Research On Small Bending Radius Forming Technology Of Thin-Walled Tubes

With the rapid development of Chinese industrial modernization,the integral plastic forming tube bending parts are widely used in aerospace,automobile,ships and other industrial fields.etc.However,due to the particularity and complexity of the deformation of billet material in the whole bending process of thin-walled tubes,it is easy to produce defects such as buckling,thinning,cracking,and cross-section distortion.This paper used the combination method of theoretical analysis,finite element simulation and experimental study on LF2 M Aluminum Alloy thin-tube which external diameter is 32 mm and thickness is 1mm,respectively,with long straight thin-walled elbow with small bending radius of bending and shear bending process of liquid filled pipe forming technology.The research and results of this paper are as follows:(1)The principle and parameters of the small bending radius of thin-walled tube elbow with long straight tube were analyzed;the basic mechanical properties of LF2 M thin-walled aluminum alloy tubes were obtained by tensile test at room temperature;the process of tube bending is studied by choosing the way of compensating the material at both ends by the comparison and analysis of three kinds of tube under pushing and bending are carried out.(2)The finite element model of the small bending radius of thin wall elbow with long straight tube was established by using the ABAQUS finite element simulation software.The numerical simulation of the bending process of the pipe was carried out with different process parameters.The results show that: the internal pressure was too large to cause accumulation of wrinkling and the shortage of the pipe and elbow forming pushing head contact;the small internal pressure would cause the defects of buckling of the tube and the distortion of the cross section.The proper increase of the friction coefficient could effectively restrain the thinning of the lateral wall of the tube and reduce the ellipticity of the section of the tube.However,the excessive friction coefficient will reduce the quality of the tube forming and affect the life of the die.(3)The experimental study on the 1 time relative bending radius(1D)of thin-walled tubes was carried out by using polyurethane as the elastic medium filled with the tube.The inner pressure of the bending of the tube is adjusted by changing theback pressure of the core shaft.The friction coefficient between the tube blank and the mold cavity is adjusted by changing the lubrication method.The experimental results show that:The qualified forming tube could be prepared by using molybdenum disulfide lubricant and the backstepping pressure was 0.8MPa.(4)Through theoretical analysis,the principle of shear bending forming of thin-walled tube is studied.The finite element model of thin-walled tube filling shear bending forming was established,and the influence of different internal pressure and feed ratio on the quality of pipe bending forming was studied.The results show that:The inner pressure is too small to support the tube and the wall of the tube is wrinkled.The internal pressure is too big to cause the excessive thinning of elbow and even crack.The sealing failure of the tube will occur when the feed ratio is too small,and wrinkling when the feed ratio is too big.(5)A set of special equipment and die for tube filling and shearing bending forming has been developed.Using LF2 M aluminum alloy tube,the bending forming experiment of the tube material with relative bending radius of 0.8 was carried out.By changing the forming process parameters,the influence of different internal pressure and feed ratio on the quality of tube forming was studied.The experiment shows that:When the internal pressure is 20 MPa,the feed ratio parameters under 1.0 can get better effect of tube shear bending.