1 The necessity of teaching reform of mechanical design course and the establishment of teaching objectives
Mechanical design course is an important professional technical foundation course for mechanical majors, with strong theoretical and high practicality, and plays the role of carrying forward and backward in the whole teaching process. The traditional teaching mode emphasizes the transmission of knowledge without paying attention to the application of knowledge and the cultivation of practical ability, and the drawbacks are becoming more and more obvious.
Therefore, it is imperative to actively study the teaching rules of the curriculum and carry out curriculum reform. Based on the implementation of the national “Excellent Engineer Training Program” [1, 2] and our university’s three educational concepts of “Great Moral Education, Great Engineering, and Great Practice”, the teaching objectives of this course are formulated based on the orientation of our university as a teaching and service university: after studying this course In other words, students are required to have the ability of general mechanical design through the study of this course, to have a certain sense of innovation and innovative design ability, and to be able to decompose the knowledge used in the design and have a deeper understanding and grasp of it.
2 Case teaching method based on teaching objectives
Under the careful planning and guidance of teachers, the case teaching method is a method that uses typical cases to mobilize students to participate in discussions and in-depth analysis and practice, to further improve their ability to identify, analyze and solve a specific engineering problem through independent thinking or collective collaboration, to cultivate students’ consciousness of linking theory to practice, and to cultivate the awareness of innovative thinking, active learning methods, communication skills and cooperation spirit. teaching method.
Therefore, the construction of the teaching content and system of mechanical design must be based on the teaching objectives of the course, based on the teaching of concepts, knowledge and methods, arrange the teaching content around the cultivation of ability, and design and refine the project cases related to the teaching content of the course. Different tasks and cases are proposed for different majors of mechanical class, so that they can be more closely integrated with the professional courses.
For example, for mechanical manufacturing majors, the analysis and design of typical machines, such as internal combustion engines, bullhead planers, belt conveyors, lathes, reducers, etc., are used as tasks throughout the teaching process to complete the overall scheme design, simple mechanical analysis, mechanism analysis and design, parts design and assembly design of products; for electromechanical majors, the analysis and design of automatic production lines and electromechanical-hydraulic integration products are used as typical tasks For electromechanical majors, automatic production line and mechatronic-hydraulic integration product analysis and design are typical tasks; for students’ lack of engineering background, they should pay more attention to concretization and life in the selection of cases in terms of learning and understanding of knowledge points.
3 Research on the implementation of case study teaching method
3.1 Combine with life, production practice and scientific research projects, select mechanical cases
When applying the case study method, students’ learning efficiency will be greatly improved if they are guided to take the initiative to think and explore the problems through appropriate questioning and the extraction of engineering cases that are closely related to life and production.
For example, when explaining the four basic types of threaded connections, the examples demonstrate the structural characteristics and applications of each type of threaded connection, and guide students to compare and find the similarities as attributes of threaded connections, and form a complete understanding of a certain type of machinery with the help of concepts.
When talking about worm gearing, the universal indexing head is used as an engineering example. The handle of the indexing head is connected to a single worm gear, and the spindle is equipped with a 40-tooth worm wheel to form a worm gear mechanism with a transmission ratio of 1:40, i.e. the handle turns one revolution and the spindle turns 1/40th of a revolution. If the workpiece is to be divided into z equal parts on the circumference, each equal part on the workpiece is 1/z circle, set the spindle rotate 1/z circle, the handle should rotate n = 40/z circle. By guiding students to carefully analyze the characteristics of worm drive, inspire students’ thinking to find out the differences and similarities between worm drive and gear drive, so as to establish the essential connection between them.
The ultimate purpose of learning mechanical design is to conduct scientific research and innovation, and the birth of each mechanical system will be accompanied by the conception of mechanical system solutions and the generation of new mechanical structures. In the teaching, we can use creative techniques in combination with our own research, and analyze and explain the birth of new things from the discovery of their shortcomings, which will have twice the effect with half the effort.
For example, combined with their own scientific research, the design of highland gap tobacco topping car and its typical structure case into the classroom teaching. In the introduction to mechanical design chapter, the basic requirements of mechanical design are explained with the design requirements of the high clearance tobacco topping car, and the general procedures of mechanical design are explained with the design process and program selection of the topping car.
In the chapter of belt drive, we show the belt drive structure in the topping suspension of the topping car, see Fig. 1, and ask students the following questions with the practical problems encountered in the development of topping suspension equipment: which type of belt is used in the belt drive? What type of belt drive does it belong to? What are the requirements for the installation and operation of this drive form? The questions not only aroused students’ curiosity and debate, but also set up the divergence point of thinking in the classroom, so that students have the space to fully express their opinions, active classroom teaching atmosphere, and in a subtle way accept the new knowledge.
