武科大机械专业英语L.ppt

Lesson 39 Gear Manufacturing Methods Terminology Text tour *1 机械工程专业英语教程 Terminology *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* Helical gear 斜齿轮 3 Hob 滚刀 *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 *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 。 *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。 *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 * 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 “soft” materials which must be subsequently（ 随后） case-hardened or heat treated（表面硬化或者热处 理），giving distortion（产生变形）. Gear Shaving（剃齿）Gear shaving is used as finishing processes for gears in the “soft” state. The objective is to improve surface roughness and profile（降低齿面粗糙度 和改善齿廓形状）by mating the roughed-out gear with a “cutter” which will improve form（通过采用具有较高齿 形精度的“刀具”与经过粗加工的齿轮进行啮合）. A gear shaving cutter looks like a gear which has extra clearance（附加的凹槽）at the root (for swarf and coolant removal细铁屑冷却液排除) and whose tooth flanks have been grooved（开小槽）to give cutting edges（形成切削刃）. It is run in mesh with the rough gear with crossed axes（剃齿刀与经过粗加工的齿轮成交错轴啮合传动） so that there is in theory point contact （点接触）with a relative velocity along the teeth（沿轮齿）giving scraping action（刮削作用）. The gear shaving cutter teeth are relatively flexible in bending and so will only operate effectively when they are in double contact between two gear teeth（剃齿刀的刀齿 具有相当的弯曲柔性，因此，只有当它们在两个轮齿之 间并且与这两个轮齿都接触时，才能有效地进行切削工 作）. The gear and cutter operate at high rotational speeds with traversing（通过、穿过）of the workface and about 100 micron of material is removed. Cycle times （周期时 间）can be less than half a minute and the machines are not expensive but cutter are delicate（精密）and difficult to manufacture. Gear Grinding （磨齿）Gear grinding is extremely important because it is the main way hardened gears（淬硬 齿轮）are machined. When high accuracy is required it is not sufficient to pre-correct （预先校正）for heat treatment distortion and grinding is then necessary. The simplest approach to gear grinding is form grinding（ 成形磨削法）. The wheel profile is dressed（修整） accurately to shape using single point diamonds which are controlled by templates cut to the exact shape required（采 用由精密切削成形的样板控制的单刃金刚石可以将砂轮修整成精 确的形状）. The profiled wheel is then reciprocated（往返进给） axially along the gear（沿轴向）, when one tooth shape has been finished, involving typically 100 micron metal removal, the gear is indexed to（索引、分度到）the next tooth space. This method is fairly slow but gives high accuracy consistently. Setting up is lengthy because different dressing templates（砂轮修整样板）are needed if module, number of teeth, helix angle, or profile correction（齿廓修形量） are changed. The fastest gear grinding method uses the same principle as gear hobbing（滚齿）but replaces a gashed and relieved worm（有排屑槽的蜗杆形滚齿刀）by a grinding wheel which is a rack in section（截面为齿条的砂轮）.