Visual inspection

Visual inspection ( visual inspection) is the optical or visual control of a product or product part to errors as a regular production step at the end or after the completion of part of the production of the product or product part of quality assurance. Similarly, one performs visual inspections carried on in-service components. The visual inspection as non-destructive testing has been standardized in DIN EN 13018 ( General principles of visual inspection). This standard is also a distinction between:

  • Direct visual inspection without tools (ie consideration of the test surface with the naked eye)
  • Direct visual inspection with aids ( visual aids such as magnifiers, endoscopes, mirror )
  • Remote Visual Inspection ( with camera, video scope, etc. )

The distinction between direct and indirect visual inspection is defined in the standard as follows;

  • Direct visual inspection = visual inspection without interrupting the path between test and eye of the beholder.
  • Remote Visual Inspection = visual inspection with interruption of the path between test and eye of the beholder, that is, converting the light beam into another form of energy, ie electrical information ( camera )

A special form of visual inspection is the automatic optical inspection (AOI ) is computer-assisted each component photographically recorded at the and compared with the computer's own library of components. As a result, an assembly very quickly to the presence or absence, or right or wrong polarity of the components to be checked. Also, this method is also applicable to each solder joint for the relevant module.

Other special forms; Triangulation line camera metrology, photogrammetry, phase delay measurement interferometry. ( These special forms of visual inspection will be explained later ).

Typical defects that should be detected by visual inspection

Mechanical damage (scratches, cracks), dirt, assembly errors, burrs, end crater cracks and undercuts. In addition, color changes ( temper colors in eg austenitic steels ), surface roughness and neck binding errors can be easily identified by visual inspection.

Applications

Production of electronic printed circuit boards, electronic and mechanical ( surface finish ) assembly production, in food production: cleaning of returnable bottles and egg inspection, also for non-destructive testing of all kinds (such as aviation )

Aid

  • Optical magnification ( magnifying glass, microscope, endoscope )
  • Cameras
  • Special lighting ( different colors of light, directional light or diffused light, ...)
  • Automatic optical inspection

Disadvantages of visual inspection

Since the visual inspection is carried out mainly as an activity by people, it is therefore subject just opposite automated tests a poor efficiency. Reasons for this are e.g. Concentration fluctuations, work pressure, fatigue, environmental influences, etc. This results in a " slip through " (not found error ), which can range depending on the complexity of the test specimen and the corresponding working conditions between 5% and 30 %. Even more identical visual inspections in succession improve the effectiveness of only moderate.

  • Quality assurance
  • Material testing
728615
de