Not only know the V-belt drive, but also have the most direct understanding of the half-cross drive requirements, indirectly gain practical experience, that is, the belt half-cross drive can not be reversed, should be installed so that the wide symmetry surface of one pulley through the belt winding out point of the other pulley. After such a process, students learn not only mechanical knowledge, but also how to identify problems to be solved and effective ways to conceive solutions to problems.
3.2 Adopt heuristic and interactive teaching mode and organize teaching flexibly
The teacher is the leader of teaching, and the students are the main body of teaching. In classroom teaching, the teacher should establish equal and democratic relationship with students to reach unity in thought, consciousness and action. In the teaching of mechanical design course, teachers follow the premise of students’ cognitive law, through creating a learning environment, taking inspiring questions as a carrier, making full use of the role of inspiration and nudging to arouse students’ interest in discovering and exploring problems, so as to activate students’ thinking, make students enter the mental state of conscious learning, and create an active and orderly classroom atmosphere.
In case teaching, it is important to inculcate scientific thinking, scientific method and engineering consciousness in college students and cultivate their team spirit, communication ability, independent learning ability and innovation spirit. For this purpose, flexible teaching methods must be adopted, combining classroom teaching and student group discussion. Some contents of the mechanical design course are not taught specifically, such as the chapter of keys, pins and keyless connections, the classroom lectures on the types of flat keys, characteristics, applications and design verification methods, the spline connection, pin connection, keyless connection of this part of the content is left to students to learn, and finally the teacher to make appropriate summary.
For example, when talking about rolling bearings, after introducing the types of rolling bearings and life verification calculation with multimedia courseware, questions are raised: How to choose the type and model of bearings in the reducer during the design of belt conveyor system? How to position the bearings? How to prevent the axial runout and the shaft from jamming after heating? How to adjust the bearing clearance? How to install and disassemble the bearings? Through the mechanical design “Design and Analysis of Shaft System Components” laboratory class, students analyze the structure and dimensions of each part of the shaft system, and the suitability of each part of the shaft for mounting, positioning and fixing, etc., and make a written report. Students gain a sense of accomplishment while using their own initiative. And at the appropriate time in the classroom, a mechanical design course assignment is assigned: after studying the course, a simple mechanical product report with a complete design process is submitted.
3.3 Combination of modern education technology and traditional teaching methods, do not rely on multimedia
Multimedia teaching is an important tool of modern education. Through multimedia presentation, it can greatly stimulate students’ learning interest, facilitate the breakthrough of teaching difficulties, improve students’ learning enthusiasm, and thus improve learning efficiency .
For example, to teach the structure of roller chain, first show the roller chain with physical pictures and set questions: What are the main parts of roller chain? How are they connected to each other? At this point, students who have a lot of experience in life and have disassembled and assembled chains will speak actively, but most of them are not very clear about the specific structure of the chain.
At this time, we will demonstrate the formation of chain links in the form of animation: the outer link is formed by the interference between the outer chain plate and the pin, the inner link is formed by the interference between the inner chain plate and the sleeve, and the gap between the inner and outer links forms a link, i.e. the hinge. The animation has a first and second, demonstrating the process of connection formation and assembly, and the parts are color-coded and clear at a glance.
At this time, multimedia plays an incomparable advantage of traditional teaching methods, and because of this, some teachers rely too much on multimedia in teaching, a large amount of information in a short period of time, resulting in students often can not grasp the focus, the main and secondary, the teaching content is forgotten after, the teaching effect is often unsatisfactory.
Therefore, in the process of multimedia courseware design and use should do the following.
(1) to focus on updating cutting-edge information, but also to consider the students’ knowledge reserves and cognitive level.
(2) multimedia courseware should be colorful, not all text, pictures, videos and animations should be used appropriately.
(3) pay attention to the combination of traditional teaching tools such as the board, some formulas for the necessary board derivation, important concepts, conclusions written on the blackboard, as a summary of the role. In addition, the use of multimedia and board books should be used more or less to maximize the impression of students and optimize the teaching effect.
Teaching practice shows that the case teaching method has the characteristics of vivid, intuitive, and closely related to the actual situation, etc. In the teaching of mechanical design, as long as the mechanical case is carefully selected, flexible teaching methods and the use of modern media technology can well solve the problems encountered in traditional teaching, can effectively combine classroom teaching, innovative theory and practice, can fully mobilize students’ enthusiasm for learning, improve students’ It can fully mobilize students’ learning enthusiasm, improve students’ practical hands-on ability and exploration, cooperation and innovation ability, and achieve the established teaching objectives of mechanical design course reform.