Abstract
The absorptivity of a material is a major uncertainty in numerical simulations of laser welding and additive manufacturing, and its value is often calibrated through trial-and-error exercises. This adversely affects the capability of numerical simulations when predicting the process behaviour and can eventually hinder the exploitation of fully digitised manufacturing processes, which is a goal of “industry 4.0”. In the present work, an enhanced absorption model that takes into account the effects of laser characteristics, incident angle, surface temperature, and material composition is utilised to predict internal heat and fluid flow in laser melting of stainless steel 316L. Employing such an absorption model is physically more realistic than assuming a constant absorptivity and can reduce the costs associated with calibrating an appropriate value. High-fidelity three-dimensional numerical simulations were performed using both variable and constant absorptivity models and the predictions compared with experimental data. The results of the present work unravel the crucial effect of absorptivity on the physics of internal flow in laser material processing. The difference between melt-pool shapes obtained using fibre and CO2 laser sources is explained, and factors affecting the local energy absorption are discussed.
Highlights
Laser-beam melting of metallic substrates forms the basis of many advanced fusion-based manufacturing processes (such as laser welding, laser cladding, laser metal deposition (LMD), and selective laser melting (SLM)) and has brought new perspectives on advancement of materials processing and manufacturing of high-integrity products
For cases in batch 1 and 2, the power density is too low to cause significant vaporisation and surface deformations are small compared to the melt-pool depth
The influence of laser characteristics on internal molten metal flow in laser-beam melting of a metallic substrate was investigated numerically using a high-fidelity three-dimensional model
Summary
Laser-beam melting of metallic substrates forms the basis of many advanced fusion-based manufacturing processes (such as laser welding, laser cladding, laser metal deposition (LMD), and selective laser melting (SLM)) and has brought new perspectives on advancement of materials processing and manufacturing of high-integrity products. Successful adoption of simulation-based approaches for process development and optimisation relies predominantly on adequate modelling of various physical phenomena that occur during laser melting (e.g. laser-matter interaction, heat and fluid flow, and solid-liquid phase transformation) [6]. There seems to be an important bi-directional coupling between laser powerdensity distribution and melt-pool behaviour Neglecting such effects in numerical simulations of laser-beam melting can negatively affect the quality of numerical predictions of thermal fields, microstructures and properties of the product [8,14]. Assumptions made to develop a computational model may necessitate the incorporation of unphysical tuning parameters to obtain agreement between numerical and experimental data [8,15] This can reduce the model reliability for design-space explorations since a change in process parameters or material properties may require recalibrating the tuning parameters [16,17]. Understanding the influence of such assumptions on numerical predictions is essential and can guide the modelling efforts to enhance the current numerical simulations
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