EDMs help cut machining time on aircraft parts by 40 percent

Modern Machine Shop, March, 2003 by John M. Jordan, Shauna Steigerwald

Integrity EDM (Tipton, Indiana) is a contract electrical discharge machining shop producing high accuracy components, made mostly from high nickel-based alloys, for the aircraft engine and land-based turbine market. The company has worked to establish its place among the highly specialized shops that serve this industry.

Founded in January 2002 and run by manager/owner Don Rowland, Integrity EDM is hardly a "new" company in electrical discharge machining. Mr. Rowland and his staff bring decades of combined experience, both in EDMing and in the production of aircraft parts. This experience produces several outcomes that benefit the company and its customers, all of whom supply combustion systems, fan blade assemblies or other equipment for aircraft engines or land-based turbine power generation.

Chief among the upsides at Integrity, according to the compay, is an EDM scenario that today produces finished parts at a 40 percent reduction in cutting time compared to other technologies, while improving surface characteristics and dimensional accuracy.

At the core of this process are two Beaumont CNC six-axis Fast Hole EDMs (Beaumont EDM FH40/6-axis), designed, engineered and built by Beaumont Machine (Williamsburg, Ohio). Mr. Rowland worked closely with Ed Beaumont and the Beaumont engineering team to devise an optimum solution for the challenges of aircraft engine parts and the related materials, such as Hastelloy, Inconel and others.

As Mr. Rowland explains, "We typically put a large number of very small and sometimes very deep holes into some incredibly hard-to-machine materials. We contacted all the holemaking EDM suppliers we knew from our past companies and detailed the specifics of one part, an airframe for a transition duct on a gas turbine exhaust system. There were 194 holes needed, each 0.060 inch diameter by 1.70 inches deep in a very high nickel-based alloy material.

"One of the machine suppliers simply could not do the job. Another could do it, after some extensive modification to its power supply. Beaumont could do it, plus its machine had a [ or -]120-degree swiveling head, a better power supply and servo system, a unique dielectric system, plus a control package for better hole entry/exit functions which sealed the decision.

"As an added benefit, the greater flexibility of the swiveling head and generous machine base allowed us to simplify our tooling, further reducing our start-up cost. These factors, coupled with a documented 40 percent reduction in per-hole cutting time, meant integrity would have improved performance, faster turnaround and a greater responsiveness capability for our customers," Mr. Rowland says.

"On other parts such as fan blades," he continues, "the swiveling head really makes a difference in the tooling costs. The contours and deep holes usually mean expensive fixturing with lots of starts and stops in the machining process. The head, the rotating electrode and 15-second electrode all combine to give us the desired results at far less cost. Plus, the entry/exit strategies at steep angles had always been a problem for fast hole machines, and the power supply/servo setup on the Beaumont machines minimized this condition."

Airframe and fan blade components are a challenging market for fast-hole EDMs. As the industry continues to demand lower emission engines, the need to run hotter results in much more critical airflow pattern requirements.

Responding to these requirements necessitates a thorough investigation of all available cutting technologies, according to Mr. Rowland. "We've looked at all the traditional cutting methods, plus waterjet, plasma, e-beam and laser," he says. "The latter is probably the strongest contender to EDM, but dimensional roundness, consistency and hole depth are still problematic for laser. And, of course, the materials we cut simply put the conventional hole drilling methods out of the running altogether."

Mr. Rowland further details the airflow challenges his company faces. "When you look at a typical jet engine, the total distance from the intake to the exhaust is one issue. Now, with the higher pressure intake and air cooling strategies needed for hotter operation to achieve the international standards of emission control, engineers at GE, Pratt & Whitney, Rolls Royce and the other engine customers we serve are placing higher than ever accuracy requirements on our holemaking."

Mr. Rowland notes that there are heavy fines imposed on commercial carriers to Europe who exceed the emission standards, and this further drives a quick improvement in engine design. "The hotter engines consume more of the fuel, which makes cooling airflow all the more critical. It doesn't take long for that condition to impact our machining techniques."

Investigation is under way on seven-axis EDMs to improve holemaking as well as throughput.

Also in review are electrode materials, one of which can cut a 10-inch deep, 0.60-inch diameter hole with less than 0.005 inch tolerance in some of the latest aerospace-grade alloys.