Research On Multi-stage Hot Incremental Forming And Numerical Simulation Of AZ31B Magnesium Alloy

As a new technology of sheet metal flexible forming,single point incremental forming process has been paid close attention to by scholars at home and abroad for the superiorities of no need of complicate brace,improving material formability,rapid prototyping and forming complex shape parts.it is very suitable for small batch and rapid prototype production,which meet the growing demands of modern marker to highly customized products.Therefore,single point incremental forming process will have bright future.The formability of AZ31B magnesium alloy sheet used in this paper is insufficient for forming parts with large angle or straight wall at ambient temperature.Therefore,this paper will study the influence of the process parameters on the forming quality and the optimum process parameters of the straight wall cylinder parts with the combination of multi-pass single point incremental forming and hot forming.Firstly,the elastic modulus,Poisson’s ratio and thickness anisotropy coefficient of AZ31B magnesium alloy sheet at different temperatures were collected by consulting literatures,and the stress and strain data under the temperature of 150 ℃,200℃ 250 ℃,300 ℃ and room temperature were obtained by tensile test.It is found that at room temperature the flow stress curves of AZ31B magnesium alloy were 0°,90°,and 45°from high to low,and the mechanical properties of the three directions were not significant;as the temperature rising to medium high,the peak value of flow stress of AZ31B magnesium alloy in all directions(0°,90° and 45° along the rolling direction)decreases gradually,and the elongation of the specimen increases gradually.Then,the finite element model of AZ31B magnesium alloy multi-pass single forming was developed,finding that a convex part appeared in the bottom of the conventional design.Two path forming strategies are designed for the boss phenomenon,and the boss was well solved according to the simulation.Next,taking the thickness uniformity of the forming parts as the research object,the effects on the thickness uniformity of the differences of pass forming depth,the shape of the section,the number of forming passes,forming temperature,the diameter of the forming tool,the feed rate,and the amount of reduction were studied.Finally,influences of various factors on the thickness uniformity were ranked under three and four passes by orthogonal test,the optimal combination of process parameters obtained.Comparing the optimal simulation of three and four passes to the actual results,we found that the quality of the forming parts under the four conditions is better.The optimal process combination is:forming temperature is 250°,feed rate is 250mm/min,diameter of the forming tool is 10mm,and reduction amount is 0.8mm.