Murphy and Checking Fixtures

This week we have lived through a tough experience. One week before delivering a cubing for a bumper, as we where finishing the adjustings, our large CMM machine broke down. Three months of work, with a team of more than 15 people specialised in several areas, and this breakdown had to happen now…

The CMM machine works, but the problem is that it gives us non-repeatable values of more than 0.1mm. These values do not provide us with the guarantee we need. We have studied the possible causes of the problem with the CMM manufacturer but have not got neither clear conclusions nor solutions easy to implement in such a short period of time.

We know that we must change our CMM machine, so we will not spend too much time in trying to solve such a problem. Actually, we have already started to look for a CNC CMM machine of 3000×1500×1500 with Metrolog XG, but Murphy’s laws prevail once again…a few weeks before organising the replacement of our current CMM machine by a new one we had found, we have started to have problems with our CMM machine that could affect the delivery of the cubing. This could not have happened at a worst moment…

The positive part of this story is that with the market crisis you can find CMM machines in a good state and with very reasonable prices.

To come back to our story, we quickly started to think about possible solutions that would enable us to meet the deadline initially set. Our priority was to measure and adjust correctly the cubing in a company where, besides having measurement means available, there would be tools to rectify the parts with deviations, as well as a Catia license to check our design and do calculations. Where would we be better than in our own premises?

The first thing we did was to enter in contact with companies renting portable measurement arm in order to see if they could help Tecnomatrix. As the precision required had to be as close as possible of 0.05mm, we managed to get a 1.8mm FARO Platinum arm with a metrologist. This would be our first experience with such a device, as we had never had the opportunity to try it before.

Then, once we had made sure that this solution could provide us with guarantees of success for meeting the deadline, we have had to inform our customer (TIER1) of the situation and ask him if we could do the validation of the cubing with this FARO arm. This type of checking fixtures are usually validated by our customer together with the OEM (car manufacturer). Consequently, the customer asked the same question to the OEM. The answer was no. They could not accept to have the checking fixture validated with a portable measurement arm, only a CMM machine was acceptable as its precision is much higher than the arm’s.

The conclusion is clear: we have to find a CMM machine for the validation of the checking fixture.
As I am writing this article, we have already finished to adjust the checking fixture. It took us three days. Our current problem is to find a place where we could measure again the checking fixture to make sure that there are no differences with the values obtained with the FARO arm. Once we have found where we can do these measurements, we will have to take the checking fixture there very carefully to prevent anything from moving or varying and hope that the CMM results will not vary from the ones obtained with the portable arm. Once the fixture is there and before starting to measure it will have to let it temper at least during 24h to avoid bad surprises.

The simplest solution that we have thought about is using our customer’s CMM machine. This is the cheapest and the most effective option – even more so as we will deliver the checking fixture with its corresponding dimensional report and commit ourselves to do the relevant changes should the customer detect a deviation -. We will try to fix the problem that way…

In about one week we should be able to explain you how this project has finished.