Reduction of spring back when cutting off rolled profiles
Roll forming is a manufacturing process, whose profitability is predicated on its high output. When rolled profiles are cut to length, residual shear stresses are released and increased spring back deformation at the profile ends, near the cut off occurs, also known as end flare [Figure 1]. Due to this deformation, deviations from the dimensional accuracy can occur, which cause problems during further processing of the parts. Additional operations are necessary to compensate for the end flare, thereby increasing the plant deployment time and the production costs.
The objective of this research is to reduce the shear stresses in sheet metal direction during roll forming, thereby reducing the deformation caused by the occurrence of end flare. With the help of the identified influencing factors and counter measures, guidelines are developed, which allow the enterprises to dimension the roll forming process in a way that the springback deformation at the profile ends is reduced and the dimensional accuracy of the rolled profiles is increased. By reducing the time used for compensation measures, the production costs are decreased and smaller lot sizes get economically more attractive.
At first, by means of a survey, the current status of how the enterprises cope with the occurrence of end flare is investigated, thereby determining the influencing factors on end flare. Subsequently a numerical finite-element-model, which is able to correctly reproduce and predict the springback deformation at the profile ends, is developed and validated by experiments. Based on the numerical and experimental investigations, countermeasures, which reduce the end flare, are developed and their potential for industrial implementation researched. In the end the results are converted into guidelines for the enterprises, which describe how to dimension the roll forming process with regard to low shear stresses.
Identified factors of influence and countermeasures
During the project the following factors of influence could be identified:
- sheet thickness, yield stress, number of forming steps, side rolls
- bending angle sequence (profile flower), type of profile (U, C, …)
- distance between forming stations, profile height
- calibration method, bending radius, roll diameter
The following factors were found to not have a significant influence on end flare:
- Holes within the profile, lubrication, cutting method
Based on the survey and numerical parameter study the following effective countermeasures could be identified:
- Overbending -> Bending back
- Superposition of compressive stresses
- Implementation of additional forming steps during the design of the process
The PtU would like to thank the “Arbeitsgemeinschaft industrieller Forschungsvereinigungen “Otto von Guericke” e.V. (AiF)”, the Research Association for Steel Application (FOSTA) and the following companies for their support.
HÖRMANN Automotive Gustavsburg GmbH
LINDE + WIEMANN GmbH KG
Paul Hettich GmbH & Co. KG
Tillmann Profil GmbH
Voest Alpine Krems GmbH KG