Forged gears are gear parts made through a forging process, where the metal blank is plastically deformed to achieve a specific shape and performance; its internal structure is dense and strong, more wear-resistant and efficient than cast gears; it is widely used in transmission systems in automotive, engineering machinery, aerospace and other fields.

Product Material

Carbon steel: High-quality carbon steels such as 35, 45, and 50 are widely used. 45 steel has good comprehensive performance, and after proper heat treatment, it can obtain high strength and toughness, suitable for manufacturing gears with general requirements. For gears with smaller loads or less importance, ordinary carbon steel such as Q235 and Q255 can be used.

Alloy steel: Alloy steel is often used to manufacture gears with large loads, limited axial dimensions and weight, or special performance requirements. For example:

40Cr is a commonly used alloy structural steel with high strength and good hardenability. After tempering treatment, it has good comprehensive mechanical properties and is widely used in medium-precision gears with high speeds.

Low-carbon alloy steels such as 20Cr, 20CrMnTi, and 20Mn2B, after carburizing and quenching, have high surface hardness, good wear resistance, and strong core toughness, suitable for manufacturing important gears that withstand high-speed, medium or heavy loads, as well as impact and friction, such as gears in automobile and tractor gearboxes.

42CrMo alloy steel has high strength, high hardenability, good toughness, small quenching deformation, and high creep strength and endurance strength at high temperatures. It can be used to manufacture forgings with higher strength requirements than 35CrMo steel and larger tempered sections, such as large gears for locomotive traction and supercharger drive gears.

Alloy steels such as Cr15 and 65Mn can be used to manufacture gears with higher precision and worse working conditions, which can improve the wear resistance and fatigue resistance of gears.

38CrMoA1A and other carburizing steels are often used to manufacture high-speed, heavy-duty gears with extremely high requirements for dimensional accuracy and surface quality. After nitriding treatment, they have high surface hardness, good wear resistance, and corrosion resistance.

Cast steel: When the gear diameter d>400mm, the structure is complex, and forging is difficult, cast steel can be used. Cast steel gears have good strength and toughness, and can meet the use requirements of some large gears.

Cast iron: Gray cast iron, ductile iron, etc., have good casting performance, friction reduction, and machinability, and the cost is relatively low, suitable for manufacturing some low-speed, light-load gears with low noise requirements. Among them, ductile iron has better mechanical properties than gray cast iron and can be used to manufacture gears that withstand certain loads.

Non-metallic materials: In some special occasions, such as high-speed light-load, low-noise requirements, or transmission systems with special functions, non-metallic materials such as cloth, wood, plastic, and nylon are used to manufacture gears. These non-metallic materials have the advantages of light weight, good self-lubrication, and low noise, but their strength and wear resistance are relatively low.

Performance Parameters and Technical Standards

(1) Performance Parameters

Module (m): The module is an important parameter in gear design and manufacturing, reflecting the size of the gear teeth. The larger the module, the larger the tooth size, and the stronger the load-carrying capacity. The calculation formula is: module m = pitch diameter d / number of teeth z.

Number of teeth (z): Determined according to the transmission ratio requirements, different tooth combinations can achieve different transmission ratios. Transmission ratio i = number of teeth of the driving wheel z1 / number of teeth of the driven wheel z2.

Pressure angle (α): The pressure angle generally stipulated by Chinese standards is 20°. The pressure angle affects the tooth shape and stress of the gear. A suitable pressure angle can ensure the stability and load-carrying capacity of the gear transmission.

Addendum coefficient (ha) and clearance coefficient (c): For standard gears, the addendum coefficient ha* = 1, and the clearance coefficient c* = 0.25. They determine the size of the gear addendum and clearance, which have an important impact on the meshing performance and transmission accuracy of the gear.

Tooth surface hardness: According to the working conditions and materials of the gear, the tooth surface hardness requirements vary. In general, soft-tooth gears (tooth surface hardness ≤350HBW) are often used in medium and low-speed, light-load occasions; hard-tooth gears (tooth surface hardness >350HBW) are suitable for high-speed, heavy-load, high-precision transmission systems, with stronger load-carrying capacity and wear resistance.

Contact fatigue strength and bending fatigue strength: These two parameters are important indicators for measuring the load-carrying capacity of gears. Contact fatigue strength determines the ability of the gear tooth surface to resist fatigue pitting, while bending fatigue strength reflects the ability of the gear tooth root to resist fatigue fracture. When designing gears, it is necessary to ensure that the contact fatigue strength and bending fatigue strength of the gears meet the requirements according to the actual working load and use requirements through calculation.

