Abrasive jet machining uses high water pressure or abrasive additives to cut materials. It can cut softer materials with water and precision patterns in stronger ones. The process uses pumps and abrasive materials, and the cutting speed is affected by material properties. The machines are used in manufacturing, handicrafts, and construction. The process is similar to other jet blasting machines, and innovation continues with cryogenic abrasive jet processing. Waterjet machining is becoming more available in local machine shops.
The abrasive jet machining process uses only high water pressure or with an abrasive additive to provide a jet cutting force of 30,000 to 60,000 pounds per square inch (psi). This highly concentrated beam of water energy emits from a machine part designed to assist in the custom cutting of numerous materials. Water alone cuts through softer materials like foam, rubber, and plastic; the cold cutting process produces little heat, which makes it possible to cut flammable materials without heat-affected zones. The addition of abrasives allows you to cut precision patterns in stronger materials such as metals, glass and tile.
Sometimes called a water jet cutter or water jet cutting center, abrasive jet processing equipment cuts almost any material that can be placed in sheet form. High-precision cuts produce intricate shapes and patterns with sharp edges. These machines cut stone, marble and glass, although tempered glass, such as from a car windshield, cannot be cut without shattering. Diamond is another material that cannot be cut with this process. These machines are used in manufacturing and processing, cutting metals such as aluminum for manufacturing; in handicrafts such as decorative glass cutting; and in construction, modeling products such as custom tile and inlaid marble medallions.
Forcing ordinary tap water at high pressures through an extremely narrow channel creates a shear stream that removes the target material by erosion. These powerful bits typically occupy professional garages and machine shops, often working as a finishing process due to their slow removal rate. The equipment employs pumps; these draw not only water, but up to 250 amps just to start the abrasive jetting and use up to 50 amps in the process.
The machine works by compressing gas through a mixing chamber, perhaps with a garnet abrasive, which is a hard mineral and a safe, natural abrasive material. The gas flows through a convergent-divergent nozzle, mixing chamber and exits from a fixed or portable convergent nozzle. Abrasion resistant nozzles are made from tough materials such as synthetic sapphire or tungsten carbide. Sapphire nozzles have a life of approximately 300 hours, while tungsten carbide types have a short life of 12-30 hours.
A high-velocity jet of water exits the nozzle creating a vacuum that draws the abrasive through a mixing tube. This stream accelerates particles to shear rates through an exit hole with a diameter of 0.007 inch to 0.02 inch (0.18 – 0.4 mm), to speeds of approximately 600 mph (966 km/h), approaching the speed of sound. Factors that can affect abrasive jetting include material properties and desired shapes. Additionally, the water pressure and the type of abrasive must be controlled to achieve the desired cut, which is also affected by the 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-cutting (EDM) and flame, laser and plasma cutting. Innovation continues in the development of cryogenic abrasive jet processing with non-residual CO2 crystals, to minimize waste and reduce environmental costs. The growing availability of waterjet machining in local machine shops makes outsourcing the process an affordable option for hobbyists. Comprehensive configurations of pumps, locating surfaces, tanks and fuel systems mean that these sometimes bulky machines mainly occupy professional workshops.
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