I. INTRODUCTION <br> <br> mechanical design school I machinery of the professional basic course. At the same time, the course is also a basic compulsory course for engineering majors. In terms of teaching content, this course focuses on basic knowledge, basic theories and basic methods, and focuses on the basic training of designing and designing skills in cultivating practical skills. In this course, we will comprehensively apply the relevant knowledge and skills learned in the pre-requisite course, combine various teaching practice links and the basic exercise of course design, and lay the foundation for a smooth transition to study related professional courses and professional graduation design.
The mechanical design course design is an important teaching practice session for mechanical and near-class students after completing mechanical design and similar courses. It is also the first time that students have more comprehensive and standardized design training mechanical design teaching. Important practice links. Its main purpose is to cultivate students' theoretical and practical design skills, train students to comprehensively apply the basic theories of mechanical design courses and other pre-requisite courses, and combine the actual production to analyze and solve practical problems of engineering, consolidate, deepen and expand students' relevant Knowledge of mechanical design; through the design of general mechanical transmission or simple machinery, students can master the procedures and methods of general mechanical design, establish correct engineering design ideas, and cultivate independent, comprehensive and scientific engineering design capabilities; In practice, students are trained in designing basic skills to develop students' ability to access and use standards, specifications, manuals, atlases, and related technical materials, as well as computing, mapping, data processing, and computer-aided design capabilities.
Based on the above understanding, combined with the reform of the mechanical design curriculum system, course content and three-dimensional teaching mode and the construction of key courses in recent years, in the design of the two-year student mechanical design course and graduation design practice, mainly from the design of mechanical design course design The reforms and practices of methods and means have been carried out, and the transition from manual drawing to 2D AUTOCAD application to 3D CAD/CAE has been gradually implemented. It has played a positive response among students and improved the design of students. The ability and overall quality have achieved good results.
Second, the status of mechanical design practices and problems <br> <br> For centuries, people use hand drawings to express their design ideas. As the language of the engineer, the drawings bring great convenience to the effective communication between engineering and design personnel. However, with the development of science and technology, especially the wide application of computer technology, manual drawing can no longer meet the requirements of mechanical design. Nowadays, mechanical design has shifted from manual drawing in the 1970s to computer graphics, greatly improving drawing efficiency and drawing quality.
At present, CAD technology is mainly represented by two-dimensional drawing software AUTOCAD. In the mechanical design practice, only students are taught to operate and draw simple parts drawings. It is very inconvenient and difficult to draw assembly drawings and perform related engineering analysis with AUTOCAD. . To this end, in order to be able to easily draw the assembly drawing, CAXA electronic drawing plate, open eye CAD and other two-dimensional drawing software are gradually used as drawing tools in the mechanical design practice teaching and graduation design to assist in the design of parts. Figure 1 shows a two-dimensional assembly drawing of a gear shaft drawn with AOTUCAD. At present, China's manufacturing industry has fully completed the slab drawing project. The popularization of 2D CAD technology has ended the history of manual drawing, which has played an obvious role in reducing the labor intensity and improving economic efficiency. With the development of technology, CAD technology is transitioning from 2D CAD to 3D CAD. A considerable number of CAD applications have completed the conversion from 2D CAD to 3D CAD, and have achieved great economic and social benefits. Enterprises need to master the professional talents of 3D CAD/CAE technology, mastering 3D CAD/CAE technology has become the most basic requirement for engineering graduates. Therefore, the use of three-dimensional CAD/CAE technology in the teaching of mechanical design practice has become an important content of our current mechanical design practice teaching reform and an urgent problem to be solved.
Figure 1 2D assembly drawing of the reducer shaft
Third, the three-dimensional CAD / CAE key technologies <br> <br> three-dimensional CAD modeling technology, also known as modeling technology, which is the core CAD technology. The research, development and application of modeling technology represent the research, development and application of CAD technology. From the 1960s to the present, the development of 3D modeling technology has experienced wireframe modeling, surface modeling, solid modeling, feature modeling, parametric modeling, variable modeling, and product integration being studied today. Development process such as modeling and behavior modeling. 3D CAD is based on 3D modeling, and as long as a 3D model is formed, various 2D views are at your fingertips. The 3D CAD/CAE technology brings revolutionary breakthroughs in product 3D modeling, virtual matching, engineering drawing generation, dynamic interference testing, mechanism motion analysis and dynamic simulation, finite element analysis, etc., improving design efficiency and design quality. . The true meaning of 3D design is not only the design of the model itself, but the post-processing of the model. Its basic idea is shown in Figure 2.
Figure 2 CAD/CAE key technologies
Figure 3 shows the three-dimensional virtual assembly model of the cylindrical gear reducer, and Figure 4 shows the three-dimensional virtual assembly explosion model of the cylindrical gear reducer. Figure 5 shows the finite element analysis model of the gear shaft of the reducer.
Figure 3 3D virtual assembly model of cylindrical gear reducer 
Figure 4 Three-dimensional virtual assembly explosion model of cylindrical gear reducer
The 3D CAD/CAE technology mainly includes the following contents: 3D modeling/3D design, computer aided engineering analysis, mechanism motion analysis/simulation, assembly interference inspection, 3D to 2D, pattern file management, etc. After completing the design using this full-process 3D CAD/CAE system, not only the geometry and performance of the design object can be met, but also the indicators (strength, stiffness, weight and cost) of all aspects are optimized. It is the fundamental purpose of computer-aided design and auxiliary engineering analysis. 3D CAD/CAE meets the designer's thinking habits and can fully utilize the designer's creativity and imagination. 3D CAD/CAE technology not only solves the problems of product design and engineering drawing, but more importantly, realizes virtual design, motion simulation and optimization design of products by using 3D CAD/CAE technology. The 3D parts produced can be directly connected with CAE/CAM. CIMS technology such as /CAPP for data exchange and convergence is one of the key technologies for realizing no-pattern production in the future, and is an important means to realize virtual manufacturing. Mastering the use of 3D CAD/CAE technology has gradually become a basic skill for product development and design personnel, just like using computer for word processing.
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