1. Description of Shadows
Turning tool pattern is the macro morphology composed of the remaining machining traces on the machined surface after turning. In high gloss turning, the workpiece materials are mainly copper and aluminum, and diamond blade with 0.4mm radius of tool tip is commonly used. After turning, the surface roughness of the workpiece can reach Ra0.8 μ m (see Figure 1), and the appearance is smooth and bright under naked eye observation.
Figure 1 workpiece appearance and roughness value
Whether there is shadow phenomenon in the workpiece can not be directly observed or measured by the roughness value. When observing the outer surface with a high-power magnifier, strip texture can be seen, which is similar to coarse turning tool pattern. The width of light and dark stripes of workpiece without shadow is basically uniform (see Fig. 2). The light and dark stripes with irregular width can be observed for the workpiece with shadow, and the stripe at the shadow is wide (see Fig. 3).
Using three-dimensional profilometer to detect the outer surface of the workpiece, it can be found that the shadow is caused by the uneven width of convex peak and concave valley of turning tool pattern and the fluctuation of wave crest and trough value, which is mainly manifested in the relatively wide concave Valley, resulting in shadow phenomenon (see Fig. 4 and Fig. 5).