Investigations of the through-thickness residual stress distribution during the partial heating roll forming process of square and rectangular hollow steel sections

With the growing demand for rectangular and square hollow steel sections in the last few decades, the cold roll forming process has become a widely acknowledged hollow sections manufacturing method; however, residual stress generated during the roll forming process is one of the primary concerns on roll-formed products. In this regard, several researchers have conducted numerical and experimental investigations of residual stress distributions on roll-formed steel sections. However, most of the studies found in the literature have been confined to the measurement of residual surface stresses. On the other hand, experimental studies conducted on fatigue and load-carrying capacity of hollow structural steels have shown that there is indeed a simple relation between the through-thickness residual stress distributions and mechanical properties of structures. Thus, this paper employed a proper numerical modelling procedure using LS-DYNA’s finite element code to explore through-thickness residual stress distributions generated during the roll forming process of rectangular and square hollow steel sections from different material grades. Moreover, a small-scale parametric study was conducted to explore the effects of the partial heating roll forming method on through-the-thickness residual stress distributions to satisfy the growing demand for residual stress-free roll-formed products.

The origin of end flare in roll formed profiles

Roll forming is a continuous manufacturing process designed for large batch sizes. In order to economically produce roll formed parts with smaller batch sizes, the process setup times have to be reduced. During the setup, profile defects and especially the deformation caused by the release of the process-inherent residual stresses, also known as end flare, have to be counteracted. However, the knowledge regarding the creation of residual stresses is limited and the ability to reduce end flare usually depends on the experience of the process designer and the machine operator, which makes the setup time-consuming and cost-intensive. Therefore, in this paper the creation of end flare during the roll forming process is investigated in depth. As a result of this study explanation models for U-, C- and Hat-profiles, which link the creation of residual stresses to the local deformation during the forming process, are developed. Knowing how changes in the forming curve affect the creation of end flare allows to use a knowledge-based approach during the design and setup process, thereby reducing time and costs.

A Method for Rapid Prediction of Edge Defects in Cold Roll Forming Process

In order to implement rapid prediction of edge defects in the cold roll forming process, a new analytical method based on the mean longitudinal strain of the racks is presented. A cubic spline curve with the parameters of the cumulative chord length is applied to fit the corresponding points and center points of different passes, and fitting curves are obtained. As the cold roll forming is micro-tension forming, the tensions between racks are ignored. Then the mean longitudinal strains between racks are obtained. By comparing the mean longitudinal strain between racks and the yield strain of the material, we can judge whether there are defects at the edges. Finally, the reasonableness of this method is illustrated and validated by an example. With this method, the roll forming effect can be quickly predicted, and the position where a greater longitudinal strain occurred can be determined. In order to prevent the defects, the deformation angles need to be modified when the result is beyond the yield strain. To further prove the correctness of the theory, the results of the analytical method are compared with the ones of the non-linear finite element software ABAQUS. The analytical results have the same trend as the finite element results. This method can provide useful guidance to the actual design process.

Effect of Plastic Anisotropy and Process Parameters on the Final Geometry of U-shaped Product in Cold Roll Forming

Since the cold roll forming process is currently used in the production of different sections, it is necessary for manufacturers to further improve the quality of these products. Therefore, it is essential to study various factors influencing the production of these products in detail and provide effective solutions to reduce the factors causing defects in such products. This paper investigates the effect of plastic anisotropy and various factors such as strip thickness, the inter distance between stands, web width, and angle increment on the longitudinal bowing and then compares the results with the practical experiments. Accordingly, a model considering the effect of these parameters on the longitudinal bowing of the final section is considered with the accuracy of 88%. The results show that strip thickness and the increment angle at each stand, and the web width have the most influence on the longitudinal bowing, while strip anisotropy and the inter distance has the least effect on bowing.

Application of Support Vector Regression and Genetic Algorithm to Reduce Web Warping in Flexible Roll-Forming Process

In a flexible roll-forming process, a metal blank is incrementally deformed into the desired shape with a variable cross-sectional profile by passing the blank through a series of forming rolls. Because of the combined effects of process and material parameters on the quality of the roll-formed product, the approaches used to optimize the roll-forming process have been largely based on experience and trial-and-error methods. Web warping is one of the major shape defects encountered in flexible roll forming. In this study, an optimization method was developed using support vector regression (SVR) and a genetic algorithm (GA) to reduce web warping in flexible roll forming. An SVR model was developed to predict the web-warping height, and a response surface method was used to investigate the effect of the process parameters. In the development of these predictive models, three process parameters—the forming-roll speed condition, leveling-roll height, and bend angle—were considered as the model inputs, and the web-warping height was used as the response variable. The GA used the web-warping height and the cost of the roll-forming system as the fitness function to optimize the process parameters of the flexible roll-forming process. When the flexible roll-forming process was carried out using the optimized process parameters, the obtained experimental results indicated a reduction in web warping. Hence, the feasibility of the proposed optimization method was confirmed.