Since its introduction
in 1969, wire-electrical discharge machining (WEDM) has achieved
a monopoly position in tool-making and in series production of aerospace
components. The process entails the virtually force-free and fully
automated precision cutting of electrically conductive materials
- mainly metals - with a continuously turning wire electrode. All
operations are carried out under water and at a constant temperature,
ensuring high accuracy and low thermal distortion. Weaknesses in
the procedure include lengthy processing times and the poor coatability
of WEDM processed pieces due to surface roughness.
Coating processes improve the surface characteristics and performance
of many important items. Super-hard coatings allow the use of lighter
and less-expensive materials in applications where only hardened
steel would have served before. Such processes can help to extend
the lives of industrial tools, and provide an environmentally friendly
alternative to more traditional surface treatment processes.
Next step in wire-EDM technology
WECAT aimed to develop new super-finishing WEDM
machines for the production of coatable pressing and punching machine
tools. First, new wire electrodes had to be developed to suit both
the particular pieces to be produced and different power supplies.
The project was able to define specific wire electrode requirements
for different applications, allowing rapid and informed selection
of the optimal system configuration for a given operation. Valuable
fundamental knowledge about wire stress during conveyance and cutting
was also acquired.
Once appropriate wire electrodes had been developed, a new high-speed
generator, an expert process control system and features such as
automatic wire threading to produce a staggering 380% increase in
productivity compared to previous machines. Moreover, component
surface roughness was reduced down to a level sufficient to allow
coating without the mechanical pre-treatment (smoothing) previously
found to be necessary.
Finally, a modified physical vapour deposition coating technology
known as arc bond sputtering was developed. This method can replace
traditional zinc-based galvanising, a highly environmentally unfriendly
process because of the polluting liquid effluents it produces. A
reduction in production, maintenance and waste treatment costs will
help to strengthen the competitiveness of potential users, while
increases in industrial tool performance will mean reduced residue
volumes resulting from 'waste' during cutting and coating.
Europe takes on its competitors
Partners are convinced that WECAT represents
an important step forward in super-finish machining and is a solid
European industrial initiative in a market traditionally controlled
by Japanese and Swiss companies. The project has undeniably consolidated
the position of prime partner ONA Electro-Erosion as an important
supplier of WEDM machines. When the project started, this Spanish
company was in serious trouble due to fierce competition and an
extremely difficult market situation. Now, having sold more than
1000 machines, its main challenge is maintaining its position as
a developer and marketer of new and innovative products.
All of the partners, including Spanish, Dutch and German participants,
made important contributions and have, in turn, benefited from the
project. Most are continuing to participate in other joint technological
initiatives, and new developments include the coating of very small
machine parts and the further reduction of residues resulting from
cutting processes. New market launches stemming from WECAT are expected
in the short to medium term.