Our business is applying coatings to components of many shapes and sizes. It is typically possible to either draft the nominal shape of the component as a solid model or to build a representation of the piece prior to coating from CMM data. My interest is in measuring applied coating thickness after deposition by taking hits on the modified surface and determining the distance of the hit point away from the original surface. I cannot seem to find a constructed geometry that will fit this need. Does such a tool exist in PC DMIS? In the example below, we measured the conical surface CON1 prior to coating, using CYL1 and PLN1 for alignment. Coating was applied to the interior surface of the cone at PNT1 and PNT2. I'd like to know how far away (in a direction normal to the surface below) PNT 1 and PNT2 are from CON1.
I'm going to make a rough guess here, but please wait for more experienced folks to comment whether I'm on track!
Level to your plane.
Create a line from center of cone to PNT1, rotate XPLUS to that line.
Origin to plane and cone.
Switch to YMINUS workplane
Report your distance in 3D, choosing distance from feature and option: Perpendicular to feature.
Again, please see if I'm shot down before spending a bunch of time on my suggestion, or feel free to point out my errors in thinking! This is how I learn!
Then take a bunch of hits in the cone & report their T value.
T value is the surface deviation from nominal in comparison to perfect vectors off of the CAD. If everything is around 0.005" lets say, then you know thats how much paint you've got in your csk.
It's not exactly as simple as the thickness of a conical coating over a conical surface... the coating is only applied in localized areas and may be non-uniform. Indeed, in many cases, enough of the original uncoated geometry still exists to re-establish the basic shape. My concern is finding the thickness of the new surface in the area where material has been added. I would guess that this would be a matter of finding the vector distance of the point from the underlying surface along a normal vector, however, I cannot see how I can easily get that number.
This sounds like the right approach. I'll give it a go. I was being thrown by the idea of the "center of the cone", which will be the center of the cone body, rather than the intersection of a line normal to the conic surface through point PNT1 and intersecting with the rotational axis of the cone... which would be simpler to interpret.
Thank you for the inspiration... I'll see what it yields
Maybe use an auto cone, You can adjust the angle, size, length based off of perfection. This way each hit is the correct vector and you could extract the hits and make generic points by ASSIGMENT and report polar points and compare before and after?
A CMM is not always the right tool. I've worked with painting shops that do AS9100 level work so they're accredited to their own sort of QMS like NADCAP or something..Anyway, these guys had a gun with a laser & they just had to shoot it at the painted material and it would tell you +/- a few microns how thick the coating was.
If you need to use a CMM then I stand by my original advise.. Establish an origin on your non-coated surface & take as many hits as you can. Once aligned take vector points on your coated surface(s) & report T values of those points.
The only other way I can think of to measure this would be to section the part and measure the coating thickness with some sort of vision system like an OGP or optic-mic
Thanks Dan_M and Jefman.... I think the key was the T value. I need the deviation from nominal of the hits I take, and I wasn't able to identify this parameter from the PC-DMIS literature I'd checked out so far. Dan_M, the gauge you mentioned in your last post is probably an eddy current thickness gauge, and it is great for getting an accurate thickness of a non-ferromagnetic coating applied to a metallic substrate. In my case, I'm literally spraying steel onto steel, and there is not enough dissimilarity in the base and applied materials to use this approach... CMM is my only option. Thanks for the guidance, all!
