Potential of abrasive waterjet cutting

Abrasive waterjet cutting is gaining popularity as a means for cutting a wide variety of materials. Ease of programming and the jet’s ability to cut almost all materials and any thickness make it suitable for all shape cutting applications except extremely hard materials. Its most significant attribute as an accurate cold cutting process allows it to cut metals without leaving a heat affected zone.

There are many applications where abrasive waterjet is the superior cutting method. Although waterjet should be considered for all applications, it will not replace conventional cutting methods such as stamping, laser or plasma cutting. It will continue to experience increasing use for cutting a wide variety of specialty materials.

Abrasive jet process description
Abrasive waterjet cutting utilises a high velocity coherent stream of water and abrasive that can be used to cut almost all materials. Water at 40,000 to 55,000 psi accelerates through a sapphire, ruby or diamond orifice. The stream passes through a mixing region where the vacuum, induced by the stream, sucks in abrasive. Momentum of the water stream accelerates and entrains abrasive as it passes through the nozzle. The stream exits the nozzle as a three phase mixture of air, water and abrasive particles with a cutting diameter of 0.020” to 0.060”. The high velocity abrasive particles impact on the kerf face and do the actual cutting. Kerf material is removed as microchips, with no negligible affects on the material.

The cutting stream carries 0.5 to 1.5 pounds per minute of abrasive. The quantity of abrasive is dependent on the cutting stream size, which is selected based on the material to be cut. Garnet is by far the most commonly used abrasive. It is environmentally clean, contains no free silica, and combines good cutting ability with reasonable wear on the consumables. Other less commonly used abrasives are olivine sand, silica sand and slag by-products. Due to its high Moh’s hardness, aluminium oxide has been rarely used, for cutting of very hard materials. Because of its high hardness aluminium oxide rapidly wears out the nozzle and is expensive to operate. Most shops use the abrasive once and then it is disposed as land fill waste.

The main attributes of the cut are: no heat, narrow kerf, good edge finish, and high accuracy. Successful, cost effective, abrasive waterjet applications take advantage of these characteristics.
Benefits of abrasive jet cutting
Abrasive waterjet offers many advantages not found in other cutting techniques.

a. No heat affected zone (HAZ)
b. Low contact force of cutting stream.
c. No distortion and warping
d. Burr-free
e. Can cut any material and thickness
f. Near net shape cutting eliminates secondary operations.
g. Can achieve high accuracy’s of up to +/- 0.001.
h. Material thickness of 0.002 to 12” can be cut.
i. Small kerf width allows for tight nesting and optimal material usage.
j. Flexibility

Most commonly cut materials
Materials that are reflective, conductive, heat resisting, or heat sensitive are ideal candidates for abrasive water jet cutting. As the material thickness increases AWJ becomes the preferred cutting technique, especially where accuracy must be maintained.

Heat sensitive and heat resisting materials such as stainless steel, alloy steel, titanium, inconel and hastelloy can be cut with no material effects. Some distortion may occur due to the residual stresses already present in the material. In thicker materials (over ?”) the edge finish and cut accuracy are superior to heat cutting methods. There is no burr or dross that may require secondary operations. Conductive materials such as aluminium and coppermj.monde