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!

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.

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

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

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.

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,

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.

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.

Flatness at that degree of accuracy can be checked with optical flats...

Whether or not optical flats can be used is a function of the size of the part, in general. The OP says the parts are small, so it's doubtful that optical flats could be used effectively, if at all.

...or laser scanners.


This is probably the best non-contact solution, but pretty expensive.

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?

Do you mean by rotating the part and observing the variation with a microscope/projector?

Without actually seeing a part and the specifications, it's hard to say. I'm assuming that a standard optical comparator isn't appropriate for all of what you're trying to measure.

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.

Perhaps a trip back to the drawing board is in order. If the people who designed these parts are available, you need to sit down with them and ask them how you're supposed to measure what they've designed. The answer is likely to be a blank stare, but designers need to understand that they have to consider the state of the art in measurement (and its potential costs) when they do these things. Verifying measurement capabilities--both yours and your suppliers'--should be part of the design process. I know that might not be particularly helpful in getting you out of the fix you're in presently, but it's useful information for others reading this.

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?
Again, without seeing the parts, it's hard to say. If you're talking about measuring flats on the OD of a cylinder, then optical flats probably won't work. If you're drilling on the ends of a cylinder, it might work, depending on the surface area available. You also have to consider the light source when using optical flats; it needs to be monochromatic (waves of a single length) in order for optical flats to be effective. It's a fairly tricky business if it's to be done correctly, and best avoided if there are other options.

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? I don't know. If you've got a cylinder with a hole drilled through it lengthwise, and you need to measure the parallelism of the ends and the perpendicularity of the bore, you might be able to make a fixture for it, but it would probably involve (A) considerable expense, and (B) only attributes data.

Do you think it's better to have a non-contact solution? Only if contact methods aren't feasible. Direct measurement is usually the best option if it can be done.

Without actually seeing a part and the specifications, it's hard to say. I'm assuming that a standard optical comparator isn't appropriate for all of what you're trying to measure.

I made a small drawing of an example part (in attachment) that puts together most of the specifications I'm talking about. Imagine you have to measure this part, how would you do? Any input is really welcome, because I thought about it a lot and I don't see a simple way of doing this...


Perhaps a trip back to the drawing board is in order. If the people who designed these parts are available, you need to sit down with them and ask them how you're supposed to measure what they've designed. The answer is likely to be a blank stare, but designers need to understand that they have to consider the state of the art in measurement (and its potential costs) when they do these things. Verifying measurement capabilities--both yours and your suppliers'--should be part of the design process. I know that might not be particularly helpful in getting you out of the fix you're in presently, but it's useful information for others reading this.

I know it's probably the better way. I just wanted to know the solution in the case I really have to measure these dimensions. Once I know the different possibililties, I can explain them the situation (what precision I can reach, at what cost, and what time it takes to perform the measurement) and they can take a decision. I don't have a very long experience in metrology, that's the reason why I wanted the point of view of more experienced people.

I made a small drawing of an example part (in attachment) that puts together most of the specifications I'm talking about. Imagine you have to measure this part, how would you do? Any input is really welcome, because I thought about it a lot and I don't see a simple way of doing this.

What are the tolerances on the outside diameter, inside diameter, and the length?

You are correct, there is no "simple" way of doing this. Come to think of it, you are located in Switzerland, a country well-known for the manufacturing of extremely high-precision parts, is there any way you could possible talk to a supplier of that type of high-precision measuring equipment? The geometrical (and dimensional?) requirements are pretty clear to me; it's the "smallness" of the part that makes me wonder.

Stijloor.

What are the tolerances on the outside diameter, inside diameter, and the length?

Well I just made up that part as an example. The length is not critical, so take 1.0±0.05. You can take Ø2.0h9(-0.025;0) and Ø1.6H9(0;+0.025).


You are correct, there is no "simple" way of doing this. Come to think of it, you are located in Switzerland, a country well-known for the manufacturing of extremely high-precision parts, is there any way you could possible talk to a supplier of that type of high-precision measuring equipment? The geometrical (and dimensional?) requirements are pretty clear to me; it's the "smallness" of the part that makes me wonder.

Yes I talked to some of them. The only solution I found was to use a Talyrond machine (this is an equipment specifically designed to measure geometrical tolerances on cylindrical parts with an extreme precision). Then I need to design a very precise fixation system to be able to measure it, because I can't put the part directly on the machine (too small...). But the equipment is quite expensive, and the whole process is really lengthy (several minutes for one measurement).

Well I just made up that part as an example. The length is not critical, so take 1.0±0.05. You can take Ø2.0h9(-0.025;0) and Ø1.6H9(0;+0.025).

Yes I talked to some of them. The only solution I found was to use a Talyrond machine (this is an equipment specifically designed to measure geometrical tolerances on cylindrical parts with an extreme precision). Then I need to design a very precise fixation system to be able to measure it, because I can't put the part directly on the machine (too small...). But the equipment is quite expensive, and the whole process is really lengthy (several minutes for one measurement).

I am not knowledgeable enough to think of a solution beyond what the metrology equipment companies are suggesting. No matter how you look at this; it's not going to be "cheap" and not easy. I will continue to look into this further, but I do not know if I am able to come with suggestion that would meet your criteria.

What do my Fellow Covers think?

Stijloor

Well I just made up that part as an example. The length is not critical, so take 1.0±0.05. You can take Ø2.0h9(-0.025;0) and Ø1.6H9(0;+0.025).




Yes I talked to some of them. The only solution I found was to use a Talyrond machine (this is an equipment specifically designed to measure geometrical tolerances on cylindrical parts with an extreme precision). Then I need to design a very precise fixation system to be able to measure it, because I can't put the part directly on the machine (too small...). But the equipment is quite expensive, and the whole process is really lengthy (several minutes for one measurement).

In the example given, you might be able to check the parallelism and perpendicularity without too much trouble using a surface plate, pin and indicator (although you might have a problem with the tolerance) but the flatness and concentricity will be a real challenge. In particular, the concentricity seems nearly impossible to verify on a part of that size. Have a look at this discussion thread (http://elsmar.com/Forums/showthread.php?t=14223&highlight=concentricity) about GD&T concentricity. Whatever it is that can do it will be expensive, and I would definitely review the situation with the designer(s) before spending a lot of money.

Experts here have given very useful advise.

You may also try 'contactless devices' working on pneumatic pressure,having accuracy in micro inches;that work on signals returned by the surface in question,without touching the surface.These devices are perhaps cheaper than the lasers,I don't know for sure;I used them long back in 1972/73 while serving the Indian Railways.

Umang :2cents:

In the example given, you might be able to check the parallelism and perpendicularity without too much trouble using a surface plate, pin and indicator (although you might have a problem with the tolerance) but the flatness and concentricity will be a real challenge. In particular, the concentricity seems nearly impossible to verify on a part of that size. Have a look at this discussion thread (http://elsmar.com/Forums/showthread.php?t=14223&highlight=concentricity) about GD&T concentricity. Whatever it is that can do it will be expensive, and I would definitely review the situation with the designer(s) before spending a lot of money.

Just a side note: The OP is from Switzerland. The interpretation of concentricity per ISO 1101:2004 is significantly different from the ASME Y14.5M-1994 Standard.

Stijloor.

Just a side note: The OP is from Switzerland. The interpretation of concentricity per ISO 1101:2004 is significantly different from the ASME Y14.5M-1994 Standard.

Stijloor.

Good point--thanks for pointing that out.