Lesson 39 Gear Manufacturing Methods,Terminology Text tour,04.08.2019,1,机械工程专业英语教程,Terminology,04.08.2019,2,机械工程专业英语教程,Annular Shaped like or forming a ring. 环形的，轮状的：形状像环或形成环状。 Annular gear 内齿轮, 齿圈（也称为internal gear）,机械工程专业英语教程,04.08.2019,Helical gear 斜齿轮,3,Hob 滚刀,04.08.2019,机械工程专业英语教程,4,Worm 蜗杆 Worm gear 1. A gear consisting of a spirally threaded shaft and a wheel with marginal teeth that mesh into it 蜗轮蜗杆副 2. The toothed wheel of this gear, a worm wheel 蜗轮,04.08.2019,机械工程专业英语教程,5,Broach 拉刀 Swarf Fine metallic filings or shavings removed by a cutting tool. 小铁屑：用锉或剃等加工方法去除的细小金属屑。,04.08.2019,机械工程专业英语教程,6,Dressing Dressing is the process of conditioning worn grains on the surface of a grinding wheel by producing sharp new edges on grains so that they can cut more efficiently. 砂轮修整：使砂轮表面磨钝的磨粒上产生新的锋利的切削刃，使其能够更有效地进行切削工作。,04.08.2019,机械工程专业英语教程,7,Gear Planing（刨齿） 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（模数），so most gear manufacturing methods generate the tooth flank (齿腹) instead of forming（采用展成法加工齿面而不是采用成形法加工）.,机械工程专业英语教程,04.08.2019,Text tour,8,Gear planing uses a reciprocating rack（往复运动的齿条刀）, stroking（击、打、切）in the direction of the helix（螺旋） on a gear with a gradual generation of form as the rack effectively rolls round the gear blank (齿轮毛坯) （当齿条刀绕齿轮坯料滚切并沿其螺旋线方向运动时，齿形就会被逐渐展成）. ,The rack is relieved out of contact（脱离接触）for the return stroke as in normal shaping or planing（与普通的刨削加工相同）. It has the great advantage that the cutting tool is a simple rack with (nearly) straight sided teeth which can easily be ground accurately(刀具为具有直线齿形或者接近与直线齿形的齿条，其齿面易于进行精确磨削加工). ,This method is little used (几乎不用) for high production because it is relatively slow in operation due to the high tool and slide mass(由于刀具和滑枕的质量较大)；for jobbing（重复性很小的工作）purposes the slow stroking rate does not matter and low tool costs give an advantage where unusual sizes or profile modifications are required. （对于单件或者少量的齿轮加工而言，缓慢的行程速度带来的影响不大，而且较低的刀具成本对于那些特殊规格和需要进行齿廓修形的齿轮来说则是一个有利的条件）,Gear Shaping（插齿） Gear shaping is inherently similar to gear planing（刨齿加工）but uses a circular cutter （圆形刀具）instead of a rack(齿条刀) and the resulting reduction in the reciprocating inertia （运动惯性）allows much higher stroking speeds（行程速度）；,modern gear shapers（插齿机）cutting car gears can run at 2000 cutting strokes per minute. The shape of the cutter is roughly the same as an involute gear（渐开线齿轮）but the tips of the teeth are rounded.,The generating drive between cutter and workpiece does not involve a rack or leadscrew since only circular motion is involved（由于刀具与工件之间的展成运动只包含圆周运动，因此不需要齿条或者丝杠）.,The tool and workpiece move tangentially(切向移动) typically 0.5mm for each stroke of the cutter. On the return stroke the cutter must be retracted（退让）about 1mm to give clearance otherwise tool rub occurs on the backstroke（退刀）and failure is rapid.,The advantages of gear shaping are that production rates are relatively high and that it is possible to cut right up to a shoulder（将齿插到接近轴肩处）.,Unfortunately, for helical gears（斜齿轮）, a helical guide（螺旋导轨）is required to impose a rotational motion on the stroking motion（需要有一个能够产生绕插齿运动行程本身旋转的螺旋导轨）；,such helical guides cannot be produced easily or cheaply so the method is only suitable for long runs with helical gears（斜齿轮的大批量加工） since special cutters and guides must be manufactured for each different helix angle.,A great advantage of gear shaping is its ability to cut annular（环形的，轮状的）gears such as those required for large epicyclic drives（行星齿轮传动）.,Gear Hobbing（滚齿）Gear hobbing，the most used metal cutting method，uses the rack generating principle （齿条展成原理）but avoids slow reciprocation by mounting many “racks” on a rotating cutter（旋转刀具）.,The “racks” are displaced axially to form a gashed（很深的裂缝） worm（这些“齿条”轴向排布，形成了有缝的蜗杆）.,Metal removal rates are high since no reciprocation of hob or workpiece（滚刀和工件）is required and so cutting speeds of 40 m/min can be used for conventional hobs（普通滚刀）and up to 150 m/min for carbide hobs（硬质合金滚刀）.,Typically with a 100mm 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（多头粗加工滚刀）can be used with coarse feeds of 3 mm per revolution so that 100 rpm on the cutter, a two-start hob（双头滚刀）and a 20 tooth gear will give a feed rate of 30 mm/min.,Gear Broaching（拉齿）Gear broaching is not usually used for helical gears（斜齿轮）but is useful for internal spur gears（直齿轮）；the principle use of broaching in this context（在这种情况下）is for internal splines（内花键）which cannot easily be made by any other method.,As with all broaching the method is only economic for large quantities since setup costs（设备的费用）are high.,Gear Broaching gives high accuracy and low surface roughness（低表面粗糙度）but like all cutting processes is limited to