| The advancement of industrial technology and the growing emphasis on energy conservation and efficiency have led to an increasing demand for lightweight,high-performance,and highly efficient key components.Light alloy variable section tubular components have advantages in parts lightweight,specific strength,specific stiffness and corrosion resistance,while hollow structures have the energy characteristics of absorbing impact,which gradually replaces traditional parts in the automotive and aerospace industries.At the same time,with the increasing market demand for tubular components with complex shapes,high precision and thin walls,higher requirements are put forward for forming process.Therefore,this paper puts forward a new kind of flexible and lightweight manufacturing process based on the ultrasonic-assisted granular medium forming process and ultrasonic-assisted technology.With the characteristics of easy sealing,easy loading and non-uniform distribution of internal pressure of the granular medium,the process integrates the advantages of ultrasonic vibration to increase the flow of the granular,reduce the friction between the workpiece and the die,and reduce the forming force of the metal tube,which is expected to provide a new technical method for the precision forming of the metal tube.According to the characteristics of the ultrasonic-assisted solid granular medium forming process,the shear friction tests between granular and billet,granules and granules,billet and punch were designed under ultrasonic vibration,and the friction coefficient changes under different vibration parameters and granular parameters are investigated.Based on tribology theory and powder mechanics,the curve force transmitting test of granular medium under ultrasonic vibration is carried out,and the curve force transmitting mechanical model of granular medium under different ultrasonic vibration conditions is established.On this basis,using the discrete element software PFC2 D and the finite element software ABAQUS platform,the discrete element model(meso)and the finite element-discrete element coupling model(macro)are constructed respectively,and the influence of ultrasonic vibration on the granular curve force transmitting is studied from the meso and macro perspectives respectively.The constitutive model of 6063-T5 aluminum alloy under ultrasonic vibration is established through transverse ultrasonic-assisted tensile test combined with stress superposition and softening theory.On this basis,combined with the shear friction results under ultrasonic vibration and the ultrasonic curve path force transmitting model,the free forming and convex ring hexagon forming of the tube are analyzed,and the mechanical models of the highest point of free forming,convex ring hexagon rounded corner and straight wall region are established,which provided a theoretical basis for the ultrasonic assisted solid granular medium forming process.The present study focuses on the numerical simulation of ultrasonic-assisted solid granular medium free forming and convex ring regular hexagon forming of a 6063-T5 aluminum alloy tube using a finite element and discrete element coupling simulation model established through self-programmed embedded subroutine in ABAQUS software.The aim is to investigate the impact of process parameters such as amplitude,frequency,and granular number on the forming performance of the tube.According to the results of numerical simulations,a forming mold and an ultrasonic vibration excitation system with a vibration frequency of 20 k Hz were developed for testing the ultrasonic-assisted solid granular medium forming process of the tube.The influence of different amplitudes on the formation of solid granular medium was investigated,and the experimental results validated both the numerical simulation outcomes and theoretical predictions for free forming and regular hexagonal convex ring formations.The results show that the ultrasonic assisted solid granular medium forming process can promote the material flow in the straight wall section of the tube to the deformation zone,reduce the forming force required for the tube forming to a certain extent,improve the wall thickness uniformity of the formed part,and reduce the corner radius of the convex ring hexagon section.This provides a new method and approach to solve the problem of low plasticity and difficult to form tube processing. |
