Research On Influence Factors Of Flexible Three-dimensional Multi-point Dies Stretch-bending Formed Parts Thinning Rate

The flexible three-dimensional multi-point dies stretch bending process of the profile can not only meet the requirements of quickly forming three-dimensional parts at one time,but also the multi-point dies can be quickly reconstructed to meet the threedimensional forming requirements of different profiles types.However,the stress state of the profile is more complicated in this process,which makes it difficult to ensure the forming quality of the product,and it is extremely easy to appear quality defects such as wall thickness reduction.In order to make the process more stable,improve the part forming quality and reduce the production cost,it is necessary to study the wall thickness reducing rule of the profile.In order to ensure the forming quality of flexible three-dimensional multi-point dies stretch bending parts,the influence of various process parameters on the wall thickness thinning rate was explored,and an optimization plan for the process parameters was proposed.A prediction model of the wall thickness thinning rate was established by the SVR algorithm,and the determination processing range of flexible three-dimensional multi-point dies stretch bending process.The research contents and conclusions of this article are as follows:Based on the finite element theory and the technical characteristics of the flexible three-dimensional multi-point dies stretch bending process,a finite element model of the flexible three-dimensional multi-point dies stretch bending process of aluminum profile is established.The aluminum alloy profile applied to the front frame of the highspeed train is used as the research object to carry out flexible three-dimensional multipoint dies stretch bending process.Using ABAQUS finite element simulation software to simulate the forming process,the effects of pre-stretching amount,post stretching amount,the number of multi-point dies and friction coefficient on the profile thinning were studied.The results show that the thinning rate gradually increases along the axial direction of the profile from the symmetrical section.The change in the thinning rate caused by the change in the number of multi-point dies is the largest process parameter.The reduction of the inner and outer webs of the profile is the largest.Thinning rate decreases as the number of multi-point mold unit bodies increases.Under the condition that other process parameters remain unchanged,when the number of unit bodies is 12,the thinning rate of the outer web is 1.682% at the maximum and 1.317% at the minimum,and the thinning rate variation range is 0.365%.The average thinning rate is 1.317%.The maximum thinning rate of the inner web is 1.657%,the minimum thinning rate is 1.198%,the variation range is 0.459%,and the average thinning rate is 1.198%.In the actual flexible three-dimensional multi-point dies stretch bending process test,the difference between the thinning rate of the profile outer web and the simulated data is up to 0.06%,and the difference between the thinning rate of the profile inner web and the simulated data is up to 0.33%,which shows that the finite element model can effectively compare flexible three-dimensional multi-point dies stretch bending process is simulated.(2)Orthogonal test design is carried out for the process parameters that affect the thinning defects of the profile,and the significance of the influence of the process parameters on the thinning defects is analyzed by the range analysis method.The result is that,the number of multi-point dies> friction coefficient> The pre-stretch amount> post stretch amount.The process parameters are optimized and the combination of process parameters is as shown: the number of multi-point die is 12,the friction coefficient is 0.1,the pre-stretch amount is 1%,and the post stretch amount is 1%.In this case,the maximum thickness reduction of the outer web is 0.094 mm,and the maximum thickness reduction of the inner web is 0.086 mm.The stress distribution is relatively uniform,which is the best combination of process parameters.In the actual flexible three-dimensional multi-point dies stretch bending process test,the maximum value of the thinning of the outer web is 0.101 mm,and the maximum value of the thinning of the inner web is 0.087 mm,which is close to the results of finite element numerical simulation.(3)Analysis of the relationship between the change in the average thinning rate of the outer and inner webs of the rectangular cross-section profile and the bending angle.The results show that the average thinning rate of the outer and inner webs of the rectangular cross-section profile is related to the the vertical bending angles increasing,and the average thinning rate of the outer web of rectangular cross-section aluminum profiles under common bending angles is recorded and used as a training sample.The Gaussian kernel function is selected by the SVR algorithm to establish the profile outer web prediction model of average thinning rate,where penalty parameter c is 1.5,parameter g is 0.01,and correlation coefficient is 0.94.The model is used to predict the average thinning rate of the outer web under different combinations of horizontal bending angle and vertical bending angle and establish engineering limit maps.The image reflects the inconsistency of the orizontal bending and vertical bending two processing stages in thickness reducing of the rectangular section profile.In actual production,the production plan with a large horizontal bending angle should be selected as much as possible in order to reduce the amount of thinning of the rectangular cross-section profile.This image has positive significance for guiding production.