Prediction And Improving Methods Of Forming Limit In Incremental Forming Of Aluminum Alloy Sheets

Incremental sheet forming relies on the movement of the tool along a predetermined forming path to change the shape of the sheet by squeezing it to obtain the desired part.The incremental forming process requires no tooling and therefore has significant advantages in the production of individual products.However,during the incremental sheet forming process,the surface area of the part increases,leading to a gradual thinning and eventual rupture of the part,which is the main factor limiting the limits of incremental sheet forming of the sheet.To achieve effective prediction of the forming limit of sheet metal in the forming process,this study introduces Lemaitre's ductile rupture criterion to the incremental sheet forming based on its effective use in the conventional plastic forming process.In addition,the process of improving the incremental sheet forming limit of sheet metal is investigated by means of experiments,and a combined thermal spraying process and incremental sheet forming process is proposed for the first time to improve the forming limit of sheet metal in the incremental sheet forming process.Based on this,the main research contents and results of this paper are as follows.(1)The forming limit prediction model based on Lemaitre's ductile fracture criterion was constructed.A 2.0-mm-thick AA-2024-T3 aluminum alloy sheet was used to determine the basic mechanical properties of the selected material by unidirectional tensile testing and cyclic loading testing to construct a finite element model for predicting the limit of incremental sheet forming based on Lemaitre's ductile fracture criterion.The prediction results of the model for the unidirectional tensile test and the incremental sheet forming test are compared with the test results to verify the validity of the established Lemaitre criterion finite element model for the prediction of sheet rupture.(2)The influence of the main parameters of the incremental sheet forming process and the introduction of the heat-assisted process on the forming limit is investigated.The effect of tool diameter,step down and spindle speed on the forming limit is analyzed by response surface test.The results show that the forming limit increases with the increase of tool diameter at larger step down;at smaller tool size,the forming limit decreases with the increase of step down;the appropriate spindle speed has a positive effect on the improvement of the forming limit.In addition,it was found that there was an interaction between the tool diameter and the step down on the forming limit.The thermal assisted process has a significant effect on the improvement of the incremental sheet forming limit.(3)A combined thermal spray-incremental sheet forming process is proposed to compensate for the sidewall thinning during the forming process.It is shown that the strength of the sheet is significantly reduced after thermal spraying,and the yield strength of the sheet is reduced by 70%and the elongation is increased by 65%at a suitable thermal spraying power.In the incremental sheet forming process,the axial force of the sheet is significantly reduced after thermal spray treatment and the forming limit is also significantly increased.In addition,the effect of different process steps(sandblasting and heating)of thermal spraying on the forming properties(forming force and forming limit)of the plate was investigated,and it was found that the effect of heating in the thermal spraying process had the most obvious effect on the improvement of the forming properties,while the sandblasting process would reduce the forming properties.Finally,in order to optimize the thermal spraying area,the forming force and forming limit in the incremental sheet forming process were investigated after the thermal spraying treatment with different parameters in different areas.