Machining Equipment Gear Shaft
In mechanical processing equipment, transmission gears are mainly used to transmit power and motion. It can change the speed, direction and torque of motion. For example, in the main transmission system of a lathe, the high-speed rotation of the motor is transmitted through a series of gears to reduce the speed to a speed suitable for the lathe spindle cutting process, while increasing the torque so that the spindle can drive the tool to cut the workpiece.
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Product Introduction
The Role Of Transmission Gears
In mechanical processing equipment, transmission gears are mainly used to transmit power and motion. It can change the speed, direction and torque of motion. For example, in the main transmission system of a lathe, the high-speed rotation of the motor is transmitted through a series of gears to reduce the speed to a speed suitable for the lathe spindle cutting process, while increasing the torque so that the spindle can drive the tool to cut the workpiece. Moreover, when the direction of motion needs to be changed, such as converting the horizontal power transmission to the vertical direction, bevel gears can play a role.
The Basic Principle Of Transmission Gear
Working Principle
Gears are mechanical elements that use teeth to mesh with each other to transmit power and motion. When the driving gear (the gear that inputs power) rotates, the power is transmitted to the driven gear (the gear that outputs power) through the contact between the teeth. For example, in a simple two-stage gear transmission system, assuming that the driving gear has 20 teeth and the driven gear has 40 teeth, the driven gear will rotate half a circle for every rotation of the driving gear. This is because the gear ratio is equal to the ratio of the number of teeth on the driven gear to the number of teeth on the driving gear, which is 2:1 in this example.
Motion conversion function
It can realize the conversion of various motion forms. For example, it can convert high-speed rotational motion into low-speed rotational motion, or convert rotational motion into linear motion (through the combination of racks and gears). In the screw transmission mechanism of the machine tool, the gear meshes with the rack on the screw. When the gear rotates, the screw will move linearly, thereby driving the workbench and other parts to achieve precise linear feed.
Type of Transmission Gear
Classification by tooth shape
Involute gear: This is the most common type of gear in machining equipment. The advantage of involute tooth shape is that the manufacturing process is relatively simple and can ensure a stable transmission ratio. Its tooth profile curve is formed by the trajectory of a point on a straight line when it rolls purely on a base circle. During the meshing process of involute gears, the transmission ratio is constant and divisible, that is, when the center distance changes slightly, the transmission ratio can remain unchanged.
Cycloid gear: The tooth profile curve of the cycloid gear is an epicycloid or hypocycloid. Its advantage is that it has a strong load-bearing capacity and is widely used in some small precision machinery or clocks and other equipment. However, its processing technology is relatively complex and the cost is high.
Classification By Relative Position Of Two Axes
Cylindrical Gears
Used for transmission between parallel axes. According to the different tooth directions, they can be divided into spur gears, helical gears and herringbone gears. The teeth of spur gears are parallel to the gear axis, which is easy to produce impact and vibration during transmission, but simple to manufacture; the teeth of helical gears are inclined, which has a high overlap during transmission, large load-bearing capacity, and stable transmission, but will generate axial force; herringbone gears are equivalent to two helical gears combined together, which overcomes the disadvantage of axial force of helical gears and has strong load-bearing capacity.
Bevel Gears
Mainly used for transmission between intersecting axes, common ones are spur bevel gears and spiral bevel gears. The teeth of spur bevel gears are straight teeth evenly distributed on the cone, and their design and manufacturing are relatively simple, but the transmission stability is slightly poor; the teeth of spiral bevel gears are spiral, and their transmission is more stable and the load-bearing capacity is also higher, but the processing is more difficult.
Worm Gears
Used for transmission between staggered axes, usually the staggered angle between the two axes is 90°. The worm is a part similar to a screw, and the worm wheel is a gear with a special tooth shape. The worm gear transmission has a large transmission ratio and a compact structure, but the transmission efficiency is relatively low and it is easy to generate heat and wear.
Materials And Manufacturing Processes For Transmission Gears
Material Selection
Generally speaking, gear materials need to have high strength, hardness, wear resistance and toughness. Common gear materials include medium carbon steel (such as 45 steel), which can obtain good comprehensive mechanical properties after quenching and tempering (quenching + high temperature tempering), and the hardness is generally between HB217-255. For gears that are subjected to large loads and impacts, alloy steels such as 20CrMnTi may be used. This material can be carburized and quenched to make the surface hardness reach HRC58-62, while the core still maintains high toughness, which can effectively resist fatigue and wear.
