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119 M ay 2009 ›
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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.
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
 Figure 10 : Simulation forming result of strip
Transverse unfolding coordinate (mm)
0
-1
-0.8
-0.6
-0.4
-0.2
0
10 20 30 40 50 60
Normal error (mm)
 Figure 14: Even normal error between simulation section and idea parabolic
section
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.
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
 Figure 11 : Even normal error between simulation and formed section
 Figure 12: Simulation of aluminium sheet with
0.5mm
 Figure 13: Simulation section compared with idea
contour
Transverse unfolding coordinate (mm)
-0.1
-0.2
0
0.1
0.2
0.3
0.4
Normal error (mm)