Gear Production

MAR 2015

Gear Production

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March 2015—17 intermittent basis. Gear production on an abrasive waterjet machine can range from mere minutes (for example, a miniature planetary gear) to several hours (such as in the repair of a 4-inch-thick wind turbine gear), depending on the thickness of the workpiece material and the total linear perimeter of the cutting area. Common gear geometry types that shops can cut on abrasive waterjet machines include standard, planetary, bevel, square and helical, made from various workpiece materials such as steels of different hardness levels and carbon fber-reinforced plastics. Racks and sprockets are also made using abrasive waterjet machines. Shops can cut all of these gear shapes on the same machine with minimal—if any—setup, fxturing or tool changes between parts. Abrasive waterjet machines also allow for the creation of nonstandard gear geometries. Oftentimes, shops base the gear tooth profle on the actual manufacturing method that they will use to generate the teeth. If a tooth profle can be generated with a thin cylindrical stream, a gear can be quickly manufactured, which opens up new opportunities for gear designers. This is particularly true during the research and development and prototype stages, where multiple gear iterations are required to determine the geometry that offers the best balance of cost and turnaround time. When it comes to gear applications that require tight tolerances and good surface fnish, a shop must be able to tilt a machine's cutting head to compensate for the natural taper of the jet. As a result, abrasive waterjet machine manufacturers offer special tilting-head accessories that enable shops to achieve near-zero taper in their fnished gears. An abrasive waterjet machine's nozzle type, abrasive type and size, and cutting speed also contribute to the level of surface fnish a shop can achieve in gear production. Slow cutting speeds usually provide a reasonably good surface fnish, but factor in a small cutting nozzle with a fne abrasive, and the fnish is further improved. In most cases, it is reasonably easy for abrasive waterjet machines to achieve tolerances of ±0.003 inch (0.075 mm). Shops producing small gears from thin materials have also been known to achieve tolerances as tight as ±0.001 inch (0.025 mm) or better. For production of high-precision gears, shops can use the abrasive waterjet to perform high-speed rough cutting operations to create near-net shapes that are within a few thousandths of an inch of the fnal surface profle. A secondary process could then be used to trim or polish the surface fnish to the required specifcations. Also highly benefcial is the fact that abrasive Miniature planetary gears can be cut quickly with an abrasive waterjet. Gear geometries such as these racks can be machined in segments with tight tolerances for assembly.

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