Thickness measurement QA for large surface areas (1500x1500)

[marcFACT]

Hi All,

I'm looking for a way to check the thickness of large pieces of honeycomb (1500mmx1500mm)

Until now we've been measuring the thickness at various points along the edges and averaging out, however this is not very accurate as it doesn't take any measure of the points within the edges.

Our process is very thickness sensitive and there seems to be a considerable amount of variation coming from our suppliers.

Ideally I would like a method to ensure the majority of the honeycomb piece is NOT LESS than X mm, with a precision of at least 0.05mm

Are there any standard methods of making this kind of dimensional check?

Thanks for your help!

 

[IRstuff]

How much sampling is required, i.e., over what area do these these thickness variations appear?

Obvious choices are surface profilometers or laser distance measurement devices.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529

 

[Compositepro]

What are you using now, a spring-loaded dial indicator with large anvils? All you need is a reasonably stiff and flat table top (a granite table would be idea but not necessary) to support the core while measuring. Mount the dial indicator over the center of the table on a beam that allows the core to move freely under the indicator. There are electronic indicators if you need to collect data electronically.

 

[marcFACT]

IRstuff: the variation we're getting depends on suppliers, it ranges from +/-0.2mm to +/-0.05mm every 200mm along the edge periphery. I'm looking to get a clearer picture of the average thickness of the entire honeycomb sheet by getting a grid of measurements of maximum 200mm x 200mm apart across the whole area (so about 60 measurements per 1500x1500 sheet)

Compositepro: We have been taking measurements along the edges with vernier calipers until now.
I imagine it would be difficult to measure over the non-continuous surface of the honeycomb using spring loaded indicators, have you had success in doing so? I should think the indicator tip would fall into each individual honeycomb cell and then catch on the cell sidewalls as it passes over the sheet.

Thanks

 

[DraftingMan]

marcFACT,

Get a flat point for your indicator like this. Link​

John H. Dunten, CD
Certified Drafter

 

[marcFACT]

DraftingMan/Compositepro: I've just understood the "spring loaded indicator with large anvils" is in fact what draftingman has proposed.. That certainly sounds like a good solution to try out - I had never seen one of those before.
I might attempt the beam setup with a "large anvil" LVDT, if can find one with the required accuracy, so that I can capture the data for QA.

Thanks All for your input!

Marc

 

[IRstuff]

There are optical profilometers, obviously way more expensive, but they could potentially given you a complete picture of the honeycomb:

http://nanovea.com/wp-content/themes/wp-nanovea/brochures/profilers.pdf

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529

 

[pylfrm]

marcFACT,

My first thought was basically the same as Compositepro's suggestion. However, depending on the stiffness and flatness of the honeycomb, you may have a gap between it and the table at the measurement location. To avoid including the gap in your local thickness measurement, you could mount another indicator tip-up through a hole in the table and then sum the readings. Display units capable of addition and subtraction are available for electronic gages.


pylfrm