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Surface measurement boosts radiator quality.

Surface measurement boosts radiator quality Surface finish is critical to the Harrison Radiator Div, General Motors Corp. In Plant No 5, Lockport, NY, the firm manufactures air-conditioning modules, radiators, and parts for other divisions. Operators work closely with the Dayton, OH, plant to make compressors and accumulator-dehydrator parts for the modules, and they must certify that printed specifications are met.

"To improve efficiency, we centralized our measurement functions with the product-audit department to verify outgoing product quality," says Walter "Skip" Hartman, reliability representative. "But we didn't know until recently that surface finish was one of the most important measurable characteristics."

In beefing up its QC activities, Harrison Radiator Div purchased a Form Talysurf(R) instrument from Rank Taylor-Hobson. This device measures surface finish and geometry. Now, the metrology laboratory can check forms not measurable with former equipment.

"At a Rank-sponsored seminar in Rochester, NY, we learned a lot about what we didn't know in the area of surface finish," notes Hartman. "Our new knowledge helped the engineering department verify product performance, and we soon discovered that surface finish plays a critical role in leak paths that might occur in air-conditioning systems."

Seat leaks

O-ring seats present particular leakage problems. Hartman explains: "These formed parts have always been difficult to measure. The parts have small radii, and they must match up. In the past, certain slopes have been difficult to measure on conventional optical comparators, forcing us to rely heavily on visual interpretation.

"The Form Talysurf now gives accurate measurement of form, surface texture, radius, and angle of surface inclination--with a resolution of 0.4 microinch. Wherever lines meet at joints, we can now easily measure finishes of 32 micro-inches. As a result, we can determine when manufacturing is out of specification; we can detect tooling wear by noting degradation of surface finish."

All glitter isn't good

Hartman cited an example of knowledge gained at the Rank seminar: "We were seeking new suppliers of tubing and discovered samples of a material that was very shiny and smooth. With our new instrument, we measured the finish on these samples and found it to be 9 Ra. Surprisingly, although the material appeared to be unusually good, we got orange-peeling and cracks when we formed parts.

In other words, the actual surface of the O-ring seat was so good it was bad. Our regular vendors supplied product having ratings of 18 to 25 Ra, but this stock didn't give us the problems of the better-looking material. The seminar helped us to understand this phenomenon."

Hartman summarizes that the new instrument and new knowledge are useful for checking various aluminum-sheet materials from vendors and predicting performance in the presses. He believes that standard procedures used to check physical properties (tensile strength, elongation, grain size) and chemical properties often are not adequate. "When we put material in a press, and it won't run satisfactorily, the reason often is improper surface finish."

Other aspects of Harrison's QC program include extensive training programs in statistical process control (SPC), Crosby Training, education in Juran methodology, and making use of in-house diagnosticians.

"Awareness of quality," Hartman concludes, "is the real thing, and it begins with the man on the production floor. Test instruments only confirm where problems exist. Fortunately, they do give us a clue as to how we can correct them."
COPYRIGHT 1989 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1989 Gale, Cengage Learning. All rights reserved.

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Publication:Tooling & Production
Article Type:product announcement
Date:Jul 1, 1989
Words:552
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