(2) Technical Standards

Dimensional accuracy: The dimensional accuracy of the gear directly affects its transmission accuracy and meshing performance. Common dimensional accuracy indicators include the tolerance of the tip circle diameter, the tolerance of the pitch circle diameter, and the tolerance of the tooth width. In general, the dimensional accuracy grade of the gear is determined according to the use requirements. The commonly used accuracy grades are 6-9 grades (GB/T 10095.1-2008 "Cylindrical gears Precision grade Part 1: Definition and permissible values of tooth flank deviation on the same side" and GB/T 10095.2-2008 "Cylindrical gears Precision grade Part 2: Definition and permissible values of radial composite deviation and radial runout").

Form and position tolerance: Including tooth profile tolerance, tooth direction tolerance, and cumulative tooth pitch tolerance. Tooth profile tolerance affects the accuracy of the gear tooth profile, tooth direction tolerance controls the contact accuracy of the tooth surface, and cumulative tooth pitch tolerance reflects the cumulative error of the tooth pitch in one revolution of the gear. Strict control of form and position tolerance can effectively improve the stability and accuracy of gear transmission.

Surface Roughness: The surface roughness of gear teeth significantly impacts transmission noise, wear, and lubrication performance. Generally, a smaller surface roughness value results in lower transmission noise, less wear, and better lubrication. Different precision levels and usage requirements for gears have corresponding surface roughness standards.

Material Property Standards: Gear materials must meet relevant national or industry standards. Indicators such as the chemical composition and mechanical properties of steel must meet specified requirements. For example, the chemical composition and mechanical properties of 45 steel should conform to the standard GB/T 699-2015 "High-quality carbon structural steel".

Heat Treatment Quality Standards: Heat-treated gears must meet corresponding heat treatment quality standards. For example, there are strict regulations for parameters such as the carburizing layer depth and hardness gradient of carburized gears, and the quenching hardness and deformation of quenched gears. By controlling heat treatment process parameters, good comprehensive mechanical properties of the gears are ensured.

Manufacturing Process

(1) Forging Process

Free Forging: Suitable for the manufacturing of single-piece, small-batch production, or large gear forgings. Pressure is applied to the billet through forging equipment to cause plastic deformation, gradually forming the required gear shape. Free forging has high flexibility but low production efficiency and relatively poor dimensional accuracy.

Die Forging: Forging the billet in a dedicated die can produce gear forgings with complex shapes and high dimensional accuracy. Die forging can be divided into open die forging and closed die forging. Closed die forging can better control metal flow, improve material utilization and forging quality, and is suitable for mass production.

(2) Machining Process

Hobbing: Using a hobbing machine and hob to machine gears based on the principle of generating, it can machine spur cylindrical gears, helical cylindrical gears, etc. Hobbing has high machining accuracy and high production efficiency, and can machine a wide range of modules, generally gears below module 8.

Gear Shaping: Using a gear shaping machine and gear shaping cutter for machining, it is especially suitable for machining internal gears, multi-stage gears, etc. Gear shaping has high tooth profile accuracy and small surface roughness, but relatively low production efficiency.

Gear Milling: Machining gears using a milling machine and a forming milling cutter, suitable for machining spur gears, gears with low precision requirements, or single-piece small-batch production. Gear milling is simple, but the machining accuracy is low, and the production efficiency is not high.

Gear Grinding: Used for finishing gear teeth, it can improve gear accuracy and surface quality, and reduce surface roughness. Gear grinding is divided into generating grinding and forming grinding, with generating grinding being more common. For high-precision gears or hard-toothed gears, gear grinding is an important machining process.

Gear Shaving: A metal-cutting machine tool for gear finishing, used to improve gear tooth profile accuracy and reduce surface roughness, usually performed after hobbing or shaping.

(3) Heat Treatment Process

Carburizing and Quenching: Mainly used for low-carbon alloy steel gears. By carburizing, the carbon content of the tooth surface is increased, then quenched and tempered at low temperature, so that the tooth surface obtains high hardness, high wear resistance, and good fatigue strength, while the core still maintains sufficient toughness. Carburizing and quenching is the mainstream process for manufacturing high-parameter hard-toothed gears.

