June 2008 Edition

QM Enterprise Metrology Sleuth

Case of the elusive seal slots

EM Sleuth saves the day with solution to capture more data points

It was a beautiful summer day and the corridors in the corporate zone of Parts ‘R’ Us were abuzz with happy gossip about a big new contract the company had just won. A major jet engine manufacturer was going to triple the number of blades it would be ordering from this agile manufacturer.

The Sleuth wanted to linger in these happy halls and converse with the sales and marketing people, but he had to move into the bowels of the facility where he had business to conduct in the Quality Lab. It had something to do with these very same blades.

No sooner than he had slipped into the climate control lab was he assaulted by the words "bloody hell." They were coming from his friend Andy Salter who was now extracting a broken measurement probe tip from a nearby CMM.

"Blast it," Salter continued. "That’s the third one in two days. They’ll be wanting to dock my pay a thousand dollars."

"What are you trying to measure?" asked Sleuth.

Actionable information

"Seal slots," he said, looking up. "We used to measure these out in the shop with slip gages and in the lab with an optical comparator. Pass/fail was good enough. But now the customer is insisting that we capture more actionable information," he said, emphasizing the last two words with an eye roll and a sneer.

"Now they want to know the actual width of the slot and the slots’ positions in relation to the blade and to each other. So we keep breaking these 3-mil probe tips trying to measure 4-mil slots."

"That’s crazy," said the Sleuth. "Even if you could move the probe in that small space, the tip is too big in relationship to the width of slot to give you any respectable degree of accuracy. What’s more, I know that most of the slots you’ll be measuring are even smaller than a probe tip."

"I know that," said Salter, "and I think my boss does too. He was just hoping we could come up with some magic solution, so we don’t have to add a lot of costs collecting all that new data."

Then Salter motioned for Sleuth to come closer, darting his eyes right and left quickly, to see if the boss was nearby.

"That’s how we won the new contract, you know. We kept our pricing the same, and we’re not going to charge them extra for all the measurement data they are looking for."

"Yikes," said the Sleuth with a flash of understanding. "How much extra?"

"First off, they are thinking about buying a pretty big vision measurement system. They’ll be training me and another guy to use it. I’ve never used one before. It has totally different software. They want us to get up to speed fast, so there goes my summer vacation. And that’s just the beginning."

"How so?"

"We’ll have to buy a lot of custom fixtures for each of the different sizes and types of blades we make. The fixtures will allow us to position the slots normal to the vision system camera. Otherwise, you can’t measure them accurately. Since there are usually slots on two sides of the blade, we will probably need two fixtures per blade. So we will be spending even more on fixtures than we will on the vision equipment," concluded Salter.

"Well, thanks for the rundown on this problem, Andy. Now I’ll let your boss tell me all this and pretend I’m hearing it for the first time. Then I’ll be back here in about a week, and I think I will have some very good news for you."

As he was leaving, Sleuth looked back over his shoulder and said, "Don’t cancel your vacation plans just yet."

Solution in a week

True to his word, the Sleuth was back the next week. After conferring with the heads of manufacturing and quality for about an hour, he sauntered out to talk with Salter.

"Hey Andy," Sleuth said with a smile. "Your vacation is back on."

"It is? How did you swing that?"

"They’re canceling your training on the vision system because Parts ‘R’ Us won’t be needing one."

"So what equipment will be used to measure the seal slots," Salter asked.

"Your CMM."

"But you said that was crazy."

"No, I said it was crazy to measure the slots with touch probes. You’ll be using a vision probe.

"And I won’t need training?" he asked.

"Just a little," said the Sleuth. "You’ll be using the same software, but some of the vision-probing software tools will be new to you. They’ll teach you to illuminate the slots for accurate edge detection with the vision probe. That’s about it."

"So we’ll still have to do that finicky set-up with the custom fixtures, right?"

"Not really. Inexpensive modular fixturing will be enough. You will use your touch probe to do an automatic alignment of the blade to locate the parts in space. Then the CMM software can align the wrist-mounted vision camera in 3D space so that it is normal to each slot as it measures it. The vision probe can capture hundreds of data points as soon as the slots are in its field of vision — more data than your customer ever dreamed of."

"You mean collecting all that extra measurement data is not going to turn this new blade contract into a giant fiasco?"

"The very opposite, my good man," said the Sleuth with an emphatic nod. "That’s what I was just talking to your boss and the manufacturing manager about. This actionable information will allow manufacturing to make process corrections on the fly so that the seal slots will always be where they should be, and out-of-spec blades will take a tail spin."

"So someone actually knew what he was doing,"

"Yes he did," chortled the Sleuth.

"Doesn’t that beat all?" said Salter, with a shake of his head as he returned to his work.

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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