Applications
Comparison of aurface areas of engine cylinder faces before and after test runs.
The BMT instrument finds exactly the same location automatically.
Below: honing structure of a new engine
(courtesy of Daimler)
Below: axial wear grooves in the honing structure after test runs
(courtesy of Daimler)
Below: surface structure of new engine
Below: after test runs
Below: surface honing structure of new engine
Below: after 350000 km
Diskussion:
As can easily be seen both measurement files represent exactly the same location on the cylinder face. The honing grooves are interrupted in the bottom image due to scuffing. In addition a pore can be seen which was located directly beneath the surface of the virgin engine. Axial scratches are visible.
Optical Surface Measurement of AluSil Cylinders using the WLICyl profilometer
Measurement with 50x objective:
From the false colour display of the profile amplitudes the Si crystals are clearly visible but also the holes (green) whre the crystals have been torn out.
The following 3D view is less informative since the surface roughness makes the image look noisy. All parameters of interest like grain distribution, average height and in general the visual impression of the surface can be taken from the above measurement file.
Different measurement location:
As can be seen this view represents an area with practically no crystals but one can clearly see the honing grooves. The greenish areas are lower than the blue ones.
This is the corresponding 3D view:
Another measurement location:
The profile amplitudes can be read from the scale on the right hand side. The green areas are holes where the grains fell out. The white spots represent areas from which not sufficient light returned into the instrument. These areas are either too deep or have too high slopes. Precise measurements of individual crystals can be done only by using the large resolution as shown above.
The measurement area is then approx. 200x200 µm. A larger magnification doesn’t make much sense since not more information could be gained. There are very little invalid data points anyway and most of the crystal edges can be measured. Honing grooves and holes can be seen clearly.
A better impression of the grain distribution is obtained by using a less magnifying objective. The following measurements were performed with a x10 objective resulting in a measurement area of approx. 1 mm².
A somewhat unequal grain distribution of the approx. 20 µm crystals is seen.
Different location:
The blue particle distribution is seen and some structured deeper zones (red-yellow).
The average particle height was determined to be approx. 1 µm. This is calculated from the amplitude distribution over the entire area. The statistical relevance is much better than from a single profile line.
Naturally arbitray line zooms can be taken from the area file. The one below corresponds to the line as drawn across the previous image:
Resumeé
Employing the short coherence measurement technique silcion doped surfaces can successfully be measured and the results be analysed. The average particle height and the roughness parameters of interest are determined as well as the distribution of the silicon particles over the area. Broken out crystals can easily be detected.
For detail investigations the x50 objective is used, if areas up to 1 mm² need to be measured the x10 objective is suitable and even larger areas can be measured by a stitching process.
