Introduction


Gear types

Milling of gears includes different types of gears. The gear types can be divided into the following groups:

Cylindrical gears
External gears​ Internal gears​
 

Splines

Splines are similar to internal and external cylindrical gears but the tooth profile is different. Splines are used to transmit torque between two components.

 

Bevel gears and pinions

A set of bevel gears is used for transmission of a movement in an angle. They are commonly used in different types of vehicles, trains, cranes and in marine propulsion systems.

Pinion​
Bevel gear​

 

Gear manufacturing

Manufacturing of gear teeth can be done in different ways. Most common is some form of metal cutting where material is removed from a cylindrical blank. Different gear cutting methods are e.g. hobbing, disc cutting, shaving, shaping or skiving. Which method to be used depends on factors like productivity requirements, batch sizes, gear size and accessibility, where some methods do not work for all types of gears.

The following methods are common for roughing of gears:

  • Disc cutting
  • Hobbing
  • Skiving
  • Shaping

In addition to removal of most material, some form of finishing operation is often used in order to improve gear surface and tolerances. Tolerances are very important in many cases where high revolutions or high forces are present. Too high noise level in an automotive gear box, for example, is not acceptable.

For finishing, the following methods are commonly used:

  • Grinding
  • Honing
  • Shaving
  • Shaping

 

Machine tools

Machine tools used for gear milling are often dedicated to a specific manufacturing method. Common gear machines are of that reason machines dedicated for using a specific tool type.

In addition to these machines, use of 4- and 5-axis multi-task machines in gear production has increased due to their flexibility and lower investment costs. In small batch production it is also often an advantage to make all operations in the same machine and set up, including turning, milling and gear milling.