Water-Jet Cutting

Introduction: In the battle to reduce costs, engineering and manufacturing departments are constantly on the lookout for an edge. The water jet process provides many unique capabilities and advantages that can prove very effective in the cost battle. Learning more about the water jet technology will give us an opportunity to put these cost-cutting capabilities to work. Beyond cost cutting, the water jet process is recognized as the most versatile and fastest growing process in the world. Water jets are used in high production applications across the globe. They compliment other technologies such as milling, laser, EDM, plasma and routers. No poisonous gases or liquids are used in water jet cutting, and water-jets do not create hazardous materials or vapors. No heat effected zones or mechanical stresses are left on a water-jet cut surface. It is truly a versatile, productive, cold cutting process. The water jet has shown that it can do things that other technologies simply cannot. From cutting whisper, thin details in stone, glass and metals; to rapid whole drilling of titanium; for cutting of food, to the killing of pathogens in beverages and dips, the water jet has proven itself unique.
Theory Of Water-jet Cutting: Most water-jet cutting theories explain water-jet cutting as a form of micro erosion as described here. Water-jet cutting works by forcing a large volume of water through a small orifice in the nozzle. The constant volume of water traveling through a reduced cross sectional area causes the particles to rapidly accelerate. This accelerated stream leaving the nozzle impacts the material to be cut. The extreme pressure of the accelerated water particles contacts a small area of the work piece. In this small area the work piece develops small cracks due to stream impact. The water-jet washes away the material that "erodes" from the surface of the work piece. The crack caused by the water-jet impact is now exposed to the water-jet  The extreme pressure and impact of particles in the following stream cause the small crack to propagate until the material is cut through.

Water-jet Cutting Process: Pure water-jet is the original water cutting method.  Water-jet cutting uses only a pressurized stream of water to cut through material. This type of cutting is limited to material with naturally occurring small cracks or softer materials like disposable diapers, tissue paper, and automotive interiors. In the cases of tissue paper and disposable diapers the water-jet process creates less moisture on the material than touching or breathing on it. The figure shows the water-jet cutting process.

   In this process water is increased in pressure by high-pressure pump to about 40000-60000 PSI and is forced through the orifice on to the target material. This high-pressure water on striking the surface performs the machining operation. The potential energy contained in the water is converted in the process to kinetic energy, i.e., into jet velocity, thus achieving its "cutting" effect.

pure water-jet

The basic water-jet process involves water flowing from a pump, through plumbing, and out a cutting head.

   In water-jet cutting, the material removal process can be described as a supersonic erosion process. It is not pressure, but stream velocity that tears away microscopic pieces or grains of material. Pressure and velocity are two distinct forms of energy. The pump’s water pressure is converted to the other form of energy, water velocity by a tiny jewel. A jewel is affixed to the end of the plumbing tubing. The jewel has a tiny hole in it. The pressurized water passes through this tiny opening changing the pressure to velocity. At approximately 40,000 psi the resulting stream that passes out of the orifice is traveling at Mach 2. And at 60,000 psi the speed is over Mach 3.

Applications Of Water-jet Cutting:
• Sheet metal: Stainless steel, carbon steel, high-alloy nickel steels, aluminum, titanium, copper
• Building: Decorative stone, marble, granite, tiles, plasterboard, glass and mineral wool
• Glass: Laminated glass, safety glass, and bulletproof glass
• Foodstuffs: Baked goods, deep-frozen products and fish
• Paper: Cardboard, corrugated cardboard, printing papers
• Miscellaneous: Plywood, leather, textiles, composites, rubber, plastics, sealing materials and foams .