Investigation On Deformation Mechanisms And Microstructure Evolution During Ultrasonic-assisted Incremental Forming

With the rapid development of biomedicine,aerospace and other industrial fields,the small-batch,personalized and low-cost production modes and technologies are becoming more and more significant.Featured with high flexibility,short production cycle and low cost,incremental sheet forming(ISF)technique has drawn wide attentions from many researchers.However,limitations such as low forming accuracy,poor surface quality and low formability for hard-to-form materials still hinder the wide application of ISF technique.Moreover,the beneficial effects of ultrasonic vibration(UV)have been verified in several manufacturing processes,but the influence mechanisms are not clear.Therefore,in this study,aimed at AA1050-O material,the ultrasonic vibration was introduced to the ISF process.And,the influence mechanisms were investigated through the constitutive modeling,numerical simulation and microstructure analysisFirst,the experiment-simulation platform for ultrasonic assisted incremental forming(UISF)was established.On the one hand,combining the vertical machining center(VMC)with the ultrasonic generator,the transducer and the horn,the high-frequency electric signal was transformed into the mechanical vibration.On the other hand,ABAQUS/Explicit module was applied to simulate the forming process,and the toolpath and the ultrasonic vibration were simulated through the user subroutine.Comparing the simulation and experiment,it was found that the current FE model can reasonably predict the forming process without UV,but the forming process with UV has a larger error.Then,to further improve the simulation accuracy,based on the phenomenological constitutive model,the thermal activation and the dislocation annihilation effect of UV were considered to establish the hybrid constitutive model.And,the key parameters in the model were determined through the curve fitting and the reverse modeling.Moreover,the established constitutive model was employed in the FE model.A series of experiments were implemented to verify the accuracy and applicability of the model,and the error between the simulation and experiment is less than 10%.Then,based on simulation and experiment results,the deformation mechanisms under UV condition were analyzed.First,the experimental forming forces were investigated,and it was noticed that the application of UV can effectively decrease the vertical and transverse force.Furthermore,the stress-strain state,thickness distribution were analyzed through FE simulation.The results show that the application of UV can reduce the flow stress,improve the forming performance and thickness distribution.Final,through the Electron Back-Scattered Diffraction(EBSD)technique,the microstructural features were analyzed and the dynamic recovery was observed Moreover,the forming experiments for truncated cone with variable apex angle to investigate the forming limit under UV condition,and the results show that the UV can increase the forming limit.And,the fracture morphology was analyzed through the scanning clectron microscepe(SEM)to reveal the fracture mechanisms.