April 2008 Edition

QM Enterprise Metrology Sleuth

Sleuth takes a true position

It was 5 a.m. and Sleuth's phones were ringing incessantly — first his cell, then his landline, and then his cell. . . ad nauseam. After about five minutes of this, he concluded that whoever-it-was was not going away.

The raspy voice at the other end of the line belonged to none other than Major Albert Payne of the Army's top-secret CGIU (Counter Gadgetry Intelligence Unit). "Sleuth," it said, "you got any plans today?"

"I did," said Sleuth.

"Well, cancel them and meet me over at Major Motor's Aerospace Division at 0700."

"Yes, Major Payne," said Sleuth meekly. "May I ask what this is about?"

"It's the GIZMO and now I've already said too much, so get your butt over here on the double."

The Gyroscopic Intermitting Zero Motion Oscillator, otherwise known as the GIZMO was so secret that Sleuth himself did not know anybody who even knew anybody who knew what it did or what it was for. He did know that the GIZMO had two intricate titanium components that had to mate perfectly in order for it to have any chance of working. The design of GIZMO was so sensitive that prototypes of these X and Y modules were being manufactured by two different companies and shipped to the Army's CGIU R&D lab for final assembly.

After arriving at Major Motors Aerospace, Sleuth was ushered into the metrology lab. A shiny X-mating GIZMO module was mounted on the CMM. It looked like a twisted Belgium waffle iron but with about a dozen bolt holes in it.

"There it is," said Major Payne. "MM Aerospace has already shipped us a hundred of these babies and they were perfect. But the Y-mating module is a different story. Parts 'R Us —a company you recommended for this no-bid contract, Sleuth, fell down on the job. They shipped us 100 parts and we had to send 15 of them back because they didn't pass our true position CMM inspection. We've got just a month to get 250 GIZMOs assembled for field trials and we need all the mating modules we can get our hands on.

Payne let Sleuth know that Major Motors Aerospace people were the good guys in this tragedy. Both companies received their drawings at the same time, and both were manufacturing their mating components on nearly identical equipment. In addition, the CGIU provided both manufacturers with the latest version of measurement programs that were used on comparable CMMs.

While Major Payne was heaping praise and blame on the two parties, Sleuth was watching the CMM as it went through its true position measurement routine, meticulously aligning the part to its datum before each critical part feature was measured.

"I think the difference is that Major Motors Aerospace spent a lot of time tweaking their toolpaths and manufacturing equipment to make sure they produced parts exactly to our specs. I know their rejects were pretty high the first time around, but they made enough to be able to send us 100 good parts. The Parts 'R Us guys didn't.

"We need your help, Sleuth, to figure out what those Parts 'R Us idiots are doing wrong and make sure we get the parts we need to make enough GIZMOs for the field trials. Then we'll fire them. Let's head over and meet with those fools."

Before leaving, Sleuth prevailed on Major Payne to take an X-mating part with him locked in his industrial strength CGIU brief case.

The metrology lab at Parts 'R Us was nearly identical to the one that they had just come from — except for the shelves lined with 15 rejected Y-mating GIZMO parts and the hang dog look of the staff as Major Payne glowered at them. After dressing down the Quality and Production managers for what seemed like forever, Major Payne gave them a few minutes to say their piece.

"I can't understand it," the production manager said apologetically. "We have excellent manufacturing equipment and we optimize the toolpaths in our CAM software so that we not only manufacture the parts dead-on the first time, but we also make them very efficiently. We're not accustomed to getting rejects."

Sleuth asked, "How many did you make to arrive at 100 parts that passed true position inspection."

"We made a hundred and we believed they were all good."

Sleuth asked him to measure one of the "bad" parts. Although the parts were about the same size, with a comparable number of features, the measurement sequence completed on the Parts 'R Us program seemed to go somewhat faster. When it was over, a printer clattered out a graphic report with no callouts showing that any of the critical features were out of tolerance."

Very interesting, thought the Sleuth. "Could every one here leave the room?" asked Sleuth abruptly. "The Major and I need a few minutes alone."

When everyone was gone, Sleuth asked Major Payne to produce the X-mating part. Sleuth removed the Y-Mating Gizmo part from the CMM and Major Payne gave him its Y-mating counterpart. With a part in each hand, Sleuth brought them together with a slight twist and they nested into each other perfectly.

"Major Payne," asked the Sleuth, "when did CGIU write the measurement program?"

"About a year and a half ago. That's when we came up with the design. We had to wait awhile before we had the budget for product development."

"Well, that explains it," said the Sleuth. "In that timeframe, a new version of the software came along. You and Major Motors Aerospace have that software, but you have been using the legacy version of true position measurement in the original program. It seems that Parts 'R Us invested an additional 20 minutes of time and converted your part program to run with the latest algorithms. In addition to more accurately measuring each feature, they also compensate for variations in the actual position of the data."

"What are you saying, Sleuth?" the Major interjected.

"I'm saying that Parts 'R Us has been using a truer version of true position measurement. All of the parts they sent you were in spec and back at their plant they haven't had to weed out any scrap in order to send you good ones."

"Well, this is embarrassing," said Major Payne.

"I'm heading out. Got appointments to keep," said Sleuth. "But I'll tell the guys to wait a few more minutes before they come in. That will give you some time to come up with your true position."

 

Contributors to this article include Don Ruggieri, senior applications engineer, Wilcox Associates, druggieri@wilcoxassoc.com, Rob Fabiano, Sleuth illustrator, rfabiano1@cox.net and Joel Cassola, writer, jocas@cox.net.

 

 

 

 

 

 
EM Sleuth is sponsored by Wilcox Associates Inc. (www.pcdmis-ems.com), part of the Hexagon Metrology Group and makers of PC-DMIS measurement software.

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