An Overview of Metal Gear Manufacturing

Industrial and mechanical industries rely on various large and small equipment for daily operations. Miniature gears maintain rotation from one axis to another and transmit torque to the driven shaft. The evenly spaced teeth on each conical or cylindrical gear prevent slippage by allowing the gears to interlock.

If your equipment requires high-quality gears, Allied Sinterings, Inc. is here to help! Our cutting-edge manufacturing capabilities allow us to provide quality metal gears for any purpose. Learn more about the common types of gears, the materials from which they are made, and the manufacturing processes used.

Common Types of Gears

There are various gears, and each type accomplishes different force transmissions in specific mechanical designs. Here is a detailed look at the most common types of gear:

Spur Gear

Spur gears come in various configurations, but generally, they have parallel teeth around a cylindrical circumference and a central bore that fits over the shaft. They regulate a device’s speed or torque.

Helical Gear

Helical gears have slanted tooth traces that make more contact with one another and take a helix shape. At the beginning of the engagement, the teeth make point contact, which gradually becomes line contact. This allows multiple teeth to mesh at any given time, reducing the load on each tooth.

Bevel Gear

Bevel gears transfer power between shafts at intersecting axes, whether angled or perpendicular. A bevel gear can be thought of as a truncated cone, which has lateral teeth that interlock with other gears. The gear transmitting shaft power is the driver gear, while the gear receiving power is the driven gear.

Worm Gear

A worm gear comprises two mating parts: a screw-shaped cut on a shaft known as the worm and the mating gear or the worm wheel. These parts can be cylindrical or hourglass-shaped, depending on their usage. The worm is made of a rigid material, while the worm wheel is constructed from soft material to reduce friction.

Rack and Pinion Gears

This is a combination of a pinion (a circular gear) and a rack (a linear gear). Rack and pinion gears convert rotational motion into a linear motion. It’s common in vehicles where the steering wheel engages a rack to control the linear movement of the wheels.

Miter Gear

A miter gear is a type of bevel gear used to change the direction of power transmission without affecting its speed. Miter gears can either be straight or spiral-shaped.

Screw Gear

Screw gears use a pair of helical gears set at a 45° twist angle for non-parallel, non-intersecting shafts. They have a low carrying capacity since their tooth contact is a point.

Materials Used to Manufacture Gears

A gear should have the following properties to guarantee reliable performance and long life:

  • High tensile strength to sustain static loads
  • Good endurance to withstand changes in load
  • Low coefficient of friction
  • Excellent manufacturability

A variety of materials are used to produce gears with these crucial properties. Here is an overview of each material and its unique strengths.

Cast Iron

Cast iron can withstand repeated and sustained wear, making the metal ideal for precision gear manufacturing. The casting method can easily produce complex gear shapes. Cast iron gears are often deployed in applications where smooth action is not a priority.

Steel

Steel alloy gears are high-strength because they are typically heat-treated for enhanced toughness and hardness, especially in the teeth. Carbon steel, in particular, is used to produce helical, spur, bevel, worm, and gear racks.

Brass

Brass is an alloy of copper and zinc. Manufacturers can use different brass alloys to vary the amount of zinc in the metal. Low zinc brass has more ductility than other materials, while the copper base makes the metal antimicrobial and easy to machine. Brass gears are usually found in spur gears or gear racks for low-load applications.

Bronze

In addition to brass, other copper alloys include aluminum bronze and phosphor bronze. These nonmagnetic gears are best for corrosive environments.

Phosphor bronze contains a combination of copper, tin, and phosphorus. Tin increases the alloy’s strength and corrosion resistance, while phosphorus improves its stiffness and resistance to wear. As a result, phosphor bronze gears are ideal for high-friction environments, especially worm gears, since the material resists friction generated by the wheel and degradation due to lubrication.

Aluminum bronze combines copper, aluminum, nickel, iron, and manganese. This alloy has superior wear and corrosion resistance, so it is used in highly corrosive environments with saltwater, oxidation, and organic acid exposure. In addition, their ability to withstand high-load environments makes them ideal for worm wheels and screw gears.

Aluminum Alloys

These alloys work as a good alternative to iron alloys, especially in environments that need gears with a high strength-to-weight ratio. Moreover, gears made of aluminum alloys have a protective surface finish known as passivation that protects them from corrosion and oxidation.

