Gears are mechanical parts that can cooperate with each other and have teeth. Gear transmission can complete functions such as deceleration, acceleration, and turning. It is very versatile in the field of mechanical transmission and machinery. This white paper summarizes the processing technology of gear parts.
#The function and structure of the gear
The gears are designed into different shapes and sizes according to the different functions of the machine, but they can always be divided into two parts: the ring gear and the wheel body. Common cylindrical gears are divided into the following categories (below): disc gears, sleeve gears, internal gears, shaft gears, sector gears, and racks. Among them, disc gears are the most widely used.
Cylindrical gear structure: one or more ring gears can be used for spur gears. The manufacturability of ordinary single ring gear is good. Pinion rings with double or triple gears are often affected by the shoulders, which limits the use of certain processing methods. Generally, only inserts can be used. Multi-ring gears are usually a combination of single-ring gears. When gears require high precision, sharpening or grinding is required.
#Precision requirements of cylindrical gears
The manufacturing precision of the gear itself has a great influence on the working performance, carrying capacity and service life of the whole machine. According to the usage conditions of the gear, the gear transmission needs to meet the following requirements:
1. Motion precision gear is necessary to accurately transmit motion, and the transmission ratio is constant.
That is, the gear needs to make one revolution, and the angle error does not exceed a certain range.
2. Work stability
This requires a small change in the instantaneous speed ratio when the gear rotates. In other words, you need to limit the angle error in a short time. This requirement limits the instantaneous changes in the gear rotation speed ratio. In other words, it limits the angle error in a short time.
3. Contact accuracy
When the gear is transmitting power, the contact stress is too high to avoid uneven load distribution and cause premature wear of the tooth surface. This requires uniform surface contact of the teeth when the gear moves, ensuring a specific contact area and desired contact position.
4. Gear side clearance
When gear transmission is required, store lubricating oil and leave a certain gap between the non-driving tooth surfaces to prevent dimensional changes caused by temperature and elastic deformation, as well as machining and assembly errors.
3. Gear material
The gear must be a material suitable for the working conditions used. The choice of gear material directly affects the processing performance and life of the gear. Gears generally use medium carbon steel (such as 45 steel) and low carbon medium carbon alloy steel (such as 20Cr, 40Cr, 20CrMnTi). An important requirement is that a higher gear allows you to choose 38CrMoAlA nitrided steel. The power transmission gear can also be made of cast iron, bakelite or nylon cloth or other materials. Geared
In gear processing, two heat treatment processes are arranged according to different purposes.
1. Rough heat treatment
The gear tooth blanks are preheated or tempered before and after. The main purpose is to eliminate the residual stress caused by forging and rough machining, improve the machinability of the material, and improve the comprehensive mechanical properties.
2. Heat treatment of gear tooth surface
After the gear teeth are formed, heat treatment processes such as carburizing and quenching, high-frequency induction heating quenching, carburizing and nitriding, and nitriding are often carried out to improve the hardness and wear resistance of the gear tooth surface.
Gear blanks are mainly composed of bars, forgings and castings.
Bars are used for gears with small size, simple structure and low strength. Forged products are often used for gears requiring high strength, wear resistance, and impact resistance. Gears with a diameter greater than 400-600mm are often used for casting billets.
For large, low-precision gears, gear teeth can be cast directly to reduce the amount of processing. For small and complex gears, precision casting, pressure casting, precision forging, powder metallurgy, hot rolling and cold extrusion can be used. This new process produces gear blanks with gear teeth to improve labor productivity and save raw materials.