Thermal-mechanical Coupling Simulation Research In Three Dimensional Spiral Ultrasonic Vibration Assisted Grinding Of Hard And Brittle Materials By Using SPH Method

Hard brittle materials, such as optical glass and engineering ceramics have been widely used in the field of machinery manufacturing, chemical engineering, aviation and other high-tech fields. Grinding is one of the most widely used precision processing technology, but it may generate a lot of grinding heat and grinding force, which may reduce the surface quality and using performance. Three dimensional spiral ultrasonic vibration assisted grinding(3DSUAG) method has a obvious advantage to solve these problems. But the study datas of grinding mechanism are less, previous researches are generally carried out by experiments, but the actual grinding experiments are usually expensive, the required experimental conditions are generally complex, and the formation of the chip, the stress and strain distribution, the crack initiation and propagation of the workpiece are hardly observed. So,there are scholars study the grinding mechanism by using method of finite element simulation.The Smoothed Particle Hydrodynamics method is a truly mesh-free technique, it can ideally overcome the problem which the large material distortions may lead to the terminated computing. Therefore, the SPH method is suitable for simulating the simulation of the grinding process.This research based on kinematics, metal cutting theory, knowledge of material removal mechanism, and digital computation, with the combination of numerical simulation and theoretic analysis, the mechanism of 3DSUAG method was investigated. It reveals that the crack generation and propagation and change regulation of the strain-stress, the grinding force and the grinding temperature during the process of single abrasive grinding brittle materials.This research provides theoretical foundation and technical support to the wide application of 3DSUAG technology in the field of ultra-precision machining of brittle materials. The main research contents are listed as follows:1. Discussed the modeling method based on Smoothed Particle Hydrodynamics method(SPH). Numerical simulation by using SPH method of single abrasive grain grinding and impacting ceramic workpiece process were made by using ANSYS/LS-DYNA, the constitutive model of ceramic materials is Johnson-Holmquis Ceramics. Through the analysis of the simulation results, the rationality and advantage of SPH method in the application of single abrasive grain grinding are proved.2. Simulated the process of single abrasive grain impacting ceramic workpiece. The simulation results of the indenter impacting Al2O3 ceramics are observed. The workpiece generated lateral and radial cracks after the indenter press in certain depth, and the critical indentation depth of crack formation was related to the increasing of the impact speed. The middle cracks and radial cracks occurred in the workpiece when the single-grit impacted impact SiC ceramic. In the process of grinding, the SiC ceramics is more prone to produce radial cracks and increase the workpiece damage compared with Al2O3 ceramics.3. Built four types of single abrasive grain cutting processes, i.e, conventional grinding(CG), 3DSUAG, axial ultrasonic assisted grinding(AUAG) and vertical ultrasonic assisted grinding(VUAG). Revealed the mechanism of improving surface quality and reducing the grinding forces in 3DSUAG by using SPH to simulate the process of CG and UAG. In addition, The micro fracture of the SiC ceramic was more than that of the Al2O3 ceramic, and the stress was significantly higher than that of the ceramic in the process of grinding, it shows that Al2O3 ceramics has better processability than SiC ceramics. In addition, the greater the impact speed, the higher the temperature of the contact area, and the temperature of SiC ceramics is much higher than that of Al2O3 ceramics.4. Built the temperature field model of a single abrasive grain in CG and 3DSUAG. The grinding simulations of Al2O3 ceramics and SiC ceramics were carried out, and the distribution of temperature field was observed. Compared with CG, the grinding temperature of AUAG was not changed, while the grinding temperature of VUAG and 3DSUAG were both decreased. In addition, the temperature increases with the increasement of cutting depth.Introduced the the characteristics of thermo mechanical coupling problem,and observed the simulation results of CG and UAG for stress analysis and thermo mechanical coupling analysis. The stress field distribution in the thermal coupling analysis is more larger, while the average stress value is less than that of the workpiece in the stress analysis.