Safe, fast, flexible

Once considered a mature machining technology with little use in the production of complex, high-value, flight-critical aerospace components, wire-cutting electrical discharge machining (WEDM) is now giving wings to aero engine manufacturers. In fact, with technology now in development by Switzerland-based GF Machining Solutions, WEDM is poised to become a self-optimising process.

In 2011, the Swiss machine tool manufacturer, a Division of GF, launched its CUT 200 Dedicated WEDM solution delivering high levels of speed, performance and quality in the production of turbine disks. Customers using the solution report increased ability to control their production costs, according to Antoine Marty, aerospace market segment manager with GF Machining Solutions Business Development-Segmentation.

With its own R&D department, close ties to the aerospace industry, and long-term collaborations with research institutes worldwide, GF Machining Solutions is positioned as an innovator on behalf of its customers in aerospace component manufacturing. The solutions provider is pushing the boundaries of technology to advance customers' productivity, process security, traceability and cost-effectiveness.

“The emergence of lightweight, difficult to machine materials is driven by international mandates to reduce aircraft fuel consumption, partly by reducing mechanical parts' weight or increasing the operational temperatures that optimise engine efficiency,” states Marty.

In parallel, aerospace manufacturers have strong order books due to massive increases in air traffic from Asia and are ramping up production and setting new records year after year.

“This puts enormous pressure on the aerospace supply chain, where manufacturers have an increased need for technologies that deliver reliability, high productivity and compactness, without compromising their commitment to process quality and traceability.”

The CUT 200 Dedicated is perfectly aligned with the needs of aerospace manufacturers. With a built-in tilting rotary table to accommodate machining of complex, alloyed aerospace components—including turbine disks—the machine uses C-axis rotation and ±20° B-axis tilt.

“This solution delivers some of the industry's highest levels of speed, performance, quality and productivity, and allows aero component manufacturers to better control their production costs,” Marty continues. “Highly flexible, the CUT 200 Dedicated is also finding application in energy component production. Most profile slots for turbine industry disks can easily be machined with the CUT 200 Dedicated, thanks to its large working area. Moreover, cutting of fir-tree root profiles for aero and energy turbine blades are potential applications.”

Defying decades-old doubt

While it has a solid following today, the CUT 200 Dedicated emerged in defiance of decades-old misgivings about WEDM's value in aerospace component manufacturing.

“Manufacturers' caution about WEDM is based on pre-1975 indications that it was a slower process and that it could leave critical components vulnerable to fatigue due to recast layer formation, cracks, tensile residual stress, and variations in microstructure,” says Roberto Perez, a physicist and head of applied research, innovation, R&D at GF Machining Solutions' headquarters in Geneva.

But plenty has changed in the past two decades. WEDM cutting speed has quintupled for more general applications and doubled for more complex profiles, like fir tree slots in aero engine disks. GF Machining Solutions and its research and industrial partners have been advancing WEDM technology with enhanced generators, use of coated wires, heightened system control efficiency, monitoring capabilities, improved onboard machining strategies, process traceability, and anti-electrolysis methods.

The GF Division was a contributor to the UK's 2012 University of Birmingham research proving the important contribution WEDM can make in aerospace machining as a replacement for broaching. The broaching process removes workpiece material by continuous shearing and deformation, and can result in compressive residual stress in aero engine components' machined surfaces. That stress may leave sub-surface defects.

WEDM, on the other hand, erodes the workpiece surface through melting and evaporation without any contact between the workpiece and the tool—and the latest WEDM development produce next to no residual stress of the surface of the workpiece and no defects after the final finishing cut.

As further evidence: University of Birmingham Professor David Aspinwall's research shows that, compared to broaching, aerospace customers gain advantages when using WEDM. These advantages become even clearer in light of the WEDM's productivity gains, high quality results, onboard eTracking technology for process traceability in comparison to the expense and footprint of broaching. Case in point: Depending on its size and application, a broaching machine can cost $3.4 million, and replacing a broken broaching tool can cost more than $226,000. Take into account the cost of a 100mm x 50cm disk of Udimet 720 and the related costs of machining errors, and the value of WEDM as an alternative to broaching becomes even clearer.

The evidence of WEDM's value in aerospace manufacturing continues to pour in: For example, new research from the University of Aachen (DE) indicates that WEDM is capable of replacing broaching to become the go-to machining technology in the production of fir tree slots for high-pressure compressor and turbine disks. At the same time, a GF Machining Solutions customer using the CUT 200 Dedicated in aerospace component manufacturing is doing its own internal studies and the machine's performance to date confirms scientific research conducted over the past five years.

Built-in process monitoring

The CUT 200 Dedicated's eTracking software allows manufacturers to identify key process parameters to follow up in surveying part quality—another clear advantage over broaching.

“Conventional aerospace machining processes, such as broaching do not have this capacity to follow up the machining process with the high-quality indicators that are made possible by WEDM electronic process controls,” states Perez. “With eTracking, all information related to the process is digitized and closely controlled. This capability is extremely particular to WEDM solutions for aerospace manufacturing and of very high value to our aerospace customers.”

Onboard eTracking lays the groundwork for intelligent WEDM with zero-defect manufacturing and self-optimising machines and systems.

“As we are following up on all the key process parameters and data generated by our eTracking module and its ability to track part quality, the next development will be the machine's ability to automatically adjust itself to improve quality with no operator intervention,” says Perez. “With the knowledge the machine will have of the system, it will be able to self-optimise.”

And that, Perez emphasises, is very close to the concepts envisioned in Industry 4.0 or the “sustainable factory of the future.” GF Machining Solutions is at the forefront of the drive to commercialisation these solutions of the future—within the next five years.

“There already is a demand for these capabilities and we expect that demand to grow as manufacturers are now facing new and critical challenges in productivity, flexibility and resource efficiency for optimizing their profitability,” concludes Perez.

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