Gear CNC: Types, Processing and Trends
Gears are important basic parts in industrial production, and their processing quality and processing capabilities can reflect the industrial level at that time. The current development trend of gear processing is to realize the CNC and automation of gear processing, and the integration of processing and testing. This article will start with the methods of gear processing and the types of gears to help everyone understand the importance of the development of gear CNC technology for industrial production.
1.What is a gear?
A gear is a rotating mechanical device with teeth that can transmit torque and speed. Usually, mechanical gears are cylindrical and have several sets of teeth around the main body. When two or more gears work synchronously, they are in a transmission state. Power transmission is the cause of speed or torque changes.
2.Gear processing methods
With the increase in the number and variety of gears, the requirements for gear precision are constantly improving, and new gear processing methods are constantly emerging. At present, gear processing includes casting, cold rolling, hot rolling, stamping, die forging, powder metallurgy and cutting, etc. The most commonly used method is cutting. The main methods of gear cutting include: gear hobbing, gear shaping, gear shaving, gear honing, gear grinding, gear lapping, gear milling, etc.
(1) Gear hobbing
Gear hobbing is the most widely used gear cutting method at present. Gear hobbing with a hob on a gear hobbing machine is equivalent to the meshing of a pair of helical gears. The hob and the workpiece maintain a strict speed ratio relationship, mesh in space, and complete various tooth shapes such as involute, cycloid, circular arc, rectangle, etc. according to the development motion. The gear hobbing accuracy is generally 7 to 9 levels. When high-precision hobs and high-precision gear hobbing machines are used, gears with a gear hobbing accuracy of 5 can be hobbed.
The current advanced gear hobbing technologies include:
① Multi-head hobbing can greatly improve production efficiency.
② Hard tooth surface hobbing technology.
③ CNC gear hobbing can greatly improve gear processing accuracy and efficiency and expand the processing range of machine tools.
④ Dry cutting process. It has high productivity, high precision and high workpiece quality.
(2) Gear shaping
Gear shaping is a widely used gear cutting method, especially suitable for machining internal gears and multi-gears. The machining accuracy can be as high as 5-6 levels, generally 7-9 levels.
CNC trend of gear shaping technology:
① CNC gear shaping machine to facilitate machining of non-circular gears and gears with special shapes.
② Increase the number of strokes of the gear shaping machine to improve gear shaping efficiency.
③ Research on the shaping process of hardened gears.
④ CNC helical gear shaping to improve the machining accuracy of helical gears.
(3) Gear shaving
The principle of gear shaving is that the staggered helical gear pair meshes without side clearance, and the gear shaving cutter drives the workpiece to rotate, generating relative sliding speed on the meshing surface, and removing material from the workpiece surface. Gear shaving is an efficient gear finishing method.
(4) Gear honing
Gear honing is equivalent to a pair of staggered helical gear meshing transmission. Gear honing machine is a gear finishing machine tool, which is mainly used to improve the tooth surface quality of gears after heat treatment.
During processing, a plastic honing wheel (gear or worm shape) containing abrasive is used to mesh with the workpiece without gap and rotate freely, and the relative sliding speed between the tooth surfaces and the feed pressure are used for cutting.
(5) Gear grinding
Gear grinding is the most effective and reliable method to obtain high-precision gears. Since hardened gears are now mostly used, gear grinding has become the main processing method for high-precision gears. There are many types of gear grinding methods, which can be divided into two categories: development grinding and form grinding.
3.Different types of gears and their applications
In mechanics, gears are divided into different categories according to their configuration, purpose and direction of movement. The following are the most important types of gears.
(1) Spur gears
When two shafts (driving shaft and driven shaft) are parallel, spur gears transmit power in the same plane. The teeth of spur gears are parallel to the axis of the shaft. They are the most common form of gears and can be used in automobiles, conveying systems, gear pumps and motors, reducers, etc.
(2) Helical gears
Compared with parallel spur gears, the teeth of helical gears are at a certain angle to the shaft. They have multiple teeth in contact during transmission and can carry larger loads. Due to better load distribution and less friction, they operate with less noise and vibration and less wear and tear. The following are the different types of helical gears.
① Single or double helical gears
Single helical gears have teeth in either the left-hand or right-hand spiral. However, double helical gears have teeth in both directions. Using double helical gears ensures more significant tooth overlap, resulting in a smoother transmission.
