No heat zone for metal cutting
Waterjet cutting machines are very popular for 2D flat plate cutting, even in heavy-plate applications like steel service centers, equipment makers, and fabricators. Waterjet cutting is renowned for its straight cuts and absence of heat affected zones. Let’s look at the process of waterjet cutting to understand how it works.
Waterjet is non-thermal
The waterjet process is not a thermal cutting process like laser, oxyfuel or plasma. It is a mechanical sawing procedure. It can be compared to a band-saw. This is a thin metal strip with sharp teeth that are pulled through the material you are cutting. The waterjet cutting process is similar. It uses a thin stream of water and sharp bits of rock that are pushed through your material.
Crushed garnet is usually used to make the pieces of rock or abrasives. While there are other materials that can be used in some cases, garnet is the most commonly used for metal plate cutting. Garnet, a hard rock, is often used on sandpaper. Every grain of abrasive passes through the material, causing it to wear a little.
It works because it is fast
It is not enough to just pour sandy water on a plate of metal. It is how fast the abrasive hits the plate that makes it work. The momentum of an object equals its mass multiplied with its velocity. A grain of abrasive is very light in mass so it cannot have an effect on a plate of steel. The water is pressured to “ultra high” to accelerate the abrasive to cut through hard materials. You can see that if you make the nozzle opening smaller you get less water volume, but it releases at a faster rate. This is what happens with the waterjet cutting head.
Waterjet cutting pressures range from 50,000 to 60,000 PSI. Modern waterjet systems can be pressurized to up to 90,000. PSI. This pressure allows water to be released through a small opening that is usually made into a diamond, sapphire or other similar shape. Its diameter is typically between 5 and 15 thousandths of an in. This supersonic water stream is faster than sound. It is only about 1/2 gallon per hour, which is a good thing.
Waterjet cutting head – Click for larger viewAdding abrasive
The waterjet cutting head is responsible for the formation of the water stream through the jewel orifice, and the mixing of the abrasive in the stream. The stream goes through a funnel-shaped chamber, where the abrasive particles are absorbed by the water stream. After the water stream has been contaminated with abrasive particles it passes through a tube or nozzle. This entraps all the abrasive in the stream and keeps it moving in the same direction.
Once the focusing tube is present, the supersonic stream and abrasive will pass through almost any material. This includes aluminum, steel and stainless steel as well as granite, tile and laminates. Tempered glass, however, is too fragile.
Results
Each abrasive particle removes only a small amount of material through erosion. This means that very little heat is produced. Any heat produced by abrasives particles is quickly cooled by the water stream, before the surrounding material can heat up. These fast-moving abrasive particles can be cut without heat effect zone. The water stream’s momentum keeps them moving in a straight path long after they leave the focusing tube. This results in a very straight edge for many materials.
