Heat transfer and fluid flow modelling of conduction mode CuOF-316L SS dissimilar laser welding

Abstract

Emerging novel technologies in the manufacturing industries require parts of dissimilar metals to be joined in order to harvest beneficial properties from both metals. Studies on joining metals with widely different physical properties such as Copper and Stainless Steel, are scarce due to processing complexities despite their high industrial demand. Laser welding has gained tremendous popularity in fusion welding domain due to its inherent advantages of superior weld quality at higher processing rates. Various mathematical models were developed in the past to obtain insight of the physical process behind laser welding. The majority of these work focuses on similar welding models and a handful of work is done in the area of dissimilar laser welding. Most of the developed dissimilar welding models are conduction heat transfer based models with stationary power input and thus lack proper representation of actual physical phenomena. The present work focuses on developing a 3-D steady state heat transfer and fluid flow model of conduction mode dissimilar laser welding with a moving heat source using Control Volume method. This model is based on numerical solution of mass, momentum and energy conservation equation in the weld pool while incorporating both conduction and convective heat transfer physics. The developed model was validated using welding data of pure Copper and Nickel from literature which showed a remarkable similarity with available literature results. The validated model was then utilised to gain insight of the evolution of temperature and velocity fields inside weld pool of Oxygen free copper (CuOF) with 316L Stainless Steel. Parametric study of three critical welding parameters i.e. welding speed, laser beam radius, and laser power input was carried out on weld pool geometry. The results were also used to conduct a dimensionless analysis to understand the dominant heat transfer mode and various driving forces inside the weld pool. The parametric study implied that weld pool geometry grows proportionally with increasing laser power while reduces at high welding speed and larger laser beam radius. However, the optimisation of all three parameters will result in desirable weld geometry. It was also evident from the dimensional analysis that convection heat transfer and surface tension forces are dominant inside the weld pool. The developed model is reliable to predict the weld pool geometry, temperature and velocity fields of not only dissimilar laser welding but also for similar welding. Transient calculation addition and temperature dependence of physical properties will be a valuable future scope for this developed model.