Solving a one-time problem: Drilling Performance

While some shops shy away from difficult projects, others welcome them. According to Bob Perkins, president of PDS (Precision Defense Services) Industries, Irwin, Pa., the company has built its business on doing things others can’t do.

Bill Krause, director of engineering and estimating, described the shop’s approach simply: “When a customer comes to you with a problem, it’s time to listen.”

Manufacturing parts for the defense industry, the shop handles tough jobs, ranging from producing small fasteners made of exotic materials to machining complex components from 4,000- to 5,000-lb. forgings. The shop has even built custom machines to handle unusually difficult parts. Production runs rarely exceed 200 pieces.

For one complex aerospace component, the production volume was one. A few years ago, Lockheed Martin Space Systems came to PDS with a problem. To launch the last example of the Titan missile, the company needed one copy of a component called an oxidizer housing.

The approximately 10 “-dia., 12 “-long housing presented a long list of challenges. More than 140 dimensions were specified, many of which had total tolerances tighter than 0.005 “. Some true position tolerances were 0.002 “. In addition, flange configurations on the ends of the part were angled at 15° from a common centerline. “You prefer part surfaces to be square, perpendicular and parallel, so when you get a part like this, it just complicates how you go about manufacturing it,” Krause said.

Lockheed told PDS that the part’s original vendor declined to make the housing again, claiming that new fixturing alone would cost in excess of $50,000.

PDS was only given 2-D paper drawings of the housing. “It is one thing to look at a 3-D model; it is another thing to look at numerous drawings as long as the table with 20 section views,” Krause said. “When you look at real busy drawings, you wonder what you could be missing.”

The PDS team concluded it could handle the job. “It was about developing a process that would yield a part that met the drawing,” Krause said. “Quality was the goal.”

Lockheed said it would supply five of the proprietary forgings to yield one good part and purchase any additional acceptable parts.

PDS decided to first process a mockup part from a 10½ “-dia., 14 “-long piece of 6061 aluminum. “We would program it, machine it, inspect it, assess the issues we ran into and make adjustments before we got into machining the expensive, proprietary material,” Krause said.

PDS decided to process the part in five operations on a vertical machining center, a horizontal machining center and a CNC turning center.

For the first operation, the workpiece was chucked in an A-axis indexer mounted to the VMC’s machine table. The rotating A-axis enabled access to multiple part surfaces without reclamping. “If you can figure out how to fixture the part and machine as many dimensions as possible in one machine setup,” Krause said, “the better your feature-to-feature relationships will be.”