Numerical Analysis Of Wall-thickness Thinning During The NC Tube Bending Process

The numerical controlled (NC) thin-walled tube bending process has virtues of high efficiency, low consumption and high precision, so it is widely utilized in the fields of aviation, aerospace and automobile industries and so on. However, in the NC tube bending process, there exist failures of wall-thickness extreme thinning and so on. The failures have seriously restricted the development and utility of the NC tube bending technique. For the wall-thickness extreme thinning, the trail-and-error employed in practice, due to its long cycle and high cost, cannot satisfy the demand of NC tube bending technique. Consequently in this thesis, the FEM is used for simulation of NC tube bending process in order to determine the reasonable forming parameters for the process. The main research and its results are as follows:Combined with the TBS-3D system, an analysis module for the thickness during NC thin-walled tube bending process has been developed. The module can be used to analyze and predict the thickness thinning.The effects of different forming parameters on the thinning-rate of wall-thickness are investigated on the basis of the system developed for NC tube bending process simulation and change of wall-thickness predict. The results are described as follows:The relative bending radius has a distinct effect on the wall-thickness thinning-rate. With the increase of relative bending radius, the thinning-rate of wall-thickness has the trend of decrease. However, when the relative bending radius is very small, the change of thinning-rate of wall-thickness has the contrary trend.1) The length of mandrel extension has an important effect on the thinning-rate. As the length of mandrel extension increases, the trend of thinning-rate change can be failed into three stages, namely linear decrease stage, transitional stage and nonlinear increase stage.2) The effect of bending velocity on the thinning-rate of wall-thickness should be considered under two conditions, one with mandrel and the other without mandrel. If the bending process is carried out with mandrel and the increase of bending velocity is limited in a small range, the thinning of wall-thickness tends to decrease. However the thinning-rate of wall-thickness has a minimum value. When the thinning-rate reaches the minimum value, by contrary the thinning-rate decreases with the increase of bending velocity. If the bending runs without mandrel, the thinning-rate of wall-thickness tends to decreases.3) The material hardening exponent and the relative bending radius have great influence on the thinning-rate of wall-thickness, the larger hardening exponent and relative bending radius, the smaller the wall-thickness thinning-rate. However the material strength coefficient has little effect on the wall-thickness thinning-rate.