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Numerical Simulation of Residual Stress Formation During Selective Laser Melting Process

Maleki, Pedram | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 52674 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Tavakoli, Rouhollah
  7. Abstract:
  8. One of the major challenges in Additive Manufacturing is the creation of residual stresses due to the high temperature gradient in the solidification zone. This will cause problems such as cracks in the structure, metallurgical defects as well as deformation and dimensional accuracy reduction in the finished product. The purpose of this study is to perform mathematical modeling and computer simulation of the selective laser melting process (SLM) to predict these stresses as well as identify the effective parameters on this phenomenon. The conditions were adjusted in this model with the actual coefficients of the device. Additionally, the powder used in this project is Ti6Al4V material. By studying three variables of speed (at values of 0.8, 1 and 1.2 m / s), power (at values of 50, 80 and 100 watts) and laser diameter (at values of 20, 50 and 80 μm), we investigate the results of the solution of heat transfer and mechanical solutions to identify the effect of these parameters on the process. Troubleshooting was done through finite element computer programming, using the software package available in MATLAB to solve partial differential equations called PDE Toolbox, which also uses finite element method to solve, and COMSOL software. The results indicate a predictable effect for changes in diameter and laser power and for the laser speed to determine precisely its relationship with the factors causing the residual stress. As the laser diameter increases, the energy concentration on the powder bed decreases and the maximum temperature as well as the temperature gradient decrease, leading to a decrease in the residual stress in the fragment. A 50% reduction in laser diameter will result in an increase in the temperature of the powder bed to 400 ° C. As the laser power increases, the amount of energy transferred to the powder bed increases and also the temperature increases. This increase in temperature increases the temperature gradient and thermal stress in the piece as well. A 50% increase in power will increase the residual stress by 40%. As the laser velocity increases, the interaction between the laser beam and the powder substrate decreases and consequently the temperature decreases. This will help to reduce residual stress, but the laser should be at a speed that prevents the lower layers from melting while creating the melting zone
  9. Keywords:
  10. Additive Manufacturing ; Residual Stress ; Finite Element Method ; Numerical Simulation ; Selective Laser Melting (SLM)

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