The suitability of a workpiece for its purpose depends on the inner properties (material properties, inner discontinuities, e.g. shrink holes, inner imperfections, e.g. segregations) and on its surface condition.

The surface condition comprises the properties of the surface border zone. These are chemical, mechanical and geometrical properties, Fig. 1.1.

Figure 1.1: Properties of surfaces and their tests and inspections

The chemical and mechanical properties comprise chemical composition, grain, hardness, strength and inhomogeneities. The properties of the surface border zone may be different from those in the core zone.

The geometrical properties are defined as deviations from geometrical ideal elements (features) of the workpiece. Geometrical ideal elements (features) are parts of the entire workpiece surface, which have geometrical, unique and nominal form as e.g. planes, cylinders, spheres, cones and tori. They can also be derived as, for example, axes, section lines, generator lines, lines of highest points and edges, Fig. 1.2. Geometrical deviations are

• size deviations

• waviness

• form deviations

• roughness

• orientational deviations

• surface discontinuities

• locational deviations

• edge deviations

Figure 1.2: Examples of geometrical elements

Size deviation is the difference between actual size and nominal size. It has to be distinguished between

• deviation of the actual local size from the nominal linear size or from the nominal angular size;

• deviation of the actual substitute size from the nominal substitute size, see 8.

The actual local linear sizes are assessed by two-point-measurements (ISO 8015, ISO 286 and ISO 14 660-2), see Fig. 8.26. The actual local angular sizes are assessed by angular...