Investigationonthe Warm Incremental Forming Process Of 2060 Al-Li Alloy Sheet

Al-Li alloy,a kind of aluminum alloy with excellent property,is widely used in the engineering field of aeronautics and astronautics.The 2060 aluminum alloy is the 3rd generation Al-Li alloy.It is suitable for aircraft skin and other structural parts.However,because of its low plasticity at room temperature,it is generally formed by heating.Incremental forming is an advanced flexible manufacturing technology.Meanwhile,it can be used for the development of new products and manufacturing of small batch parts with high efficiency and low cost,especially for aerospace product development and manufacturing.In this paper,2060 Al-Li alloy sheet and warm incremental forming technology were combined.The influence of process parameters on the wall thickness quality,geometric accuracy,surface roughness,mechanical properties after deformation and forming limit of 2060 Al-Li alloy warm incremental forming was studied by finite element simulation and experimental method.Moreover,the process optimization was carried out.The main contents are as follows:(1)The constitutive equation of 2060 Al-Li alloy sheet was constructed.The material performance parameters of 2060 Al-Li alloy in range of 25 °C to 240 °C were obtained by uniaxial tensile test.And the deformation law of material performance parameters was analyzed.Meanwhile,the Fields and Backofen constitutive equation was established to accurately characterize the deformation of 2060 Al-Li alloy sheet,which laid an important foundation for numerical simulation of warm incremental forming of 2060 Al-Li alloy.(2)The formulas of the instantaneous strain and strain rate during incremental forming were deduced.It was found that the strain rate of incremental forming strain was only related to the step down,forming tool head size,wall angle and feed rate.Furthermore,based on the tensile results,the finite element model of warm incremental forming of 2060 Al-Li alloy was established.Furthermore,the effects of step down,forming tool head diameter,wall angle,forming temperature and feed rate on the uniformity of wall thickness distribution and the maximum thinning rate were analyzed.The results shown that the part with the optimum wall thickness quality was obtained when the step down was 0.2 ~ 0.4 mm,the diameter of forming tool head was 8 ~ 10 mm,the feed rate was 900 mm/min and the forming temperature was 240 °C.(3)The heating device of sheet warm incremental forming was designed.Meanwhile,the effects of forming temperature and feed rate on the geometric accuracy,surface roughness,mechanical properties after deformation and forming limit of 2060 aluminum lithium alloy were experimentally investigated.The results shown that the part had a certain degree of recovery at 200 °C.The maximum tensile strength of the part under the forming temperature was slightly lower than the mechanical property of the material.The maximum forming limit angle was 65°08?,which greatly improved the material forming limit.And a certain degree of recrystallization occurred at 240 °C.The tensile strength of the part was 363.94 MPa,which was much lower than the tensile strength of the material.The maximum forming limit angle was 69°39?.In order to make the parts with good strength,hardness and forming limit,the optimum forming temperature was 200 °C and the optimum feed rate was 1200 mm/min.(4)Based on the mechanical properties of the parts,the prediction models of tensile strength and microhardness were established by response surface analysis.The model was verified by the experiment with a forming temperature of 185°C and a feed rate of 1100 mm/min.