Gear shaping principle
Gear shaping is a tooth surface processing method that uses a gear shaping cutter to process internal and external gears or racks on a gear shaping machine.
The gear shaping process is, in principle, equivalent to meshing a pair of spur gears. The movement form of the workpiece and the gear-shaping cutter is shown in Figure a. The gear shaper is equivalent to a gear that grinds the rake and relief angles on the gear to form a cutting edge, while the gear tooth blank serves as another gear. During gear shaping, the tool makes high-speed reciprocating linear motion along the workpiece’s axis, forming the cutting process’s primary motion. At the same time, it also engages in gapless meshing motion with the workpiece to process all the gear tooth profiles on the workpiece. During machining, the tool only cuts out a small part of the workpiece tooth slot each time it reciprocates. The tooth surface curve of the workpiece tooth slot is composed of the envelope of multiple cuts by the gear shaper cutting edge, as shown in Figure b.
During gear shaping processing, the gear shaping machine must have the following movements:
(1) Main motion: The gear-shaping cutter’s reciprocating upward and downward motion is called the main motion. Expressed in the number of reciprocations per minute, the downward stroke is the cutting stroke, and the upward stroke is the return stroke.
(2) When generating motion gear shaping, the meshing motion relationship of a pair of gear pairs must be maintained between the gear shaping cutter and the workpiece. Every time the gear shaping cutter rotates through one tooth (1/Z knife rotation), the workpiece must also rotate. Pass one tooth (1/Z work rotation).
(3) Radial feed motion To gradually cut to the full tooth depth of the workpiece, the gear shaping cutter must have radial feed motion. The radial feed is expressed by the number of millimeters of radial movement of the workpiece or tool during each reciprocating stroke of the gear-shaping cutter. When the full tooth depth is reached, the machine tool automatically stops the radial feed movement, and the workpiece and the tool must roll against each other once to process all the gear teeth.
(4) Circular feed motion The generation motion only determines the relative motion relationship between the gear shaping cutter and the workpiece, and the circular feed motion determines the speed and slowness of the motion. The arc length that the gear shaping cutter rotates on the indexing circle during each reciprocating stroke is called the circumferential feed, and its unit is mm/reciprocating stroke.
(5) Let the tool move. To prevent the gear shaper cutter from scratching the machined surface during the return stroke and reduce tool wear, a gap should be allowed between the cutter and the workpiece. When the gear shaper cutter restarts its downward working stroke, it should be immediately returned to the original position so the tool cuts downward into the workpiece. This movement of getting out of the way and returning to the original position is called the knife-letting movement. Generally, new models of gear-shaping machines realize the movement of the cutter through the swing of the cutter spindle seat to reduce the vibration generated by the cutter.
Characteristics of gear shaping processing
(1) The precision of gear shaping is higher. Because the manufacturing, sharpening, and inspection of gear shaping cutters are simpler than that of hobs, and it is easy to ensure the manufacturing accuracy, it can ensure high accuracy of gear shaping. However, during gear shaping processing, the tool has Each cutter tooth sequentially cuts each tooth groove of the workpiece. Therefore, the cumulative error of the tooth pitch of the gear shaping cutter will be directly transmitted to the gear being processed, affecting the movement accuracy of the gear being cut.
(2) The tooth direction deviation of gear shaping is larger than that of hobbing. Due to the parallelism error between the main shaft rotation axis of the gear shaping machine and the rotation axis of the workbench, and the frequent reciprocating motion of the gear shaping cutter, the main shaft and sleeve are easily worn, so the gear shaping The tooth deviation is usually larger than that of hobbling.
(3) The tooth surface roughness value is small. Because the gear shaping cutter continuously cuts chips along the entire length of the gear teeth, and because the number of tangents forming the tooth envelope is more than that of hobbing, the tooth surface processed by gear shaping Roughness is better than hobbling.
(4) The productivity of gear shaping is lower than that of gear hobbing. The inertia of the reciprocating motion limits the cutting speed of the gear shaping cutter and is difficult to increase. In addition, the loss of free travel is large, so the productivity is lower than that of gear hobbing. Gear shaping is suitable for processing internal gears, double or multiple gears, racks, sector teeth, etc., with a small module and narrow tooth width.
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