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 US and Europe is virtually collapsing.

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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