This article describes an automatic induction brazing operation that has more than doubled production of steel shoes used in hydraulic pumps that move control surfaces in commercial aircraft.

Fig. 1 Four-position automatic brazing machine used to braze bronze rings to hydraulic pump shoe bodies.
Vickers, Inc., an Eaton Corporation company, designs, develops and manufactures power and motion control components and systems for a variety of industrial commercial, agricultural, aerospace, marine and defense applications. Vickers Aerospace Marine Division manufactures hydraulic pumps, motors and controls, producing nearly 400 products and more than 34,000 components used in commercial and military aircraft, ships and combat vehicles. The Jackson, MS, plant employs over 700 people and produces hydraulic and electrohydraulic pumps and motors for critical aerospace applications such as moving control surfaces, retracting and raising landing gear, and actuating brakes in military and commercial aircraft.

Vickers' operation of manually brazing bronze rings onto the steel shoes used in the hydraulic pumps used to be so difficult and time-consuming that it was the bottleneck of the entire pump manufacturing process. Engineers from Aeroquip-Vickers Limited, Jackson, MS, manufacturers of the pumps, worked with Lepel Corporation, Edgewood, NY, to develop a four-station index machine that has reduced cycle time for the operation from about 40 seconds to about 18 seconds. In addition, the new machine requires only one operator rather than two.

Process Selection

Most of the pumps produced by the facility include one of a family of steel shoes that are made from several different materials including 4140, 4160 and 6150 steel. Because of the critical nature of the application, products are tracked throughout the entire manufacturing cycle.

One of the most difficult operations in producing these shoes is the brazing of a bronze ring onto the shoe body. The importance of this brazing operation is demonstrated by the 100% x-ray inspection required for each part to verify the quality of the braze joint. In previous years, Vickers engineers had considered several brazing alternatives including flame brazing and furnace brazing. Flame brazing was rejected because it is very difficult to maintain the consistent temperatures required for high quality brazing and because the open flames can create safety and environmental problems. The furnace brazing method was rejected because of the high capital investment and because the cycle times were inadequate to meet production requirements for this component.

Vickers engineers instead specified induction brazing for this application. The induction heating process is a non-contact technique that provides localized heating through custom-designed coils. The process also made it possible to achieve the high production rates required for this application and was capable of providing extremely accurate heating in a controlled environment, producing uniform and reliable joints with smooth fillets.

Original Manual Brazing Process

In the manual process developed originally for the brazing operation, one operator would place the part to be brazed in a fixture and would then manually center the fixture in the induction coil. As the part was being heated, a second operator would manually push down on the bronze ring while turning it in a circle in order to squeeze out air pockets in the solder. This process was mentally and physically challenging, particularly for the second operator, and for this reason production would generally taper off toward the end of the day.

The low production rates that were previously achieved in the manual brazing operation caused a serious production bottleneck. Vickers had been experiencing higher demand for their hydraulic pumps, but were unable to significantly ramp up production because of this slow operation. The company decided to automate the process in order to increase production volume.

The Automated Solution

As it turned out, Lepel had just developed a four-station automated brazing machine (BZ4000) that is designed for medium to high production volumes of small to medium-size parts. Vickers and Lepel engineering teams worked closely to adapt the machine to meet the hydraulic pump manufacturer's special needs.

"The process that we jointly developed begins when the operator loads the part into a nest at the first station," says George Clapper, Industrial Engineer at Vickers. "The machine indexes the nest into the second station where the part is automatically centered inside the induction coil. Within 8 seconds, the parts are heated to 1310¯F and a ceramic guide moves up against the ring and begins spinning while applying pressure to remove the voids. The next station provides a place for the part to cool and set under an air blast. The fourth and final station is where the operator unloads the part." All moving parts of the 58" x 45" x 60" machine (Fig. 1) are enclosed with Lexan shielding, and the machine contains a light curtain, emergency stop button and ready light for operator safety. Sensors detect any interruption in cooling air or water flow and will stop operation automatically to prevent damage to the machine or workpieces.

Interchangeable coils and nests and adjustable cycle times allow the machine to accommodate a wide range of shoe sizes. Power output on the machine can be adjusted from 6 kW to 30 kW, providing appropriate heat for each size shoe while minimizing power consumption. A significant factor in the success of this application is the ability of the regulated solid state power supply provided with the machine to maintain brazing temperature despite line voltage variations.

Results

By decreasing the cycle time to only 15 to 18 seconds, Vickers was able to more than double their production volume from 400 to 1000 units per day with the current two-shift operation. At the same time, since only one operator is needed to run the machine, the second operator could be moved to a different part of the plant where help was needed. With yields typically running about 98%, part quality is slightly higher than the previous manual operation.

For more information contact Lepel Corporation, 50 Heartland Blvd, Edgewood, NY 11717. Phone: 516-586-3300 Fax: 516-586-3232