Townley Engineering & Manufactur-ing Co. Inc. (Candler, FL), a manufacturer of replacement bearing assemblies for large, severe-service matrix pumps used in mining, solved a service-life problem with dimensional measurement and inspection. And because short service life is an industry-wide quality control issue, Townley turned the solution into a competitive edge.
Dimensional measurement and inspection at Townley is done with an Infinite Arm portable coordinate measuring machine (CMM) from Romer Inc. (Wixom, MI), combined with PowerInspect software from Delcam Inc. (Windsor, Ontario). PowerInspect is sold bundled with the Infinite arm and supported by Romer.
Lack of Good Data
Townley began encountering unexpected field-wear issues with its UBD Matrix line of pump assembly bearings in 2002. UBDs are among the biggest pump bearing assemblies Townley makes. By 2004, bearings for as many as one pump in five suffered a failure, some after just one month’s service, says Howard Record, Townley’s quality assurance manager.
Big matrix pumps are generally used in in-line groups of five. The arrangement means if one pump fails, the others go out of service so they will not overload and burn out.
Careful dimensional measurement quickly pinpointed root causes in concentricity, perpendicularity and bore diameters of the bearing housings supplied by a contract machining company. The supplier’s management found and fixed the root cause. It was an out-of-calibration horizontal machining center used to machine housing bores.
Townley immediately began 100% inspection of all incoming housings and set up a clean room for assembly. The initial solution was to build an inspection fixture, a replica of the pump’s central shaft with machined and welded steel plates representing the bearings. As in anything that rotates, precise shaft alignment is vital to service life. Townley UBD Matrix bearing assemblies have two double-tapered roller bearings and a tapered-thrust bearing.
But the inspection fixture was still a feeler-gage solution. “Unfortunately,” says Record, “a feeler gage generates almost no data a machinist can use to correct a dimensional problem.” While accurate in trained hands, feeler gages give only simple go/no-go determinations.
For quality assurance, a lot more was needed. “We still had to give the machinist exact numbers on how much the parts were out, and where,” says Record.
Good QA DataLooking back, Townley actually got a handle on the dimensional problem in just a few hours. The larger issue was getting good quality assurance (QA) data to the machinists. For that, Delcam’s Power Inspect IGES file generation ability proved invaluable. Combined with the portable Romer arm, the system paid for itself in two weeks, Record says, basing that return on investment on the warranty cost of replacing a failed bearing assembly.
The payback period was so short “because right away we could give the machinist exact numbers on concentricity and perpendicularity with IGES files,” Record says. The IGES data was uploaded to the CAD files used by the machine shops’ programmers.
The portability of the Romer arm lets Record, Hill and co-worker Ben Philips bring the entire inspection system right to the bearing housing, or any other large workpiece. After machining, the cast-iron housings measure about 47 by 36 by 37 inches and weigh about 1,000 pounds. Inside each housing are three outer bearings races measuring 8 inches wide and almost 19 inches in diameter. Each race is checked with about 35 touch-probed points.
“Because of the size and weight of the housings, the simplicity of setting up and repositioning the arm pays big dividends,” Record says. The Infinite also has a built-in digital camera to capture the physical part layout for the inspection reports, and WIFI communications to eliminate all cabling between the arm and whatever laptop computer is running PowerInspect.
Taking No Chances with Dimensions“We overnighted the first inspection results and our new dimensions to the machine shops,” Record says, “and got better housings from them almost immediately. Now that we can give our vendors sound numbers and inspection reports, we can expect them to step up to the plate and help us hit a home run on the success of our bearing assemblies.”
Townley’s suppliers of machined components now check dimensions on all their parts before they ship, but Townley takes no chances. “To give us the confidence to warranty our products to our mining customer, we inspect the housings and we inspect the final assembly,” Record says.
Other dimensional measurement applications soon followed. In addition to dimensional measurements from the arm and the software, Townley verifies temperature and records vibration analyses on full bearing assemblies. Townley does these analyses on a test system called the mule. Fully computerized, the mule generates physical test data under initial load-pounds of force-revolutions per minute (RPM), time at RPM, temperature under load and specific load data. The full test takes 48 hours.
All mule test data plus the Romer-PowerInspect dimensional inspection reports go to the customer. “That birth certificate is a set of fingerprints for each bearing assembly,” Record points out.
As a result of the mule, Romer and Delcam inspections, machining tolerances for the bearing assemblies were tightened to ±0.002 inch. “We want to go to 0.001,” says Record. “That would give us an even bigger competitive edge, with even better bearing life, longer housing life, less vibration and less wear.”
Romer Inc., a Hexagon Co.
- Townley’s business benefits from dimensional measurement include better quality parts from its vendors and better quality products.
- Townley has sharply reduced warranty claims and employs faster prototyping of new products for market.
- Other Townley plants now request help from the QA unit in Candler, FL, which has company-wide responsibility.
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