Waterjet cutting is a cold process that, using garnet abrasive, can cut virtually any material. Given the range of garnet abrasive products available in the market, does the quality of the garnet really matter?
To answer this question, let's revisit the basics on how the waterjet cutting process works when cutting hard materials like metal, glass, granite or marble.
How Waterjet Cutting Works
A high pressure pump (intensifier) generates high pressure water at 60,000 psi, which is then transitioned into high velocity water as it flows through an orifice (made from ruby. sapphire, diamond or tetraCORE™) into the cutting head (Figure I: Abrasive Cutting Head). However, even at this high pressure and velocity, the water alone cannot cut hard materials and garnet particles are introduced into the water stream to produce the necessary cutting force. In the mixing chamber (Figure 2 : Mixing Chamber), the high velocity water stream - which travels at more than three times the speed of sound — creates a Venturi effect that pulls the garnet particles into the water stream from a separate abrasive line. The rubbing action between the outer wall of the water stream and inner wall of the mixing tube accelerates the garnet particles from zero to one fifth of the water stream velocity. The garnet particles are not able to penetrate the water stream due to shear force but are entrained along the outerwall of the water stream.
The high velocity garnet particles are essential in the cutting process while the primary function of the high pressure water is to accelerate the garnet particles to the maximum possible velocity. This generates the energy to cut a variety of hard materials.
Ideal Properties for Waterjet Cutting
After extensive cutting trials, the almandine variety of garnet is recommended by renown waterjet manufacturers to produce the best cutting results. High purity garnet does not contain other materials that reduce cutting performance. Producing higher purity garnet requires more sophisticated and meticulous processing.
Accurate Particle Sizing Maximises Performance
Accurate and consistent particle sizing is crucial to uninterrupted production and lower maintenance costs. Oversize particles can block the nozzle, stopping machine operation and potentially damaging the workpiece. Undersized particles can accumulate in the feed line or cutting head causing irregular abrasive flow.
Accurate Cutting and Precision Edge Quality
The cutting accuracy and edge quality are determined by quality of garnet used. A high precision edge requires a waterjet flow with a high garnet content and quality.
Advancing Waterjet Technology
Today waterjet cutting technology has moved to the next level, with waterjet machines operating at 90,000 psi pressures, significantly increasing cutting power and speed. Design advancements are also eliminating secondary operations and higher quality parts are being produced. Investment in these progressive technologies justifies investment in using high quality garnet to protect equipment and maximise returns. I conclude and confirm that it is extremely important to choose the right garnet abrasive for your project - it will not only have an appreciable effect on your product finish and daily operations, but also help to maximise the useful equipment life of your waterjet machine.
By Tiziano Cher, International Product Manager - Waterjet Parts