TPT May 2009

 Figure 3 : Forming machine used for experiments

 Figure 4 : Formed samples for experiments

 Figure 5 : Detection facility

The adopted samples were precut aluminium sheets; there was an unavoidable error at the beginning and end of the forming section. When checking the forming section of the samples, it was decided to select three cross sections along the forming direction. The distances from the beginning section were 400mm, 500mm and 600mm respectively. The detection facilities included a FaroArm Tumbler trilinear coordinates measuring instrument and one PC with CAM2 Measure software. The two detection facilities are shown in figure 5. To ensure that the checked section was normal to the axes of section, a V-type tank combined fixture was used to orient in the course of checking. Discrete points on the section contour were measured by detection facilities. In this study, discrete points on the section were fitted by reverse engineering using soft Imageware and create section contour curve. Three forming sections of each sample were fitted and compared with the theoretical parabolic contour. Then, the symmetrical point of section was used as a coordinate (0, 0), shown in figure 6. Because of the symmetry, only the positive half axle of a transversely unfolding coordinate of section was taken into account. This strip is divided equally into six parts, and on the divided point, the normal error between the forming section and theoretical parabolic contour is shown in table 1.

 Figure 6 : Formed section and theoretical parabolic contour

2 2.5

0 5 1 5

Normal error (mm)

0

10

20

30

40

50

60

Transverse unfolding coordinate (mm)

 Figure 7 : Mean normal error between formed section and theoretical parabolic contour

 Table 1 : A normal error between formed section and theoretical parabolic contour (mm)

The mean value of normal errors of every divided point is shown in figure 7. Given the data of table 1, the maximum error lies in the edge part of the formed section, and its value is 2.13mm. According to the fitting curve of the formed section, the curvature and direction of the normal line can be received. It is possible to determine the reflection path of the random beam reflected by formed section. Figure 8 shows the reflection path of the parallel light with a normal incidence reflected by the formed section and theoretical parabolic contour.

Transverse unfolding coordinate of section (mm)

Formed section in Z coordinate (mm)

Sample No.

X=0 X=10 X=20 X=30 X=40 X=50 X=60

Z=400

0 0.34 0.63 1.24 1.71 1.89 2.03

1

Z=500

0 0.35 0.69 1.54 1.97 2.06 2.08

Z=600

0 0.32 0.77 1.48 1.92 2.10 2.20

Z=400

0 0.27 0.50 1.09 1.62 1.97 2.17

2

Z=500

0 0.27 0.59 1.26 1.79 2.02 2.18

Z=600

0 0.23 0.49 1.15 1.78 2.02 2.22

Z=400

0 0.23 0.45 1.05 1.56 1.84 2.10

 Figure 8 : Collation of spotlight performance of formed section and parabolic contour

3

Z=500

0 0.32 0.58 1.17 1.68 1.98 2.23

Z=600

0 0.41 0.81 1.48 1.62 1.85 1.99

117

www.read-tpt.com

M ay 2009

›