Numerical Simulation And Process Optimization Of Single Point Positive Incremental Forming Of Magnesium Alloy

AZ31 magnesium alloy is a representative mg-al-zn alloy with good room temperature strength,strong corrosion resistance and good processibility,which has been widely used in automobile manufacturing,3C products,aerospace and military industry.Compared with other common metal materials,AZ31 magnesium alloy has poor plasticity at room temperature,which greatly limits its further wide application.With the increase of temperature,the formability of AZ31 magnesium alloy sheet is improved significantly.With the increasing of product lightweight and personalized demand,the shortening of trial production cycle of new products and the accelerating application of new materials,the traditional manufacturing process of magnesium alloy thin-walled components is facing great challenges.Single point incremental hot forming process can be used for complex thin-walled components with large deformation,high mechanical properties and dimensional accuracy requirements.It has been widely concerned for advantages of simple equipment,low noise,good flexibility,especially suitable for new product trial and small batch production of multiple products.The density,Poisson's ratio,modulus of elasticity,barlat constant and other parameters of AZ31 B magnesium alloy sheet at different temperatures were important material parameters.The strain hardening coefficient and the anisotropic coefficient in the directions of 0°,45° and 90° can be obtained through the uniaxial thermal tensile test and the corresponding calculation.The Barlat material model is established and applied to the establishment of finite element model of the single point incremental forming for AZ31 magnesium alloy sheet.With the side wall thickness of AZ31 B magnesium alloy sheet metal as the research target,numerical simulation experiments were carried out on the single point incremental positive forming process for a frustum part.The effects of forming angle,tool head diameter,horizontal feed speed and step size on the uniformity of the wall thickness were studied.On this basis,the limit angle of single-pass single-point incremental positive forming is studied,and it is concluded that there exists a forming limit angle of this process.Under the condition of 250?,the forming limit angle of magnesium alloy sheet is 67°.The response surface method is adopted to carry out the multiple factor analysis to determine the order of forming angle,step size,horizontal feed speed,forming depth on the thickness of the formed parts.At 250?,the optimal set of process parameter is the forming angle of 40°,feed speed 100 mm/min,forming depth of 20 mm and step size of 1 mm.In view of the bulge defects of straight wall cylindrical parts in full support positive forming,the floating part positive forming method is proposed to optimize the process,and the interval planning is carried out for the forming angle which affects the maximum formability of the sheet.It is concluded that when the forming method of partial support is adopted,40° in the first step,25° in the second step and 25° in the third step,the wall thickness of the formed straight wall cylindrical parts is relatively uniform and there is no bulge defect.By comparing the numerical simulation with the simulation experiment of a stepped cylindrical part,the error between the experimental value and the simulation result is within 10%,which proves that the numerical simulation is in good agreement with the experiment.