Role of filling material on defects of thin-walled tube bending process

This paper investigates approaches to avoid common defects such as the wrinkling, cross section distortion and changing in wall thickness in the bending process of a thin-walled tube. A series of experimental tests has been carried out by filling the tube with melted lead and different types of rubbers. Firstly, tubes were filled by several kinds of rubbers and bended, but the wrinkling was observed at the inner side of the tubes. Also the cross section distortions happened to be above the acceptable range. Therefore, rubbers could not be a suitable filling material for steel tubes. As the second case, lead was used as the filling material to avoid the defects. For this purpose, the tubes were filled by liquid lead and it was solidified to form a leady core to support the inner part of the tube bend. After the bending process, lead is melted and removed. This removable leady core was called the ‘Leady Lost Core’. To study the process numerically, a 3D finite element model of the horizontal bending process has been built using a commercial code. Experimental tests have been carried out to verify the simulation results and developed to provide additional insight. To consider the friction coefficient, in this work, “The Barrel Compression Test” method has been used. Comparisons between the experimental and finite element results have shown remarkable agreement. They show that wrinkle initiation and cross section distortion can be avoided with a lost core of low temperature melting metal like lead or tin.