Springback Prediction And Compensation Of Extruded Profiles In Stretch Bending

Stretch bending is very important for improving precision and widely used for forming difficult-to-deform materials in aerospace,weapon,automobile industry.However,increasing demands of high-performance structure,precision stretch bending technologies of extruded profiles become very urgent.On one hand,the usual way is replacement of the primary material by another one with better weight specific characteristics,e.g.using high strength titanium,light metals like aluminum or aluminum-lithium alloy,but it faces difficulties of large springback and low forming limit.On the other hand improved method to solve the problem using hot forming is widely researched.Meanwhile,for understanding of the complicated mechanism of the interaction of multi-physical fields,the coupling behaviors of thermo-electro-mechanics are investigated for electric heating stretch bending.To solve these problems,prediction model and compensation method of springback consideing coupling effects of material,geometric,processing and temperature parameters are proposed for precision and stable stretch bending,considering forming limit.Its main research contents and innovative works are as follows:1)Effects of material properties and geometric paremeters modeling in springback prediction is proposed.First of all,an empirical plasticity constitutive form describing the flow stress as a function of strain,strain-rate,temperature and aging hardening has been developed,fit to data for W temper aluminium,aluminum lithium and titanium alloy,and compared with independent experiments outside of the fit domain.Secondly,based on principle of virtual work,springback model of stretch bending is developed considering neutral layer shift and friction influence.Lastly,verified experiments are carried out and coupling effects of material properties and geometric paremeters on the springback is proposed.It is observed that Young's modulus,yield stress,and strain hardening exponent as well as interactions of these parameters with the bending radius,have a significant influence on the springback radius.It will be very useful in predicting,compensating for and controlling the springback of stretch bending.2)Effects of processs and friction paremeters modeling in springback prediction is proposed.Firstly,an analytical model of displacement controlled cold stretch bending(DCSB)is developed based on effects of material properties and geometric paremeters modeling are carried out.Secondly,the connector element in FEM is used to simulate DCSB and trajectory algorithm of gerneral die is proposed.Furthermore,the roles of processing parameters and friction condition are revealed with verifying by experiments of age-hardened 2196-T8511 and 2099-T83 Al–Li alloys extrusions with Z-section and T-section.Finally,coupling effects of processing and friction paremeters on the springback are developed.The results show that:the analytical model and finite element method can be used to evaluate effectively the effects of material and process parameters on springback of Al–Li alloys extrusions;2196-T8511 and2099-T83 Al–Li alloys extrusions show significant springback at room temperature because of its higher strength to Young's modulus;increasing pre-stretching or post-stretching strain can significantly reduce the radius springback and time-dependent springback of 2196-T8511 and2099-T83 Al–Li alloys extrusions,but it is limited by the lower fracture strain;the lubricant between extrusions with die reduces the stable radius springback ratio greatly for Al–Li alloys in the T8 temper.3)Effects of temperature condition modeling in springback prediction is proposed.Firstly,baesd on heat transfer,thermal expansion deformation and principle of virtual work,a new analytical model of hot stretch bending is developed to prediction springback.Secondly,a new force-controlled HRSB test was developed,carried out,simulated using a sequentially coupled electro-thermo-mechanical finite element model.The model incorporates 3D solid elements and consists of two Abaqus/Standard runs: a thermal-electrical heat transfer analysis and a subsequent stress analysis.The simulation results were compared with companion stretch bending tests for extruded Ti-6Al-4V titanium alloy profile over a range of process conditions.Furthermore,the roles of initial temperature,pre-stretching and post-stretching are revealed.Finally,coupling effects of temperature condition on the springback is developed using respond surface.The results show that: the finite element and analytical method can be used to evaluate effectively the effects of process parameters on springback of extruded Ti-6Al-4V Alloy profile in HRSB.Temperature distribution dominantly effects springback because the higher is the temperature,the lower is the flow stress of material.When initial temperature of Ti-6Al-4V titanium alloy profile ranges from 700 to 750?C,and temperature of die surface ranges from100 to 200?C,the forming quality and precision are higher.Increasing pre-stretching or poststretching strain can reduce the angle springback of Ti-6Al-4V titanium alloy profile,but it is limited by the temperature.4)Compensation method of springback in stretch bending is proposed.Firstly,the attention is focused on the minimum bending radii of stretch bending.To predict the failure,sheet and extrusion bending tests are developed,carried out,and simulated using finite element model which incorporates 3D solid elements and ductile damage modeling.The experimental results show that extrusions in stretch bending show three types of failure,occurring at the unbent region near the entrance of the jaws,at the region below the exit of the die,and within the region in contact with the die,respectively.Secondly,a strategy considering material,geometric,processing and temperature parameters are proposed for stable springback,then compensation algorithm and compensability analysis incorporating pure geometry correction with fundamental mechanics analysis are developed to design tooling rapidly.Lastly,the compensation method is used to engineering example,the forming results show high precision and efficiency.The prediction,compensation and stability control of springback in extruded profile stretch bending is developed.The research results are applied to frames parts manufacturing of ARJ21 and C919 aircraft.