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Numerical Modeling and Experimental Investigation of the Efficiency of the Laser-assisted Machining for Ceramics

Roostaei, Hossein | 2019

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 52464 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Movahhedy, Mohammad Reza; Shoja Razavi, Reza
  7. Abstract:
  8. Laser-assisted machining is nowadays considered as an alternative to conventional machining processes including ceramics grinding, which has provided the basis for extensive experimental and numerical studies in this field. Since the main difference between laser-assisted machining and conventional machining is in the presence of lasers, the main purpose of this study was to investigate the effects of laser on the laser assisted machining process. In this regard, in the first step the process of laser heating to the ceramic workpiece has been studied experimentally and numerically by finite element method. The material used in this research is a slip cast fused silica ceramic. The absorptivity of the ceramic is determined as a function of laser power and laser feed velocity by experimental tests. The numerical and experimental results are highly consistent and the maximum error does not exceed 5%. Because a low pulsed frequency Nd:YAG laser is used in this study, the overlapping rate of successive pulses of laser irradiation has a significant impact on the absorptivity and thermal distribution of the coated ceramic material. For this purpose, laser pulse overlap rates are formulated for different operating conditions of the laser heating process and their effects on the absorptivity are investigated. This step consequently determines the proper operating conditions for optimum heating in the laser-assisted machining process. In the next step, the conventional and laser-assisted turning of ceramics are numerically and experimentally investigated. In this step, the discrete element method (DEM) is used for numerical simulations. Also, the flat joint contact model is utilized as a model for the interconnection of discrete particles. For this purpose, first, micro-parameters of the discrete element model were adjusted by the calibration method to match the model properties with the real material. Then, the calibrated model is updated by the experimental results of laser-assisted machining of the ceramic. The effect of the temperatures induced by laser irradiation on the numerical model has been applied as a change in the mechanical properties of the material and consequently a change in the corresponding micro-parameters of the model. This numerical model predicts experimental machining forces with an error in the range of 10% to 35%, which is acceptable for the complex process of machining ceramics in the brittle regime. This numerical model well simulates initiation, propagation, and coalescence of cracks and finally chip formation
  9. Keywords:
  10. Laser Assisted Machining ; Brittle Fracture ; Discrete Element Method ; Ceramic Machining ; Flat-Joint Contact Model ; Laser Spot Overlapping

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