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The process of abrasive jet machining uses high water pressure alone, or with an abrasive additive, to deliver a jet cutting force 30,000 to 60,000 pounds per square inch (psi). This extremely concentrated beam of water energy emits from a machine workpiece designed to assist in custom cutting of numerous materials. Water alone cuts softer materials such as foam, rubber, and plastic; the cold cutting process produces little heat, which makes it possible to cut flammable materials with no heat affected zone. The addition of abrasives permits cutting precision patterns in stronger materials such as metals, glass and tiles.
Sometimes called a water jet cutter or water cut center, abrasive jet machining equipment cuts almost any material that can be placed in sheet form. High-precision cuts produce intricate shapes and patterns with neat edges. These machines cut stone, marble, and glass, though tempered glass, as from a car windshield, cannot be cut without shattering. Diamond is another material that cannot be cut using this process. These machines are employed in manufacturing and machining, cutting metals such as aluminum for fabrication; in crafts such as decorative glass cutting; and in construction, shaping products such as custom tiles and inlaid marble medallions.
Forcing ordinary tap water at high pressures through an extremely narrow channel creates a cutting stream that removes target material by erosion. These powerful workpieces typically occupy professional workshops and machine shops, often working as a finishing process due to their slow rate of removal. The equipment employs pumps; these draw not only water, but as many as 250 amps just to begin abrasive jet machining, and use up to 50 amps during the process.
The machine operates by compressing gas through a mixing chamber, perhaps with a garnet abrasive, which is a hard mineral and a safe, natural abrasive material. Gas flows through a convergent-divergent nozzle, a mixing chamber, and out a fixed or handheld convergent nozzle. Abrasion-resistant nozzles are made from tough materials such as synthetic sapphire or tungsten carbide. Sapphire nozzles have a life of about 300 hours, while tungsten carbide types have a brief lifespan of 12 to 30 hours.
A high-velocity jet of water exits the nozzle, creating a vacuum that draws the abrasive through a mixing tube. This stream accelerates the particles to cutting speeds through an exit hole with a diameter of 0.007 inch to 0.02 inch (0.18 - 0.4 mm), at speeds of about 600 mph (966 kph), approaching the speed of sound. Factors that can affect abrasive jet machining include material properties and desired shapes. Additionally, water pressure and type of abrasive must be controlled to achieve the desired cut, which is also influenced by cutting speed.
Sometimes referred to as water lasers, abrasive jet machining processes share the concept of custom, computer-controlled, extractive shaping with other types of jet blasting machines. These can include wire electrical discharge machining (EDM), and flame, laser, and plasma cutters. Innovation continues in the development of cryogenic abrasive jet machining with non-residual CO2 crystals, to minimize waste and ease environmental costs. The increasing availability of water jet machining in local workshops makes contracting out the process an affordable option for hobbyists. Complete setups of pumps, positioning surfaces, tanks, and feed systems mean these sometimes unwieldy machines mainly occupy professional workshops.
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