Induction Quenching or Flame Quenching: The gear tooth surface is quickly heated to the quenching temperature and then quickly cooled to obtain high hardness on the tooth surface. This method is suitable for medium carbon steel or medium carbon alloy steel gears, which can improve the wear resistance and fatigue strength of the tooth surface, and the quenching deformation is small.

Tempering: After quenching medium carbon steel or medium carbon alloy steel gears, high-temperature tempering can obtain good comprehensive mechanical properties, suitable for manufacturing small and medium-sized, medium-load and light-load gears.

Normalizing: Improves the machinability of gear materials, refines grains, and eliminates internal stress. Previously, normalized gears were mainly used for large marine noise gears, but they are rarely used now due to their poor tooth surface wear resistance.

(4) Surface Treatment Process

Nitriding: Nitrogen atoms penetrate the gear surface to form a nitriding layer with high hardness, wear resistance, and corrosion resistance. Nitriding can improve the surface quality and service life of gears, and is suitable for gears with extremely high requirements for dimensional accuracy and surface quality, such as high-speed gears and precision machine tool gears.

Copper Plating: Improves the contact state of the gear tooth surface, reduces the friction coefficient, and improves the anti-bonding ability. Often used for gears with special requirements for tooth surface contact performance.

Shot Peening: High-speed shot peening impacts the gear surface, causing residual compressive stress on the surface, improving the fatigue strength and stress corrosion resistance of the gear.

Quality Inspection

Appearance Inspection: Using the naked eye or simple tools to check whether there are cracks, pinholes, pores, folds, etc., on the surface of the gear forging, and whether the size and shape meet the design requirements.

Dimensional Accuracy Inspection: Using calipers, micrometers, gear measuring centers, and other measuring tools and equipment to measure various dimensional parameters of the gear, compare them with the design drawings, and determine whether the dimensional accuracy meets the standard requirements.

Hardness Testing: Using Rockwell hardness testers, Brinell hardness testers, Vickers hardness testers, etc., to test the hardness of the gear tooth surface and core to ensure that the hardness meets the heat treatment process requirements and relevant standards.

Metallographic Structure Inspection: Observing the metallographic structure of the gear material through a metallographic microscope to determine whether it meets the material standards and heat treatment process requirements, such as grain size, organizational morphology, and carburizing layer depth.

Non-destructive testing: Common non-destructive testing methods include magnetic particle inspection, ultrasonic testing, and liquid penetrant testing. Magnetic particle inspection is used to detect surface and near-surface cracks; ultrasonic testing can detect internal defects; and liquid penetrant testing is used to detect surface-opening defects. Through non-destructive testing,

ensure the internal quality of the gear forging is reliable and free of defects that affect performance.

Mechanical property testing: Tensile tests, impact tests, bending tests, etc., are performed on gear forgings to determine their strength, toughness, and other mechanical properties to verify that they meet design requirements and relevant standards.

Product Advantages

High strength and high toughness: The forging process makes the internal structure of the metal dense and the grains refined, thereby improving the strength and toughness of the gear, allowing it to withstand greater loads and impacts, and extending its service life.

Good wear resistance: After appropriate heat treatment and surface treatment, the gear tooth surface has high hardness and good wear resistance, which can effectively reduce tooth surface wear and ensure transmission accuracy and stability.

High precision: Advanced manufacturing processes and strict quality control ensure that gear forgings have high dimensional accuracy, shape and position accuracy, and tooth surface quality to meet the requirements of high-precision transmission.

High reliability: The product quality is stable and reliable, and has undergone strict quality inspection, and can reliably operate under various complex working conditions, reducing equipment failure rate and improving production efficiency.

Strong customization capabilities: According to the different needs of customers, gears of various specifications, shapes, materials, and performance requirements can be designed and manufactured to meet diverse application scenarios.

After-sales Service

Quality assurance: A quality assurance period is provided. Within the warranty period, if a failure or damage is caused by product quality problems, free repair or replacement will be provided.

Technical support: Provide customers with technical consultation and solutions, and assist customers with gear selection, installation and commissioning, and troubleshooting.

Regular return visits: Regularly visit customers to understand the product usage, collect customer opinions and suggestions, and continuously improve product quality and service level.

Rapid response: Establish a rapid response mechanism for customer feedback.

Application Areas

Wind power industry	Shipbuilding	Mechanical manufacturing
Nuclear power industry	Oilfield industry	Chemical industry