Optimal weld bead profiles in the conduction mode LBW of thin Ti–6Al–4V alloy sheets

<abstract> <p>Day by day laser welding (LW) is gaining industrial importance. Good quality of weld joints can be realized through this process. Because this process yields low distortion and small weld bead. Aerospace, nuclear, automotive, and biomedical industries are opting for the lightweight and corrosion resistance titanium alloys. This paper deals with the generation of optimal weld bead profiles in the conduction mode laser beam welding (LBW) of thin Ti–6Al–4V alloy sheets. Laser beam diameter, power and welding speed are the 3 LBW parameters, whereas, bead width, depth of penetration, heat affected zone and maximum temperature are the performance indicators (PIs). 3 levels are set for each LBW parameter. Taguchi's L₉ OA (orthogonal array) is selected to minimize the numerical simulations. ANSYS Fluent V16.0 with Vc++ code is used to develop a generic model. %Contribution of each process variable on the PIs is assessed performing ANOVA analysis. The range of PIs is assessed adopting the modified Taguchi approach. A set of optimal LBW parameters are identified considering a multi-objective optimization technique. For these optimal LBW parameters weld bead width is minimum, and the depth of penetration is maximum. Empirical relations for PIs are developed and validated with simulations. Utilizing the Taguchi's design of experiments, empirical relations are developed for the performance indicators in laser beam welding (LBW) simulations performing few trial runs and identified the optimal LBW process parameters.</p> </abstract>

A Study on the Effect of the Fatigue Life Due to the Processing of the Buttweld Specimens and the Fatigue Life Estimation Due to the Weld Zone Profiles for Railway Vehicle Structure

This study investigates the effects of the material properties and the fatigue behaviors in the SM490A material weld specimens, which are made by same method of railway vehicle structure, due to the heat-treatment and the grinding. In the fatigue behavior, the heat treatment affects the fatigue life. The S-N curves of both base metal specimens and butt weld specimens are reversed at some cycle by with or without heat treatment. The grindings on the beads make the fatigue limit decrease in the all specimens. But the reinforcement removed, the fatigue limit increases at the high cycle. Also, this study investigates the fatigue life estimation by examining butt weld bead profiles. The butt weld beads, which are welded by semi-robot method, have non-uniform bead profiles described by angle θ, radius ρ and height h. The stress concentration factors Kt, are changed by each different θ, ρ and h. In combination among θ, ρ and h, as θ becomes lower and ρ and h become higher, Kt increases. And the fatigue life for the AAY specimens can be estimated very closely using only butt weld bead profiles.