3D Model Surface Preparation for Laser Scanning
Customers can reduce the cost of laser scanning by doing their own surface preparation.
The ZScanner 800 (Creaform EXAscanner) is a versatile scanner capable of .2mm resolution and up to .04mm accuracy. One drawback to this scanner is that it is sensitive to surface color and specularity. Colors like red and black are difficult to scan and highly reflective surfaces can be impossible to scan. Proper surface preparation can improve feature detection, scanning speed and scanning accuracy.
The ideal surface for scanning is smooth, white and matte. As colors get darker, scanning speed decreases; a black surface can take 4 or 5 times as long to scan as a white surface. As surfaces get more specular (shiny), scanning noise increases; a highly reflective surface is all noise and no signal making it impossible to scan. And the scan data is always rougher than the surface, as surfaces get rougher, it becomes harder and harder to resolve features.
Of course, before any surface preparation can be done, the part to be scanned must be thoroughly cleaned and dried. Once this is done, the surfaces can be prepped in 1 of 4 ways:
1. Painting
Painting is the method of choice. Aerosol paint is relatively easy to apply and covers well. For scanning accuracy, Krylon Gray Primer is best. For scanning speed, Krylon Flat White works well. Whichever is chosen, the paint should be applied as thinly and as evenly as possible. Usually .0006" to .0010" is plenty. Of course the paint thickness alters the scanning results, but the results can be offset in software by the paint thickness, which will cancel out the paint thickness. But only one thickness value can be entered so it’s important to keep the thickness uniform.
Of course paint can only be used on parts that you don’t mind being painted or which are sturdy enough to hold up to removing the paint. Methyl Ethyl Ketone (MEK) will remove paint easily, but will damage many surfaces and dissolve some plastics. Be sure to read the safety precautions on the MEK container before using.
2. Powder Coating
An aerosol powder like Magnaflux SKD-S2 can be applied much like aerosol paint. The difference being that the powder is easily removed by rinsing, brushing or blowing off with compressed air on most surfaces. The powder is diatomaceous earth, which are essentially tiny silicon crystals. It’s nearly impossible to get out of porous materials and it can be very abrasive making it a poor choice for mechanical assemblies and mechanisms. The propellant can also slightly alter some finishes, especially painted surfaces and plastics.
Being easy to remove also means having to handle the part with extreme care. Even the slightest bump or breeze can knock off the powder.
3. Waxing
For high quality painted surfaces or plated surfaces, a light coat of paste wax works pretty well. Just apply the wax and let it dry to a haze. The thicker the better, but I’ve scanned chromed handle bars with only a very light coat of wax. Once the part has been scanned, just wipe/polish off the wax.
While this method works, the scanning rate is usually much slower than with paint or powder.
4. Replicate Casting
Replicate casting is used when the part is too complex for wax and too important or too delicate for paint or powder. Special low shrink silicone rubber is used to make a negative of the part and then the negative is scanned instead of the part. This method is also used to scan internal features that the scanner can’t normally "see".
Replicate casting can significantly increase the time and cost to process a part and is usually the method of last resort.
Not all surfaces require preparation prior to scanning. But for surfaces that do require it, customers can save money by doing as much of the preparation as possible.
