High-pressure water jets containing grit have
long been used for heavy duty cleaning and cutting in applications such
as descaling large oil pipes and decommissioning offshore platforms. The
abrasive water injection jetting (AWIJ) technique has been further developed
to much smaller cutting tasks in a CRAFT project under the BRITE-EURAM
Industrial and Materials Technologies programme. The project was based
at Böhler Hochdrucktechnik and the Institut
für Werkstoffkunde (IW) at the University of Hanover. SME partners
in the two-year project developed a smaller abrasive water jet, through
careful examination of the parameters of the cutting head, and opened
up a wide range of new applications.
Instead of just smashing through concrete and heavy
grade steel, abrasive cutting can now be applied to finer materials such
as ceramics, composites and thin magnetic steel. The key to this improvement
was the redesign of the cutting head, which mixes water and fine sand
and ejects it in a high-velocity stream.
||Developing the cutting head
If the focussing tube in the abrasive system
is miniaturised, the cutting head has to be completely redesigned.
The project at IW began by investigating the essential parameters
that determined the cutting dimensions of the head. The abrasive
material had to have a small grain size for a finer cut, but this
gives a 'stickier' mixture with greater adhesive forces. To overcome
this problem, the teams developed a special dosing unit for the
abrasive and a forced feeding mechanism. Following studies on optimising
the geometric parameters, a prototype small abrasive cutting head
One important requirement was to keep the cost
of the new unit as low as possible to give it a competitive market
position. The solution was a pre-aligned cutting head that was easier
to put on stream and to manufacture than the conventional manually
adjustable type. The prototype head was qualified in terms of efficiency
and quality of cut, and then tested for precision in a complete
cutting system. This included a new multi-axis handling system,
designed to make the smaller system easier to use.
||Accurate and versatile cutting
The different partners in the project produced
various tasks for the new cutting heads to accomplish. The reference
material was 10 mm of aluminium, which was used to evaluate the
field conditions. But they found that the heads could also make
fine cuts in composite materials, thin magnetic metal sheets, thick
plastics and ceramics. The quality of the cutting was impressive.
The width of the cut could be reduced to less than 0.3 mm, whereas
0.6 mm was the best previously achievable. These results mean that
it is safe to cut more expensive and sensitive materials with the
Moreover, the surface of the cut was much smoother
that the one normally obtained by abrasive cutting. The redesign
meant that the cutting was also speeded up with reference to the
use of hydraulic power and abrasive material, so that small AWIJs
have much higher productivity than their predecessors. Small heads
use less water and energy - about a quarter of the amount - and
only 8% of the amount of abrasive material, compared with the conventional
kind. There is a resultant rise in efficiency of 36%.
Small AWIJs also compare well with different
methods of making fine cuts in more expensive materials. The competing
methods are laser cutting and wire electric discharge machining
(EDM). Abrasive jets have a higher cutting performance than wire
EDM and are more powerful than Excimer lasers, the only ones that
can deliver a cut of 0.3 mm or less.
Additionally they allow the processing of advanced
non-metallic materials of high strength or wear resistance, such
as reinforced plastics and ceramic materials. Cutting the thin magnetic
steel sheets used in transformers and electric motors is a unique
application, as abrasive jetting is the only method that does not
affect the magnetic properties of the steel. This saves a further
stage in the manufacturing process.
Water jetting is also environmentally benign
in comparison with other cutting methods. It uses natural materials,
water and sand, that do not have to be manufactured and can be recycled
or disposed of without risk. It is relatively quiet, and produces
no gaseous pollutants, harmful aerosols or greenhouse gases.
||Exceptionally good results
The exceptionally good results of the test programme
give the new head great promise of success. The results of the project
will significantly strengthen the competitiveness of the participating
European companies, manufacturers and users.
The lead industrial contractor in the two-year
Hochdrucktechnik of Kapfenberg, Austria, is already putting
the miniature abrasive water injection jet head on the market. And
the various SME members of the project - manufacturers of components
for abrasive water jet technology, such as cutting heads, nozzles
or ceramic products, and users of abrasive water jets - are developing
further novel applications for the new head.