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Precision machining using abrasive water jets

Objective

The project will provide the experimental and theoritical base necessary to design and safely use a range of precision abrasive jet machine tools. These tools will help in the exploitation of advanced materials, stenghten the EEC's manufacturing base and provide the basis for exports of a new range of machine tools.
Critical parameters for Abrasive Water Jet Cutting were identified and characterised during the cutting trials and subsequent measuring activities. The work has yielded a standard methodology to evaluate the performance of water jets for cutting parts in different types of material. During the cutting trials, the following defects were detected: overshoot, striation and material removal. These variables have a large influence on the final cut surface quality.

The innovative aspects of this work were to define, quantify and qualify the quality and cost effectiveness of abrasive water jet cutting with respect to :
- Surface roughness
- Cutting/profiling velocity
- Overshoot or Undershoot
- Abrasive and abrasive flow rate
- System pressure
- Edge taper

The project developed a standard test shape and defined an extensive array of test conditions including :

- 4 Abrasive concentrations
- 4 Abrasive materials
- 4 Abrasive flow rates
- 4 Cutting pressures
- 4 Cutting speeds
- 8 Sample materials (ductile and brittle)
- 2 to 4 Sample thickness'

A recommended Abrasive Water Jet quality standard document was proposed within the programme, establishing guidelines based on the French standard for thermal cutting (NF A 87-000).

The difference between both types of Abrasive water jetting systems in use has been examined and the increased efficiency of the suspension system (DIAJET) can be explained from consideration of jet pump efficiency and abrasive degradation within each system.

The cutting tests on brittle and ductile materials, have allowed us to establish a vast database giving the cutting results (edge quality and accuracy) versus the cutting parameters (pressure, abrasive, cutting speed, flow etc).

Mathematical models were developed for both brittle and ductile materials, and provide a good fit to the experimental data.

Guidelines for carrying out trials to test the suitability for Abrasive water jet systems for Aerospace industry use have been developed. However, in order to prove the fatigue requirements for the cutting of advanced Aerospace materials, further work is required.

The project has quantified the impact of the jet, once its exits the material being cut, on the surrounding environment. Subsequently, it has been possible to select material resistant to the impact of the jet and construct the architecture of jet catchers designed to collect the jet.

Two types of catcher, flat and cylindrical, have been designed the efficiency of such catchers has reached now a high degree of perfection, Four catchers (1 flat type and 3 cylindrical) have already been sold for aerospace and nuclear applications.
Abrasive water jets can cut a wide variety of advanced materials that are very difficult to cut using conventional methods. Exploitation of abrasive jet technology is being seriously delayed because of a lack of experimentally and theoretically based models of jet behaviour related to nozzle/workpiece/manipulator/catcher parameters. These models combined with a better understanding of the physical processes involved are essential to design machines to generate cuts that do not require costly secondary machining operations, achieve adequate material fatigue properties, produce acceptable surface finish and edge shapes and avoid scrap components caused by jets deviating from the expected cutting path. This project aims to : - establish the characteristics abrasive jets need to meet specific machining objectives - develop an understanding of jet/workpiece interaction and construct mathematical models of the interactions - simulate the manipulation of jet/workpiece to achieve required workpieces shapes whilst producing acceptable surface characteristics - provide models that will predict where and how a jet will leave workpiece so as to be able to catch it - develop new designs of compact jet catchers that can be manipulated by robots.

Coordinator

British Hydromechanics Research Group Ltd
Address

MK43 0AJ Cranfield
United Kingdom

Participants (4)

Aquarese Industries SA
France
Address
1 Allée Des Garays
91120 Palaiseau
British Aerospace plc
United Kingdom
INSTITUTO DE SOLDADURA E QUALIDADE
Portugal
Address
Av. Professor Doutor Cavaco Silva Na° 33, Talaide, Taguspark
MECANIC SYSTEMS LTD
Belgium