Waterjet vs. Abrasive Waterjet: Important Differences
Many people use the terms “waterjet” and “abrasive waterjet” interchangeably, but there is a fundamental difference between the two—they cut in totally different ways and are used for different purposes. There are several mechanisms a jet of pure water uses to cut depending upon the material being cut. Granular materials like sand stone are picked apart on a grain by grain basis. Fabrics and woody materials are cut by breaking fibers. Jets of pure water can be very effective in softer materials ranging from fabrics to rubber and a wide variety of food products. , but metals, ceramics and most plastics require the addition of abrasive.
The abrasive waterjet cutting mechanism is similar to a grinding wheel. The abrasive particles are moved by the water jet rather than the wheel and chip out small pieces just like the abrasive particles in the wheel does. By using a hard abrasive such as garnet, an abrasive waterjet can cut a very wide range of metals and other hard materials and thus become a useful technology for machine and fabricating shops.
The key thing to remember is that in an abrasive waterjet the abrasive particles are doing the cutting, not the water. The role of the water is to entrain the abrasive particles that are introduced at the nozzle and accelerate enough of them to a high enough speed to cut effectively. Faster cutting is achieved by increasing the speed of the particles and/or by increasing the number of particles entrained in the water stream.
Interestingly enough, this gets us right back to the two basic ways of increasing hydraulic horsepower at the nozzle discussed in my entry of last November— increase pressure or increase water flow rate. Increased pressure increases the speed of the water passing through the nozzle and has the potential to increase the speed of the entrained abrasive particles. Increased water flow rate increases the ability of the water stream to entrain more abrasive and thus create a cutting jet with more “teeth”.
Either approach can increase cutting speed and either approach has associated costs. The “more flow” approach results in an increase in consumption of water and abrasive, but at a known and predictable cost. The “more pressure” approach results in higher maintenance costs, increased unpredictability of high-pressure component life and reduced system reliability.