Surface Texture Parameters

Some form of texture and roughness is exhibited by the surface of each component. These parameters vary due to various production methods and the structure of the part itself. It is essential to measure the surface in two and three dimensions (2D and 3D) to control the production process to the degree needed in present applications and to obtain a better understanding about the surface of a component. Surface texture parameters can be categorized as follows:

  • Hybrid
  • Waviness
  • Spacing
  • Roughness

Terminology and Surface Texture Parameters

Cutoff filter is capable of measuring the wavelength at which the surface structure is differentiated between roughness and waviness data. For precise measurements, it is very important to choose the correct filter cutoff in software; profile refers to a 2D slice through an area; areal is a 3D surface area; and evaluation length refers to the area from which data is collected.

A 2D area corresponds to the slice length as defined in the filled plot, and a 3D area corresponds to the field of view of the instrument. Cutoff length or sampling length is the area selected for assessing the roughness parameter, with the cutoff wavelength and surface unevenness spaced well beyond the sampling length being considered as waviness. Centre line or mean line refers to a straight line that is created by measuring a weighted average for each data point, resulting in equal areas above and below the line; and surface texture is the surface’s topography showing certain deviations, which are characteristics of the actual surface. It includes roughness and waviness.

Additionally, hybrid parameters are a mixture of spacing and roughness parameters. Spacing parameters refer to a measure of the horizontal or lateral periodic characteristics of the surface; roughness parameters refer to the finer, non-periodic unevenness in the surface texture during the production process; and waviness parameters refer to a biggar component of surface texture on which roughness is overlaid.

Roughness Parameters

Among the largest set of parameters, roughness parameters include Swedish height (H), areal flatness deviation (ISO flatness), total peak-to-valley profile height (Pt ISO), base roughness depth (R3z), base roughness profile depth (R3z ISO), arithmetical mean deviation (Ra), Kurtosis (Rku), maximum peak-to-valley profile height.(Rmax ISO), highest peak (Rp), mean peak profile height (Rpm ISO), root-mean-square (rms) roughness (Rq (rms), maximum peak-to-valley height (Rt (PV), mean peak-to-valley roughness (Rtm), mean peak-to-valley profile roughness (Rtm ISO), lowest valley (Rv), mean valley profile depth (Rvm), maximum peak-to-valley roughness (), ten-point height (Rz), average peak-to-valley profile roughness (Rz ISO), total peak-to-valley areal height (SPt ISO), base roughness areal depth (SR3z ISO), maximum peak-to-valley height (SRmax ISO), mean peak areal height (SRpm ISO), mean peak- to-valley areal roughness (SRtm ISO), mean valley areal depth (SRvm ISO), average radial peak-to-valley areal roughness (SRz), average peak-to-valley areal roughness (SRz ISO), the average of individual Rz results, measured by slicing the data array in the x-axis (SRzX), and the average of individual Rz results, measured by slicing the data array in the y-axis (SRzY).

Sampling length

Figure 1. Sampling length

ISO flatness

Figure 2. ISO flatness

Pt ISO

Figure 3. Pt ISO

R3z

Figure 4. R3z

Waviness Parameters

Wq is the root-mean-square roughness of all points from a plane fit to the waviness data; Wa is the average deviation or average roughness of all points from a plane fit to the waviness data; and Wy (Wmax) is the maximum height of the waviness data.

Spacing Parameters

Pc (Peaks) represents the number of peaks comprised in the analysis. The average distance between peaks is peak spacing, and the number of peaks per unit area is peak density. S indicates the average spacing between local peaks across the evaluation length, and Sm is the average spacing between peaks at the mean line over the evaluation length. Summits are the number of summits comprised in the analysis; summit spacing refers to the average distance between summits; and summit density refers to the number of summits per unit area. Similarly, valleys are the number of valleys contained in the analysis. The average distance between valleys is called valley spacing, and the number of valleys per unit area is called valley density.

Hybrid Parameters

The arithmetic average surface slope of the entire data matrix is called Δa (Slope Ra), while Δq (Slope rms) refers to the geometric average slope of the whole data matrix. Δtm (Slope Rtm) refers to the average peak-to-valley slope of nine sample areas on the entire data matrix; Iq refers to the root-mean-square deviation of all points from a plane fit to the input data, Ia indicates the average deviation, or average surface height, of all points from a plane fit to the input data; Iy (Imax) refers to the maximum height of the input data; Rvolume is the volume of the roughness data as specified by software as either above or below the surface; RSurfAreaRatio refers to the ratio of the planar area taken up by the data to the roughness surface area; ISurfAreaRatio means the ratio of input surface area to the planar area taken up by the data; and WSurfAreaRatio refers to the ratio of input surface area to the planar area taken up by the data. Bearing ratio parameters such as Rk, Rvk, Rpk, Tp etc. are other hybrid parameters.

Conclusion

The surface texture parameters listed above are important to gain a better insight into the surface of an component and to manage the production process to the extent required in present applications.

This information has been sourced, reviewed and adapted from materials provided by Zygo Corporation.

For more information on this source, please visit Zygo Corporation.

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