A semi-analytical thermal modelling approach for selective laser melting

Abstract

Selective laser melting (SLM) wherein a metal part is built in a layer-by-layer manner in a powder bed is a promising and versatile way for manufacturing components with complex geometry. However, components built by SLM suffer from substantial deformation of the part and residual stresses. Residual stresses arise due to temperature gradients inherent to the process and the accompanying deformation. It is well known that the SLM process parameters and the laser scanning strategy have a substantial effect on the temperature transients of the part and henceforth on the degree of deformations and residual stresses. In order to provide a tool to investigate this relation, a semi-analytical thermal model of the SLM process is presented which determines the temperature evolution in a 3D part by way of representing the moving laser spot with a finite number of point heat sources. The solution of the thermal problem is constructed from the superposition of analytical solutions for point sources which are known in semi-infinite space and complimentary numerical/analytical fields to impose the boundary conditions. The unique property of the formulation is that numerical discretisation of the problem domain is decoupled from the steep gradients in the temperature field associated with localised laser heat input. This enables accurate and numerically tractable simulation of the process. The predictions of this semi-analytical model are validated by experiments and the exact solution known for a simple thermal problem. Simulations for building a complete layer using two different scanning patterns and subsequently building of multiple layers with constant and rotating scanning patterns in successive layers are performed. The computational efficiency of the semi-analytical tool is assessed which demonstrates its potential to gain physical insight in the full SLM process with acceptable computational costs.

Laser Powder Bed Fusion of Inconel 718: Residual Stress Analysis Before and After Heat Treatment

“…Furthermore, such models may allow prediction of the microstructure evolution, RS, and part distortions [45]. Ideally, the models need to be accurate, high computationally efficient and intuitive; however, PBF-LB is a multi-physics complex problem to analyze [53]. The high computational cost is the main drawback to the development of more accurate models and methods of predicting and simulating the AM processes [50].…”

On process-step parallel computability and linear superposition of mechanical responses in additive manufacturing process simulation

“…Zeng and co-workers [29,30] employ a dynamically meshed finite element (FE) model to reduce the number of degrees of freedom (and thereby reduce the computational burden) [29,30]. Yang et al [31] also manage to decouple (to some extent) the FE discretization from the accuracy of the thermal history calculation. To reduce computation time, cheap analytical solutions of the steep thermal gradients in and around the heat source are superimposed on a relatively course FE mesh [31].…”

“…Yang et al [31] also manage to decouple (to some extent) the FE discretization from the accuracy of the thermal history calculation. To reduce computation time, cheap analytical solutions of the steep thermal gradients in and around the heat source are superimposed on a relatively course FE mesh [31]. Both approaches [29][30][31] permit the simulation of specific scanning paths and patterns in SLM.…”

“…To reduce computation time, cheap analytical solutions of the steep thermal gradients in and around the heat source are superimposed on a relatively course FE mesh [31]. Both approaches [29][30][31] permit the simulation of specific scanning paths and patterns in SLM. However, Heigel et al [32] point out that a measurement-based convection model may be necessary in order to predict accurate thermal histories in metal AM.…”

Mechanical response of a Laser Cladding repaired structure: localization of plastic strain due to microstructure gradient

“…The material experiences a first solidification with the displacement of the melt pool together with the laser but it can be remelted when the above layer is built. It is then annealed as the part stays at high temperatures until the end of the process [17,28] what can lead to metallurgical transformations.…”