Visual testing (VT)

Recognising external features – simple, standardised and non-destructive

Visual testing is the fundamental method of non-destructive inspection and is based on targeted visual assessment of component surfaces. The aim is to detect visible deviations from defined quality characteristics and evaluate them systematically.

Depending on inspection requirements, testing is performed directly with the human eye or using optical aids such as magnifiers, endoscopes, video borescopes or technical borescopes. A norm-compliant defined inspection illumination and magnification that ensures reproducible detection of surface features is decisive. Parameters such as illuminance, viewing angle and inspection distance are set in accordance with applicable specifications.

During inspection, the component surface is checked systematically. Items assessed include, for example, surface condition, damage, cracks, pores, contamination or assembly states. Evaluation is based on agreed defect catalogues, drawings, limit samples or customer specifications.

For areas that are difficult to access, indirect methods are used, for example optical extension by endoscopy. In safety-relevant applications, visual testing may additionally be supported by photographic documentation or digital image evaluation.

Visual testing enables immediate assessment of component condition without intervention in the material. It often forms the first inspection stage within an inspection concept and supplements other non-destructive methods by quickly and efficiently identifying obvious surface features.

Which defects or characteristics are inspected?

Visual testing can capture the following characteristics in particular:

• Surface damage such as scratches, dents or impact marks
• Cracks and irregularities, insofar as they are openly visible at the surface
• Burrs and shape deviations, for example after forming or machining processes
• Soiling or foreign matter that impairs further processing or function

What advantages does visual testing offer?

Visual testing is the fundamental method of non-destructive inspection and offers the following advantages in particular:

• Broadly applicable, independent of material type and component geometry, provided adequate accessibility and lighting are ensured
• Immediate availability of results, because evaluation is performed directly by visual means
• Non-destructive execution without impairing component function
• Economical first inspection step, in particular as part of a tiered inspection concept

In which application cases is visual testing appropriate?

Visual testing is used in almost all areas of industrial quality assurance. Typical application cases are incoming inspections, in-process controls and final inspections before dispatch.

It is particularly suitable as a first inspection step to sort out obviously defective parts at an early stage and to deploy further inspections in a targeted way.

In which industries is visual testing typically used?

Visual testing is used across industries wherever component surfaces, visible features or assembly states must be assessed systematically, including:

• Automotive and supply industry
• Aerospace
• Mechanical and plant engineering
• Energy and power plant industry
• Rail vehicle and railway technology
• Metal processing as well as forging and foundry operations

The specific design of the inspection depends on the component, accessibility, lighting situation and the respective quality requirements.

Which norms and standards are relevant?

Visual testing is carried out on the basis of the agreed customer specifications, drawings and inspection plans. Organisational and documentary handling is integrated into our quality management system according to DIN EN ISO 9001.