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RISS 인기검색어
- 검색키워드
- 저자 : Christian Löbbe (검색결과 2 건)
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Closed Loop Springback Control in Progressive Die Bending by Induction Heating
Christian Löbbe,Christoph Hoppe,Christoph Becker,A. Erman Tekkaya 한국정밀공학회 2015 International Journal of Precision Engineering and Vol. No.
Large springback of high strength steels in progressive dies hinders accurate manufacturing because a proper prediction of elastic unloading is not possible due to material variations, tool wear, and varying ambient conditions. In order to compensate springback and enhance the forming limit when brittle materials are bent, a warm bending technology for progressive dies through inline induction heating is developed. Within a certain temperature range, there is a linear relation to the springback angle, which allows a direct influence on the final bending angle. Based on this principle, a closed loop control with a feedback of the angle after unloading is implemented, which adjusts the sheet temperature before bending. With the developed discrete controller, finally a stable and fast control mode is achieved so that an initial deviation from the target value is reduced to less than Δθ = ±0.30°.
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Stress state analysis of radial stress superposed bending
Rickmer Meya,Christian Löbbe,A. Erman Tekkaya 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.20 No.1
Radial stress superposed bending is a sheet metal bending process, which superposes predetermined radial stresses. Stress superposition is mandatory to enable the reduction of the triaxiality in bending, resulting in delayed damage evolution and an improved product performance. The knowledge of the stress state is essential for damage-controlled bending as the triaxiality is the driving force for the void evolution. To control the stress state in radial stress superposed bending, an additional counter force responsible for the pressure in the outer fiber is applied. To predict the effect of the counter force on the radial stress and the triaxiality an analytical model is proposed. The prediction of the reaction forces in the system is required for the process design and for the calculation of the stress superposition. The stress state for plane strain bending with stress superposition is derived, and pressure calculations are made using the theory of Hertz. The model and the assumptions are verified in numerical and experimental studies for various counter pressures and bending ratios. Finally, a discussion of the load path depending on the transient counter pressure is carried out and experimental evidence for a inhibited damage evolution due to stress superposition is given.
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