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Sheet metal channels with variable sections or local features have been widely used in automobile and construction industries, and novel forming techniques, such as flexible roll forming process, flexibly reconfigurable roll forming process, Deakin's flexible forming facility, and chain-die forming recently have been developed to manufacture those channels. In this paper, the feasibility of chain-die forming technique to manufacture channels with variable sections is systematically investigated through experiment and finite element simulation by taking 6 types of channel products as demonstration, including three variable-width and three variable-depth profiles. The forming process of the channels shows a combination of roll forming and stamping, and this roll-stamp mode has great potential in manufacturing a wide variety of channels with variable cross-sections. The formability for roll-stamp forming variable-depth channels is evaluated through finite element simulation and forming limit diagram. The roll-stamp mode can be discomposed into roll forming longitudinally and stamping vertically, and can achieve a reduction in forming load by the maximum of 33.9% compared with the conventional stamping in forming the flange step product. The forming direction sensitivity of the variable-width feature is discussed from the aspect of web arch height development. [ABSTRACT FROM AUTHOR]

As a kind of progressive sheet metal forming process, chain-die forming is suitable to form thin-walled high-strength channels. However, sidewall wrinkling is one of typical shape defects on the chain-die formed parts and hard to be predicted accurately. In this paper, the mechanism of sidewall wrinkling during the chain-die forming process is investigated numerically and experimentally. Considering the twist of transitional surface which is a characteristic feature of chain-die forming, a new theoretical model for predicting sidewall wrinkling is established by combining the energy method with finite element simulation. A typical channel with variable widths is designed as a benchmark case and the chain-die forming experiment is carried out to verify the accuracy of the proposed model. Moreover, based on the proposed model and response surface methodology, the influence of radial stress on sidewall wrinkling is analyzed and wrinkling limit diagrams in terms of geometrical parameters are established. The results show that the fold angle has the greatest influence on the sidewall wrinkling. Finally, a two-pass chain-die forming scheme is proposed and implemented to suppress the sidewall wrinkling on the channel. The present work provides a wrinkling prediction tool for the process design of thin-walled channels in the chain-die forming. • A new wrinkling prediction model for progressive forming is established. • Twisted transitional surface reduces the anti-wrinkle ability of sidewall. • Image recognition method is used to identify onset of sidewall wrinkling. • Effects of geometric parameters and stress state on sidewall wrinkling are studied. [ABSTRACT FROM AUTHOR]

High-strength metal channels with local features are widely used in the automobile industry. In this study, the chain-die forming of long channels with local features is investigated. Two key problems in forming local features under the unique roll-stamping mode, position lag and interference between the workpiece and die blocks, are analyzed by kinematic modeling of die blocks at the forming and release stages. Considering the progressive rotational movement of discrete die blocks, design criteria for the die blocks and local features are proposed. Finally, a flat blank and U-channel with local features are designed as two benchmark cases to validate the proposed design criteria by simulation and experiment. The results show that the forming problems are solved, and the forming precision of the local features can be significantly improved. This study provides effective process design guidance for the chain-die forming of long channels with local features. [Display omitted] • Chain-die forming of channels with local features by roll-stamping mode is studied. • Two forming problems, position lag and interference, are found and investigated. • Position lag can be effectively compensated by shortening die blocks. • A taper angle design criterion is proposed to avoid interference of local features. [ABSTRACT FROM AUTHOR]