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Speeding up blade milling.

Speeding up blade milling

Parker Hannifin's Air & Space Div, City of Industry, CA, supplies their assembly plant in Irving, CA, with precision bladed stator and rotor components for turbine-engine starter motors. With conventional machining, production was not fast enough - only four parts/shift - and reject rate was 20 percent, so they needed to improve both speed and quality.

A major bottleneck was a four-spindle tracer mill. After checking the alternatives, they bought a multi-spiwndle, four-axis, precision CNC milling machine from Rigid Machine Tool Inc, enhanced with four high-speed (24,000 rpm) spindles from IBAG North America, Milford, CT. Since installation, the components are being produced four times faster, with a reject rate of less than 1 percent. This solved both their quality and quantity problems.

One part is a 416 stainless stator, 0.375" wide by 4.5" dia. A stationary part, it directs air flow into the rotor of the turbine engine's starter motor. There are a dozen different stator and rotor configurations.

Each of this stator's 41 contoured, thin-wall blades is generated with a 3.970" pitch diameter. Total depth of cut is 0.600". Four work-pieces are each mounted on horizontal rotary tables and milled simutaneously by the four IBAG spindles. The machining cycle requires ten roughing passes and two finishing passes. All four spindles use 0.110" dia end mills for both operations. Feed rate is 9.4 ipm for roughing and 4.5 ipm during finishing. Four parts are produced in two hours, in batch runs of 75 to 100 parts to meet just-in-time (JIT) requirements.

"The improvement is much more than simply a time factor," points out Joseph Dowling, manufacturing manager. "The new high-speed, milling process has had a positive effect on subsequent operations, mainly because of better part quality. For example, before, it was never certain how much time part-balancing would require. Now, the balancing time is held to a minimum because the machine and high-speed spindles combine to produce components with virtually absolute concentricity. Spin tests at up to 80,000 rpm are now more of a quality verification than a check to determine what corrections are necessary. Part repeatability is within 50 millionths."

Using small cutters at very high speeds results in extremely clean cuts - a 32 rms surface finish. "Higher speeds also help keep costs down," adds Dowling. "Longer tool life is a product of high rpm's. If the cutter is running too slowly, excessive heat is generated, which adversely affects tools and parts. In a high-speed application, chips are evacuated quickly and carry the heat out with them." Roughing cutters for the 4.5"-dia stators last two cycles and finishing cutters last eight cycles. Changing tools takes 15 sec.

For more information, IBAG North America, unit of Siber Hegner North America Inc, 84 Research Dr, Milford, CT 06460 or circle 380.

PHOTO : Stator blank before and after high-speed milling
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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Title Annotation:turbine-engine starter motor component production
Publication:Tooling & Production
Date:Nov 1, 1989
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