Pulleys are disc-shaped components used for power transmission, employed together with belts. While there are other mechanisms for power transmission, such as gears, a distinctive feature of the belt and pulley system is its ability to absorb some impacts during power transmission due to the slippage between the belt and the pulley. This can mitigate the effects of issues that may arise in the power transmission process. However, due to this slippage, the efficiency of power transmission can be inferior compared to other mechanisms. This article explains the types of pulleys, their typical processing methods, and the challenges involved.
Pulleys, widely used in power transmission mechanisms, come in various types, including general-purpose V-pulleys and toothed pulleys.
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General-purpose V-pulleys, specified in "JIS B1854," are used in combination with V-belts. These pulleys have V-shaped grooves around their circumference, offering a larger contact area which results in less slippage and higher transmission efficiency compared to flat pulleys without grooves. They can handle various sizes of loads, making them suitable for a wide range of products such as home appliances, machine tools, and conveyance equipment.
Toothed pulleys, defined in "JIS B1856," are used with toothed belts that have ribs or teeth. Unlike general-purpose V-pulleys that transmit power through friction, toothed pulleys engage with the belt's teeth for more stable power transmission. They can be made small and light, and they generate less noise, which makes them ideal for precision instruments and automotive timing belts.
Several methods are used to process pulleys, including milling and turning. Keyway machining and gear cutting are among the more efficient representative processing methods.
Keyway machining involves cutting slots in toothed pulleys using machines and tools like broaching machines and slotting tools.
Broaching machines are used for broaching, a type of machining process that uses a long, specially shaped cutting tool called a broach. Broaching can process parts quickly and with high repeatability in a few steps, but it requires specialized tools and equipment, making it unsuitable for low-volume production.
Keyway machining can also be done using slotting tools on lathes or machining centers, making it possible to perform keyway machining on standard NC machines without specialized equipment.
Pulley grooves can be produced through gear cutting, using machines and methods like hobbing and gear skiving.
Hobbing is a machining process where a hob, a specialized cutting tool, is rotated against the workpiece to cut gears, splines, or sprockets. By changing the hob, a variety of parts can be machined, not just pulleys.
Gear skiving is a method for machining gears where the tool is tilted and synchronized with the workpiece at high speed, gradually cutting the material through sliding contact points. It utilizes complex machinery like 5-axis machines, allowing for process consolidation.
Creating pulleys involves multiple steps using lathes, machining centers, broaching machines, and hobbing machines, requiring frequent setup changes. This can lead to inefficiencies and increased work-in-process inventory, making it difficult to improve productivity.
Recently, the development of new tools has increased the capabilities of composite machining centers, and lathes equipped with milling functions (turning centers) have been developed, significantly reducing the need for specialized machines like broaching and hobbing machines. Using composite machining centers is one option for reducing setup changes and improving efficiency in low-volume, high-variety production.
For high-volume production of fewer varieties, combining general-purpose machines like lathes with specialized machines like hobbing machines can enhance productivity. Improving pulley production efficiency requires a thorough understanding of each equipment's strengths and limitations, and selecting the appropriate machine type—general-purpose, specialized, or composite—based on the situation and objectives.
This article discussed the types of pulleys, their typical processing methods, and the challenges involved. Pulleys, a key component in various power transmission mechanisms, have led to the development of numerous processing methods due to productivity challenges. Combining general-purpose and specialized machines, understanding the characteristics of each processing method, and choosing the right approach based on the goal and situation are crucial for efficient pulley manufacturing.
