Abstract
Reliable and time efficient joining processes are crucial to cut down lead times and thus elevating the productivity of automotive manufacturing. In recent years, Refill Friction Spot Welding (Refill FSSW) due to its superior quality welds, emerged as a joining method pertinent for industrial applications. However, significantly longer cycle time traditionally falling in range of several seconds, has strenuously dormant the application of Refill FSSW. In this context, this study explored the optimum operating parameters of Refill FSSW for joining AA6016-T6 for producing weld joints with superior strength within an ultra-short cycle time. This research work investigated the feasibility of Refill FSSW, by conducting a systematic evaluation of processing parameters and their effects on weld strength using design of experiment. Analysis of Variance method was used to statistically analyse the effect of tool rotational speed and plunge depth on weld strength. Initially, the effect of process parameters on weld strength was gauged using lap shear tensile testing. Later on, fractured surfaces of the welds were observed under scanning electron microscope for assessing the failure mode and mechanism. Moreover, fatigue testing and dynamic tensile testing were also carried out to assess the reliability of the welds and joint response under impact loading. All the welds produced in this study met the lap shear strength criteria according to SAE standards for weld strength. The optimised parameters with an ultra-short cycle time of 0.7 s, yielded a joint strength of 4.9 kN, which was 40 % higher than the strength required by SAE standards. L-N curves for the 10%, 33.3%, 50 %, 66.7% and 99% reliability levels for the fatigue life indicated superior fatigue life at optimised weld parameters. Dynamic tensile testing results showed the welds produced in this study had a positive strain rate sensitivity up to 5%. In conclusion, this study established feasibility of Refill FSSW for producing superior quality welds within an ultra-short cycle time of less than 1 s. Thereby, a prospective viability of Refill FSSW to be used as joining method for automotive materials is demonstrated.
