Abstract
In welding, the depth of penetration, weld profile and the corresponding thermal cycle are the three basic outcomes that a user wishes to control flexibly. In laser welding applications, controlled application of power and energy density is the key to achieve predictable control of these characteristics. Creation of an analytical model is an important step towards understanding the underpinning science of laser metal interaction in controlling the depth, bead geometry and thereby temperature profile of a weld. The “power factor model”, which correlates the power applied per unit length to the laser metal interaction time, has been originally developed and validated for mild steel, guides a user on the selection laser system parameters, to achieve specific weld profile. This study is performed to extend the power factor–interaction time model to aluminium alloys by understanding the underpinning laser aluminium interaction parameters in terms of power density, interaction time, specific point energy and their correlation with the weld bead profiles. Although the power factor and interaction time showed a rectangular hyperbolic relationship, as observed in low carbon steel, for a specific weld depth and profile, the absolute magnitude and the characteristic profile of the curve is different due to the intrinsic differences in physical and thermal properties of aluminium as compared to steel. It was shown that identical depth of penetration but different weld metal profile can be obtained for a specific beam diameter for a range of power and travel speed by keeping the energy input per unit length constant.
Highlights
Joining processes and procedures, using laser as power source is undergoing rapid development with new applications, extend to new materials and new joint design
The results suggested that the power density and the specific point energy control the depth of penetration whilst the interaction time controls the weld width
There is a strong correlation between power density and specific point energy for different values of depth of penetration
Summary
Joining processes and procedures, using laser as power source is undergoing rapid development with new applications, extend to new materials and new joint design. The size and shape of the beam (axial [7] and radial [8]) associated with different combinations of power and travel speed generate different power and energy density and the overall energy application within the laser spot These parameters affect the flow dynamics of the weld pool during the process [9] and have a direct influence on the final weld seam, including the depth of penetration, which is one of the main outputs that users wish to control. For a specific penetration depth, the weld profiles can be widely different which would alter the heat-affected zone dimension and in turn the mechanical properties of the graded structure This gives the desired flexibility in laser joining; a complete understanding of the interaction between laser and the substrate alloy is vital to exploit the flexibility in joint formation. An analytical model would enable understanding the laser–alloy interaction for aluminium and develop the necessary underpinning understanding to transfer processing parameters to achieve similar results using different laser systems
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