Measurement of Geometrical Tolerances on Small Parts

Q

qainsppai

#1
Hello!

I'm looking for recommandations for equipment to inspect geometrical tolerances (circularity, concentricity, flatness, squareness, etc.) on very small parts. The smaller tolerances are 0.005mm (that's 0.0002" I think). The parts are all cylindrical. Their diameters range from Ø0.8-4mm and their lengths from 0.8-8mm.

Are there other solutions than a CMM or Talyrond machine?

Does it make a difference if I just want to make a qualitative test (pass/fail)?



Thank you in advance

Qainsppai
 
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Stijloor

Staff member
Super Moderator
#2
Re: Measurement of geomtrical tolerances on small parts

Hello!

I'm looking for recommandations for equipment to inspect geometrical tolerances (circularity, concentricity, flatness, squareness, etc.) on very small parts. The smaller tolerances are 0.005mm (that's 0.0002" I think). The parts are all cylindrical. Their diameters range from Ø0.8-4mm and their lengths from 0.8-8mm.

Are there other solutions than a CMM or Talyrond machine?

Does it make a difference if I just want to make a qualitative test (pass/fail)?

Thank you in advance

Qainsppai

Hello Qainsppai,

You may want to do some research on vision systems. The volume of parts to be inspected must be considered as well. Geometric characteristics to be inspected would require variable-type gaging. A qualitative test (attributes) only gives you a pass-fail outcome. In addition, variable data is more useful in terms of process control. A few questions: What are your internal requirements? Any customer requirements that must be considered?

Stijloor.
 
Q

qainsppai

#3
Re: Measurement of geomtrical tolerances on small parts

Stijloor,

Thank you for your answer!

We have no customer, these parts are made for us by suppliers and we have to inspect them on delivery (incoming inspection). The requirements are defined by R&D, who decides of the inspection criteria.
As we don't manufacture the parts, we have no direct interest in process control, and so an attributes test could be an interesting alternative if it allows us to have simpler instruments.
The parts are used in a medical implant, so the measurement process has to be validated.

May I ask you what you mean by vision systems? We have an optical coordinate measuring machine (Mitutoyo), but I don't think it can do measurements wtih such an accuracy.

The volume of inspection is about several hundreds of parts per week.


Qainsppai
 
D

Dean Frederickson

#4
You might want to look into some high resolution microscopes. Digital Microscope.
Google high resolution microscopes, there is a lot to choose from. :2cents:
 

Jim Wynne

Staff member
Admin
#5
Re: Measurement of geomtrical tolerances on small parts

Stijloor,

Thank you for your answer!

We have no customer, these parts are made for us by suppliers and we have to inspect them on delivery (incoming inspection). The requirements are defined by R&D, who decides of the inspection criteria.
As we don't manufacture the parts, we have no direct interest in process control, and so an attributes test could be an interesting alternative if it allows us to have simpler instruments.
The parts are used in a medical implant, so the measurement process has to be validated.

May I ask you what you mean by vision systems? We have an optical coordinate measuring machine (Mitutoyo), but I don't think it can do measurements wtih such an accuracy.

The volume of inspection is about several hundreds of parts per week.


Qainsppai
Have you looked at how your suppliers are doing the measurements? Those are the measurement processes that should be validated.
 
Q

qainsppai

#6
Jim,

Well that's one part of the problem: our suppliers don't measure these dimensions... they suppose the lathe is accurate enough to have these tolerances, but they can't prove it.:nope: Some of them check the parts with visual methods (on profile projectors for example).

I suppose one solution could be to validate the manufacturing process and so the measurement wouldn't be necessary anymore, but it's difficult to validate a process which is not in-house.


Stijloor, Dean,

Please could you explain me how to measure cicularity or flatness with a vision system/microscope, because I don't get it? :(
Can you measure with that or is it just a visual test?



Qainsppai
 

Jim Wynne

Staff member
Admin
#7
Jim,

Well that's one part of the problem: our suppliers don't measure these dimensions... they suppose the lathe is accurate enough to have these tolerances, but they can't prove it.:nope: Some of them check the parts with visual methods (on profile projectors for example).

I suppose one solution could be to validate the manufacturing process and so the measurement wouldn't be necessary anymore, but it's difficult to validate a process which is not in-house.


Stijloor, Dean,

Please could you explain me how to measure cicularity or flatness with a vision system/microscope, because I don't get it? :(
Can you measure with that or is it just a visual test?



Qainsppai
You might be able to measure circularity with a vision system, but flatness, I don't know. Measurement of flatness requires isolation of the plane in question, and I don't know how you could do that with a vision system. It's often helpful to contact the manufacturers or local distributors of various types of measuring devices and letting them look at your application. They'll usually be happy to send someone out to have a look (depending on where you're located, of course) and give advice.
 

Stijloor

Staff member
Super Moderator
#8
You might be able to measure circularity with a vision system, but flatness, I don't know. Measurement of flatness requires isolation of the plane in question, and I don't know how you could do that with a vision system. It's often helpful to contact the manufacturers or local distributors of various types of measuring devices and letting them look at your application. They'll usually be happy to send someone out to have a look (depending on where you're located, of course) and give advice.
Flatness at that degree of accuracy can be checked with optical flats or laser scanners. Search the 'net for equipment suppliers. Jim is correct; equipment suppliers would be happy to advise you (and make a sale..)

Stijloor.
 
Q

qainsppai

#10
You might be able to measure circularity with a vision system
Do you mean by rotating the part and observing the variation with a microscope/projector?

It's often helpful to contact the manufacturers or local distributors of various types of measuring devices and letting them look at your application
I've contacted several equipment suppliers, and also one measurement laboratory. My understanding was that the only way to measure these tolerances was by using a tactile system. But this solution is quite expensive, and it makes the inspection very time-consuming. That's the reason why I want to be sure that it's the only way.

Flatness at that degree of accuracy can be checked with optical flats
Most parts are actually drilled cylinders (i.e. tubes..) and the wall thickness is quite small (0.5 mm) and the surface to be checked for flatness are the extremities... As Jim mentioned, do you think it is possible to use optical flats on such small parts?



I have also requirements on paralellism and perpendicularity on some of these parts, do you think they could also be measured with a vision system at that accuracy?

This is probably the best non-contact solution, but pretty expensive.
Do you think it's better to have a non-contact solution?
 
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