PC-DMIS NC Fundamentals

[wewon]

Hi,


I'm just getting started in trying to understand on-machine verification and would like to get some basic knowledge of PC-DMIS.

I've read several articals and testimonials about it's applications and uses, but am having a hard time finding information that will help me get started.

Any information that you guys could provide would be greatly appreciated.


Moise

[Jan d.]

Have you tried the Hexagon sales force? They are quite good at providing applicable documentation.

I am a user. Here are the basics.

There are 2 types of on-machine measurements you can do:
1: set-up assistance (like aiding with leveling and finding exact location of surfaces): these can be simple routines and presuming you have a Renishaw probe, Inspection Plus is very adeqaute for that.
2: on-machine acceptance: this is far more difficult because you will have to measure AND analyze the part per the print (which means you have to analyze back to datums). If you want to do acceptance, PC-DMIS is your ticket.

In order to do on-machine acceptance, first make sure that your machines are regualrly calibrated. Mine are calibrated at least once a year. They are also in 68 degrees yearround. On top of that, you may need artifacts to verify machine accuracy. This will all add up quickly. Also look at your fixtures. If you have bad fixtures - the kind that let the part spring when you take the part out - you will not be successful.

However, if you do all this right, my experience is that a well constructed and well maintained machine with an MP700, Inpection Plus and PC-DMIS can absolutely compete with medium to high end CMM's. And with that I mean Prismos, DEA's, LK's etc.

When you have all that, you'll find the justification real easy. You can do process development right where you need it, adjust the process, reduce the defects and leave the operators with a much more thorough understanding of the behavior of the machine.

On-machine acceptance can NEVER replace off-machine verification. You still need to sample to make sure batches of parts are conforming. We tend to do first-part inspection plus 1 part every 5 following. (so roughly 8 out 10 never see the CMM; we process parts that take roughly 16 hours to finish complete).


Jan.

[wewon]

Questions

Hi Jan, thanks for responding.

My primary focus was on-machine acceptance of the parts.

If you have an artifact, do you need the temperature control for your machines? Isn't the artifact meant to account for your thermal growth? Or is that not a very effective tool to account for that?

Also, what all did you have to purchase to make this system work? Extra software, probes, ect.

I'm starting pretty much from scratch and want to start getting the lab prepared for implementation.

[Jan d.]

Yes, artifacts can correct for that. It depends on the tolerances you are looking for because there are also things like uncertainty of the coefficient of thermal expansion. I like to take temperature out of the equation so my whole shop is at 68 degrees year-round.

But if you have wider tolerances, the artifact measurement can help you a lot. But it must have something to do with your part. A 4" artifact can not correct for phenomena on a part that is 6ft long.

I'll PM with some more info.


Jan.

[wewon]

Thanks a lot Jan.