Tilman Traub

Experimental and Numerical Determination of the Required Initial Sheet Width in Die Bending

So far, determining the necessary precut dimensions of metal sheets prior to bending has been an unsolved question. During the last decades numerous calculation methods have been suggested. However, comparing these different methods indicates that different calculation methods suggest diverging precut dimensions. Especially in roll-forming, where multiple bend operations occur within the same bend part, these differences between several calculation methods can add up to some millimetres. The accuracy of presently available methods can hardly be compared. Thus an optimized method is needed. One possibility to determine the initial sheet width is identifying the position of the unlengthened layer in the bend zone. This study compares the position of the unlengthened layer determined in experiments and numerical simulations for different bend geometries and materials. The results indicate that even state of the art measuring technique is not accurate enough to determine the position of the unlengthened layer properly. Due to high measurement uncertainties, numerical simulations are required to assess the influence of geometry or material parameters on the position of the unlengthened layer. However, combining numerical and experimental results shows that the geometry of the bend part influences the position of the unlengthened layer and thus the required precut dimension. In contrast, a significant influence of material strength on the position of the unlegthened layer was not found.

Energy efficient roll forming processes through numerical simulations

Due to ongoing efforts to mitigate climate change especially large scale manufacturing methods such as roll forming have to be optimized with respect to energy consumption. The required amount of drive power in roll forming is strongly affected by the rotational velocity of the tools. Due to the contoured shape of the rolls resulting in varying circumferential speed, the relative speed between tool and blank sheet can be positive, negative or zero. In consequence, neighboring sections of the same forming roll can accelerate or decelerate the blank sheet. Inappropriate speed ratios between different shafts cause some shafts to decelerate the blank sheet while other shafts have to compensate this deceleration and waste energy. Presently, the rotational speed of the shafts is mainly chosen based on the operators experience leading to a high risk of an energy inefficient process setup. This paper demonstrates how numerical simulations can optimize the energy demand in roll forming and validates the results experimentally. The drive power for each individual shaft is minimized by balancing accelerating and decelerating tool sections. Thus, the optimal rotational velocity for each shaft is derived. The numerical simulation predicts an energy saving potential of 50 %. However, due to limited control accuracy only 14 % could be realized in experiments to date.