measuring wall thickness
measuring wall thickness
(OP)
hi,
i need to measure the wall thickness of a certain product , the product is made of ceramics and has an egg like shape which makes it very difficult to measure, in addition the wall thickness is not constant and varies along the profile . the average wall thickness is about 8.5 mm.
i tried using standard mechanical measuring tools (all sorts of big calibers and similar methods) , an ultrasonic gauge and i even found a kind of magnet based gauge but they all have the same problem- not accurate enough, i need an accuracy of at least +- 0.01 mm , if anyone has an idea on how to do it id love to hear it.
thanks
i need to measure the wall thickness of a certain product , the product is made of ceramics and has an egg like shape which makes it very difficult to measure, in addition the wall thickness is not constant and varies along the profile . the average wall thickness is about 8.5 mm.
i tried using standard mechanical measuring tools (all sorts of big calibers and similar methods) , an ultrasonic gauge and i even found a kind of magnet based gauge but they all have the same problem- not accurate enough, i need an accuracy of at least +- 0.01 mm , if anyone has an idea on how to do it id love to hear it.
thanks





RE: measuring wall thickness
RE: measuring wall thickness
There are external calipers that look similar to what MintJulep posted, that have digital readouts and read thicknesses directly. We have some that read to 0.005mm (and are therefore probably good to about 0.01 perhaps). Get one with the right tips, or even get one and grind the tips to the right shape for your application, calibrate, and go?
RE: measuring wall thickness
average thickness is 8.5mm and you need an accuracy of 0.01mm ? boy you must have defined a lot of (three?) deciminal places in your dimensions.
how did the manufacturer inspect it ? (to verify that it was to drawing)
is it a complete "egg" shape, or open ?
are you prepared to sacrifice a sample ?
another day in paradise, or is paradise one day closer ?
RE: measuring wall thickness
Another trick would be to cast (using eg. replicast or a low expansion wax) both i.d. and o.d. surfaces, with a tooling insert cast into both surfaces so that the distances from a datum can be measured and the two profiles reconstructed. The problem is that you need to be able to extract both castings, which means no re-entrant surfaces, so you are limited to only parts of the egg shape in any given casting.
RE: measuring wall thickness
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: measuring wall thickness
RE: measuring wall thickness
displacement (archimedes) if you can get the external volume (easy) and the internal volume (accessable ?) and as pointed out above will give the average thickness only.
another day in paradise, or is paradise one day closer ?
RE: measuring wall thickness
RE: measuring wall thickness
RE: measuring wall thickness
RE: measuring wall thickness
another day in paradise, or is paradise one day closer ?
RE: measuring wall thickness
Expensive, but you are going to have to spend it -> if you really, really really need that accuracy.
RE: measuring wall thickness
My thoughts also. And the laser / non-contact approach, too.
Define your project parameters better. I'm still trying to discern the size of the object you want to measure. I see 8.5 mm thick (variable) and 400 mm long. Give more specifics if you want good answers (W x D x H, material, surface roughness, etc.). AND what is your budget? This can be done, but I suspect it will be a custom gage. Do you have a budget for that? And what throughput do you require for measuring parts? One or two, or twenty per shift?
If you could relax the +/- 0.01 mm resolution requirement, then I would propose a robotic system. Could be done with a used robot.
1. Use the CAD model to develop measurement scanning paths on the top/bottom surfaces. Each path point has a normal surface vector for perpendicularity. Easy with CAD tools available today (<wink> of which I sell).
2. Use a high resolution laser displacement sensor (Keyence is my favorite, but there are many others) to measure top/bottom.
3. Do the 6DOF arithmetic to generate thickness values.
4. The challenge to this is the best robots on the market today have repeatabilities of +/-0.020 mm or so. Darn good for a robot, but won't meet your +/-0.01 mm requirement.
Option2: You could continue with the laser displacement sensor concept, but mount it on a CMM or an articulated arm CMM (if the repeatability is suitable). Fixturing your part repeatably would be critical.
Option3: Look at the Keyence applications guides, they will give ideas of mounting TWO sensors through which a product is passed to determine thickness. Many types of laser displacement sensors available: 1D with a tiny laser spot, 2D with a scanning line, 3D (magic) to provide depth. Contact Keyence Applications, maybe they have a solution already.
Option4: go the ol' skool hard tooled gage route. Can be done, but $$.
TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering
www.bluetechnik.com
RE: measuring wall thickness
I didn't know robots could get a positioner within 0.02 mm accuracy in 3D! Nor that a radar/laser/ir sensor could repeat a 0.02 mm reading without hitting the surface.
RE: measuring wall thickness
Not for this particular application, but if the use is sensitive to a characteristic, that suggests the usage itself is a means of measuring it.
For example, no one makes AFAIK, a CMM that can track 1/10th wave over a 2 meter mirror as is required for space telescopes, but the optics used in the telescope certainly can - hence that is the method used to measure the precision of the optics rather than mechanical measures.
OTOH translucency is a related characteristic that is very sensitive to thickness. Maybe that's an option, though the OP is looking for a 0.1% or less variation.
RE: measuring wall thickness
RE: measuring wall thickness
At each of 200 or 300 holes in 3 - 10 - 30 - 40 eggs, you measure the wall thickness at the hole.
RE: measuring wall thickness
RE: measuring wall thickness
If you can't figure it out yourself, designing an instrument like that seems possible. I'd be thinking strain gages
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: measuring wall thickness
the 0.01mm would be dificult even if a accesable with most micrometers
RE: measuring wall thickness
in that case i'd've looked for something that would mould in place.
another day in paradise, or is paradise one day closer ?
RE: measuring wall thickness
RE: measuring wall thickness
RE: measuring wall thickness
Just out of curiosity, what process did you use to manufacture a 400mm long tubular ceramic component having a non-circular radial profile and a wall thickness tolerance of +/-0.01mm? Sounds like a pretty impressive piece of manufacturing work.
RE: measuring wall thickness
A very very large chicken.
RE: measuring wall thickness
RE: measuring wall thickness
I'm picturing a dial indicator mounted to a flat surface on a "c" clamp. Zero the indicator on the opposing surface, lift the plunger to slip the C over the wall of the part, and read the result. If the C frame and surface are not too heavy it might work well.