SCIENCE AND TECHNOLOGY ENGLIAH FOR MECHANICAL ENGINEERING LESSON SIX GEAR MANUFACTURING METHODS There are two basic methods of generating process manufacturing gear teeth, the展成法 generating process and the forming forming process process. When a gear tooth is 成形法 generated, the workpiece and the grinding磨削 cutting or grinding tool are in continuous mesh and the tooth form ismesh啮合,网格 generated by the tool. In other word the work and the tool are conjugate to conjugate共轭的 each other. Hobbing machines, shaper cutters, shaving machines, and many‖ hobbing滚削,滚刀 grinders use this principle
SCIENCE AND TECHNOLOGY ENGLISH FOR MECHANICAL ENGINEERING LESSON SIX GEAR MANUFACTURING METHODS There are two basic methods of manufacturing gear teeth, the generating process and the forming process. When a gear tooth is generated, the workpiece and the cutting or grinding tool are in continuous mesh and the tooth form is generated by the tool. In other word, the work and the tool are conjugate to each other. Hobbing machines, shaper cutters, shaving machines, and many grinders use this principle. generating process 展成法 forming process 成形法 grinding 磨削 mesh 啮合，网格 conjugate 共轭的 hobbing 滚削，滚刀
SCIENCE AND TECHNOLOGY ENGLIAH FOR MECHANICAL ENGINEERING When a gear tooth is formed, the tool is in the shape of the space that is being machined out. Some grinding machines use this principle with an indexing mechanism which allows the gear teeth to be formed tooth by tooth Broaches are examples of form tools that machine all the gear teeth simultaneously Shaping成形,插齿 Shaping is inherently similar to planing but uses a circular cutter instead of a rack and the resulting reduction in the reciprocating inertia allows much higher stroking speeds; modern shapers cutting car gears can run at 2,000 cutting strokes per minute. The shape of the cutter is roughly the same as an involute gear but the tips of the teeth are rounded
SCIENCE AND TECHNOLOGY ENGLISH FOR MECHANICAL ENGINEERING Shaping Shaping is inherently similar to planing but uses a circular cutter instead of a rack and the resulting reduction in the reciprocating inertia allows much higher stroking speeds; modern shapers cutting car gears can run at 2,000 cutting strokes per minute. The shape of the cutter is roughly the same as an involute gear but the tips of the teeth are rounded. When a gear tooth is formed, the tool is in the shape of the space that is being machined out. Some grinding machines use this principle with an indexing mechanism, which allows the gear teeth to be formed tooth by tooth. Broaches are examples of form tools that machine all the gear teeth simultaneously. 成形，插齿
SCIENCE AND TECHNOLOGY ENGLIAH FOR MECHANICAL ENGINEERING he generating drive between cutter and workpiece does not involve a rack or leadscrew since only circular motion is involved. The tool and workpiece move tangential typically 0.5 mm for each stroke of the cutter. On the return stroke the cutter must be retracted about I mm to give clearance otherwise tool rub occurs on the back stroke and failure is rapid. The speed on this type of machine is limited by the rate at which some 50kg of cutter and bearings can be moved a distance of l mm. The accelerations involved require forces of the order of 5000 N(0.5 Ton) yet high accuracy must be maintained leadscrew丝杆
SCIENCE AND TECHNOLOGY ENGLISH FOR MECHANICAL ENGINEERING The generating drive between cutter and workpiece does not involve a rack or leadscrew since only circular motion is involved. The tool and workpiece move tangential typically 0.5 mm for each stroke of the cutter. On the return stroke the cutter must be retracted about l mm to give clearance otherwise tool rub occurs on the backstroke and failure is rapid. The speed on this type of machine is limited by the rate at which some 50kg of cutter and bearings can be moved a distance of 1 mm. The accelerations involved require forces of the order of 5000 N (0.5 Ton) yet high accuracy must be maintained. leadscrew 丝杆
SCIENCE AND TECHNOLOGY ENGLIAH FOR MECHANICAL ENGINEERING The advantages of shaping are that production rates are relatively high and that it is possible to cut right up to a shoulder. Unfortunately, for helical gears, a helical guide is required to impose a rotational motion on the stroking motion;such helical guides cannot be produced easily or cheaply so the method is only suitable for long runs with helical gears since special cutters and guides must be manufactured for each different helix angle. A great advantage of shaping is its ability to cut annular gears such as those required for large epicyclic drives annular gear内齿轮
SCIENCE AND TECHNOLOGY ENGLISH FOR MECHANICAL ENGINEERING The advantages of shaping are that production rates are relatively high and that it is possible to cut right up to a shoulder. Unfortunately, for helical gears, a helical guide is required to impose a rotational motion on the stroking motion; such helical guides cannot be produced easily or cheaply so the method is only suitable for long runs with helical gears since special cutters and guides must be manufactured for each different helix angle. A great advantage of shaping is its ability to cut annular gears such as those required for large epicyclic drives. annular gear 内齿轮
SCIENCE AND TECHNOLOGY ENGLIAH FOR MECHANICAL ENGINEERING When very high accuracy is of importance the inaccuracies in the shaping cutter matter since they may transfer to the cut gear. It is obvious that profile errors will transfer but it is less 偏 obvious than an eccentrically mounted or ground cutter will C give a characteristic dropped tooth?. There are several causes 的 for " dropped tooth" but it occurs most commonly when the diameter of the workpiece is about half, one and a half, two and a half etc times the cutter diameter If the cutter starts on a high point and finishes on a low point during the final finishing revolution of the gear the peak to peak eccentricity error in the cutter occurs between the last and first tooth of the final revolution of the cut gear; as the cumulative pitch error of the cutter may well be over 25 microns there is a sudden pitch error of this amount on the cut gear. The next gear cut on the machine may however be very good on adjacent pitch if the final cut happened to start in a favorable position on the cutter
SCIENCE AND TECHNOLOGY ENGLISH FOR MECHANICAL ENGINEERING When very high accuracy is of importance the inaccuracies in the shaping cutter matter since they may transfer to the cut gear. It is obvious that profile errors will transfer but it is less obvious than an eccentrically mounted or ground cutter will give a characteristic “dropped tooth”. There are several causes for "dropped tooth" but it occurs most commonly when the diameter of the workpiece is about half, one and a half, two and a half, etc. times the cutter diameter. If the cutter starts on a high point and finishes on a low point during the final finishing revolution of the gear the peak to peak eccentricity error in the cutter occurs between the last and first tooth of the final revolution of the cut gear; as the cumulative pitch error of the cutter may well be over 25 microns there is a sudden pitch error of this amount on the cut gear. The next gear cut on the machine may however be very good on adjacent pitch if the final cut happened to start in a favorable position on the cutter. 偏 心 的