Gear Cutting Operations

Basic Purpose Of Use Of Gears Gears are widely used in various mechanisms and devices to transmit power and motion positively (without slip) between parallel, intersecting ( axis) or non-intersecting non parallel shafts, without change in the direction of rotation with change in the direction of rotation without change of speed (of rotation) with change in speed at any desired ratio

Categories of gear manufacturing process

General Applications Of Gears Speed gear box, feed gear box and some other kinematic units of machine tools Speed drives in textile, jute and similar machineries Gear boxes of automobiles Speed and / or feed drives of several metal forming machines •Machineries for mining, tea processing etc. Large and heavy duty gear boxes used in cement industries, sugar industries, cranes, conveyors etc. Precision equipments, clocks and watches Industrial robots and toys.

Types Of Gears And Their Characteristics 1.According to configuration • External gear • Internal gear

2. According to axes of transmission • Spur gears – transmitting rotation between parallel shafts as shown in o Straight toothed o Helical toothed ⎯ Single helical ⎯ double helical (herringbone)

3. According to pattern of motion Rotation to rotation : wheel type gears Rotation to translation or vice versa – e.g. rack and pinion Straight toothed Helical toothed

Types of Gear Cutting Operations Gear milling or Forming Gear shaping Gear Hobbing Gear Finishing

1.Gear Milling or Forming The gear milling operation is used for gear cutting. All types of gears can be made by using gear milling. Milling cutter is selected specifically for a particular type of gear and module. The periphery of the gear blank is divided into required number of equi-spaced parts. The required number of parts should be equal to the number teeth to be made on the gear blank. The method of dividing the periphery is called indexing which is an integral part of the operation of gear milling.

Gear Milling In gear form cutting, the cutting edge of the cutting tool has a shape identical with the shape of the space between the gear teeth.

Disadvantages of Gear Milling Gear milling is a slower process of gear generation as compared to other gear generation process. In this process gear is generated by cutting one- by-one tooth. Gears are to be made, it is not suitable for larger batch size. The other methods required very high capital cost and setup cost as compared to gear milling so these are not economical for smaller batch size, only gear cutting by milling operation is recommended for smaller batch size.

2. Gear Shaping Gear shaping used a cutting tool in the shape of a gear which is reciprocated axially across the gear blank to cut the teeth while the blank rotates around the shaper tool. It is a true shape-generation process in which the gear- shaped tool cuts itself into mesh with the gear blank as shown in fig. The accuracy is good, but any errors in one tooth of the shaper cutter will be directly transferred to the gear. Internal gears can be cut with this method as well.

i). Shaping with a pinion-shaped cutter

Gear Shaping Machine

ii).Shaping with a rack-shaped cutter

2. Gear Hobbing Gear hobbing is a machining process in which gear teeth are progressively generated by a series of cuts with a helical cutting tool (hob). All motions in hobbing are rotary, and the hob and gear blank rotate continuously as in two gears meshing until all teeth are cut.

4. Gear Finishing As produced by any of the process described, the surface finish and dimensional accuracy may not be accurate enough for certain applications. Several finishing operations are available, including the conventional process of shaving, and a number of abrasive operations, including grinding, honing, and lapping , shaping.

1. Grinding

II. Lapping and Honing:

III. Gear shaving While interacting with the gears, the cutting teeth of the shaving cutter keep on smoothening the mating gear flanks by fine machining to high accuracy and surface finish.