(A) study on thermal elasto-plastic analysis of stud-to-plate laser brazing

Abstract

A numerical thermo-mechanical model of materials in the region of laser brazing joint is presented. The proposed thermal and mechanical models of laser brazing are axisymmetric, in which the axis of joint geometry is coincident with the optical one of laser beams. The joining materials used were AISI Type 304 stainless steel stud and Al 5052 aluminium plate, and the alloy 88Al-12Si for the ring shaped filler metal. The source of heating used was the continuous wave $CO_2$ laser beam of a pseudo-$TM_{01}^*$ mode, which was optically modulated from the $TM_{00}$ mode produced in beam oscillator. The finite element models developed were to analyse the thermo-mechanical behaviour in stud-to-plate laser brazing. During laser brazing, the heat input by incident laser beams is fluxed through surfaces, and the materials undergo plastic deformation due to the thermal loading. To calculate the transient temperature fields in brazing joint, the non-linear heat transfer model was applied in which the effect of temperature-dependent thermal properties, latent heat, and the convection and radiation heat losses were considered. The numerical domains and thermal boundary conditions of workpieces in the brazing heat transfer model were defined based on the result of a real-time motion analysis of brazing process. By using axisymmetric thermal model, the characteristics of laser heating of dissimilar materials were simulated with variations of the degree of the beam defocussing and radial shift of the maximum flux in $TM_{01}^*$ mode. Of particular interests was the thermal imbalance in the region of brazing gap, caused by different rates of temperature rise in the materials involved. A three-dimensional model was also studied on the asymmetric heat transfer, such as due to eccentric alignments of the incident beams as well as the loss of materials adjacent to joint region. The non-linear mechanical analysis was also studied to calculate the transient displacement and stress fie...