机电技术专业英语课件作者徐起贺张庆良pataalessonSeventeen.pptVIP

尚辅网 / 机电技术专业英语 Lesson Seventeen Text Gear Planning The shape of the space between gear teeth is complex and varies with the number of teeth on the gear as well as tooth module, so most gear manufacturing methods generate the tooth flank instead of forming. Gear Shaping Gear shaping is inherently similar to gear planning but uses a circular cutter instead of a rack and the resulting reduction in the reciprocating inertia allows much high stroking speeds1; modern gear shapers cutting car gears can run at cutting strokes per minute. The shape of the cutter is roughly the same as an involute gear but the tips of the teeth are rounded2. Gear Manufacturing Methods Lesson Seventeen Gear Hobbing Gear hobbing, the most used metal cutting method, uses the rack generating principle but avoids slow reciprocation by mounting many “racks” on a rotating cutter4. The “racks” are displaced axially to form a gashed worm. Gear Broaching Gear broaching is not usually used for helical gears but is useful for internal spur gears; the principle use of broaching in this context is for internal splines which cannot easily be made by any other method. As with all broaching the method is only economic for large quantities since setup cost are high. Gear Shaving Gear shaving is used as finishing processes for gears in the “soft” state. The objective is to improve surface roughness and profile by mating the roughedout gear with a “cutter” which will improve form. Lesson Seventeen Gear Grinding Gear grinding is extremely important because it is the main way hardened gears are machined. When high accuracy is required it is not sufficient to precorrect for heat treatment distortion and grinding is then necessary. Lesson Seventeen New Words and Expressions Lesson Seventeen Lesson Seventeen Lesson Seventeen Lesson Seventeen Notes 1.Gear shaping is inherently similar to gear planning but uses a circular cutter instead of a rack an