The following are the most commonly used methods of manufacturing gears: 1. Casting 2. Hot-Rolling 3. Stamping 4. Powder-Metallurgy 5. Extruding 6. Coining 7. Machining.
Method # 1. Casting:
Gears are cast in sand moulds, permanent moulds, shell moulds, plastic mould dies and lost-wax moulds. The characteristics of gears produced by casting are same as those of other products made by these processes.
Sand casting is particularly used for making heavy gears of cast-iron and steel. Gears made by this process have poor accuracy. These are mostly used for slow speed drive and are also not very efficient in power-transmission. Die casted gears are used where light loads are to be transmitted.
These are made from low melting temperature metals such as aluminium, zinc etc. The process of casting is normally used where economy is main criterion. The sand cast gears may be machined for a good finish, or left as cast for rough-machinery. The growing importance of shell moulding may introduce another important method of producing nearly finished gears.
Method # 2. Hot Rolling:
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Gears are made by forcing a master gear into a hot blank and the two are then rolled together until the teeth of the master have penetrated far enough to form a complete gear. The teeth are then machined. This method is little used as present, but has possibilities for future.
Method # 3. Stamping:
Stamped gears are made from sheet metals. Materials upto 3 mm thickness are practical for this process. These gears may be shaved after stamping to improve the accuracy and finish. These gears are used in watches, clocks, toys and house-hold gadgets.
Method # 4. Powder-Metallurgy:
In this process, a master gear of hard material is rolled against a heated gear-blank, thereby forming the teeth on the hot blank. Gears manufactured by this process offer the same possibilities and advantages as any product made by this process. Bakelite and other plastic materials are the most commonly used materials for manufacture of gears by this method.
Method # 5. Extruding:
In this process the brass or aluminium bar is extruded through several block dies with the final die having the shape of the desired tooth element and thus the material can finally be extruded to obtain gear form on its surfaces, and the extruded gear bar is then hack- sawed. At present only spur gears are manufactured by this method. In this process, as the material is displaced by pressure, the outside surface of the material is quite hard and smooth.
Method # 6. Coining:
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Gears are coined from blanks in a hydraulic press or forging hammer. Gears manufactured by this process require a light machining or may be used as such.
Method # 7. Machining:
Gears are machined from the blanks, usually by a roughing and a finishing operation.