Quality
Waterjet Newsletter – 12/18/2007
AWJ
Industry Snapshot: A Personal View Miller’s latest article (*) addressed various aspects of the abrasive waterjet (AWJ) industry. Here are highlights of his view
points. Market
and Research The potential market for machining systems based on the current AWJ techonology is more than 10 times of existing systems
(about ten thousands). On the contrary to this potential, abrasive waterjet research activity in the Incremental Improvements Among the cost
components of an AWJ machining system, the cost of the abrasive waterjet part may be less than 20% of the capital cost
but can account for over 80% of the operating costs. A few percent points
improvement in the cutting performance, reliability and usability become very
significant. AWTs Do Not Operate Like
Jet Pumps The mixing chamber length vs orifice
diameter (l/d) is between 40 and 60 for an AWJ nozzle and is under 4 for a
jet pump. The focus tube length vs its diameter
(L/D) is greater than 60 for an AWJ nozzle but is under 8 for a jet pump.
These differences distinguish them in terms of energy efficiency and momentum
exchange. AWJs Are Not Cold Cutting Tools Abrasive waterjet
cutting is a thermal cutting process.
Temperature in the interaction between abrasive particle and material
to be cut can exceed melting points of either the material or the abrasive
particle. But the unique cooling effect of water virtually eliminates heat
effects on cut surfaces. This also means that the focus tube material should have
extremely good wear properties at high temperatures. Operating
Envelope for Abrasive Waterjets AWJs are classified based
on these three machining areas: general machining (AWJs),
fine machining (FAWs), and micro machining (MAWs). The cutting jet has a diameter between 300 microns
and 1.5 mm for general machine, between 50 and 300 microns for fine
machining, and under 50 microns for micro machining. Because fine abrasive is
not free flowing in air, MAWs are typically
suspension jets, as opposed to entrainment jets. Key Technologies for New AWJ Systems (a)
Abrasive: When abrasive is not free flowing in air because
of electrostatic or moisture issues, an alternative solution is to suspend
fine abrasive in water. Abrasive quality control and packaging become critical. (b)
Waterjet Nozzles: Replace waterjet orifices with waterjet
nozzles to reduce focus tube wear and improve cutting performance. (c)
Focus Tubes: Discover and develop materials capable of
good wear performance at high temperatures. (d)
Valve Seats: MAW valves operate on a suspension of
abrasive particles and require valve seats to either be super-hard and not
brittle or use a sliding valve action. (e)
High Pressure Pumps: Suitable pumps to supply ultra high
pressure at a few litres of water per hour for FAWs and pressure below 1000 bar and with flows less than
3 litres per hour for MAWs. * Miller,
D.S. (2007) From a single product (AWJ) to a multi product abrasive waterjet industry, Proceedings of the 2007 American WJTA
Conference and Expo, August 19-21, Houston, Texas. |
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