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www.ADandP.media AD&P; ∕ JULY 2016 WATERJET To create a pure waterjet stream the water pressure must be converted to velocity. This conversion takes place when the water is passed through a tiny jewel orifce. A hole in the sapphire, ruby or diamond orifce ranges from 0.003 to 0.020 inches (most common: 0.014 inch). The larger the orifce, the more water and horsepower are required to maintain pressure. The top of the orifce has a very sharp edge for keeping the waterjet stream coherent. A rough or rounded edge will create a fuzzy, turbulent jet and may exhibit an angular trajectory not desired for higher-precision work, but is applicable to other applications such as surface texturing or coating removal. A waterjet orifce will blow out for two reasons. First, calcium can build up on the orifce and break of, causing instant orifce failure. Second, the orifce edge can become rounded or break from particle impact. In waterjet, an orifce is usually either good or bad—gradual degradation is less common. A sapphire or ruby orifce can last 40 to 200 hours, depending on application and pressure, with good water. A diamond might be eight to 10 times more expensive but will last eight to 10 times longer. With abrasive waterjet cutting, it's the garnet that erodes the material and makes the cut; the water is the accelerator. In the 1980s, waterjet speed averaged 1,500 mph at 55,000 psi. Flow's HyperJet pump, introduced in 2004 and rated at 94,000 psi, bumped average speed up to 2500 mph. When high-pressure pumps accelerate the jet's speed, the stream becomes smaller and it cuts with less abrasive, upping the efciency of the entire system. Once the stream exits the orifce, it's all about velocity, according to Burnham. "There is no pressure in the waterjet stream once it exits the cutting head; pressure in the water has been converted to velocity as the water exits the waterjet orifce. A faster and smaller waterjet stream means the abrasive particles move faster, carry more momentum, and remove more material, more aggressively. Less abrasive is used per length of cut because each grain can erode more material. The goal is to make the abrasive go as fast as possible. Stream velocity is the key to efciency." One important way to improve processing is optimizing tool paths, according to Burnham. This allows the cutting heads to speed up on straight cuts and slow down where there are tight geometries. Some systems feature taper compensation: an articulated wrist tilts the head over slightly to compensate for the naturally occurring V-shaped taper produced by waterjet cutting. SAVE THE DATE! AdditiveConference.com SEPTEMBER 13-14, 2016 McCormick Place (West Hall) Chicago, IL, USA Connecting Additive + Subtractive Manufacturing Make plans now to attend the conference focused on additive manufacturing for industrial applications like tooling and end-use part production! P R E S E N T E D B Y 59