Precision racks are critical components in various mechanical systems, particularly in applications requiring linear motion and accurate positioning, such as CNC machines, robotics, and automated systems. This article outlines the manufacturing processes involved in creating precision racks and the methods for selecting the appropriate rack for specific applications.
1. Precision Rack Grade
As an infinitely extended gear, the specifications of the rack basically follow the gear standard. Taking the German DIN standard as an example, it is usually divided into DIN3 to DIN10 grades, mainly used in DIN6, DIN8 and DIN9 grades. The distinction between grades is mainly based on the total pitch error, and there are strict regulations for each meter. For example, the best-selling DIN6 grade rack has a total cumulative error of no more than 0.036mm per meter, which is equivalent to the C5 grade lead accuracy of the precision ball screw. Therefore, the precision of the rack is highly trusted by machine tool manufacturers.
2. Precision Rack Grade Application Industry
In the precision machinery industry, racks are widely and critically used, and their classification is usually based on accuracy and market positioning. However, given the diversity and complexity of the industry, these classifications are only used as a rough reference.
DIN3 grade precision rack suitable for extremely high-precision measuring equipment to ensure the accuracy and reliability of data.
DIN5 used for extremely high-precision machine tools, such as precision grinders and high-speed machining centers.
DIN6 serves high-precision CNC machining composite machines, including woodworking machines, laser cutting machines, water jet machines, pipe bending machines and five-axis machining centers.
DIN7 covers various types of processing machines with medium and high precision levels, meeting various processing needs.
DIN8 suitable for processing machines or load tool machines with medium and low precision levels.
DIN9/DIN10 mainly used for low-level or heavy-load machine tools, such as gantry processing machines.
3. Material Selection of Racks
From the perspective of raw materials, in machine tools, the commonly used materials for precision racks include medium carbon steel and alloy steel. In the early days, S45C medium carbon steel was mostly used. Now, due to the market demand for higher hardness, it has gradually been upgraded to S50C, and the hardness has been increased to HRC50-55 degrees. Alloy steels such as SCM440 chrome-molybdenum alloy steel are widely used due to their excellent overall structure, rigidity and toughness. In addition, plastic POM or metals such as copper are also used in specific industries such as food machinery.
4. Rack Hardness Selection
In the field of industrial manufacturing, the selection and treatment of rack steel is crucial to mechanical performance. Soft racks that have not been heat treated can usually meet the DIN8 standard after precision milling. However, for racks that need to work in heavy-duty environments, heat treatment becomes an indispensable step to ensure that they can withstand high-intensity loads. During the heat treatment process, common methods include high-frequency quenching and tempering, which can make the rack reach a hardness of HRC55 degrees. If a higher hardness is required, such as HRC60 degrees, carburizing technology is required and SCM415 material is selected, but this also brings the risk of brittle cracking due to excessive hardness.
For racks that require wear resistance, high loads and high precision, DIN6 high-precision racks are an ideal choice. This type of rack is also ground after heat treatment to ensure that its parallelism is within 0.02mm, which is very suitable for mid-to-high-end CNC machine tools.
5. Spur and Helical Racks
In the design of precision racks, tooth shape is an important consideration, and common types include spur and helical. There are many standards for helical racks around the world, such as the German standard of 19 degrees 31 minutes 42 seconds, the American standard of 14.5 degrees, the Japanese standard of 15 degrees and 21 degrees 30 seconds, etc. In Taiwan, the German standard helical racks are the most common. Compared with spur racks, helical racks have a load-bearing capacity of about 20% higher at the same modulus, and they run more smoothly and with lower noise, so they are favored by engineers.
6. Finishing Processes
Finishing processes are essential to achieve the desired surface quality and dimensional accuracy. Common finishing techniques include:
Grinding: Used to refine the tooth surfaces and achieve precise dimensions.
Polishing: Enhances the surface finish, reducing friction and wear during operation.
Coating: Applying protective coatings can improve corrosion resistance and reduce wear.
7. Matching of Precision Racks and Gears
In the design of transmission mechanisms, the matching of precision racks and gears is essential. Spur racks need to be matched with spur gears, and helical racks need to be matched with helical gears of corresponding angles. It should be noted that since gears need to withstand a longer stroke during use, when selecting gears, it is recommended that their grade and hardness should be higher than racks to improve wear resistance and reduce replacement frequency, thereby reducing the downtime and maintenance time of the machine.
With the continuous advancement of rack production technology, the application scope of racks is no longer limited to the traditional X-axis, but has expanded to the transmission needs of the Y-axis and Z-axis. Especially in the context of Industry 4.0, the widespread application of robotic arms has driven the demand for transmission tracks, and the combination of racks and guide rails has become a new design trend. This design of racks and guide rails not only simplifies the installation process, but also eliminates the gap that may be generated when the two parts are assembled, improving the overall stability and precision.
Summary
Precision racks are vital components in various mechanical systems, and their manufacturing process involves careful material selection, machining, heat treatment, and finishing. Selecting the right rack requires consideration of load capacity, precision requirements, speed, environmental conditions, space constraints, cost, and supplier reputation. By understanding both the manufacturing processes and selection methods, engineers and designers can ensure they choose the most suitable precision rack for their specific applications, leading to improved performance and reliability in their systems.
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