Shape deviations according to DIN 4760
DIN 4760 defines the possible deviations of a workpiece from its planned shape, which can be caused, for example, by
- Tactile measuring methods
- Industrial computed tomography
- 2D measurement technology
- 3D measurement technology
can be determined.
The standard distinguishes between six orders of shape deviation. The first to fourth order can be influenced by adjusting the production process.
The fifth and sixth orders relate to the molecular structure of the base material. They can only be influenced by means of forming, reshaping and changing the material properties.
The six orders of shape deviation
The six orders of shape deviation are defined as follows according to DIN 4760:
1st order: Form deviations
2. Order: Waviness
3. Roughness due to grooves
4. Order: Roughness due to grooves, scales, scales or crests
5. Order: Roughness in the structure of the microstructure
6. Order: Deviations in the crystal lattice of the material
Shape deviations
Shape deviations are oversizes or undersizes when forming, reshaping or machining the product.
Oversizes can be corrected by appropriate reworking. If an undersize is detected, this usually means that the product can no longer be made usable.
Ripple
Waviness is usually caused by rolling errors or compression. Chemical or thermal processes can also cause waviness.
Waviness can only be reworked to a limited extent. When re-rolling or sanding the surface finish, it is easy to fall below the selected tolerance. This can be checked by measuring the surface.
Grooves
Grooves are usually rolling defects. They are caused by inadequate rolling. They imprint their structure into the workpiece and leave this characteristic defect. Correcting these is just as critical as with waviness.
Grooves
Scoring is caused by foreign bodies in the rolling process or by defects in the base material. For example, over-hard sheet metal can cause scoring and cracks during forming.
Roughness in the structure
Roughness in the microstructure is caused by defects in the rolling or hardening process. However, the roughness occurring at the molecular level is less relevant for most production processes.
Deviations in the crystal structure
The crystal structure is largely determined by the ingredients used in an alloy. Other factors include hardening processes and changes to the surface texture caused by acids or alkalis.
Classification of shape deviations according to DIN 4760
The extent to which shape deviations in accordance with DIN 4760 are relevant for the production process depends on the designer’s tolerance specifications. The surface quality is therefore defined on a drawing with a corresponding specification.
