Abstract
Selective laser melting (SLM) produces a near-net-shaped product by scanning a concentrated high-power laser beam over a thin layer of metal powder to melt and solidify it. During the SLM process, the material temperature cyclically and sharply rises and falls. Thermal analyses using the finite element method help to understand such a complex thermal history to affect the microstructure, material properties, and performance. This paper proposes a novel calibration strategy for the heat source model to validate the thermal analysis. First, in-situ temperature measurement by high-speed thermography was conducted for the absorptivity calibration. Then, the accurate simulation error was defined by processing the cross-sectional bead shape images by the experimental observations and simulations. In order to minimize the error, the optimal shape parameters of the heat source model were efficiently found by using Bayesian optimization. Bayesian optimization allowed us to find the optimal parameters with an error of less than 4% within 50 iterations of the thermal simulations. It demonstrated that our novel calibration strategy with Bayesian optimization can be effective to improve the accuracy of predicting the temperature field during the SLM process and to save the computational costs for the heat source model optimization.
Highlights
Selective laser melting (SLM), which is classified into a powder bed fusion type in additive manufacturing methods, produces a near-net-shaped product by scanning a concentrated high-power laser beam on a thin layer of metal powder to melt and solidify it
The cyclic process of spreading a thin layer of powder and scanning the laser beam is repeated until the product is completed in the form designed by computer-aided design (CAD) software
This paper proposes a novel calibration strategy for the heat source model of the finite element method (FEM)-based thermal analysis in the SLM process
Summary
Selective laser melting (SLM), which is classified into a powder bed fusion type in additive manufacturing methods, produces a near-net-shaped product by scanning a concentrated high-power laser beam on a thin layer of metal powder to melt and solidify it. The material temperature periodically and rapidly rises and falls with melting and solidification with transformations. The FEM-based simulation solves the governing equations of heat transfer with boundary conditions, including a moving heat source model for laser scanning. Such heat source models have been originally studied for many years for welding processes, and some volumetric heat sources of various shapes and distributions have been proposed [10,14,17]. Accurate thermal analysis requires calibration of shape parameters, depending on material and process conditions. This model has been applied to simulate the SLM process. The shape parameters have been calibrated so that the simulated bead shape (width, depth, and length) matches the one by the cross-sectional observation [10,11,12,13,14] or by in-situ monitoring with high-speed imaging [13]
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