Enhancing stiffness and flexural properties of dissimilar friction stir welding between 3D-Printed PLA/TiO 2 and PEEK/CNT nanocomposites: parametric optimization using Taguchi method

Abstract This paper presents a comprehensive parametric analysis and optimization of friction stir welding (FSW) for dissimilar joining of additively manufactured nanocomposites: polylactic acid reinforced with TiO 2 nanoparticles (PLA/TiO 2 ) and polyether ether ketone reinforced with carbon nanotubes (PEEK/CNT). The main focus is to evaluate the effects of welding parameters – rotation speed, traverse speed, and tool tilt angle – on the flexural strength and elastic modulus of the welded joints. The experiments were designed using the Taguchi method, and the grey relational analysis (GRA) technique was used to determine the optimal conditions for maximizing both flexural strength and elastic modulus. Signal to noise (S/N) analysis revealed that rotation speed exerts the most significant influence on both flexural strength and elastic modulus, followed by traverse speed. The optimal parameter combination was 1,500 rpm rotation speed, 10 mm/s traverse speed, and 2° tilt angle, under which elastic modulus and flexural strength improved by 11 % and 32 %, respectively. Under these optimized settings, the welded joint achieved 80 % of the elastic modulus and 75 % of the flexural strength of the weaker base nanocomposite (PLA/TiO 2 ). Microstructural analysis confirmed that adequate heat input at 1,500 rpm promoted smooth flow lines and a dense, defect-free interface, while excessive speed (2,000 rpm) induced void formation and particle detachment. This research conclusively demonstrates that FSW is a viable and effective technique for producing high-performance hybrid joints between biodegradable PLA-based and high-strength PEEK-based nanocomposites, with significant potential for advanced biomedical and structural engineering applications requiring tailored stiffness and bending resistance.