Introduction to Gear Types and Application Examples by Industry

What Is Gear Machining?

Gear machining is the technology of machining gears, which are essential parts for transmitting machine power. It is the forming of mainly metal into the shape of a gear by cutting, grinding, or other methods. Since gear accuracy directly impacts a machine's lifespan and performance, gear machining requires high accuracy.

Amid the growing demand for electric vehicles (EVs) and automated robots in recent years, gears are becoming smaller and are produced in smaller volumes. At the same time, gear machining technology is rapidly developing, and computer numerical control (CNC) technology has made it possible to machine complex and precise gears.

Gear Types

Gears come in various shapes depending on their intended application and power transmission requirements. In this section, we will introduce the typical gear types.

Bevel Gear

The bevel gear is a gear with teeth cut into a conical surface. It has an umbrella-like or conical shape, and the term bevel refers to a sloped surface in English

The greatest feature of this gear is its ability to transmit power by changing the direction of the shaft by 90 degrees, which greatly improves the freedom of the machine design. Another important feature is that it can achieve different rotational speed ratios. While the bevel gear operates more quietly than a spur gear, its machining process is more complicated. Bevel gears can be further categorized into straight bevel gears and spiral bevel gears.

Straight bevel gears are characterized by having teeth in a straight line.
Spiral bevel gears are characterized by having teeth curved in a spiral shape.

Helical Gear

The helical gear is a cylindrical gear with teeth cut at an angle to the axis. The angled teeth allow for the gears to mesh more smoothly. The teeth mesh gradually, reducing noise and vibration for quiet operation even at high-speed rotation. In addition, the teeth have a larger contact area, allowing the gear to transmit a higher load.

Spur Gear

The spur gear has one of the most common gear shapes. Teeth are cut parallel to the axis along the cylindrical periphery. Since its structure is simple and its manufacturing is relatively easy, this gear shape is used for a wide variety of applications. It is used in automotive transmissions, machine tools, electrical appliances, and other machinery. However, since fewer teeth come in contact at the same time, it has the drawback of generating noise at high-speed rotation.

Rack and Pinion Gear

A rack is a gear with straight teeth. Since it is used together with a pinion (small gear), it is generally called a rack and pinion gear.

When the circular pinion rotates, the rack moves in a linear motion, and conversely, when the rack is moved, the pinion rotates. It is characterized by its ability to convert between rotary and linear motion. Since the rack has no radius (its radius is infinite), there is no limit to the length of the gear. Therefore, it allows for long strokes and can accommodate high-speed motion and heavy loads.

Worm Wheel and Worm Gear

The worm gear is a gear mechanism consisting of a worm with spiral teeth and a worm wheel that meshes with it. The worm and worm wheel have perpendicular rotation axes and are used when a high gear ratio is required. This gear is characterized by its ability to transmit power only in one direction.

Due to the mechanism of the worm wheel and worm gear, when the worm gear on the input shaft stops, the worm wheel will not rotate even if you attempt to turn the worm wheel on the output shaft. The self-locking feature that prevents reverse drive makes this gear suitable for lifting mechanisms such as elevators and winches.

Internal Gear

An internal gear is a gear with teeth on the inside of a cylinder or disc. This gear meshes with a standard external gear, and combining an internal gear with an external gear creates a gear mechanism that rotates in the same direction. This gear enables equipment to have a more compact design to save space. Since it cannot be machined on the outside, it requires high machining technology. However, the introduction of skiving machines that have high machining accuracy in recent years has resolved this drawback of the internal gear.

Ball Screw

A ball screw is a mechanical component that converts rotary motion into linear motion. It consists of a screw shaft, a nut, and balls positioned between them. When the screw shaft rotates, the balls inside the nut move roll along the groove and move, converting the rotary motion into linear motion. Ball screws are divided into various types according to the circulation method, screw shaft shape, and preload method.

Gear Tooth Profiles

The shape of the gear teeth is called the tooth profile, and it is formed by the tooth profile curve. The tooth profile curve is broadly classified into the involute curve and the cycloid curve, and we will explore their differences below.

Involute Curve

An involute curve is the path traced by the end of a string as it is unwound from a disc. The involute curve is the most commonly used tooth profile curve, and it is easy to machine and suitable for mass production. It also has the advantage of being easy to mesh even if the center distance is slightly misaligned. It is commonly used in general machinery, automotive transmissions, and machine tools.

Cycloid Curve

A cycloid curve is the path traced by a point on a circumference of a circle as it rolls along a straight line. Gears with cycloid curves have a larger contact area between the gears, which reduces wear and makes them more resistant to shock. Since there is no interference, it offers the advantages of low rotational resistance and quiet operation. These features make gears with cycloid curves ideal for timepieces and precision equipment with low load.

Examples of Gear Machining by Industry

Lastly, let us take a look at some application examples of gears and gear machining.

Gear Machining in the Automotive Industry

In the automotive industry, gears are used in several key areas of the automobile, such as the transmission and engine.

As demand grows for EVs in recent years, we are also seeing a change in the need for gears in the automotive industry. In the EV-leading regions of Europe and China, the share of EVs in new car sales is increasing annually. In 2023, EVs accounted for approximately 14.6% of new car sales in Europe (according to the European Automobile Manufacturers Association) and around 22.2% in China (according to the China Association of Automobile Manufacturers).

EVs operate more quietly than gasoline-powered vehicles. Higher gear noise affects driving comfort, so there is a growing demand to machine quiet gears. In addition to becoming quieter, gears are also becoming smaller and more sophisticated. In terms of environmental impact, the efficiency of gears is also important, and improving energy efficiency is a key focus for gear machining.

Gear Machining in the Robotics Industry

Robotics is a rapidly advancing technology field. In Japan, which is facing a declining birthrate, an aging population, and labor shortages, the use of robots is crucial for companies to maintain global competitiveness, and technological developments for this purpose are advancing on a daily basis.

Industrial robots and collaborative robots need to perform a wide range of motions, requiring their gears to be highly sophisticated and accurate. One such example is the planetary gear. This gear mechanism is used in wind power generators and electric screwdrivers, in which multiple gears revolve while rotating on their own axis. Since planetary gears provide more sophisticated movement, they are used in the joints of robot arms and automotive engines.

Gear Machining Used in Various Industries

Gear machining technology plays a key role in various industrial fields, from automobiles and aircraft to robots and environmental equipment. As society becomes more advanced, gears are becoming more efficient, smaller, and lighter. To reduce the weight of gears, materials other than metal are being used, such as resin.

Furthermore, with the development of NC technology in recent years, workpieces with complex shapes can now be machined automatically. For manufacturers, whether in gear machining or other sectors, it is important to accurately identify market needs and focus on capital investment and the development of production systems to meet them.