② Herringbone gears
Herringbone gears have two helical gears connected side by side. They are uncommon due to high production costs and manufacturing difficulties, although they are more suitable for vibration and high shock applications.
③ Helical gears
Helical gears are a pair of helical gears running at a 45-degree twist angle. They appear on non-parallel and non-intersecting shafts and have a lower load-bearing capacity due to single tooth contact. Therefore, these gears are not suitable for transmitting high power.
Applications of helical gears
Water pumps
Mixers
Automobiles
(3) Bevel gears
Bevel gears are cone-shaped with teeth around the cone. They transmit force between perpendicular shafts. That is, shafts that intersect at right angles (90 degrees). However, bevel gears are expensive and cannot transmit as much torque as parallel shaft configurations by size.
① Straight Bevel Gears
Straight bevel gears are the most common configuration of bevel gear teeth. The reason for this is the simplicity of design and ease of manufacturing. When properly matched, the straight helical teeth mesh together immediately, rather than gradually.
② Spiral Bevel Gears
Spiral bevel gears are mechanical gears with curved tooth lines that have a better tooth surface contact ratio than straight bevel gears. Therefore, they have superior efficiency and strength and produce less vibration and noise. However, they have manufacturing difficulties.
③ Zerol® Bevel Gears
This gear incorporates the characteristics of straight and spiral bevel gears. Therefore, this gear is suitable for both applications. However, their torsion angle is zero, so the teeth can rotate in either direction.
④ Miter Gears
Miter gears are a special type of bevel gear. They are unique because they have a transmission ratio of 1. In contrast, other bevel gears have ratios ranging from 10:1 to 500:1.
⑤ Crown gears
Crown gears, sometimes called face gears, also have teeth at right angles to the wheel face. In industry, crown gears mesh with other bevel gears or spur gears in a power circular motion.
⑥ Hypoid gears
Hypoid gears look similar to spiral bevel gears, but they operate in non-crossed shafts. They operate at 90 degrees and are common in the automotive industry.
Applications of bevel gears
Mixers
Watering systems
Pressing plants
(4) Worm gears
Worm gears consist of a spiral cut on the shaft (worm) and the mating gear (worm wheel). These types of gears work by sliding contact with less friction, rather than rotating smoothly and quietly. Therefore, they are suitable for high-impact applications. However, their lower efficiency limits their use to low-power applications.
Application of worm gear
Agricultural machinery
Small conveyor
Packaging equipment
4.Advantages and disadvantages of gears
Advantages of gears:
- Gears are mechanically strong and can lift higher loads.
- With the help of gearboxes, they allow speed ratios to be changed.
- They work well at low speeds.
- Efficient power transmission.
- They are ideal for transmission of high torque values.
- Little attention is paid to maintenance, and gears only require daily lubrication.
- Durable, and the gear system has a long service life
Disadvantages of gears:
- Gears are not suitable for long-distance motion transmission.
- They are not flexible.
- Gears are noisy, especially at high speeds.
- They are not suitable when the shaft is far away.
5.Development trend of gear processing technology
The development of gear processing technology is in the continuous pursuit of improving processing accuracy and processing efficiency, which is specifically manifested in the following aspects:
(1) CNC.
CNC gear processing can improve both processing accuracy and processing efficiency.
(2) Intelligence.
According to the stress, strain and temperature rise of the machine tool, the process parameters of the machine tool cutting are dynamically adjusted.
(3) High speed.
The maximum speed of gear shaping can reach 1000-2500 times/min stroke number, and the cutting speed of high-speed steel hobs can reach 100-200 m/s.
(4) Integration.
Gear machine tools (especially large gear machine tools) tend to integrate multiple processes.
(5) Environmental protection.
For example, the use of dry cutting processing technology avoids oil pollution of air and environment due to the absence of cutting fluid.
(6) New processes continue to emerge.
Abrasive flow finishing process and grinding-honing combined process are emerging processes for gear finishing.
6.Summary
Gears have complex shapes, many technical problems, and are difficult to manufacture. The development of gear manufacturing technology is largely reflected in the improvement of precision level and production efficiency. Therefore, it is particularly important to make good use of gear CNC technology.