Influence of heat input on welding induced distortion for Yb-fibre laser welded thin sheets

Abstract

Distortion is often in a welded thin structure as it possesses extremely low stiffness. In present work, the influence of heat input on the welding induced distortion is studied. Heat input is a crucial parameter that develops driving force, i.e., tendon force for the alteration of distortion in the welded structure. Furthermore, the relationship between effective stress and associated distortion with plastic strain generation is also explained. The fiber laser welding of the AISI 304 steel sheets are performed with different heat input and evolved distortions are estimated by coordinate measuring machine (CMM). Moreover, the sequential coupled thermo-mechanical analysis is carried out to predict longitudinal shrinkage and transverse deflection by Using ABAQUS software and validated with the experimental result. It is revealed that the pattern of deformation for all weldments is found to be similar, as illustrated by the experimental result. However, magnitude is varied to some extent. Joint fabricated at the lowest heat input (60 J/mm) exhibits minimal plastic strain generation accomplished by low temperature gradient. Minimization of thermal gradient caused relatively lower Von-Mises stress which results in minimum longitudinal and transverse deformation. Thermal expansion and contraction in the weld zone create inhomogeneity and high thermal gradient with the outer part of weldments due to which elastic and plastic strain generation takes place at temperature agitated region. However, elastic strain releases at the cooling stage, but plastic strain remains within structure permanently. This permanent strain produces residual stress components in a different direction, which results in effective stress, i.e. Von-Mises stress. Additionally, to compensate the generated stress and maintain equilibrium between the welded region and farther away region, distortion in different directions arise in the welded structure.