Tri-roller swaging tools speed aircraft bearing installation

United Airlines is now using tri-roller swaging tools to install aircraft bearings in as little as one-quarter of the previous time.  When used to install grooved bearings into their housings on a variety of actuators aboard Boeing 737s and 767s, Airbus A320s and similar aircraft, the tools have dramatically reduced overall installation time while also providing more consistent quality.

Commercial aircraft incorporate hundreds of bearings on movable control components, such as flaps and ailerons, to accommodate the frequent motion needed for adjustments during flight.  Typically, these bearings are installed by "staking" or swaging a lip of the bearing configuration over the edge of a housing.  In some cases, the part that incorporates the bearing housing may be a control arm, which can be removed easily and brought to a drill press where the swaging operation can be performed.  In other cases, the part containing the bearing is too large, and it is easier to install the bearing without removing the panel.  Even when a panel can be removed, a bearing may be installed in a bracket that is attached and cannot be easily removed for bearing installation.  

In all cases, it is important to swage the bearing firmly in place from both sides without applying too much pressure, which could shear the lip off or distort the bearing and cause it to bind.

A better tool
A new tool design eliminates most of these installation inconsistencies while also speeding the process dramatically.  Almost two years ago, United began using Shafer tri-roller swaging tools for many of its applications.  The tool design incorporates three precision rollers instead of the two usually found on such tools.  In addition, the two-part housing is designed to provide better, more uniform support during the swaging process.  As a result, it is easier to achieve the correct amount of flare without distortion. The tools are made in sets for specific bearing sizes, which eliminates the time-wasting problem of finding the correct tool combination.

Previously, United used typical two-roller swaging tools at its San Francisco maintenance facility.  Here, the airline performs "C-checks," which entail a thorough three-day review of many aircraft operating systems.  Part of these checks include inspection and possible replacement of control surface actuator bearings, which may range from half-inch to approximately 3-inch outside diameter (OD).

According to George Pezzelo, of United Airlines Fleet Operations, one of the problems with the conventional swaging tools was the difficulty in keeping them in readily usable condition.  "You could use one tool set for about three different bearing sizes, and people were mixing them up," he says.  "Theyd swap pieces, and we couldnt keep them straight, so we wasted a lot of time looking for the right tools."

Another problem with the previous tools was a need for more consistent results.  The older versions, Pezzolo notes, would sometimes shear the lip off of the bearing if too much pressure was exerted during installation.

Steve Ellis, who installs bearings on the second shift at United, adds that with the old tools, "about two out of 10 bearings would tighten up.  You cant spin them, so you have to cut them off and put another one on."  This most likely was caused by distortion during the swaging process.  With the new tools, Ellis says, "I havent had a bearing tighten up yet."

According to Ellis, the new tools also operate more smoothly and have a more professional feel.

Introducing the new approach
In the effort to improve the bearing installation process, the United maintenance staff worked closely with the tooling supplier, Rexnord Corporation, and its local tooling distributor, Jamaica Bearings.  Rexnord, a member of the BTR Power Drives Group, is a manufacturer and marketer of mechanical power transmission and conveying components.  These include Rex, Link-Belt and Shafer bearings, which are used extensively in aircraft applications.  Jamaica Bearings is a nationwide bearing distributor that monitors more than 2,500 parts for United and maintains a stocking warehouse at the airlines facility.  Lester Pezo, an account manager for Jamaica Bearings, is located on site.

Many people were involved in identifying the need for new tooling and putting forth the effort to make the improvement.  Several maintenance team members brought the need to team leader Bill Hoskinsons attention.

After maintenance operations center manager Irv Gregersen approved phasing in the new tools, it was necessary to develop a plan to identify the sizes that would be included in the initial trial.  Much of the credit for this goes to Al Abidin, of the United facility, who worked closely with Jamaica Bearings Carol Newman and Bob Franzen, Rexnords chief engineer, to analyze the airlines bearing usage and identify the most common applications.  Abidin also developed a database and charted the available tools, cross-referenced by bearing size, which made it easy to select the proper tool quickly.  Once the most popular sizes were identified, tools were ordered.  New sizes continue to be added at the rate of several each month.

At a second maintenance center, in Indianapolis, lead mechanic Marvin Andersch has added the new tools as applications at the facility increase.  He particularly likes the portable tools, because they can often eliminate the need to remove components to install bearings.

On the bench or on the aircraft
The swaging tools are available in two types, one for use on production or short runs in a drill press and the other for on-wing maintenance, repair and overhaul.  Both types are easy to use, with readily available shop equipment.  Their design minimizes internal free play and torque changes due to outer ring distortion.  They ensure uniform swaging around the entire bearing circumference.  The portable version needs no power equipment and can easily swage bearings using only a small wrench.  The unit allows bearings to be swaged in confined areas, and it isn't necessary to remove the bearing housing.

For parts such as control arms, which are small enough to handle on the bench, the drill press-mounted tool is used.  A small hand-fed drill press is used to provide control.

First, the roller fixture is inserted into the drill press spindle and a speed in the range of 100 rpm is selected.  Higher speeds can be used as operator proficiency increases.  Next, the part with the bearing housing and the bearing itself are positioned on the tools locating fixture, and the pilot of the roller fixture is guided into the bearing bore.  Using light pressure during the first revolutions, the operator allows the rollers to center in the bearing groove.  More arm pressure then swages the bearing lip, usually in about five seconds.  The bearing is then turned over, and the process is repeated for the other side.  Where the part in which the bearing is installed is too large or cannot be removed easily from the aircraft, a portable tool is used.

Here, the bearing is first fitted into the housing, and the roller fixture pilot is inserted into the bearing until the rollers seat against the lip of the bearing groove.  The locating fixture is mounted on the opposite side of the bearing by threading the bolt of the locating fixture into the pilot of the roller fixture.  After snugging the assembly together, the locating fixture nut is tightened approximately 5 degrees, and the roller fixture is turned several revolutions with the wrench.  The sequence is repeated several times, until the bearing lip is properly swaged.  Then the fixture is disassembled and turned over to swage the opposite side of the bearing.

Between the time saved putting the right combination of tools together and getting the correct swaging pressure to avoid shearing or binding, Pezzolo estimates the tri-roller tools allow a typical bearing to be installed in about one-quarter the time it took with the previous tools.

Another savings occurs when a portable tool is used to install a bearing in a flap or other component without removing it from the aircraft.  Not only can the installation be done in a shorter time, but the process eliminates the functional check that's required if the flap was removed.

MRO Today.  Copyright, 2000

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