Numerical Simulation Of Temperature,Stress And Fluid Field During Wire And Arc Additive Manufacturing Process Of Aluminium Alloy

The wire and arc additive manufacturing(WAAM)has been a new approach for rapid prototyping of metal parts for its advantages of low cost and high depositing rate.Nowadays,most researches have concentrated on the process optimization and forming control of WAAM.However,the physical process during WAAM such as temperature and stress field evolution and molten metal flow,which have crucial impact on forming quality,is rarely reported.Hence,compared with experimental tests,the numerical simulation of temperature and stress distribution and molten metal flow in WAAM for aluminium alloy parts is implemented in this work,expecting to provide the basis for the comprehension of physical process and improvement of forming quality during WAAM.Firstly,the multi-layer single-pass experiment of aluminium alloy pasts is conducted by a cold metal transfer(CMT)WAAM system under different forming parameters.The component gained from experiment under the appropriate depositing parameters is selected to provide the geometry information for the simulation model.And the energy distribution produced by welding arc is described by depositing volume and double ellipsoid combined heat source model.The results indicate that the proposed heat source model is fit for WAAM simulation.For single-layer depositing process,the highest molten pool temperature at arc starting side is lower than that at arc ending side,where the heat accumulates badly.During WAAM process,the temperature and stress of the whole component experience a repeating rising and falling variation with the behavior of depositing metal re-melting and stress relief.After releasing the fixture,the dominating deformation of the component is the warping along longitudinal direction.Next,temperature and stress filed distribution during WAAM process under different forming path and inter-pass idle time are calculated based on the basis of the finite element model established before.It can be found that forming path has a great influence on the symmetry of thermal and stress distribution on the whole component.When compared with reversing deposit,nonreversing deposit results in a lower thermal and stress symmetry because the heat and stress accumulates at arc ending side under this forming path.And the increasing of inter-pass idle time leads to the reduction of heat accumulation degree and residual stress on the depositing components.Then,the molten pool flow and droplet transfer with reciprocating wire considered during CMT based WAAM process are calculated on the basis of the computational fluid dynamics(CFD)theory.The results reveal that according to the impact importance extent for molten pool flow,the effect of surface tension,arc pressure,electromagnetic force and buoyancy diminishes gradually.The gravity and surface tension play an important role in droplet transfer during CMT process.When the wire moves toward molten pool,the surface tension facilitates droplet transfer.But during the wire reciprocating,the effect of surface tension on droplet transfer is adverse.With the cooling condition of molten pool being worse,the width and permeation of the molten pool increase,which is beneficial for the spread of molten drop on the molten pool surface.Finally,the morphology of components gained from experiments under different forming path and inter-pass idle time is analyzed on the foundation of simulation results.It can be found that the height of the component decreases from arc starting side to arc ending side under nonreversing depositing direction while the height keeps consistent under reversing depositing direction.The symmetry of the thermal process determines the morphology characteristics under different forming path.When the inter-pass idle time extended,the cooling condition of the molten pool will be improved and the molten metal flow will be restrained.Hence,the average width of depositing layer decreases while the average height increases,and the width uniformity of the components is enhance at the same time.In present study,the temperature,stress and fluid flow characteristics of WAAM forming process are revealed by numerical simulation and component morphology analysis,laying the foundation of forming quality improvement during the WAAM process.