Pure waterjet cutting (pure waterjet) is a variation of waterjet technology, in which the material is separated solely by the kinetic energy of the water jet at ultra-high pressure - without the addition of abrasive. In practice, this means different process characteristics than in classic waterjet cutting: a different range of materials, different typical thicknesses and different criteria for selecting parameters.

In this article, we explain what pure waterjet is, how it works, what it is used for, and how it compares with waterjet cutting. We also show an example of the process with parameters: cutting carbon fiber with pure water on a CNC machine Opal Waterjet Combo.

What is pure waterjet (pure waterjet cutting)?

Pure waterjet (pure waterjet cutting) is a cutting technology in which a jet of water at ultra-high pressure flows through a very small nozzle opening (orifice), creating a thin and concentrated stream of high energy. The material is separated by microerosion and "tearing" of the structure in the zone of influence of the jet.

A key feature of pure waterjet is the absence of solid particles in the jet. Unlike abrasive waterjet (AWJ), where an abrasive (e.g. garnet) is dosed into the water, in pure waterjet technology the impact on the material results solely from the kinetic energy of the water jet. Therefore, this method is mainly used in cutting soft, flexible, fibrous and temperature-sensitive materials.

How pure water cutting works - step-by-step working principle

The process of pure water cutting can be described in several steps:

• Pressurization of water in a high-pressure pump to a level of several thousand bar.
• Stabilization of flow and supply of water to the cutting head.
• Uformation of water.
• Forming the jet on a nozzle with a very small diameter, which converts the pressure into kinetic energy of the jet.
• The impact of the jet on the material - eroding and separating the material along the cutting path.

In pure waterjet, the stability of the jet and the geometry and quality of the nozzle are of great importance. For processes that require high precision, among other things, nozzles with a very small diameter (e.g., 0.1 mm) are used, which improves the concentration of energy in the jet and facilitates the cutting of thin workpieces.

The process of cutting carbon fiber with pure water (pure waterjet) on Opal Waterjet Combo machine.

Pure waterjet vs. abrasive waterjet (AWJ) cutting - key differences

Although both technologies use high-pressure water, in practice they have different applications. Pure waterjet is optimized for soft and sensitive materials, while abrasive waterjet (AWJ) extends the capabilities to hard materials (including metals) through the addition of an abrasive.

It is worth considering pure waterjet and AWJ as two tools for different material groups. If the priority is the absence of abrasive, clean process and safety of delicate material - pure waterjet often proves to be the right choice. If it is necessary to cut hard or thicker materials - waterjet cutting will be necessary.

What kind of materials can be cut with pure waterjet?

Soft and flexible materials

• rubbers and elastomers,
• technical foams,
• insulation materials,
• sealants and sealing materials,

In these applications, the character of pure water jet action is crucial, allowing precise separation of the material without crushing, stretching or local damage to the structure.

Plastics and laminates

For many plastics and laminates, clean water cutting is mainly used where process cleanliness and integration with downstream production steps are important. The lack of abrasive means that parts after cutting do not require additional cleaning and can be directly routed for assembly, bonding or further processing.

Composites (e.g. carbon fiber)

One of the most important application areas for pure waterjet is composite materials, especially carbon fiber (CFRP). The absence of abrasive in the jet reduces common problems such as:

• contamination of the composite structure with abrasive grain,
• micro-damage to the fibers,
• deterioration of edge quality,

Process example: cutting carbon fiber with pure water on Opal Waterjet Combo

Carbon fiber (CFRP) is a material with a fibrous and layered structure. In many applications, it is critical to maintain edge quality and reduce the effects of temperature on the binder and fibers. For this reason, pure waterjet is sometimes chosen for cutting CFRP parts.

The example presented here uses a CNC machine Opal Waterjet Combo.

Cutting process parameters:

• Diamond nozzle: 0.1 mm
• pressure: 4000 bar
• cutting speed: 3000 mm/min

Recording the CFRP cutting process with pure water - process flow and dynamics.

The advantages and limitations of pure waterjet technology

Benefits resulting from the absence of abrasive:

• high process cleanliness - no sludge and abrasive residue on the edge and in the structure of the material,
• favorable conditions for sensitive materials (soft, fibrous, layered),
• possibility of obtaining a very narrow cutting gap with small nozzle diameters,

Limitations that need to be taken into account when selecting technology:

• limited ability to cut hard materials (including metals),
• dependence of edge quality on the choice of parameters (pressure, nozzle diameter, feed speed),
• in many thicker materials, the need to switch to water-wall cutting,

Frequently Asked Questions (FAQ)

Does pure waterjet cut metals?
No. For waterjet metal cutting, water-wall cutting (AWJ) is most often used because water alone usually does not provide sufficient cutting capacity.

Do you need abrasive to cut carbon fiber?
No. In many cases, pure water provides better edge quality than abrasive waterjet.

Why are very small nozzles (e.g., 0.1 mm) used?
The smaller nozzle diameter allows for a narrower and more concentrated jet, which supports precise cutting of thin materials and small radius details.

How does cutting speed affect edge quality?
Too high speed can degrade material structure separation (e.g., in fiber composites), and too low speed can unnecessarily increase process time. Therefore, the parameters are selected according to the material, thickness and required edge quality.

Summary

Pure waterjet cutting (pure waterjet) is a specialized CNC cutting technology designed for precision machining of sensitive, soft and composite materials. The absence of abrasive, the lack of thermal effects and the high purity of the process make this method applicable where classic technologies fail.

Pure waterjet does not replace abrasive waterjet or other cutting methods, but complements them