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 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 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 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 ( Ton) yet high accuracy must be maintained. leadscrew 丝杆 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 hel
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