Machining Glass with Abrasive Waterjet
Thirty years ago, the abrasive waterjet process was primarily reserved for cutting 2D geometries in relatively thin aluminum, and the quality of the cuts were very rough to say the least. Today, in addition to cutting all thicknesses of aluminum and other metals, accuracy has improved to fractions of a millimeter. Additionally, abrasive waterjets are also used to cold cut everything from 1mm thick chemically toughened glass for cell phones and appliances to six-layered bullet proof glass.
The same attributes that make glass perfect for applications such as guard rails on staircases or shower enclosures also make glass very difficult to machine using traditional machining methods such as CNC. However, non-tempered glass is surprisingly easy to machine using an abrasive waterjet. Glass for architectural applications is cut to size (including cutting small holes for mounting hardware) and then run through an oven for tempering. Using extra fine abrasive minimizes glass chipping and cracking that ultimately reduces secondary polishing operations.
Abrasive waterjet is the process of accelerating a jet of water to two times the speed of sound, then introducing abrasive into the jet. The abrasive is accelerated by the jet and as it hits material, the abrasive erodes the material. Computer controlled pressure and abrasive flows eliminate cracking during the piercing cycles.
For example, 1/4" thick glass can be machined by abrasive waterjet at speeds of up to 120 inches per minute using 55,000 psi pressure and a 0.015" orifice. This cutting speed along with a relatively small 0.04" kerf width means that this very expensive material can be machined quickly, to near net size, with minimal material waste.
Unlike metal cutting tools used on a CNC, the abrasive jet is a fluid tool that can be deflected by the material being machined. But advances in modeling how the abrasive jet bends during the machining process make it possible to improve the accuracy of cuts, as well as the repeatability: in short this all translates into more accurate parts and the elimination of costly waste.
Abrasive waterjet cutting introduces taper in a cut. Taper is the result of the jet dwelling longer at the top of the material than at the bottom. Taper compensation can be achieved by slowing down the speed of the cut or by articulating the nozzle using sophisticated computer modeling.
Of course, in addition to cutting glass, abrasive waterjet also cuts metals and superalloys. Abrasive waterjet is also used extensively to pierce and cut laminates (such as DIBOND®) and fiber-reinforced polymers (such as carbon fiber). These diverse applications allow manufactures to easily combine a wide variety of materials in architectural designs.
Each of these materials present unique problems to the traditional machining techniques, but the erosion process used by abrasive waterjet machining allow manufactures to quickly and cleanly cut them without changing tools.
Lastly, it should be noted that abrasive waterjet is an environmentally green process. The abrasive itself is dredged from rivers around the world, separated by grit size, and does not contain any harmful chemicals. The abrasive is used once and then sent to a land fill. Potable water is used to accelerate the abrasive, and after cutting, the water is chemical free and can go to the sewer.
Today’s abrasive waterjet systems are highly capable machines that can cut delicate materials such as glass and laminates as easily as it cuts aluminum, copper, and steel. Advances in software control allow for better material utilization, while the green cutting process reduces waste. Together these features make abrasive waterjet the ideal tool to expand and diversify production.