Waterjet Cutting Characteristics

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For perfect abrasive waterjet cutting, there are several factors at the cutting head that determine the precision and quality of the waterjet stream and will affect the quality of part you are able to cut with an abrasive waterjet or without the abrasive. 

There are other factors that will effect cutting a precise and accurate part (machine design, controls, software and high-pressure pump) you can send email to us learn more about it . 

Here will focus on the cutting head and the waterjet as it interacts with the work piece.

Factors affecting cutting

       Abrasive mixing tube length
A longer abrasive mixing tube produces a more coherentwaterjet stream. The optimum mixing tube length is 3" - 4" (75 mm - 100 mm).

 •      Alignment of components

 •      The orifice, mixing chamber and abrasive nozzle must be precisely machined and fit perfectly together to avoid damage of consumables by the waterjet stream.

 •      Precise orifice

The inside of the abrasive nozzle must be machined to ensure perfect alignment with the waterjet stream.

 •      Low, controlled stand-off from work

Maintaining a close distance between the nozzle and the work piece, between 0.040" and 0.060" (1.0 - 1.5 mm), is critical for producing accurate parts while also getting the maximum efficiency from the waterjet. Cutting closer to the material limits the amount of atmosphere that the jet has to travel through before reaching the work piece. This limits the expansion of the waterjet stream, since as the jet expands, the effective power of the jet is reduced. Cutting speeds will need to be reduced to compensate.  If the distance between the nozzle and the work piece is increased by ?", cutting speeds must be reduced by approximately 20% to achieve similar results with respect to tolerance and edge quality.  Cutting under water with CNC height control will allow for ultimate control of the waterjet stream.

 •      Diameter of stream

A small diameter waterjet stream, as produced by a .010" (0.25 mm) orifice produces an efficient, high-quality stream. As a trade-off, cutting speeds are slower than when using a 0.014" (0.36 mm) or larger orifice, since less water and abrasive are used. 

Creation waterjet stream

 •      Water pressurized at 50,000 psi or greater enters the cutting head at relatively slow speed, in the order of a few feet per second.

 •      The water is forced through the orifice that has a small diameter orifice, anywhere from 0.004" to 0.045" depending upon the appli cation. These orifices are made of extremely hard material, such as diamond, sapphire or ruby. This step converts the water stream from a high pressure stream to a high velocity stream. At this point the water is moving in excess of 2200 miles per hour (3657 kilometers per hour).

 •      The high velocity of the jet creates vacuum, in the mixing chamber located immediately beneath the orifice. Abrasive, typically garnet, is metered from a mini-hopper through a plastic tube down to the cutting head and is sucked into the waterjet stream in the mixing chamber. 

 •      One of the exciting advancements in waterjet cutting in the past few years is the appearance on CNC- controlled abrasive metering systems. These systems precisely control the amount of abrasive that is allowed to flow to the cutting head. During the piercing process, cutting pressure and abrasive amount are reduced and the cutting head makes small, circular motions in the X and Y axes. This piercing procedure allows for difficult applications, such as piercing of glass and stone, to be processed with relative ease.

 •      The abrasive is fully mixed in the waterjet stream and is accelerated to approximately the speed of the waterjet stream.  This step does steal some energy from the waterjet stream, slowing it down slightly.

 •      The abrasive waterjet stream exits the mixing tube with extreme speed and power. The abrasive erodes the material to be cut. The process is referred to as "abrasive waterjet cutting" because it is the abrasive that is actually doing the cutting. The water's role is simply to give speed and power to the abrasive. In pure waterjet cutting, used for soft materials like foam and food, the force of the waterjet stream alone is enough to cut the material and abrasive is not required.

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