Mechanical design is an important part of mechanical engineering, the first step in mechanical production, and the most important factor determining mechanical properties. The goal of mechanical design is to design the best machine under various limited conditions (such as materials, processing capabilities, theoretical knowledge and calculation methods, etc.), that is, to make an optimal design. Optimal design needs to comprehensively consider many requirements, generally: the best performance, the lowest manufacturing cost, the smallest size and weight, the most reliable in use, the lowest consumption and the least environmental pollution. These requirements are often contradictory, and their relative importance varies by machine type and use. The designer's task is to weigh the weight according to the specific situation and make overall plans to make the designed machinery have the best comprehensive technical and economic effect. In the past, the optimization of the design mainly relied on the knowledge, experience and vision of the designer. With the development of basic theories of mechanical engineering and new disciplines such as value engineering and system analysis, the accumulation of technical and economic data for manufacturing and use, and the popularization and application of computers, optimization gradually abandons subjective judgments and relies on scientific calculations. Different machines serving different industries apply different working principles and require different functions and characteristics.