Re: SLS Technology

From: David K. Leigh (
Date: Tue Aug 01 2000 - 19:53:33 EEST

> 1. Can anyone tell me how to calculate the beam diameter or laser spot
> of a CO2 laser as it sinters the powder at 3W or 4W? Does anyone know the
> maximum intensity of the CO2 laser?

Spot size is best measured, not calculated. You can place a laser
profilometer at the height of the powder bed and get a micron measurement.
The spot size is usually 400 microns.

The effective diameter has almost infinite possibilities. If you took a low
melt material (wax) with a 400 micron beam at 5 watts and let the beam sit
for a full minute, you would get a hugh "blob" of melted material that could
measure several inches. If you took the same laser at the same power and
scanned a bed of higher temp plastic and a fast speed, you might not even
"melt" the powder.

The variable of dwell time probably has more to do with the effective
diameter than the actual spot size.

> 2. How can you find the average number of scan vectors per slice for any
> *.stl file?

This is done in the software and DTM would have to tell you this. But, you
can look at your setting for fill scan spacing. If you have the spacing at
0.010" you would have 100 vectors per inch in the Y direction. So, if you
were scanning a solid that measured 4 inches in Y, you would have roughly
400 scan vectors. If it were a square with a hole in it, with simple
geometry, you could figure this out as well.

> 3. How can you determine the average scan vector length per slice? Is this
> value based on the orientation in the X-Y plane?

You would have to calculate the area of the slice and divide that by the Y
dimension. This will give you the average X dimension which corresponds to
vector length. But, in complex geometries with thin walls, this number will
not be accurate. You can probably correlate the cross sectional area with
the number of vectors and the overall Y dimension to get a more accurate

But, again, the sliced vector file sent to the scanner has all the
information in it to get these numbers. If I'm not mistaken, I believe it
is a text file. You could take the text files and get a General Scanning
manual to figure out the "code" and generate all the stats you need.

David K. Leigh ph(254) 933-1000
Harvest Technologies fax(254) 298-0125

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