Surface roughness is an important technical indicator reflecting the micro-geometric error of the surface of the part, and it is the main basis for inspecting the surface quality of the part; the rationality of its selection is directly related to the quality, service life and production cost of the product. There are three methods for selecting the surface roughness of mechanical parts, namely calculation method, test method and analogy method. In the design of mechanical parts, the most common application is the analogy method, which is simple, fast and effective. The application of the analogy method requires sufficient reference materials, and comprehensive information and literature are provided in various existing mechanical design manuals. The most commonly used is the surface roughness that is compatible with the tolerance class. Under normal circumstances, the smaller the dimensional tolerance of mechanical parts is, the smaller the surface roughness value of mechanical parts is, but there is no fixed functional relationship between them. For example, the modified surfaces of some machines, handles, handwheels on instruments, sanitary equipment, and some mechanical parts on food machinery are required to be processed very smoothly, that is, the surface roughness is required to be high, but the dimensional tolerance requirements are very high. Low. In general, for parts with dimensional tolerance requirements, there is still a certain correspondence between the tolerance level and the surface roughness value.  

Examples

In some mechanical parts design manuals and mechanical manufacturing monographs, there are many introductions to the experience and calculation formulas of the relationship between the surface roughness of mechanical parts and the dimensional tolerance of mechanical parts. , you will find that although the exact same empirical calculation formula is adopted, the values ​​in the list are not the same, and some are quite different. This creates confusion for those unfamiliar with the situation. It also increases the difficulty of choosing surface roughness for their work on mechanical parts. In actual work, for different types of machines, the parts have different requirements for surface roughness under the same dimensional tolerance. This is the stability of the cooperation. In the design and manufacture of mechanical parts, different types of machines have different requirements on the stability and interchangeability of their parts.  

Material application

As a mechanical designer, you must understand the industrial development trend when selecting materials. According to national standards, combined with my country's resources and production conditions, comprehensively consider materials and select materials from the actual situation. The most commonly used materials in mechanical manufacturing are steel and cast iron, Followed by non-ferrous metal alloys. Non-metallic materials such as plastics, rubber, etc. also have unique use value in machinery manufacturing.