Harnessing the quality engine: Honeywell's phoenix aerospace plant uses a dedicated CMM to ensure quality and reduce costs in a high-volume manufacturing cell

Modern Machine Shop, March, 2002 by Bill Dundas

During the heart-pounding seconds after an airline pilot guns his engines for takeoff, passengers are hushed by the extraordinary thrust that sends the jet hurtling down the runway. The modern jet engine is a technological marvel that generates its thunderous power by burning a mixture of compressed air and gas, then expelling this superheated stream through a relatively small nozzle outlet. As the engine's basic operating principle illustrates, bottlenecks don't necessarily represent obstacles to performance. Indeed, the point at which a process is most tightly constrained can sometimes hold the greatest potential for progress.

Travelers at Sky Harbor International Airport in Phoenix can't miss the huge Honeywell building that abuts the runway area. This property covers approximately 1 square mile and houses 604,000 square feet of manufacturing and assembly space. This facility is the headquarters of Honeywell Engines, Systems and Services, part of Honeywell Aerospace, a leading worldwide manufacturer of engines, integrated avionics, systems and service solutions. This division of the firm is the world's largest producer of small gas turbine engines used for auxiliary power on commercial jets and for main propulsion on business jets. The firm's aerospace business earned sales of $10.5 billion last year, producing a variety of aircraft components for customers around the globe.

A Matter Of Thrust

The powerful thrust that propels a jet airliner is generated within a relatively small area inside each engine. When hot gas exits from the engine's combustor, vanes in a ring-shaped part known as the "turbine nozzle assembly" direct it into the turbine rotors. In the process, this stream accelerates dramatically as it passes through small vane openings and relinquishes heat and pressure. The resulting high-velocity exhaust powers the gas turbine engine that is the source of the aircraft's motive power.

The circular turbine nozzle assembly is composed of 11 to 17 turbine nozzle segments. These segments are carefully machined and matched during assembly to achieve optimum aerodynamic performance. Because the parts must withstand red-hot temperatures during engine operation, they are machined from nickel and cobalt-based superalloys.

Although some turbine nozzle segments have been produced by outside vendors, the company estimated that it would save substantial expense and improve quality by bringing this production in house. The plant's current production of these new segments began in March 2001.

Lower Costs And Higher Efficiency

Because a typical nozzle segment incorporates 30 key features that require inspection, the cost of inspecting every feature with conventional gages would have been excessive. "Our decision to use a designated CMM for this manufacturing cell was not based on reducing the time necessary to perform the inspection work itself," says James Rebenar, Honeywell's CMM programmer. "But without the CMM, a separate hard gage would be necessary to inspect each operation. At a cost of $10,000-$25,000 per gage, it was more sensible to purchase a dedicated, shopfloor CMM rather than to create hard gaging." This is particularly true because any future changes in part specifications would require modifying or purchasing additional hard gages.

Another factor that weighed heavily in Honeywell's decision was the need to avoid queuing these parts with other parts awaiting inspection by CMMs the plant uses for general part-layout purposes. Because Honeywell produces approximately 20,000 nozzle segments per year, not having a dedicated CMM for this particular cell would drastically increase lead time and expense per part.

Honeywell addressed these needs by installing a Bright Apex 707 CMM manufactured by Mitutoyo America Corporation (Aurora, Illinois) in its production cell. This CMM incorporates real-time, automatic temperature compensation that employs a sensor in each axis, as well as two sensors that monitor the workpiece temperature. Equipped with a high-precision probe head manufactured by Renishaw Inc. (Schaumburg, Illinois), the CMM has a working range of 27.75 inches in both the X and Y axes, and 23.81 inches in the Z axis. The workpiece weight capacity is 1,102 pounds. The CMM currently inspects every feature on every part manufactured by this machine.

According to Mr. Rebenar, the maximum time necessary for the CMM to inspect the most complex of these nozzle segments is approximately 8 minutes. Each of four fixtures used to hold the parts is color-coded to eliminate errors, and the CMM verifies the required inspection routine by probing the inside diameter of a circular bushing at the base of each fixture. This dimension corresponds to the specific part and operation, as well as to its required inspection routine. Having an automated CMM on the shop floor provides the important advantage of freeing the operator to perform other tasks while the inspection routine is running.

The Single-Machine Strategy

The heart of Honeywell's production cell for the nozzle segments is a multi-process machining center manufactured by Hitachi Seiki USA, Inc. (Itasca, Illinois). The horizontal, five-axis HS500 machining center performs all grinding and machining required to produce these parts in four operations. The machine also incorporates a vertical workpiece changer that enables the operator to merely load the fixtured castings then retrieve the parts after machining.