Loading...

Effect of Process Parameters in Selective Laser Melting on Quality (Porosity) of the Component

Deldar Masrour, Pouria | 2023

43 Viewed
  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56703 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Farrahi, Gholamhossein; Tangestani, Reza
  7. Abstract:
  8. In the present research, a new material model utilizing anisotropic conduction and track-scale heat input model is used to predict the melt pool geometry, material state and thermal history during the selective laser melting process of SS316L in a large range of laser parameters. The model takes into account the phase transition of the material during the process. Furthermore, the phase transition problem in the track-scale model has been analyzed and a solution has been presented. The simulated melt pools in beam-scale and track-scale simulations are compared with experimental measurements in different laser parameters. It is found that the proposed material model is able to maintain accuracy between the beam-scale and track-scale at an average of 5µm regarding melt pool dimensions. Furthermore, it can be inferred that both track-scale and beam-scale models exhibit the capability to provide precise predictions of thermal histories during the simulations while the former being about 100 times faster than the latter. An average error of 10% is calculated regarding the prediction of material state during the process. Additionally, the track-scale model is able to capture the temperature profile and cooling rate accurately in comparison with the beam-scale model. Following the material model, a multi-layer model has been developed to estimate the porosity within the component. The experimental methodology for measuring the porosity of the components has been presented. Additionally, the methodologies used to calculate the dimensions as well as the porosity within the multi-layer model has been analyzed. The calculated porosity within the multi-layer model has been compared with the experimental measurements in different laser parameters. Furthermore, the geometry dimensions threshold has been studied regarding porosity levels below 0.5%. Finally, a comparison of the melt pool boundaries has been conducted between the cross sections of the multi-layer model and the corresponding experimental cases. An average difference of 0.58% is calculated between the developed multi-layer model and experimental data. In addition, the calculated geometry dimensions threshold in the multi-layer model corresponds to the ones estimated using the experimental results. Lastly, the simulated melt pool boundaries yield acceptable agreement with experimental results while capturing the pattern of how the melt pools evolve within the cross section. Using the multi-layer model, a data set consisting of 100 data points is prepared which includes laser parameters and their corresponding porosity. Moreover, porosity is mathematically presented as a function of laser speed and laser power which is then used to calculate the optimum laser parameters to reach a specified porosity level. Ultimately, in order to validate the results, the optimum laser parameters are calculated for two different porosity levels and are then compared with the experimental components constructed with the same laser parameters. Zero percent and three percent porosity levels have been chosen as the case of validation. An average difference of 0.27% is calculated between the mathematical model and the data base while an average difference of 0.61% is calculated between the mathematical model and the experimental data. Additionally, the average difference calculated is below 1% for over 80 percent of the experimental case. Using the mathematical model, optimum laser parameters for two different porosity levels have been calculated. The results are then compared experimentally for validation. Porosity difference of 4 and 9 percent is calculated regarding the validation which is caused by using empirical equation for the zero percent porosity level and not accounting for the porosity of the powder bed in the three porosity level cases
  9. Keywords:
  10. Finite Element Method ; Additive Manufacturing ; Selective Laser Melting (SLM) ; Porosity ; Optimization ; Optimum Parameters ; Track-Scale Heat Input ; Anisotropic Heat Conduction

 Digital Object List

 Bookmark

No TOC