Explanation of Gear generating processes

Gear Shaper and Gear Hobbing

TABLE OF CONTENTS

1. Gear Shapping

        1.1 Construction and working

        1.2 Advatngaes

        1.3 Limitations

        1.4 Applications

2. Gear Hobbing

        2.1 Construction and working

        2.2 Advantagaes

        2.3 Limitations

        2.4 Applications

The following gear generating methods are used for gear production

1. Gear shaping.
2. Gear planning.
3. Gear hobbing.

In this article student may know about the gear shaping machine and gear hobbing machine

1. Gear Shaping

1.1 Construction & Working of gear shaper

• Gear is manufactured by using a special type of machine called gear shaper. 
• In gear shaping, a pinion type cutter is used.
• The cutter teeth are ground with a top rake and clearance. It is mounted on a vertical spindle. 
• The axes of the cutter and blank are aligned as a parallel. 
• The cutter and the blank are made to rotate together as two gears which are in mesh. Both cutter and the blank are rotate at same speed.
• The cutter reciprocates in a vertical direction along the width of the blank. 
• The pinion cutter is feed radially into the gear blank to give the depth of cut. 
• The cutter and the blank slowly rotate together till all the teeth are generated on the blank.
• During each return stroke of the cutter, the blank is withdrawn. This is done to prevent rubbing of the cutting edges and damage to gear teeth being cut.

1.2 Advantages of gear shaping

• Single cutter can be used for cutting spur gears of any number of teeth having the same module as that of cutter.
• Internal gears can be easily cut.
• As the cutting action is continuous, the rate of production is high.
• Cluster gears can be cut.

1.3 Limitations gear shaping

• Worm gears cannot be produced in this method.

1.4 Application of gear shaping

• Gear shaping is used for cutting external and internal spur gears. 
• Helical gears can also be shaped using special attachments.

2. Gear Hobbing

2.1 Construction and working of gear hobbing machine

• It is a process of generating a gear by using a rotating cutter called hob 
• Hob has helical threads. 
• Grooves are cut in the threads parallel to the axis and this will provide the cutting edges.
•  Proper rake and clearance angles are ground on these cutting edges. 
• The rotating hob acts like a continuously moving rack as it cuts. 
• The gear blank is mounted on a vertical arbor. 
• The hob is mounted on a rotating arbor.
• The hob axis is tilted through the hob lead angle α so that its teeth are parallel to the axis of the gear blank.
• Then α = (90°-α)
• Where α1 = helix angle of the hob thread.
• The hob axis is inclined at α° with the horizontal as shown in the figure 
• The hob is rotated at suitable cutting speed. 
• It is fed across the blank face. 
• The hob and blank are made to rotate in correct relationship to each other i.e., they rotate like a worm and worm gear in mesh.

2.2 Advantages  of gear Hobbing

• A single hob with the given module can be used for generating gear with any number of teeth of the same module.
• The same hob can be used for spur and helical gears.
• Operations are continuous. So very fast rate of production.
• Perfect tooth shape is obtained.
• Process is automatic and so less skilled operator is sufficient.
• Worm gears are generated only by hobbing.
• Multiple blanks can be cut at a time. Hence high rate of production.

2.3 Limitations of gear Hobbing

• Internal gears cannot be generated.
• Hobbing cannot be used for producing gear teeth very near to shoulders

2.4 Applications of gear Hobbing

• Hobbing is used for generating spur, helical and worm gears.