Application Note | Surface Finish
Machining Surface Finish Quality Using 3D Profilometry
Roughness and Machining Marks on Polished, Rough and Cut Faces of a Marble Tile
Research & Experimental Testing
Duanjie Li
Visual Design & Editorial
Andrew Shore
Introduction
Cutting tools remove material from the workpiece through shear deformation. Quality cutting tools possess high hardness, toughness and wear resistance. There are different types of cutting tool techniques, including but not limited to linear cutting tools such as tool bits and broaches, and rotary cutting tools such as drill bits, countersinks and chop saws. Cutting tools are selected depending on the specific requirements of the applications.
Importance of Surface Roughness and Texture on Cut Surfaces
Different cutting techniques create cut sections exhibiting different surface features. Flatness, roughness and texture of a cut/machined surface is vital to its end use. Accurate clean cut reduces the further work on grinding and rough edge removal. For example, when marble tiles are manufactured, inaccurate and rough cutting may lead to mismatch during the tile floor installation. Quantitative measurement of the surface texture, consistency, roughness and others is critical in improving the cutting/machining processing and quality control measures.
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Measurement Objective
The roughness and texture of three faces of a marble tile with different surface finish were measured and compared using the NANOVEA ST400 optical profilometer to showcase the capability of the NANOVEA optical profilometer in providing comprehensive and user friendly surface analysis of cut/machined surfaces.
NANOVEA ST400 Standard
Optical 3D Profilometer
Results and Discussion
The false color view and Abbott-Firestone curves of the three faces of the marble tile with different surface finish are compared in Fig. 2. Table 1 summarizes the roughness values. The Abbott-Firestone curve is the cumulative probability density function of the surface profile’s height, and it describes the surface texture of the sample.
The polished top Face 1 shows a relatively smooth surface with an Sa of 0.41 μm. The surface height has a very small variation as shown in the Abbott-Firestone curve. In comparison, Face 2 at the back of the tile without polishing possesses a rough surface with a large height variation ranging from ~10 to above 60 μm. It therefore possesses a much higher roughness Sa of 5.94 μm. Face 3 at the side of the tile shows a patterned surface with directional grooves which were created during the cutting process. The height difference of the peak and valley of the grooves is reflected in the Abbott-Firestone curve. Two maximums at a height of ~50 and 120 μm appear in the plot, resulting in a high roughness Sa of 34 μm.
Fig. 2: False color view and Abbott-Firestone curves of three faces of the marble tile.
| ISO 25178 parameter | Face 1 | Face 2 | Face 3 |
|---|---|---|---|
| Sa (µm) | 0.41 | 5.94 | 33.99 |
| Sq (µm) | 0.61 | 7.71 | 38.10 |
| Sp (µm) | 6.04 | 29.02 | 91.10 |
| Sv (µm) | 7.19 | 47.64 | 377.24 |
| Ssk | −2.38 | −0.89 | −0.34 |
| Sku | 29.54 | 4.56 | 3.79 |
Table 1: Comparison of roughness values of the three faces.
The 3D views of the three surfaces with different finish as displayed in Fig. 3 provide users an ideal tool to directly observe the surface morphology from different angles in detail and to evaluate the shape, flatness and roughness of the marble tile for the purpose of quality control.
Fig. 3: 3D view of the scanned surfaces.
The 2D profiles across the machine mark direction of Face 3 are shown in Fig. 4 as an example. The depth and distance of the valleys of the surface texture is fairly uniform. The valleys have an average depth of ~77 μm, in agreement with the result shown in the Abbott-Firestone curve.
| Groove parameter | Step 1 | Step 2 | Step 3 | Step 4 |
|---|---|---|---|---|
| Width (mm) | 0.453 | 0.684 | 0.717 | 0.369 |
| Maximum depth (µm) | 99.7 | 98.6 | 109 | 96.6 |
| Mean depth (µm) | 77.9 | 77.7 | 82.3 | 76.2 |
Table 2: Groove dimensions on Face 3 (from Fig. 4).
Conclusion
The roughness and texture of three faces of a marble tile with different surface finish are measured using the NANOVEA ST400 non-contact profilometer. We show that the NANOVEA 3D profilometer is a useful tool in quality control of the surface finish after cutting and machining. NANOVEA Profilometers measure a variety of materials, including but not limited to metals, polymers, ceramics and glass. The analysis software provides measurements such as uniformity and roughness, texture, peak and valley profile, enabling users to obtain comprehensive information of the surface quality.
The data shown here represents only a portion of the calculations available in the analysis software. NANOVEA Profilometers measure virtually any surface in fields including Semiconductor, Microelectronics, Solar, Fiber Optics, Automotive, Aerospace, Metallurgy, Machining, Coatings, Pharmaceutical, Biomedical, Environmental and many others.
Frequently Asked Questions About Machined Surface Finish
Why measure the surface finish of a cut or machined part?
Flatness, roughness and texture determine how a part performs and fits; an accurate clean cut reduces grinding and edge removal, and rough cutting of tiles, for example, causes mismatch during installation.
How rough were the three marble faces?
The polished top face had an Sa of 0.41 µm, the unpolished back 5.94 µm, and the saw-cut side 33.99 µm.
What does the Abbott-Firestone curve show?
It is the cumulative height distribution of the surface. On the cut face it shows two maxima, at about 50 and 120 µm, from the peaks and valleys of the cutting grooves.
Can cutting marks be measured individually?
Yes. A profile across the machine marks gave four grooves with widths of 0.369 to 0.717 mm and mean depths of 76.2 to 82.3 µm, a fairly uniform average of about 77 µm.
Which materials can be measured?
Metals, polymers, ceramics, glass and stone, polished or rough, since the chromatic confocal pen measures without contact and with no influence from reflectivity.
Which instrument was used?
The NANOVEA ST400 3D non-contact optical profilometer.
