SCIENCE AND TECHNOLOGY ENGLIAH FOR MECHANICAL ENGINEERING Various attempts have been made to prevent this effect. in particular by continuing rotation without any further cutter infeed but if the shaping machine is not very rigid and the cutter very sharp then no further cutting will occur and the error will not be removed Hobbing Hobbing, the most used metal cutting method, uses the rack generating principle but avoids slow reciprocation by mounting many racks" on a rotating cutter. The tacks"are displaced axially to form a gashed worm. The" racks "do not generate the correct involute shape for the whole length of the teeth since they are moving on a circular path and so the hob is fed slowly along the teeth either axially in normal hobbing or in the direction of the helix in"oblique" hobbing gash深砍,划开worm蜗杆helⅸx螺旋线 oblique倾斜的
SCIENCE AND TECHNOLOGY ENGLISH FOR MECHANICAL ENGINEERING Various attempts have been made to prevent this effect, in particular by continuing rotation without any further cutter infeed but if the shaping machine is not very rigid and the cutter very sharp then no further cutting will occur and the error will not be removed. Hobbing Hobbing, the most used metal cutting method, uses the rack generating principle but avoids slow reciprocation by mounting many "racks" on a rotating cutter. The "tacks" are displaced axially to form a gashed worm. The "racks" do not generate the correct involute shape for the whole length of the teeth since they are moving on a circular path and so the hob is fed slowly along the teeth either axially in normal hobbing or in the direction of the helix in "oblique" hobbing. gash 深砍，划开 worm 蜗杆 helix 螺旋线 oblique 倾斜的
SCIENCE AND TECHNOLOGY ENGLIAH FOR MECHANICAL ENGINEERING Metal removal rates are high since no reciprocation of hob or workpiece is required and so cutting speeds of 40 m/min can be used for conventional hobs and up to 150 m/ min for carbide hobs. Typically with a100 carbide硬质合金 mm diameter hob the rotation speed will be 100 pm and so a twenty tooth workpiece roughing粗加工 will rotate at 5 rpm. Each revolution of the workpiece will correspond to0.75 mm feedcoarse大的,粗的 so the hob will advance through the workpiece at about 4 mm per minute. For car production roughing multiple start hobs can be used with coarse feeds of 3 mm per revolution so that 100 rpm on the cutter,a two-Start hob and a 20 tooth gear will give a feed rate of 30mm/minute
SCIENCE AND TECHNOLOGY ENGLISH FOR MECHANICAL ENGINEERING Metal removal rates are high since no reciprocation of hob or workpiece is required and so cutting speeds 0f 40 m/min can be used for conventional hobs and up to 150 m/min for carbide hobs. Typically with a 100 mm diameter hob the rotation speed will be 100 rpm and so a twenty tooth workpiece will rotate at 5 rpm. Each revolution of the workpiece will correspond to 0.75 mm feed so the hob will advance through the workpiece at about 4 mm per minute. For car production roughing multiple start hobs can be used with coarse feeds of 3 mm per revolution so that 100 rpm on the cutter, a two-start hob and a 20 tooth gear will give a feed rate of 30mm/minute. carbide 硬质合金 roughing 粗加工 coarse 大的，粗的
SCIENCE AND TECHNOLOGY ENGLIAH FOR MECHANICAL ENGINEERING The disad vantage of a coarse feed rate is that a clear marking is left on the workpiece, particularly in the root showing a pattern at a spacing of the feed rate per revolution. This surface undulation is less marked on the 波 fianks than in the root and is not important when there is a 'x subsequent finishing operation such as shaving or grinding. 剃 When there are no further operations the feed per revolution 齿 must be restricted to keep the undulations below a limit which is usually dictated by lubrication conditions. The height of the undulations in the root of the gear is given by quaring the feed per revolution and dividing by four times he diameter of the hob.I mm feed and 100 mm diameter gives 2. 5 micron high undulations in the root. On the gear flank (at 70 on a large gear) the undulation is roughly cos 70o as large, 1. e, about 0.85 micron
SCIENCE AND TECHNOLOGY ENGLISH FOR MECHANICAL ENGINEERING The disadvantage of a coarse feed rate is that a clear marking is left on the workpiece, particularly in the root, showing a pattern at a spacing of the feed rate per revolution. This surface undulation is less marked on the flanks than in the root and is not important when there is a subsequent finishing operation such as shaving or grinding. When there are no further operations the feed per revolution must be restricted to keep the undulations below a limit, which is usually dictated by lubrication conditions. The height of the undulations in the root of the gear is given by squaring the feed per revolution and dividing by four times the diameter of the hob, l mm feed and 100 mm diameter gives 2.5 micron high undulations in the root. On the gear flank (at 70ºon a large gear) the undulation is roughly cos 70ºas large, i.e., about 0.85 micron. 波 纹 剃 齿