The most common aluminum alloys used to produce gears include 2024, 6061, and 7075. Regardless of grade, all aluminum gears are best for low to moderate-temperature applications, as they begin to degrade at around 400 °F.

Powdered Metals

These metals are composed of different metal material combinations, such as iron-nickel steel, pre-alloyed steel, and other custom blends. They also allow the gears to operate more quietly due to their porosity and can be self-lubricating by being vacuum impregnated with various oils.

The process involves three steps:

  1. Formulating the ideal combination that matches specifications for durability, accuracy, and reliability
  2. Compacting the mixture under controlled pressure to meet precise requirements
  3. Heating or sintering the blend to produce a permanent form

Powder metallurgy can produce bevel, spiral bevel, spur, helical, pinion, and combination gears.

Thermoplastics

Thermoplastics are vital in the precision manufacturing of lightweight gears. Thermoplastic gears can be manufactured like metallic gears, although injection molding is usually the best method. However, many manufacturers prefer acetal because of its stability over wide temperature ranges, low coefficient of friction, and creep resistance.

Gear Manufacturing Methods & Process

Different manufacturing processes for gears produce different results. See this table for more detailed information.

Method/

Process

Process Description Types of Gears Produced Advantages & Limitations Applications
Casting A refractory mold is filled with molten metal to solidify it into the desired shape. As the metal solidifies, it shrinks in volume, and feed metal is added to prevent a cavity from forming in the middle. Spur, helical, worm, cluster, bevel Any degree of complexity and any size can be produced

 

Low melting point metals used don’t have enough hardness for high load-carrying capacities

Toys, washing machines, small appliances, hand tools, cameras
Forging Steel billets are heated to a specific temperature (about 1900-2450 °F), then pressed or hammered into a die to form the desired size.

 

Spur, helical, spiral bevel Produces near-net gears, reducing material cost savings by up to 30%

 

Superior strength

 

Requires specialized tooling and process knowledge to achieve AGMA 8-9 level gears

Automotive, aerospace, railroad, agriculture, material handling industries
Cold Drawing & Extrusion A bar is drawn or pushed through a series of dies to achieve the final shape with its desired tooth form. Helical, spur Minimizes tool expenditure required for mass-producing spur gears

 

Almost any tooth form can be produced

Watches, electric clocks, typewriters, small motors, cameras, mechanical toys
Powder

Metallurgy and Sintering

Alloy powders are mixed, compacted into a die, and sintered/heated in an atmosphere-controlled furnace for the particles to bond. Spur, helical, bevel Requires little to no machining

 

Material utilization is nearly 100%

 

Raw material cost is high

 

Size of product manufactured is limited to 2-20 kg

Household appliances and automotive components (oil pumps, seat adjusters)
Fine Blanking A sheet of metal is pressed between two dies to form a desired shape. Bevels, multiple gear sets, other complex forms Can produce complex shapes

 

Limited three dimensional capability

Automotive, appliance, hydraulic, medical equipment
Stamping A sheet of metal is put in between the top and bottom parts of a die. The upper die is pressed down and cuts the gear from the sheet metal. Spur gears, thin/flat forms Cost-effective

 

Efficient method to manufacture lightweight gears for low to moderate load applications

 

Thickness is restricted

Toys, clocks, timer mechanisms, watches, small appliances (toasters, mixers), large appliances (washers, dryers)

Powdered & Sintered Metal Gears at Allied Sinterings, Inc.

Allied Sinterings can provide your ideal solution if you need powdered and sintered gears. Our Danbury, Connecticut plant operates three sintering furnaces and 42 German-engineered, high-precision Dorst compacting presses, which range from 0.5 to 50 tons. In addition, our in-house tool room and tumbling/finishing capabilities enable us to drill and tap the fine, miniature components we produce.

We manufacture and assemble small planetary gear drives that measure up to 1.5 inches in diameter and have diametral pitches up to 120, which meet AGMA Class 8 tolerances. With compacting force capabilities from 0.5 to 50 tons, we can create gears out of different materials and with varying levels of strength.

Contact us today to find out how we can manufacture the perfect metal gears for your application!

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