City Research Online

Abstract

Laser surface glazing (LSG) is widely used to improve surface hardness and wear resistance in casting tool, railroad, automotive and bioimplant industries. This PhD project focused on developing a simple and reliable model of LSG for metallic materials by FEM. Both 2D and 3D transient thermal model of LSG with cylindrical geometry were successfully developed in ANSYS mechanical APDL software. Temperature distributions, heating, cooling rates and depth of modified zone of LSG treated parts were predicted from the thermal model. The temperature distribution resulting from thermal model were used to develop a 2D coupled thermomechanical model to predict residual stress for H13 tool steel using two plasticity theories, isotropic and kinematic. The thermal model was conducted for H13 tool steel and Ti6Al4V alloy. The laser power range 200-300 W and 100-200 W were used respectively with constant 0.2 mm beam width and 0.15 ms residence time. Results showed that surface peak temperature increased proportionally with laser power. Heating and cooling rates were extremely high in the range of 106-107 Ks-1 for both alloys and increased with laser power. The depth of modified zone was in micron range and increased with laser power. The parametric study of thermal model determined threshold power level 210 W and 130 W to initiate melting of H13 tool steel and Ti6Al4V alloy respectively. Thermomechanical model showed that tensile residual stress induced in the modified surface of H13 tool steel. Isotropic plasticity model developed higher von Mises residual stress than the kinematic model. Furthermore, the developed thermal model of LSG was applied to simulate quenching and tempering heat treatment of structural steel. The temperature distribution, cooling rates and outer case depth caused by quenching were predicted from the model. The calculated case depth from the model showed good agreement with the measured case depth found in the experimental work.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TJ Mechanical engineering and machinery
Departments:	Doctoral Theses School of Science & Technology > School of Science & Technology Doctoral Theses School of Science & Technology School of Science & Technology > Engineering

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