Abstract:
This thesis concerns the development of a low cost and environment-
friendly method for the regeneration of the most widely used aqueous
etchant, ferric chloride, found in photochemical machining (PCM) facilities.
In order to implement the above process a comprehensive and automated
chemical analysis and control system was designed to fully investigate the
key parameters which previous research has suggested play a major role in
the analysis of ferric chloride. Monitoring methods have been developed
and deployed in a commercial environment such that the etchant could be
analysed remotely across the business network or via the internet. This level
of monitoring has removed much of the `black art' previously associated
with etching and has allowed proactive control of the etchant and the PCM
process in general.
Detailed analysis of the data captured has resulted in a clear understanding
of the role the free hydrochloric acid (HC1) level plays in prolonging the life
of the etchant. By keeping the free acid level high, dissolved metals remain
in solution. The regeneration uses oxygen from the air, combined with
surplus HCI, to regenerate the etchant within the etching machine itself.
This environment-friendly system has allowed etching to continue in a very
controlled way for nearly one year, during which time some 500kg of metal
have been dissolved. This has totally eliminated the need to change the
etchant which otherwise would have been carried out every 16 weeks. The
saving to the sponsoring company has been over £7000 per year.
These combined activities are considered as a major advancement in
knowledge and will be of considerable benefit to the PCM industry in
general. The monitoring systems alone would significantly benefit any
PCM company by reducing rejects and improving product quality and
productivity.
