Gears are found in numerous applications, from simple mechanisms to complex systems such industrial machinery. The manufacturing process of gears involves several critical steps and considerations.

1. Classification of Gears

1.1 Parallel-Shaft Gears

This category includes spur gears, helical gears, and rack and pinion gears. These gears are characterized by;

  • Their simple design and manufacturing
  • High efficiency, easy assembly
  • Excellent precision
  • High wear 
  • Noisy operation. 

They are commonly used in 

  • Automotive transmission,
  • Industrial drives
  • Machine tools
  • Motors and pumps
  • Agriculture equipment
  • Scientific instruments
  • Electronic devices, 
  • Large mills​

1.2 Intersecting-Shaft Gears

Straight bevel gears and spiral bevel gears are an example for these kind of gears.

The shaft axes intersect in this configuration, often at a right angle. Straight bevel gears are simple to produce and widely used, whereas spiral bevel gears are employed for higher-speed applications due to their smoother and quieter operation​.

1.3 Nonparallel Nonintersecting-Shaft Gears

 This category includes;

  • Worm gears: Worm gears are used for high-ratio speed reduction in limited spaces and are known for their quiet and smooth operation despite low transmission efficiency.
  • Hypoid gears : Hypoid gears are similar to spiral bevel gears but with hyperboloid pitch surfaces and offset pinion axes, leading to improved smoothness and lower noise
  • Cross-helical (screw) gears : Cross-helical gears are employed in light-load applications and allow a wide range of speed ratios without changing gear size and centre distance

2. Materials used in Gear Manufacturing

2.1 Ferrous Metals and Alloys

  • Cast Iron: Includes gray, ductile, and malleable cast iron. Known for low cost, good machinability, excellent noise-damping characteristics, and superior performance under dynamic conditions. Gray cast iron is not suited for gears subjected to shock loads due to low shock resistance, while ductile iron offers good impact strength and fatigue strength​
  • Steel: Several types of steel are used in gear manufacturing:
  • Low-carbon steels (e.g., AISI 1010, 1015, 1020, 1021, 1022, 1025)
  • Medium-carbon steels (e.g., AISI 1035, 1040, 1045)
  • High-carbon steel (e.g., AISI 1060)
  • Carburizing steel, through-hardening gear steels (e.g., AISI 8620, 20MnCr5, SAE5120)
  • Alloy steels like chrome-molybdenum alloy steel (AISI 4140)​
  • Stainless Steels: Used for gears exposed to high temperature and corrosive environments. Types include; 
    • austenitic (e.g., 303, 304, 316), 
    • ferritic (e.g., type 430), 
    • martensitic (e.g., type 440 C), 
    • precipitation hardening (e.g., 17-4PH, 17-7PH) stainless steels​

2.2 Nonferrous Metals and Alloys

  • Materials such as copper, brass, bronze, aluminium, and magnesium are used for machined, die-cast, and formed gears​
  • High-strength wrought aluminium alloys (e.g., 2024, 6061, 7075) and aluminium silicon alloys (e.g., A360, 383, 384, 413) are used for machined and die-cast gears​
  • Magnesium alloys (e.g., ASTM AZ91A, AZ91B, AM60, AS41) are used in lightweight die-casted gears for low-load applications​

2.3 Non-metallic Materials

  • Plastics, including thermoplastics and thermosets, are extensively used in gear manufacturing. Examples include nylon, polyacetal, polyamide, polycarbonate, polyurethane, phenolic laminates, and fluoropolymers such as polytetrafluoroethylene (Teflon). They are preferred for applications requiring light weight, smooth and quiet operation, and resistance to wear and corrosion

3. Manufacturing of Gears

3.1. Gear Milling

  • Gear milling is a cost-effective, flexible method for creating various gear types like spur, helical, bevel gears, racks, splines, and ratchets. 
  • It uses circular, disc-type, and end-mill cutters, with the cutter shape conforming to the gear tooth space.
  • Each tooth is individually cut, with the process repeating for each tooth. 
  • Suitable for small-volume, low-precision gear production. 
  • Different gears require specific milling cutters, which are less expensive than other types. 
  • Frequently used for low-speed machinery and gears where minor deviations are not critical.

Figure 1 : Gear Milling

3.2. Gear Broaching

  • Broaching is a high-precision machining process for cylindrical gears, offering excellent geometric accuracy and surface finish. 
  • Broaching involves removing metal with a broach, a multi-toothed tool
  • It also involves uniform tooth forms and robust surfaces to handle broaching pressure.
  • It is suitable for external and internal spur and helical gears, racks, splines, and sector gears.
  • Broaching requires a specific broach for each gear size, making it ideal for large-scale production. 
  • It’s effective for both small gears in a single pass and large gears using surface-type broaches. 
  • Automotive automatic transmission helical gears are commonly produced by broaching.

Figure 2: Broaching

3.3 Gear Cutting on a Shaper

  • A gear shaper is a machine tool that uses linear motion for cutting,
  • Primarily employed in the manufacturing of simpler, lower quality gears like spur gears, splines, and clutch teeth.
  • It’s effective for mass production due to its ability to economically cut large quantities with a tool whose cutting edge matches the tooth space shape. 
  • The process involves reciprocating the tool parallel to the gear blank’s center axis, cutting one tooth space at a time, and rotating the gear blank to cut successive teeth.

Figure 3: Shaper Cutting

3.4 Gear Hobbing

  • Gear hobbing is a process for generating gear teeth using a rotating cutter called a hob, resembling a worm gear with multiple flutes for cutting.
  • It’s used for making spur, helical, worm gears, and splines in various materials. 
  • It isn’t suitable for bevel or internal gears. 
  • Hobbing is economical but may require additional finishing for high precision. 
  • The process includes;
    • Axial hobbing (for spur and helical gears)
    • Radial hobbing (for worm wheels)
    • Tangential hobbing, 

each differing in the direction of the hob’s feed relative to the gear blank.

Figure 4: Gear Hobbing

3.5 Gear Planing

  • Gear planning is a traditional method for making spur and helical gears
  • It involves a reciprocating rack-type cutter working against a rotating gear blank.
  • There are two main types;
    • The Sunderland process (horizontal gear blank axis, parallel cutter motion) and 
    • The Maag process (vertical gear blank axis, adjustable cutter in any vertical angle and direction). 
  • While Sunderland uses a practical-length cutter rack, Maag involves periodic repositioning of the rack and blank. 
  • Planing is generally less precise than shaping and hobbing due to potential geometry errors from repositioning.

Novelty Structures supplies various kinds of gears for a variety of applications.

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