Manufacturing Process
Forging Process
Forging is one of the common methods for manufacturing gear blanks. Forging can improve the internal structure of gear materials, refine the grains, and improve the mechanical properties of the materials. After forging, the gear blanks also need to undergo subsequent mechanical processing, such as turning, milling, etc., to obtain precise size and shape.
Cutting Process
Including gear tooth processing. For gears that do not require particularly high precision, gear hobbing can be used. Gear hobbing is the use of a hob to roll out the tooth shape on the gear blank. It has high production efficiency and is suitable for mass production. For gears with higher precision requirements, gear grinding is required. Gear grinding is the use of a grinding wheel to grind the gear tooth surface, which can obtain high tooth shape accuracy and surface finish, but the processing cost is high.
Heat Treatment Process
Heat treatment processes such as quenching and tempering, carburizing and quenching mentioned above can significantly improve the performance of gears. After heat treatment, surface strengthening treatments such as shot peening may also be required to further improve the fatigue strength of the gear.
Transmission Gear Precision And Installation Requirements
Accuracy Standards
Gear accuracy mainly includes aspects such as motion accuracy, working stability accuracy, contact accuracy and tooth side clearance. According to national standards, gear accuracy is divided into 12 levels, from level 0 to level 11, with level 0 having the highest accuracy and level 11 having the lowest accuracy. In general mechanical processing equipment, the commonly used gear accuracy levels are between level 6 and 9. For example, for the main transmission gear of a machine tool, in order to ensure the processing accuracy, it is usually required to reach level 6-7 accuracy, while for some auxiliary transmission gears, the accuracy requirements may be slightly lower.
Installation requirements
When installing gears, ensure that the center distance of the gears is accurate, otherwise it will affect the meshing and transmission ratio of the gears. At the same time, the parallelism of the gear axes (for cylindrical gears) or the intersection angle of the axes (for bevel gears) must also be strictly controlled. During the installation process, special installation tools such as dial indicators are usually required for precise measurement and adjustment. In addition, in order to ensure good lubrication, a suitable lubrication system needs to be set up after installation to reduce the wear of the gears during operation.
Comparison Of Transmission Gears With Other Transmission Methods
Comparison with belt drive
Advantages: The transmission ratio is accurate, unlike belt drive, there will be no slippage, so it can ensure accurate motion transmission. For example, in CNC machining equipment, accurate feed motion is required, and gear drive is more suitable. In addition, the efficiency of gear drive is relatively high. Generally, the efficiency of cylindrical gear drive can reach about 98%, while the efficiency of belt drive is relatively low due to factors such as elastic sliding of the belt.
Comparison with chain drive
Advantages: Gear drive has better transmission stability, especially helical cylindrical gears, which have less vibration and noise when running at high speed. The polygonal effect of the chain during the operation of the chain drive will cause uneven motion. In addition, gear drive can achieve higher speeds, while chain drive is limited to high-speed operation due to factors such as the centrifugal force of the chain.
Application Cases Of Transmission Gears In Different Machining Equipment
Lathe
In the feed box of the lathe, different feed rates can be achieved by changing the combination of different transmission gears. For example, in the ordinary lathe CA6140, the gear system in the feed box can achieve longitudinal and lateral feed movement, and can adjust the feed rate according to the processing requirements. The minimum feed rate can reach 0.02mm/r, which is achieved through precise gear transmission ratio.
Milling Machine
The spindle drive system of a milling machine usually adopts gear transmission. Taking the universal lifting table milling machine X6132 as an example, the power of the motor is transmitted to the spindle through gear reduction, so that the spindle can obtain a suitable speed range, generally between 30-1500r/min, to meet the cutting speed requirements of different milling tools and workpiece materials. At the same time, the horizontal and vertical feed motion of the milling machine's worktable is also partially gear-driven to ensure precise feed accuracy.
Grinding Machine
The grinding wheel spindle of the grinding machine has a very high speed and is generally driven by a high-precision gear transmission. For example, the high-precision cylindrical grinder M1432A, the high-speed rotation of its grinding wheel spindle is achieved through a specially designed gear transmission system, and the gears are required to have high motion accuracy and working stability accuracy to ensure the stability of the grinding wheel at high speed rotation, thereby ensuring the accuracy and surface quality of the grinding workpiece.
Transmission gears play a vital role in mechanical processing equipment.
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