The impact of process parameters and pin-to-shoulder ratio in FSW of polycarbonate: welding forces and critical quality indicators

Abstract

Friction stir welding (FSW) as a welding process for polymers is growing steadily, owing to its inheren1t advantages. The developed forces during the joining process are sensitive to the parameters used and affect the quality of the weld in terms of voids and defect formation. This study focuses on the analysis of the effects of four FSW parameters on the developed forces in joining polycarbonate (PC) 4 mm thick sheets. The porosity of the produced seams was investigated with micro-computed tomography. The dimensional deviation (top surface retreat) was also assessed with the same method. The produced seams were further inspected with microscopy. A Taguchi L9 array was formed. Analysis of variances provided prediction models for the developed forces, the porosity, the dimensional deviation, and the welding resistance rate (Fx/Fz), which were the response metrics of the study. The model’s reliability was evaluated with a confirmation run. Low travel and high rotational speeds reduce the forces in the process and lead to higher mechanical performance. Low travel speeds also reduce the porosity of the weld and affect its dimensional accuracy. The overall results offer valuable insights for optimizing the performance of FSW welds in PC sheets, which was the aim of the study (reduced porosity, dimensional deviation, etc.). The developed models ensure their successful application in real-world scenarios. Finally, the findings and the analysis were correlated with the mechanical strength of the welded PC sheets, revealing, and interpreting the mechanisms leading to higher mechanical performance of the samples. Graphical abstract