Research Of High-frequency Vibration Assisted Aluminium Alloy Plastic Forming

Vibration assisted plastic forming is a metal processing in which workpiece or tooling is superimposed a certain direction, frequency and amplitude vibration to improve effects of process and quality of products. It has been widely accepted that vibration can lead to a reduction in forming force, a decrease in friction between die and specimens, improvement in quality of formed parts and increase in forming limit of metallic materials to some extent. This is good for the forming of some materials with high hardness, high strength and low formability. Vibration assisted plastic forming will become a new approach in the field of plastic forming to improve the plastic formability of some light alloy, such as Al alloy and Mg alloy.This paper was focused on vibration tensile and upsetting. By combining experiments and numerical simulation, the role that the vibration played during the material deformation was revealed. The main work includes the analysis and summary of ultrasonic vibration metal forming system components and basic theory, Al 6063 high-frequency vibration tensile and upsetting tests and numerical simulation analysis of high-frequency vibration tensile and upsetting.Firstly, the components of ultrasonic vibration metal plastic forming system and their role during forming were introduced. The functions, features and operating principles of three core components including ultrasonic generator, transducer, amplitude transformer were described in detail. Three main theoretical models of volume effect in current research were summarized:the constitutive model of ultrahigh-frequency vibration plastic forming based on nonlocal theory, the elastic viscoplastic model of volume effect during low-frequency vibration plastic forming based on stress superposition principle and the visco-elastoplastic model based on elastic viscoplastic model. The theoretical model of nonlocal friction and its application in the research of surface effects of vibration were presented and discussed.A series of vibration assisted tensile tests were carried out using a high frequency vibration in the form of a peak vibration displacement of 5.39μm at a frequency of 15kHz. The influence of vibration parameters and vibration period on forming force, material flow stress, tensile strength, elongation, the morphology and microstructure of fracture and failure mode were researched to reveal the mechanism of volume effect. Numerical simulations of high-frequency vibration assisted tensile were developed using ABAQUS to observe characteristics of stress distribution and stress oscillation in the tensile specimens. By comparing the experimental results with simulated results, the influence of vibration frequency and amplitude on stress superposition and acoustic softening was analysed, the internal mechanism of volume effect was discussed.Then non-vibration and vibration upsetting tests were performed. The effects of vibration on forming load, material flow stress, the biggest deformation, surface quality and microstructure of workpiece and microstructure of longitudinal section of workpiece were investigated, and also the influence of height-diameter ratios on vibration effect. Through these experiments, the mechanism of volume effect and surface effect during vibration upsetting was revealed. Combined with simulation results using ABAQUS, the research was mainly focused on the reduction in friction between die and specimens, the improvement of surface quality and the refinement of material grains caused by vibration to explore the law and mechanism of the influence of vibration parameters on upsetting considering both volume effect and surface effect.