To design a blisk using electrical discharge machining (EDM) techniques is outright inefficient.
The EDM process requires multiple setups, and a lot of time and money for a part that must be entirely scrapped if even one fir-tree profile comes out wrong. Engine-makers today are finding a way around the problem of waste and multiple setups by using electrochemical machining (ECM) techniques.
Used primarily in the aerospace industry, ECM is typically used to machine difficult materials like high nickel and heat resistant alloys.
ECM can be used to reduce material requirements and by extension, part weight.
“We’re able to produce a blisk all in one setup with no welding, roughing or finishing,” said Jonathan Chomicz, ECM technology specialist at EMAG. “It takes 60 percent less time to produce a blisk with ECM compared to 5-axis milling.”
ECM cuts materials using the DC method and, for finer surface finishes, pulse form.
“As the off time approaches, the cathodes will retract and we’ll flush with clean electrolytic solution,” Chomicz explained. “As the pulse form turns on, the cathodes come in and we machine. We do this at a very high rate of speed: those cycles are within milliseconds.”
Engineers can perform precision electrochemical machining (PECM) by time pulse form with timed oscillated tools.
With the ability to produce a finish of Ra 0.05, EDM can reliably remove 5 mm to 7 mm per minute in linear directions in roughing applications – regardless of feature size.
No changing of the tool is required; the same tool can be used for both roughing and finishing.
“You may change the parameters of the electrolytic solution and how it’s presented to the cutting gap, but more often than not, it’s the same cutting tool,” Chomicz said.
ECM and PECM techniques are best used with materials that do not have a high silicon content.
“In aerospace applications, we’re cutting Inconel, Hastelloy and Waspaloy,” Chomicz explained. “For high heat and stress applications, we’re cutting materials like Stellite.”
For more information about ECM, PECM and EMAG’s services for both, visit www.emag.com.