Characterization of laser spot welds for high-speed electrical motors

Abstract

This thesis explores the characteristics of laser spot welded joints in thin-sheet stacks of synchronous reluctance motors (SynRM) rotors. Since electrical motors do not directly rely on fossil fuels, they are considered a major technology for sustainable energy solutions. Synchronous reluctance motors operate without the need for permanent magnet, eliminating their dependency on rare-earth materials. These characteristics enhance their suitability for sustainable approach and further optimization. Laminated structure is typically a standard practice in electrical motor design and construction. This thesis investigated laser spot welding as a novel method of joining dissimilar thin sheet materials, where a stainless steel (316L) supporting layer was sandwiched between two ferromagnetic thin sheets of mild steel (340LA). Laser core power, ring power and interaction time were considered the main parameters of laser welding. The Taguchi method was used for the design of experiments, core power was kept constant, where ring power was changed at four levels and interaction time at two levels. This study evaluated the effects of these parameters on laser spot welds (LSW) protrusion, mechanical strength and failure mode.

All spot protrusion from surface were measured utilizing a laser profilometer. Despite controlled weld parameters, spot protrusion exhibited significant variability with occasional outliers. The tensile-shear test indicated that higher laser power and interaction time led to a significant increase in maximum force and strain values, indicating enhanced mechanical strength of LSWs. The failure mode transitioned from shear at lower laser power to tensile at higher laser power. The cross-section evaluation demonstrated a general upward trend in the average interfacial area between thin sheet layers.