Roughness measurement

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Roughness measurement

The roughness of a surface is the decisive feature and can be quantified by roughness measurement.

Roughness affects characteristics such as counter body wear, noise emission, oil retention volume, sliding friction and thus the stability of the system in general.

With their patented optical measurement method (combination of confocal microscopy and focus variation in a single system) and high data density, Confovis 3D surface measurement systems enable roughness measurements down to the single-digit nanometer range.

Profile-based roughness measurement

To ensure constant quality of a surface in production, parameters of profile-based roughness measurement are recorded by profile methods, referenced to specifications in the technical drawings and the manufacturing process is adapted as necessary.

The DIN 4760 standard describes surface roughness, for technical surfaces, as a surface deviation of the third to fifth orders. In this case, a profile orthogonal to the machining direction is recorded by the profile device and calculated using a Gaussian filter with a prescribed cut-off wavelength.

Profile-based surface parameters such as Ra, Rz or Rpk are determined from the roughness profile so obtained. For homogeneous surface structures, this method is a robust and well-established way of checking the processes. The analytical procedure is specified in the standards DIN EN ISO 3274 and DIN EN ISO 4287/4288 and includes, among other things, the defined measuring section and filtering with corresponding λc.

 
 

Area-based roughness measurement

The optical measuring systems from Confovis measure the roughness of surfaces in their entirety without tactile scanning. In comparison with exclusively profile-based devices, the roughness measurement not only determines a profile series for 2D parameters, but also full-surface 3D roughness parameters. The S-parameters obtained in accordance with the DIN EN ISO 25178 standard offer a multitude of new evaluation options and characterize the function of the surface at high stability.

A transfer of the tactile R-parameters of old profile devices to the modern S-parameters is guaranteed and can always be traced. A major benefit of the confocal 3D surface measurement system is the artifact-free generation of measuring points on unknown surfaces. The optical measurement method from Confovis can handle almost all metal surfaces, glasses, transparent layers, ceramics, plastics and many other materials from very shiny to very rough. In addition, roughness parameters can be determined according to all commercially available roughness standards.

The standard deviations of the roughness parameters obtained are within the same range as those specified by the German National Metrology Institute (PTB) for the quantification of the standards.

Optical roughness measurement with Confovis

In comparison with conventional profile-based methods, no stylus wear occurs when determining the roughness of the surface in the Confovis surface measuring systems. This means that there are no running costs for new probes and the surfaces of the specimens, which may be very sensitive, are not damaged by the measurement. Due to the higher lateral resolution of the Confovis measurement system, the significantly increased density of measuring point reveals additional features of the surface. The automatic generation of up to 22 profile lines per single measurement and an increased measuring point density generate much more precise roughness data of the surface. The traceability of the roughness measurements to standards DIN EN ISO 4287, 4288 and 13565 can be determined at any time using standards (e.g. the superfine KNT 4070/03 roughness standard series from HALLE).

Up to now, the profile method has been the PTB gold standard for profile-based roughness measurements, which Confovis measuring systems can reproduce without limitation. The surfaces measured with the Confovis measuring software are analyzed with the MountainsMap® software. Function-based surface parameters according to DIN EN ISO 25178 are also available.

Roughness measurement traceable to standards

Traceable to the “gold standard” of PTB

HALLE roughness standard type D2 according to ISO 5436-1 with a Rz of approx. 0.5µm.

The result table shows the agreement of the roughness parameters determined from the standard with those of PTB. The transfer of the tactile 2D roughness parameters to the optical ones is possible without restriction.

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