Gear Manufacturing (How are Gears Made?)

Gear Manufacturing

Gear manufacturing (or Gear making) can be done by following different ways.

  • Gear casting
  • Gear forming
  • Powder metallurgy
  • Metal removal (Gear cutting or Gear generation)

Out of these methods, gear manufacturing also depends on the type of gear to be made, size of gear, quality of gear, accuracy of gear, cost of gear and availability of equipment. 

Gear manufacturing by cutting (also known as gear cutting or gear machining) is the best way to make high quality gears in mass production.

Let’s see the ways how gears are made.

#1) Gear casting

Gear Manufacturing casting

Gears can be manufactured by metal casting. This gear casting can be done in sand molds, permanent molds, shell molds, plastic mold dies, as well as lost wax molds.

The properties of gear made by casting process shows the similar properties as that of the other products made by casting.

Sand casting is used to make heavy gears of larger size, and they are generally made of cast iron and steel.

The accuracy of gears made by sand casting has less accuracy.

Sand casted gears don’t show high efficiency during power transmission, and they are mostly used for slow speed drives.

The sand casted gears are easy to manufacture and their cost of production is also low.

Generally the sand casted gears are machined to get the good surface finishing.

Gears made by die casting are generally used for applications where light load transmission is required.

Die casted gears are generally made of metals like zinc, aluminium, etc which have lower melting temperatures.

They are generally used for light power transmissions in toys, hand tools, gardening equipment, etc.

Gears made by investment casting shows good strength as well as good power transmission capacity.

#2) Gear forming

gear forming

Various gear forming techniques used for gear manufacturing are listed below.

  1. Roll forming
  2. Extrusion
  3. Stamping
  4. Coining

Let’s discuss them! (You will come to know how gears are made by these techniques).

Roll forming

gear roll forming
Image credits: sciencedirect

In roll forming of gears, the hardened master gear is forced into a gear blank which is mounted on the shaft.

The hardened gear acts as a roller and when it is forced against the gear blank, it forms a replica of the teeth (i.e it forms gear teeth on the blank).

The master gear is made very accurately and hence the gear manufactured by roll forming also shows good accuracy.

Roll forming of gears can be performed as a hot rolling as well as cold rolling.

In hot forming of gears, the gear blank is first heated above its recrystallization temperature and then it is pressed against the toothed rollers.

Hot roll forming of gears is preferred where large deformation is required (generally for larger gears).

After the hot roll forming process, the cold forming can be done to give better finishing and strength to the gear.

Cold roll forming of gears requires high compression pressure as compared to hot roll forming of gears.

Due to cold roll forming, the material of gear gets strain hardened. So its strength as well as fatigue resistance increases.

During the roll forming of gears, there is no metal removal involved. Hence it is also known as chipless process.

Roll forming of gears are generally used to manufacture worm gears and involute splines.

Extrusion

In gear extrusion, the heated metal bar is forced through several dies and the final die has the shape of desired tooth element.

In this way, the rod with gear tooth is obtained by extrusion.

After this, the extruded geared bar is cut with a hacksaw blade and in this way final gear is obtained.

During the extrusion of geared bar, the material gets displaced by high pressure. So the outside surface of gear is very hard and smooth.

Soft metals like aluminum, brass, bronze, magnesium as well as hard metals like steel bars (up to 60mm diameter) can be cold extruded for gear making.

Gears made by extrusion are used in watches, clocks, etc.

Stamping

Gear stamping is a type of sheet metal forming technique that is used to make gears from the sheet metal piece.

For gear stamping, the sheet metals having thickness upto 3 mm are preferred.

Gear stamping is generally used for mass production of thin and small gears.

They are generally used for mechanisms in watches, clocks, toys, etc.

Materials like brass, aluminum, bronze, stainless steel and medium carbon steel are preferred for this operation.

Coining

Gear coining is done by coining operation by using hydraulic presses. 

The gears made by coining may require post-production machining work.

#3) Powder metallurgy

Gear Manufacturing powder metallurgy
Iron powder which is to be pressed in a die to form a gear

In powder metallurgy, the metal powder is pressed in the die which has a replica of gear.

After this, the product is sintered and then it is pressed like a coining operation to increase its density and to get a better surface finish.

By using powder metallurgy, the gears with high dimensional accuracy can be made.

Powder metallurgy is suitable for manufacturing of small sized gears only (upto 25 mm diameter).

Materials like cast iron, brass, steel, etc can be used for gear manufacturing by powder metallurgy.

Surface finish of gears is accurate and most of the time it does not require any post-production machining work.

#4) Metal removal

gear cutting by metal removal

Metal removal techniques (or gear cutting techniques) are widely used for gear manufacturing.

In metal removal techniques, the gear stock or blank made by casting, forging, etc are machined to make the teeth of desired shape and size.

For gear cutting, there are basically two techniques.

  1. Gear forming or profiling
  2. Gear generation

Let’s see each of these techniques one by one.

Gear forming (or gear profiling)

In gear forming techniques, the cutters used for gear cutting have the same dimensions as the space between the two teeth which are to be cut on the gear blank.

Gear forming is not very suitable for large scale manufacturing of gears because it requires special cutters for each application.

Various gear forming techniques that use form cutters are mentioned below.

  • Gear cutting on milling machine with formed disc cutter or end milling cutter.
  • Gear cutting in planer or shaped with a single formed tool.
  • Gear cutting with formed cutter in broaching machine.

Gear generation

In gear generation, the two involute gears meshes together. One gear is made into a cutter by attaching a cutting edge on it and the other gear is a gear blank.

When these two gears meshes together, the cutting action takes place due to relative motion of the cutter and blank.

If the cutter size is similar to the mating pinion, then it is called gear shaping.

The same gear cutter of different modules is used to cut gears of different numbers of teeth without profile deviation.

Hence gear generation is the best technique to make gears.


External links:
Gear manufacturing: Image by HELLER, CC BY-SA 3.0 DE, via Wikimedia Commons
Powder metallurgy: Image by Anonimski, CC0, via Wikimedia Commons
Gear hobbing on CNC: Image by Affoltergroup, CC BY-SA 4.0, via Wikimedia Commons

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