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Waterjets
The ultrahigh-pressure (UHP) pump technology used to create
high-velocity waterjets was developed in the 1970s. Water is
pumped at pressures up to 55,000 psi and expelled through a
sapphire orifice to form a fine, coherent cutting jet. At this
pressure, the water is traveling at about 2500 feet/second when
it emerges from the orifice. Waterjets typically have diameters
from 0.003 to 0.020 inch, requiring 2 to 90 Hp at 55,000 psi.
Pure waterjets are generally used to cut only soft
materials such as food, paper products, cloth, leather,
wood, fiberglass, and some aerospace composites. It is a
valued technology in many applications due to the fact that
it is easily automated and because of its ability to cut very
thin kerf widths with little material loss.
Abrasive Waterjets
The capability of the UHP waterjet was extended in the early 1980s
by adding abrasives to form the abrasive-waterjet (AWJ). The abrasive
particles are entrained in the waterjet and transported at supersonic
velocities to cut virtually any material. The AWJ has been shown to
produce surfaces that are free from adverse mechanical, thermal, or
metallurgical effects, and have found acceptance in cutting applications
such as aerospace sheet metals and composites.
The waterjet developed in the AWJ flows through a mixing tube where
abrasive particles are entrained in the jet. The high-velocity water
flow in the mixing tube creates a vacuum that serves to draw air, which
is used to transport abrasives from a hopper into the nozzle via a
supply hose. The primary function of the mixing tube is to force a
transfer of energy from the waterjet to the particles, while holding
the accelerated abrasive particles in a narrow collimated stream.
Garnet abrasives are commonly used as the AWJ cutting medium.
The AWJ has advantages over other machining methods in many areas:
- The AWJ easily machines titanium, nickel alloys and very hard brittle materials
- It is a cold cutting process, machining without creating thermal distortions or thermally driven changes to the metallurgical and crystal structure (no brittle recast or micro-cracks as left by laser and EDM)
- The workpiece sees very low tool loads with the abrasive-waterjet and machining delicate part features is an option
- Glass and ceramic materials can be machined to complex shapes without the sub-surface flaws created during grinding
- Drilling small, deep holes is easily performed with the AWJ
- AWJ cuts more materials and is faster than EDM
- AWJ cuts more materials and is faster than laser with thick materials
The AWJ has many advantages over other machining technologies, but
has remained a niche market in part because of limitations involved
in machining to close tolerances and therefore competing effectively
with the much larger laser and EDM markets. The technologies available
at Ormond increase the application of the AWJ to closer tolerance work
and allow the manufacturing industry to take advantage of this low cost,
low tool-load, heat-free machining process.
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