By Gary Rice

Think of it as a giant shotgun that blasts metal surfaces and saves the depot lots of time and money.

According to Mechanical Engineering Technician Chuck Wayman, that’s exactly what the Propeller Shop’s Automated Shot Peening Machine does. Through a computer numerically controlled peening process, the Shot Peener uses compressed air to throw steel balls against the aluminum airfoil section of P-3 and C-130 aircraft propellers. The one-eighth-inch diameter balls put minute indentations in the surface of the blades, which enhance the fatigue performance of the propellers.

“The propellers will be better able to withstand fatigue in flight,” Wayman, who works for the Mechanical Engineering Branch of the Industrial Production Support Department, said. “When metallic parts are in flight, they are subject to tremendous stresses. With peening, they will hold up better and stay in service longer.”

At present, the Propeller Shop’s machine is the only Shot Peener at the depot that is dedicated and programmed to handle P-3 and C-130 propellers. A second machine is on order that will use a smaller size steel shot to treat the steel parts of P-3, E-2 and C-2 propellers and components.

The machine can be operated by a single person, and several artisans from the Plating Facility have been trained and qualified as operators. Materials Engineer Carl Sauer oversees the operation. The operator takes the propeller off of a dolly and loads it into the machine, then calls up the appropriate computer program. By adjusting the air pressure setting, the operator can determine the intensity and amount of steel balls forced out of the nozzle, which controls the depth of indentation in the metal surface. When the controls are set, the operator pushes the cycle start button, and the fully automated process takes about two hours to peen the entire surface of the propeller airfoil section. During operation, the machine also tracks the performance data from each job so that a historical record of all work done is logged and maintained.

“The request for these machines came from the Production Department to Tammy Daniels of the Equipment Planning and Engineering Branch in 1998,” Wayman said. “I investigated the request, talked to people at the branch and division level, and did a lot of market research. The machine passed its final acceptance test and came on line in March.”

Wayman said that because the Shot Peener is such a complex piece of equipment, developing the performance and design specifications for procuring was a complicated process. He was responsible for the mechanical engineering and coauthored the specifications with Electronics Technician David Dixon. The machine was built by a contractor in Abilene, Kan.

“The main challenge was to develop a machine that could meet all of the depot’s performance requirements,” Wayman said. He explained that prior to acquiring the machine, the peening process was done by hand by artisans with a manually operated machine. This manual method was considerably slower and more expensive. The machine saves time and, since more propellers can now be inducted, has brought increased workload to the depot.

“This machine really does a great job,” Wayman said, “and it has helped bring the depot right to the leading edge of aerospace technology.”

Photo 1: With the Automated Shot Peening Machine behind him, Mechanical Engineering Technician Chuck Wayman examines P-3 propeller blades in the depot’s Propeller Shop. (Photo by Gary Rice)

Photo 2: Shot Peener Operator James Moore checks the machine’s computer control panel in the depot’s Propeller Shop. (Photo by Gary Rice)