Research On Forming Limit Based On Diameter Expanding During Hot Power Backward Spinning For 7075 Cast Aluminum Alloy Tube

As 7075 cast aluminum alloy has many advantages,such as low density,high specific strength,high pressure resistance,corrosion resistance and so on,it has become one of the most difficult forming materials in recent years.Hot power backward spinning of the tube has become one of the most effective processing methods of 7075 cast aluminum alloy.Because it not only can effectively reduce the wall thickness,reduce weight,improve the fatigue performance,but also can eliminate the casting defects,grain refinement and plasticity.In the process of power spinning,the defect of expanding diameter of 7075 cast aluminum alloy tube is an important defect in spinning,which affects the forming quality of spinning parts seriously.Based on ABAQUS finite element simulation platform,the finite element model is established and optimized.Then,the significance of the various process parameters in the forming process is discussed through the range analysis and variance analysis of the orthogonal test and the method of grey correlation analysis.Based on the above studies,the optimal process parameters and forming limit of diameter expanding during the process of hot power backward spinning are obtained.The main research contents and results are as follows:(1)Based on the ABAQUS/Explicit platform,the finite element model is established and optimized through solving key technology,including the selection of roller parameters,the constitutive behavior of the 7075 cast aluminum alloy under high temperature condition,the contact condition,the loading condition and the meshing.Moreover,the reliability of the model is verified by experiment.(2)Based on the established finite element model,the influence of various factors(such as: rollers' feed speed,reduction in each pass,die temperature,mandrel rotation rate,the friction coefficient between the mandrel and the tube and the friction between the roller and the tube)on the degree of expansion of the tube is studied.The results show that: With the increase of rollers' feed speed,the degree of expanding diameter in the previous three passes increases,while the degree of expanding diameter in the fourth pass decreases first and then increases.With the increase of reduction in each pass,the degree of expanding diameter showed a trend of growth.With the increase of the die temperature,the degree of expanding diameter in each pass decreases first and then increases.With the increase of the mandrel rotation rate,the degree of expanding diameter in the first and fourth passes will decrease first and then increase gradually,and the change of the degree of expanding diameter in the second and the third pass is not obvious.With the increase of the friction coefficient between the mandrel and the tube,the degree of expanding diameter in the first and second passes will decrease first and then increase gradually,while the expansion of the third and the fourth pass will increase.The increase of the friction between the roller and the tube has little influence on the degree of expanding diameter in each pass.Based on the above research,the optimum range of the process parameters is obtained.(3)By using the method of finite element simulation,orthogonal experiment and the response surface method,the coupling models between process parameters and diameter expanding are established,and the optimum process parameters of each pass are obtained as follows: The optimum parameters of the first pass are the reduction amount of 2.522 mm,the mandrel temperature of 276.3?,and the spinning rollers' feed speed at the rate of 0.521 mm/s;The optimum parameters of the second pass are the reduction amount of 1.757 mm,the mandrel temperature of 214.8?,and the spinning rollers' feed speed at the rate of 0.726 mm/s;The optimum parameters of the third pass are as follows: the friction coefficient between the mandrel and the tube is 0.079,the mandrel temperature is 138.7?,and the reduction amount of the tube is about 1.478 mm.The optimum parameters of the fourth pass are as follows: the mandrel rotational speed is 3.864r/s,the mandrel temperature is 108.3?,and the friction coefficient between the mandrel and the tube is 0.061.(4)Based on these coupling models above,the prediction model of the forming limit of each pass is established,and the influence of important process factors on forming limit is studied: with the increase of feed speed,the forming limit first increased and then decreased in the first pass;With the increase of rollers' feed speed,the forming limit decreases first and then increases,and with increase of die temperature,the forming limit enhances in the second pass;In the third pass,the forming limit decreased with die temperature increasing and the forming limit increased with the friction coefficient between the mandrel and the tube increasing In the fourth pass,the forming limit increased with die temperature increasing and the forming limit increased with the friction coefficient between the mandrel and the tube increasing.Based on the research above,the forming limit diagram based on diameter expanding during the multi-pass hot power backward spinning is established.