Butt-joint welding process of PVC Profiles: Numerical modelling, experimental validation and insights into material behaviour and flow dynamics

Polyvinyl chloride (PVC) forming operations are typified by large deformations, free-surface condition, complex conjugate heat transfer, and intricate contact phenomena. This study focuses on numerical modelling of the forming process that occurs beneath the butt-joint welding of polymeric profiles to offer a comprehensive understanding of how process parameters and boundary conditions influence the final weld. Numerical simulations are based on arbitrary and coupled Lagrangian and Eulerian models, which incorporate viscoelasticity, heat transfer, external forces, and free-surface flow. Due to the extensive temperature range encountered during the process, during heating the material transitions from a linear elastic state to a low-viscosity fluid. Consequently, the model has been developed to simultaneously solve for both solid and free-surface fluid conditions, and PVC has been modelled as a temperature-dependent viscoelastic solid, exhibiting Newtonian-like fluid characteristics under high temperatures. The proposed numerical solution methodology is employed to offer insights into the physics of the butt-welding process, widely utilised within industry. Two distinct configurations have been modelled to study material flow during the process: with and without a rigid constrain that prevents the material from moving freely upwards. These simulations aim to illuminate the impact of boundary conditions and physical constraints on the welding process and material behaviour.