Research On The Forming Limit Of Free Bending Process Of Metal Tubes

The free bending technology of metal tube is a flexible bending technology based on the control of die movement.It has great technical advantages in forming components with complex three-dimensional axis and continuous bending without straight section.It has broad application prospects and important application value in the field of complex bending component design and manufacturing in aerospace,automobile and nuclear power.However,free bending technology lags behind the mainstream numerical control bending technology in forming limit,and its application scope is limited.Therefore,it is of great significance to study the forming limit of metal tube coreless free bending,to reveal the key factors affecting the forming limit and its mechanism,and to obtain methods to improve the forming limit of metal tube to promote the further application of free bending technology in the advanced manufacturing field of our country.Based on the principles of plastic mechanics,ABAQUS finite element simulation code and three-axis free bending test device,this paper systematically studies the basic forming principle and deformation law of free bending of metal tubes,the influence of tube parameters and process parameters on forming limit.?1?Based on the established mechanical analysis model and finite element simulation analysis model of coreless free bending process,the law of free bending of metal tubes was studied.Based on the minimum energy method,the wrinkling and instability criterion of forming limit is established,and the analytical method and main influencing factors of forming limit are expounded.?2?A new type of spherical connection between bending die and guide die is proposed.The theoretical maximum travel distance is increased by optimizing the size and structure of bending die.The reliability of the spherical connection structure is verified by numerical simulation and forming simulation.?3?Taking AA6061-T6 tube?15 mm*1 mm?as the basic research object,the geometric parameters,material parameters and process parameters affecting the forming limit of free bending were systematically studied on ABAQUS finite element simulation platform.The effects of series parameters on U-R curve and wrinkling factor under different deflections of bending die were analyzed,and the free bending forming limit?R/D₀=2.5?under optimal strip was obtained,which provides a process optimization method to improve forming limit for practical test and production.?4?Based on the spherical connection mechanism and the optimized process parameters,the experimental verification research on the free bending process parameters and die structure optimization of AA6061-T6 tubes was carried out.The results show that the forming limit of AA6061-T6 tubes is increased from R/D₀=4.32 to R/D₀=2.7 by using spherical connection structure and optimized process parameters,and the thinning ratio of wall thickness is not more than 6%and the distortion ratio of section is not more than 11%in the actual forming test,which has good forming quality.At the same time,the experimental study of tube forming with different wall thickness has been carried out,which verifies that the wall thickness factor has a great influence on the forming limit of tube.Finally,the forming experiments of AA6061-T6,H2 copper and H62 brass tubes were carried out,and the yield strength was verified to be the core material parameter affecting the forming limit of metal tubes.