a friction stir welding process can weld without major process adjustment are unclear. The effects on joint strength and mechanical properties of several of the most common mating variations (i.e., faying surface gap, misalignment, mismatch, etc.) are experimentally determined as individual effects as well as among common welding parameters. Experimental results on 5-mm-thick aluminum alloy 5083-H111 show that ultimate tensile strength, yield strength, and elongation begin to decrease from nominal weld conditions when either the tool offset distance from weld centerline or gap in abutted plates exceeds 25% of the average pin diameter (6?mm). In addition, vertical plate mismatch and lack of penetration can be tolerated up to 2.5% and 10%, respectively, before adverse effects on mechanical properties are observed. The work also indicates that of all the mating variations tested in this study, tool misalignment, followed by travel angle, has the most significant effect on the measured joint strength. Process stability testing has shown that the FSW process is able to endure part fit-up and mating variations within a defined tolerance, giving the practitioner an awareness of how well stock workpiece tolerances must be controlled before joint strength is adversely effected.