Model-based Optimization of the Thermal in Laser-welding and Directed Energy Deposition (DED)

M. Sattari1*, A. Ebrahimi2, M. Luckabauer1, G.R.B.E. Römer1

1 Department of Mechanics of Solids, Surfaces and Systems, Faculty of Engineering Technology, University of Twente, Drienerlolaan 5, 7522NB Enschede, The Netherlands.

2 Department of Materials Science and Engineering, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Mekelweg 2, 2628CD Delft, The Netherlands.

*m.sattari@utwente.nl

Laser-based manufacturing processes, such as laser welding and laser Direct Energy Deposition (DED), are promising technologies for fabricating complex geometries with high accuracy and mechanical properties [1]. One of the key challenges in laser-based processes is to achieve the desired solidification microstructure. The latter strongly affects the mechanical properties of the final product. The formation of solidification microstructure depends on the laser-induced spatial and temporal temperature distribution. The latter can be controlled by manipulating the laser beam intensity profile [1].

This paper presents a modeling and simulation approach to optimize the laser beam intensity profile for laser-welding and laser-based DED, see Figure 1. In this approach the temperature gradient is minimized and the cooling is maximized in order to create a less-textured, finer solidification microstructure. Using Flow3D [2] a multi-phase thermofluid model is implemented, which takes into account various physical phenomena, including the powder stream, laser and powder interaction, temperature- and incident angle-dependent absorption coefficient, and chemcial element-dependent surface tension of the melt pool. The finite volume method (FVM) is used to solve the differential equations governing the thermofluid dynamics, and the Volume of Fluid (VoF) method is used to track the free surface evolutions of the liquid metal.

Next an optimization algorithm is developed which is used to generate an optimized thermal profile that considers the physical constraints of the process. In this algorithm an (over)simplified thermal estimates the required laser beam intensity profile for the actual optimized thermal profile. Next, the latter intensity profile is used in the thermo-fluid model to calculate the resulting thermal profile and compare this profile with the initial one in terms of temperature gradient and cooling rate.

Figure 1: Modeling and simulation approach to obtain the required laser beam intensity profile for optimizing the thermal profile.

The simulation results demonstrate that the required/optimized laser beam intensity profile for laser welding and laser-DED results in an improved solidification microstructure.

References

[1] A. Ebrahimi, M. Sattari, S. J. L. Bremer, M. Luckabauer, G. R. B. E. Römer, I. M. Richardson, C. R. Kleijn, and M. J. M. Hermans, “The influence of laser characteristics on internal flow behaviour in laser melting of metallic substrates,” Materials & Design, vol. 214, p. 110385, Feb. 2022, doi: 10.1016/j.matdes.2022.110385.

[2] “Flow Science.Inc FLOW-3D 2022 R1. https://www.flow3d.com/products/flow-3d/flow-3d-2022r1/. Accessed Sep. 2022.”