Recent studies indicate Precise Electro-Chemical Machining (PECM) drastically cuts costs for users, particularly for dressing the component surface.

Components inside an aircraft engine are exposed to extreme stresses, high temperatures and long service lives. Developers, therefore, use very hard, heat-resistant materials such as nickel-based super alloys for the construction of blisks and disks with single blades. This development presents a range of problems to manufacturing engineers, since conventional cutting methods become uneconomical as the material hardness increases and the service life of expensive tools drops, therefore causing unit costs to rise. A recent study by the specialists at the Fraunhofer Institute for Production Technology (IPT), together with the Laboratory of Machine Tools and Production Engineering (WZL) at RWTH Aachen (Germany) and EMAG ECM GmbH, compared a total of seven different blisk machining strategies, from multi-axis milling, combined with polishing to high pressure water jet cutting combined with Precise Electro-Chemical Machining (PECM) dressing. The results are impressive: for an assumed production volume of 800 nickel-based HPC blisks, the unit costs can be reduced by more than 50 percent compared to mechanical cutting if users adopt the correct machining strategy. PECM dressing proves to be the essential final process to make radical improvements to the efficiency of the production process.

Gentle material removal – fast processes

In view of this, many OEMs and their suppliers are studying very closely the PECM technology by EMAG ECM. The electro-chemical process removes material without contact and causes minimal tool wear while being fast and reliable. The basic principle is simple to explain: during the process, the workpiece becomes the positive anode and the tool the negative cathode. An electrolyte solution flows between them, removing metal ions from the workpiece. The form of the cathode (tool), with its active, conductive zones results in material removal from the workpiece at the required component contours. Ring ducts, grooves, bell hollows and other contours can be produced without contact, but with very high precision and excellent surface quality. With their PECM technology, the experts from EMAG ECM have developed this process in a targeted manner and tuned it to perfection. Two factors play a major role in this: firstly, the gap between the workpiece and tool, through which the electrolyte solution flows, is particularly narrow. And secondly, the supply of electrolyte solution is enhanced by a mechanical oscillation motion. Both factors together ensure that that material removal is even more effective and precise.

From single turbine blades to the blisk

EMAG ECM has two machine types for the different machining tasks of engine production: while the small model PO 100 SF is designed for machining single turbine blades, the larger PO 900 BF is for machining the complete, and therefore much larger, blisk. The systems differ in machining area size, footprints, generator capacity and the number of machining axes with precise PECM technology and EMAG high performance components available in both. “We launched the PO 900 BF in 2011 for blisk machining. The PO 100 SF development was the second stage in 2013 when an ever increasing number of customers demanded an electro-chemical machine solution for single blades. We now have an ideal basis for the development of precise, cost-efficient production solutions for small and large engine components,” says Richard Keller, member of the Board of Directors at EMAG ECM GmbH. Both these machines also provide the user with central EMAG innovations such as a Mineralit® polymer concrete machine base, intelligent software and hardware interfaces and efficient automation solutions.

Components certified for practice

This method has already been implemented into actual production with top results. For example, a well-known engine manufacturer has already certified single blades made on the PO 100 SF for use in aircraft in 2014 – unusually quickly after the start of production of the machine at a supplier’s plant. A similar stage is currently pending for blisk production. Components from a whole host of engine companies are currently in the qualification phase for use in practice. “The technology is currently in the validation phase in a number of test programs,” states Keller to sum up the current work of EMAG ECM. “The long-term strategic focus on these components and application technology is proving successful and each additional certification of components manufactured with PECM will only boost our sales success.”

The geometric machining precision is one of the main factors behind the technology’s success. In addition, it produces high surface quality with low peak-to-valley heights. Subsequent finishing processes on the blades, such as slide grinding, are therefore no longer required or can be completed much quicker – both of which result in a further reduction in unit costs. This is a massive plus point for a component which is becoming ever more important and whose volumes are rising massively.

EMAG India Pvt Ltd, Bangalore. Tel: 080-42544400. Email: sales.India@emag.com