Grazing Light Visual Inspection
Visual inspection with raking light illuminates a surface from below with a strong, straight light beam. This makes the smallest surface irregularities and deformations visible through shadows. It is used to check sheet metal quality and cast surfaces.
Physicochemical mechanism of action
Visual inspection with oblique lighting uses the fact that a strongly straight light beam is projected onto a surface from below. The slightest irregularities and deformations reflect the light to different degrees, which leads to visible shadows.
Metallurgical relevance & risks in welding
This method is especially helpful for checking sheet metal surfaces and cast surfaces. It can detect the slightest deformations or irregularities that would normally not be visible. This is important because such surface defects can lead to cracks or uneven stresses during welding.
Workshop practice & instructions
To perform a visual inspection with oblique lighting, a straight light beam (oblique light) is directed onto the surface to be inspected from below. The position of the light beam and the viewing angle should be selected so that the shadows are sharp and easily recognizable. This often requires a precisely adjusted light source and a clear, homogeneous background.