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Finite element method simulation of Laser engraving

Nikolidakis Evangelos

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Summary

In the present thesis an experimentally confirmed finite element method (FEM) simulation model for nanosecond pulsed laser engraving process is developed. The main purpose of the simulation model is the prediction of the final engraving geometry and the optimization of the process by studying the effect of the process parameters on machining quality and productivity. A general heat transfer model was adopted where the incident laser beam causing the material ablation was modeled using a gaussian heat source. The effect of the laser beam inclination and convergence were taken into account. The laser map containing the positions of the laser beam pulses to be sent was generated according to the unidirectional cross hatching strategy. Τhe Q-switching mechanism was modeled to define the intensity of the laser beam over the time. The laser beam absorption was modeled considering the loses due to the material reflectivity and the plasma shielding by the interaction of the incident laser beam and the generated metal vapour plasma plume. The ablation mechanism was modeled using a moving mesh method to define the geometry shape changes caused by the evaporative removal of material. Laser engraving simulation tests were performed for materials such as stainless steel SAE304, pressure vessel steel P355GH, yellow brass C26000, aluminium Al7075-T6 for various combinations of basic process parameters: average power, scanning speed, repetition rate. From the simulations the engraving geometry was predicted in the same way as it would be formed if the process was performed in practice in real conditions in a laser machining center. In addition, removed material layer thickness and material removal rate values were predicted for each case. Furthermore, the imperfections-defects that appear in the engraved geometry due to kerf formation were predicted such as the slope that appears on the side walls by calculating the values of kerf taper angle, top kerf width and bottom kerf width. The simulations results were examined and conclusions were drawn about the effect of the process parameters on the laser engraving process outcome.To validate the simulation model laser engraving experiments were performed for the purpose of comparing the experimental with the simulation results. The experiments were conducted using the DMG MORI LASERTEC 40 nanosecond pulsed Q-switched 1064nm laser engraving machine and measured using the Bruker Contour GT-K 3D optical profilometer. The experimental results positively validated the simulation model.

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