Study On The Mechanism And Experiment Of Ultrasonic Vibration Assisted Mesoscale Semisolid Forming Of Metallic Materials

The research work was supported by National Natural Science Foundation of China, (Project tittle:Research on the theory and method of ultrasonic assisted semi-solid micro thixoforming in meso-scale, Grant No.50775203).We have carried out a research on the theory and experiment about ultrasonic assisted semi-solid micro thixoforming in meso-scale by introducing semi-solid technology and ultrasonic assisted forming method into the process of micro thixoforming of metal parts. Firstly, semi-solid A356 aluminum alloy was chosen to simulation about ultrasonic vibration assisted upsetting, micro-pin forming and extrusion by ABAQUS, and the mechanism of ultrasonic in the process of semi-solid forming was analyzed. Secondly, an experimental platform was designed and set up. Semi-solid A356 aluminum alloy was chosen to upsetting with ultrasonic. Then the constitutive model on viscoplasticity of semi-solid A356 under the influence of ultrasonic was established. Finally, the experiments of ultrasonic vibration assisted micro-pin thixoforming of semi-solid A356 were carried out. The effects of ultrasonic intensity, ultrasonic vibration time, forming temperature, forming rate and forming force on micro-pin forming results were analyzed, and better parameters were obtained which can get better results of micro-pins. The research results have guiding significance for further understanding the mechanism of ultrasonic assisted semi-solid forming, the constitutive model on viscoplasticity of semi-solid metal under the influence of ultrasonic and ultrasonic assisted semi-solid micro thixoforming and so on.In Chapter 1, the background and significance of this study were introduced. Then, the current research situations of semi-solid forming technology and ultrasonic vibration assisted materials forming technology were reviewed, and clearly put forward the study direction of ultrasonic vibration assisted mesoscale semi-solid metal forming mechanism and experimental research. Based on this, the research contents of this thesis were proposed..In Chapter 2, semi-solid A356 aluminum alloy was chosen to simulation about ultrasonic vibration assisted upsetting, micro-pin forming and extrusion by ABAQUS, and the mechanism of ultrasonic in the process of semi-solid forming was anslyzed.In Chapter 3, designing scheme of experiment system of the ultrasonic assisted mesoscale semi-solid metal forming was put forward. The ultrasonic vibration system which can change forming tools conveniently and can apply in hot forming was developed. And finally the building of the experiment system was completed.In Chapter 4, the constitutive model of ultrasonic assisted semi-solid forming of A356 aluminum alloy was established. Then, the stress-strain curves of A356 aluminum alloy under different ultrasonic intensity and different solid fraction were obtained based on ultrasonic vibration assisted upsetting experiment. The expression of parameters in the constitutive modal was obtained by fitting the stress-strain curves of A356 aluminum alloy using this constitutive model.In Chapter 5, ultrasonic vibration assisted micro-pin forming experiment of A356 aluminim alloy was performed, and evaluation parameter of micro-pin’s forming quality was put forward. Then the effects of main process parameters, including ultrasonic intensity, ultrasonic time, forming speed, billet temperature, forming force and so on, on the forming quality of the micro-pin were analysised, and better parameters were obtained which can get better results of micro-pins.In Chapter 6, the chief work of this thesis was summarized, and the further research works were proposed.