Process modeling and optimization of the staggered backward flow forming process of maraging steel via finite element simulations

Flow forming is used to produce thin-walled high-precision tubular components. A 3D thermo-mechanical finite element model for staggered backward flow forming of a cylindrical workpiece of maraging steel has been developed using Abaqus/Explicit. The effect of tip radius of the rollers and friction between the rollers and the workpiece has been considered. Simulations have been carried out at different process conditions to study the state variables, such as stresses and strains obtained during the deformation. The model has been benchmarked for thickness reduction and roll forces against the experimental results and analytical solutions, respectively. The effect of flow forming process variables, such as feed rate and reduction ratio, on the stress/strain distribution and roll forces have been studied. An increase in feed rate from 1 to 2.33 mm/s leads to an increase of 7 % in effective plastic stress. An increase of 72 % in equivalent plastic strain has been observed when the reduction ratio is increased from 23 to 33 %. In addition, a parametric study has been conducted to study ovality, diametral growth, roll forces, stresses, and strains as a function of process parameters. The circularity of the tube is a very important geometrical feature in the flow forming process. It is imperative to study the key parameters affecting the circularity of the preform. Eight process variables have been considered in a response-surface-based computer design of experiments to minimize the ovality. The feed rate, reduction ratio, and the attack angle of the roller Z are found to be most significant parameters in order to control the circularity of the tube. Among all process variables, the reduction ratio is found to be the most significant parameter. The order of their relative significance is reduction ratio, feed rate, and the attack angle of the roller Z.