Product category:
EDM diesinking
News Release from: Charmilles Technologies Corporation | Subject: Roboform EDM machines
Edited by the Manufacturingtalk Editorial
Team on 20 November 2002
Difficult hole drilling by EDM is
routine
Machining hundreds of high-precision small holes in HP turbine blades, represents a formidable manufacturing challenge met on a routine basis by 12 EDM machines installed at a turbine plant.
The high-pressure turbine blade of a modern aero engine is the epitome of high-tech engineering design and manufacture It represents a unique combination of state-of-the art metallurgy, advanced precision casting technology and the very latest in machining, test and measurement
This article was originally published on Manufacturingtalk on 13 Apr 2004 at 8.00am (UK)
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Difficult hole drilling by EDM is routine
Machining hundreds of high-precision small holes in HP turbine blades, represents a formidable manufacturing challenge met on a routine basis by 12 EDM machines installed at a turbine plant.
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Award for toolmaker thanks to CNC investment
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The combination of high-precision, complexity of shape and alloys that are inherently difficult to machine, represents a formidable manufacturing challenge.
In the case of the latest generation of high-pressure turbine blades, only the EDM process is capable of turning the designer's requirements into reality.
Rolls-Royce has developed considerable expertise with this process, and its Charmilles equipment is a central element in its new GBP 42 million turbine blade processing plant in Derby.
Opened just 18 months ago, the climate-controlled New Turbine Facility operates on four shifts, 24 hours a day, seven days per week, during which period it produces 2,500 high-pressure single-crystal and directionally-solidified turbine blades.
The Company manufactures approximately ten different designs of HP blades in the facility, but they all follow the same processing route.
The first operation involves grinding the 'fir-tree' (the name given to the grooved base of the blade which anchors it to the periphery of the turbine disc).
Grinding is carried out within a dimensional tolerance of +/-0.001in and is the critical reference for subsequent operations.
All the machining operations that follow are based on the EDM process.
The Company has ten Charmilles Roboform EDM machines - three Roboform 40s, five Roboform 51s and two of the latest Roboform 55s.
Blades are machined four at a time, and up to eight features are then machined in sequence.
Typical cycle times are about 50 minutes, depending on the nature of the features, and a typical program for one feature involves eight or nine power settings.
Electrode supply and management is contracted out to Erodex, and this company ensures that electrodes for each blade type are continuously maintained at the Facility and held in readiness in boxed sets ready for use.
Manufacture of the tooling is critical, and the electrode towers are themselves produced by EDM using Charmilles machines.
Tooling changes are accomplished in about one hour, during which time the tooling towers are thoroughly cleaned using ultrasonic cleaning.
Electrodes are provisionally set up in their towers off-machine in a setting fixture, but final setting is carried out on board the EDM machine, greater faith being placed in the Roboform's own measuring facilities than independent CMM equipment.
The latest Charmilles EDM machine for the Facility, the Roboform 55, was installed in February.
It is particularly noteworthy because of its ability to help engineers write their programs and analyse actual versus optimal cutting conditions.
It was delivered and installed in two weeks.
Following the die-sinking type EDM operations, the blades receive further EDM processing.
As many as two hundred tiny holes (each typically 0.3mm in diameter) require to be let into the surface of the blades to connect the outer surface of the blade to its internal air cooling passages.
This process is carried out on a robotic line of 12 EDM machines.
Further processing, including the application of special ceramic coatings, is then carried out.
EDM parts must meet stringent metallurgical tests with regard to the extent of the recast layer.
Machine reliability on the Charmilles EDM machines is excellent, reports the Facility's Principal Technologist, Andrew Hewitt.
"These machines have by far the best reliability record of any machine tool of any type in the Facility.
In fact they go wrong so rarely that our maintenance staff have grown to become unfamiliar with them!", he said.
"Overall, we are delighted with Charmilles.
The company has provided us with the best performing EDM machines at the best price, and with the customer service to match.
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