Theories And Experimental Studies On Effects Of Ultrasonic Nergy Field In Micro/Meso Metal Forming

The development trends on the miniaturization and integration of products have greatly enhanced the demands for miniature metallic parts and micro/meso manufacturing technology.Micro/meso metal forming provides a solution for the high-efficient mass production of miniature metallic parts.However,the size effects in scaling traditional metal forming down to micro/meso scale lead to several issues including the reduction of metal formability and the decrease of the workpiece surface quality,impeding the development of micro/meso forming.Regarding the volume effect and the surface effect of ultrasonic vibration in metal forming processes,applying ultrasonic vibration in micro/meso forming is expected to solve the above issues.In this dissertation,theoretical analysis,numerical simulations and experimental studies were carried out to study the mechanisms of ultrasonic vibration in micro/meso metal forming and the manufacturing processes of ultrasound-assisted micro/meso metal forming.The research work was supported by the National Natural Science Foundation of China(Grant No.50775203,50930005)and the United States National Science Foundation(Grant No.CMMI-0800353).In Chapter 1,the research background and significance of the dissertation were stated.Then,the main research contents were proposed based on the literature survey of the relevant studies.The volume effects were studied in Chapter 2 and Chapter 3.In Chapter 2,the acoustic softening effect of metals in ultrasound energy field was explored based on theoritical and experimental stuides;in Chapter 3,the acoustic residual hardening effect of metals in ultrasound energy field was explored,and the acoustic plasticity model was developed.The surface effects were studied in Chapter 4 and Chapter 5.In Chapter 4,the effects of ultrasonic vibration on metallic surface topography of formed parts were studied,while the mechanisms of ultrasonic vibration on the contact friction in micro/meso upsetting were explored in Chapter 5.From Chapter 2 to Chapter 5,the effects of ultrasonic vibration on micro/meso forming of solid metal were studied,while the mechanisms of ultrasonic vibration in micro/meso semisolid metal forming were investigated in Chapter 6.Based on the studies of mechanisms from Chapter 2 to Chapter 6,the manufacturing platforms for ultrasonic-assisted metal forming of solid metal and semisolid metal were developed in Chapter 7,respectively,and experimental studies on the processing were conducted.In Chapter 8,the main research work of this dissertation was summarized,and the future work was prospected.The innovations of this dissertation are as follows.(1)In the crystal plasticity framework,the effects of ultrasonic energy field on the processes of thermal activation and dislocation evolution were studied.Furthermore,the acoustic plasticity model was established,which can accurately describe the mechanisms of acoustic softening and acoustic residual hardening in ultrasonic assisted metal forming.(2)The volume effects and surface effects of ultrasonic vibration on micro/meso metal forming were systematically studied.Based on experimental approaches,the coupling mechanism of the acoustic softening and residual hardening in ultrasonic assised micro/meso metal forming were discovered and identified.(3)Based on the theory of acoustic softening effect,theoretical models for the influences of ultrasonic vibration on the metal surface morphology and the contact friction factor were established.Furthermore,the prediction method of the surface roughness after ultrasonic treatment and the estimation method of the friction factor in upsetting experiments were proposed.(4)To overcome the issues of size effects and filling defects existing in micro/meso semisolid metal forming,ultrasonic vibration was applied in the process of micro/meso semisolid metal forming.A novel ultrasonic assisted micro/meso semisolid forming was proposed,and the fabrication system was developed.In addition,the process experiments as well as the application research were also carried out.The research results showed that the introduction of ultrasonic energy field into the processes of micro/meso metal forming and micro/meso semisolid forming is capable of reducing the forming load,improving the forming effect of the feature structures,improving the surface quality of the workpiece and reducing the interfacial friction.Then,the adverse effects due to the micro/meso size effects can be overcome in both the volume and surface factors.The ultrasonic assisted micro/meso semisolid forming technology proposed in this dissertation provides a new approach for industrial manufacturing of miniture parts.The research results have important theoretical significance for exploring the mechanisms of ultrasonic vibration in metallic materials and developing the manufacturing system for ultrasonic micro/meso forming,and are potentially applied in the manufacturing processes of three-dimensional miniture metallic parts in the fields of new energy,electronic communications,biomedical,etc.