TPT May 2009

 Figure 10 : Simulation forming result of strip

 Figure 12 : Simulation of aluminium sheet with 0.5mm

 Figure 13 : Simulation section compared with idea contour

0.9mm. It is observed that when using aluminium sheet with 0.5mm to form in an experiment, the parabolic contour concept and formed section are basically identical. This shows that the main reason causing relatively large deviation between experiments of formed section and idea parabolic contour, is deviation of the existing thickness between experiment materials and designed materials. At the same time, the correctness of the forming method and the roll shape design is proven. 4. Conclusions 1. It has been established that in engineering a method is possible that uses the circle arc to fit parabolic contours and uses subsection arc over the bending method to rollform a parabolic section. 2. When using rollforming to form a parabolic section, the formed section can be controlled with a limited error. The spotlight performance can work normally as a reflector of solar energy. 3. It can be observed that the simulation strip and formed sections are basically identical, and FEA simulation can provide reliable results for engineering design. 4. The Biswas formula is adequate for the calculation of rollforming springback on multi-curvature section. 5. Acknowledgements The authors would like to thank Mr Delin Guo of the Central Research Institute of Building and Construction MM, who was consulted during this study.

0.1 0.2 0.3 0.4

-0.1 -0.2 0

Normal error (mm)

Transverse unfolding coordinate (mm)

 Figure 11 : Even normal error between simulation and formed section

 Figure 14 : Even normal error between simulation section and idea parabolic section The mean value of normal errors of every equally divided point is shown in figure 14. Given the data of table 3, the maximum error is With the same simulation model, the thickness of sheet material and thickness can be changed to 0.5mm, with no other setting change kept. The simulation forming result is shown in figure 12. For the simulation forming result, three sections with a distance of 100mm, 150mm and 200mm to the beginning of forming, are taken to contrast with the contour concept. These results have been analyzed and are shown in figure 13. Here it is possible to view the positions as the simulation section, and the below concept of parabolic contour. Firstly, there are coordinates in the unfolding centre of the parabolic contour concept. Because of the symmetry, only the positive half axle of the transversely unfolding section coordinate is taken into account. Then, this strip is divided equally into six parts; on the divided point, the normal error between the forming section and parabolic contour concept is shown as table 2. In the table, the negative value shows that the simulation section is above the forming section on the divided point.

6. References

[1] Yang Hefeng, Yang Weizhi, Yang Shulan. ‘The effect and optimal design of solar energy reflector used for vacuum heat pipe’ . [J] Rural Energy, 2000(1):12 [2] Liu Fang ， Xin Yongjie. ‘The application of CPC used in solar energy heat collector’ . [J] Solar Energy, 2001 (2): p18-19 [3] data M Software GmbH. Copra RF Software user manual, [K] Germany: [sn], 2007.7 [4] Zhang Shengzhu, Cui Wenxue. ‘The principle of CPC design’ . [J] Solar Energy, 2004 (5): p41-43

-1 -0.8 -0.6 -0.4 -0.2 0

North China University of Technology Fax : +86 10 88801107 Email : Jiyingliu@vip.sohu.com Website : www.rollforming.com.cn

Normal error (mm)

10

20

30 40

50

60

0

Transverse unfolding coordinate (mm)

119

www.read-tpt.com

M ay 2009

›