Tube bending is a widely used manufacturing process in the aerospace, automotive, and other industries. During tube bending, considerable in-plane distortion and thickness variation occurs. The thickness increases at the intrados (surface of tube in contact with the die) and it reduces at the extrados (outer surface of the tube). In some cases, when the bend die radius is small, wrinkling occurs at the intrados. In industry a mandrel is used to eliminate wrinkling and reduce distortion. However, in the case of a close bend die radius, use of a mandrel should be avoided as bending with the mandrel increases the thinning of the wall at the extrados, which is undesirable in the manufacturing operation. The present research focuses on additional loadings such as axial force and internal pressure which can be used to achieve better shape control and thickness distribution of the tube. Based on plasticity theories, an analytical model is developed to predict cross section distortion and thickness change of tubes under various loading conditions. Results from both the FEA and analytical model indicated that at the intrados the increase in thickness for bending with internal pressure and bending with combined axial pull and internal pressure was nearly the same. But in the case of bending with the combination of axial pull and internal pressure there was a significant reduction of thickness at the extrados. A parametric study was conducted for the case of bending with combined internal pressure and axial pull and it was seen that with proper selection of the pressure and axial pull wrinkling can be eliminated, thickness distribution around the tube can be optimized, and cross section distortion of the tube can be reduced. Predictions of the analytical model are in good agreement with finite element simulations and published experimental results. The model can be used to evaluate tooling and process design in tube bending.

Tube bending is a widely used manufacturing process in the aerospace, automotive, and other industries. During tube bending, considerable in-plane distortion and thickness variation occurs. The thickness increases at the intrados (surface of tube in contact with the die) and it reduces at the extrados (outer surface of the tube). In some cases, when the bend die radius is small, wrinkling occurs at the intrados. In industry a mandrel is used to eliminate wrinkling and reduce distortion. However, in the case of a close bend die radius, use of a mandrel should be avoided as bending with the mandrel increases the thinning of the wall at the extrados, which is undesirable in the manufacturing operation. The present research focuses on additional loadings such as axial force and internal pressure which can be used to achieve better shape control and thickness distribution of the tube. Based on plasticity theories, an analytical model is developed to predict cross section distortion and thickness change of tubes under various loading conditions. Results from both the FEA and analytical model indicated that at the intrados the increase in thickness for bending with internal pressure and bending with combined axial pull and internal pressure was nearly the same. But in the case of bending with the combination of axial pull and internal pressure there was a significant reduction of thickness at the extrados. A parametric study was conducted for the case of bending with combined internal pressure and axial pull and it was seen that with proper selection of the pressure and axial pull wrinkling can be eliminated, thickness distribution around the tube can be optimized, and cross section distortion of the tube can be reduced. Predictions of the analytical model are in good agreement with finite element simulations and published experimental results. The model can be used to evaluate tooling and process design in tube bending.

Rotary draw bending, which has very good flexibility and easy tooling, is one of the most preferred bending types for tubular profiles. Cross-section distortion and the spring-back phenomena are commonly faced problems in bending processes. Spring-back is the inevitable problem that is to be solved by manufacturer, generally by overbending. For hollow tubes cross-section distortion is another difficulty since using hollow tubes results in higher strain rates and distortions. During the process the thickness of the hollow tube at the inner surface, which is contacting with the die, increases and the thickness of the tube at the outer surface decreases. Wrinkling is another important defect that occurs at the inner surface of the tube in large diameter thin walled tube bendings. This research compares the experimental results with the finite element analysis of the rotary draw bending process. The aim is to obtain bending characteristics of the two material types, SS304 and St37 and so, to reduce the number of the bending in manufacturing. The main parameters in rotary draw bending process are the bending angle, bend radius, material properties and the geometry of the tube that is to be bent. In this study, to deal with the process, two different materials, three different bending angles and three different tube geometries are used in experiments as well as in finite element analysis. In finite element analysis explicit method is used. It is seen that the experimental results are in good agreement with the numerical results.

Bending process is an important forming process in most industrial fields. Springback and cross-section distortion are commonly faced problems in bending process. Springback behavior of closed and open section beams changes with different parameters such as cross-section type, cross-section dimensions, bend radius and bend angle. For closed sections like tube, the dominating problem is cross-section distortion. The thickness of the tube at intrados (inner surface of tube being in contact with die) increases, whereas the thickness of the tube at extrados (outer surface of tube) decreases. Furthermore, another cross-section distortion type for tubes is flattening at extrados which is undesirable in some manufacturing operations. The present research, using finite element method, focuses on investigating the springback behavior of commonly used aluminum beams which are T-Shaped, U-Shaped and tubular for different cases. A series of analyses is performed for a beam and the changing parameters in the analyses are bend radius and thickness. Furthermore, for tubes, the effects of axial force on springback behavior are investigated. It is seen that the axial force causes stretching and the springback angles are decreased. Moreover, in order to overcome cross-section distortion in flattening for tubes, different internal pressures are used and the effects of internal pressure are investigated. By applying appropriate internal pressure, the flattening distortion is mostly eliminated. Conclusions are drawn revealing springback behaviors and cross-section distortions with respect to bend radius, bend angle, thickness, axial pull and internal pressures. They are in good agreement with other published researches and experimental results. Therefore, the models can be used to evaluate tooling and process design in bending operations.