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Manual CMMs for accuracy and value.

In the simpler world of manual inspection, the QA philosophy that "the operator is the best inspector" may have sufficed. But how well does that philosophy hold up in the world of manual CMMs? If experience at Parker-Hannifin's Nicholls Motor Div (P-HN), Gray, ME, is any indication, the answer is that it works "just fine, provided. . . "

The proviso? "The operator inspection system works under CMM as long as we pay attention to three things," says Wayne Sanborn, QA department manager: orient the operators properly, set consistent procedures, and select the CMM equipment specifically with operator use in mind."

This is exactly what P-HN did in late '91, when it installed a Mitutoyo B504 manual coordinate measuring machine. That startup, part of the company's continuoUS improvement philosophy, marked P-HN's initial move into the world of CMM. "Our motor manufacturing operation is only five years old," says Mr Sanborn. "Now that we've proven we're able to compete effectively in the market, capital is being invested to refine the operation." The plant makes a full line of hydraulic motors, mainly for industrial applications.

First-piece inspection

The primary use of the CMM is for first-piece inspection on a variety of machined components for hydraulic motors. Lot sizes are small, and most machines are changed over to a new job twice a week on average. So first-piece inspection becomes a significant element of total part cost.

Most parts are round, involving a lot of radial dimensioning and bolt circles. All fit within the CMM's 20" x 16" x 12" measuring envelope. A typical part requires 20 to 50 dimensional checks including angles, concentricity, curvature, polar coordinates, and true positions. Approximately 20 parts per day are inspected on average.

With four months of experience on the machine, P-HN is already projecting a return on investment of less than a year, from labor savings alone. "We'll easily save more than $35,000 a year in direct inspection labor," says Mr Sanborn. "And I believe CMM inspection will also reduce machine setup time by at least 30%, thereby increasing effective machine capacity."

Scrap reductions will add to the benefits, according to Mr Sanborn. "In the first weeks, somebody on the CMM caught an error he otherwise would probably have missed, saving a $1 000 part. Of course, this adds to the savings but, more important, it also means better quality."

Thorough evaluation

Because he knew operators would be doing the inspections, Mr Sanborn went about the CMM selection and implementation very carefully.

We knew from the outset that success would require the right combination of equipment, training, and procedures."

As to equipment, Mr Sanborn put a high priority on user friendliness of the software, training, and technical support. "We put as much weight on those issues as on resolution, repeatability, volumetric accuracy, warranty, and price. We knew we were setting a precedent here."

Armed with those criteria, he narrowed the list of possible candidates down to a handful. Next, he visited plant sites or demonstration centers with sample parts from their operation in hand. The samples all involved polar coordinates and/or at least four-axis dimensioning. "I figured I'd learn much more by comparing the candidate machine's performance on the actual work we do," he explains.

When that exercise narrowed the field to two or three finalists, he contacted or visited actual users of each CMM. From a price and hardware standpoint, most of the finalists were pretty much the same," he adds. "What really separated the field was the user friendliness of the software, vendor training, and support. Since this was our first move into CMMs and we were buying for operator's use, simplicity was paramount in our mind."

The model they chose, the Mitutoyo B504 package, fulfilled all their requirements and included Geopak 1000 software, vibration damping stand, air hose set, computer, printer, cabling and air dryer, installation, training, and calibration.

Two-step training

Mr Sanborn used Mitutoyo's 16hour training package to train himself, the QA engineer, and the QA technician. His thinking was that once the new procedures surrounding CMM were worked out, his people, in turn, would train the operators.

For a few months thereafter, CMM and manual inspection ran in parallel. Mr Sanborn's QA team concentrated on "learning while doing" by programming inspection procedures on parts while operators continued their manual inspections. Out of this transition phase, Mr Sanborn developed standard procedures and sequences for inspecting all parts on the CMM. "We were well aware that 15 or more different operators would be routinely using the CMM before long," explains Mr Sanborn. "Consistent procedures for all parts would be vital to success."

The QA team conducted ten hours of actual operator training in a hands-on manner. "We simply went over a few basics right at the CMM, then showed them how to check the parts they were already working on," recalls Mr Sanborn. "The emphasis was mainly on using the software, the procedures, and probe sensitivity." All the operator-inspectors were thoroughly prepared beforehand. They had previously gone through P-HN's own in-house training on geometric dimensioning and tolerancing, blueprint reading, and basic inspection.

Since the operators were accustomed to inspection anyway and took pride in being their own inspectors, acceptance was enthusiastic. "They all wanted to learn more about CMM, to do more with it," adds Mr Sanborn. "The training went well."


With the wrinkles ironed out, the CMM inspection process at P-HN is essentially as before. However, it is faster, more labor-effective, and more foolproof. Mr Sanborn establishes inspection procedures, operators do their own inspections according to those procedures, and the QA technician focuses on incoming inspection and production support. The technician helps out on the more complex jobs. But he always emphasizes enabling the operator to inspect on his own.
COPYRIGHT 1992 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1992 Gale, Cengage Learning. All rights reserved.

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Title Annotation:coordinate measuring machines
Publication:Tooling & Production
Date:Feb 1, 1992
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