Waterjet cutting

Waterjet cutting (also written water jet cutting, and called abrasive waterjet cutting when abrasive is added) is a cold cutting process in which water at very high pressure leaves a nozzle as a narrow jet traveling at several hundred meters per second and erodes the material. The cutting head moves according to a CNC program and cuts 2D contours out of plates and sheets.

A pure waterjet a few tenths of a millimeter in diameter cuts soft materials: rubber, foam, gaskets, textiles, paper, thin plastics and food. For metals, stone, glass, ceramics and composites, an abrasive, most often garnet sand, is added to the jet in a mixing chamber. The abrasive jet exits through a focusing tube and cuts a kerf that is typically about 1 mm wide.

Operating pressure is usually around 4,000 bar (400 MPa, roughly 58,000 psi), and high-pressure pumps go beyond 6,000 bar. The main advantage is that there is no heat-affected zone: the material does not harden at the edge, its microstructure does not change, it does not distort from heat and no combustion fumes are produced. Materials from thin foils to plates more than 100 mm thick can be cut, but cutting speed drops sharply as thickness increases.

The jet lags behind and loses energy deeper in the material, so the cut face shows striations near the bottom and the cut wall has a slight taper. Accuracy on thinner material is typically around ±0.1 to 0.2 mm and gets worse with thickness. Machines with a tilting cutting head compensate for the taper automatically. Controllers offer several cut quality levels, and higher quality means lower speed and a higher price.

Choose waterjet cutting when the material cannot tolerate heat (hardened steels, titanium, parts where a change in the edge microstructure is unacceptable), when it is too thick for a laser, or when it is not a metal at all: stone, glass, ceramics, composite laminates, carbon fiber composite, rubber, foam and gaskets. It also suits near-net-shape blanks for CNC machining, because they save both material and machine time on the mill, as well as one-off production without tooling.

For thin steel sheet, laser cutting is usually faster, more accurate and cheaper. The operating cost of a waterjet is driven mainly by abrasive consumption and nozzle wear.

Do not expect the accuracy and edge sharpness of milling. Taper and a rougher bottom edge are normal in thick material, so state which side of the part is cosmetic or functional, and have precise faces and holes machined. The smallest internal radius is roughly half the kerf width. Piercing brittle and layered materials (glass, composites) can cause cracking or delamination, so they are pierced from a pre-drilled hole or at reduced pressure. Tempered glass cannot be cut at all, because it shatters.

Mild steel parts come off the machine wet and rust quickly unless they are dried and protected. The cut face is matte, similar to a blasted surface, and abrasive grains can stay embedded in it, so clean any edges that will be welded. In your request for quote, state the material, thickness, required tolerances, cut quality and whether taper compensation is needed. For thin sheet and small parts, ask how they will be held during cutting, because they can vibrate in the water stream or drop between the slats of the support grid.