CNC Machine Tool and Metal Cutting Principles and Tools Course

Principles of CNC Machine Tool and Metal Cutting and Integration of Course Content and Teaching Reform

Guan Fangfang Wang Mulan Yuan Qin Nanjing Institute of Technology Nanjing 211167

Abstract: According to the training objectives and requirements of mechanical design and manufacturing and automation majors in applied undergraduate colleges, the main problems in the teaching process of the two courses of CNC machine tools and metal cutting principles and tools are analyzed in depth. On this basis, guided by the concept of large engineering education, the original two courses of teaching content were integrated and optimized, adjusted to CNC machine tools and tool systems, increased practical teaching content, reduced the total number of hours, and advanced education Teaching concepts and teaching methods are introduced into all teaching links. Finally, the integrated curriculum teaching and possible problems are discussed.
Keywords: CNC machine tools; metal cutting principles and tools; CNC machine tools and tool systems; large engineering concept; teaching reform

The educational concept of "big engineering concept" was put forward in the wave of "return engineering" set off by the engineering education circle in the United States in the 1990s. In 1994, the direction of engineering education reform proposed by Dean Joel Moses of the Massachusetts Institute of Technology (MIT) Engineering Institute was to make engineering education based on disciplines pay more attention to engineering practice and the systematic and completeness of engineering itself . It is mainly aimed at overly emphasizing the specialization and scientization of traditional engineering education, thus cutting off the phenomenon of engineering itself. The so-called "big engineering concept" refers to the comprehensiveness and systematicness of the curriculum system, that is, the integration of various courses of knowledge, technology, ability and methods required by students in future engineering activities; the large engineering concept curriculum system "Engineering" refers to practical and innovative teaching links, such as experiments, internships and graduation design courses. The essential characteristics of higher engineering education are comprehensive, systematic, practical and innovative combination.

CNC machine tool is a main professional course of mechanical design, manufacturing and automation. It mainly introduces the mechanical structure of CNC machine tools, including the main transmission system and its structure, the machine tool feed transmission system and its structure, machine tool guide rails and supports, machine tool auxiliary devices and Its structure, machine tool accuracy and inspection. The teaching purpose of the course of metal cutting principles and tools is to enable students to understand the basic principles of metal cutting and the composition, structure and selection of various commonly used standard tools. Through the teaching of these two courses, it lays a good foundation for learning the related courses and new professional knowledge and solving the problems of CNC machine tool mechanical structure and tool technology in the future work.

1. Current situation analysis

CNC machine tools are equipment for metal cutting, and tools are indispensable tools for metal cutting. The two are closely related. From the perspective of the curriculum system, the latter is one of the basic courses that must be taken before learning. According to the teaching practice of these two courses for many years, the principles and tool system of CNC machine tools and metal cutting are re-examined from the perspective of the overall and systematic perspective of the large engineering concept. It is not difficult to find that there are still some problems that need to attract enough attention:

1. The curriculum lacks holistic and systematic

The content of the two courses is relatively self-contained and lacks the necessary connection and transition.

2. Course content is old

For example, the classification, model and transmission chain of ordinary machine tools are a bit outdated compared to CNC machine tools, and need to be updated in time. Part of the course content is not very relevant to the training objectives and should be deleted.

3. Insufficient practice teaching

In the CNC machine tool course, a total of 48 hours, all of which are theoretical teaching, there is no in-class experiment, especially the lack of students' active practice.

The above curriculum system is difficult to meet the needs of students' engineering awareness and practical ability training. Therefore, the reform of the teaching of these two courses, especially the reform of the course content, is imperative.

2. Optimize knowledge structure and integrate teaching content

1. The relationship between courses

CNC machine tools and metal cutting principles and tools are the main professional courses of mechanical design, manufacturing and automation. The relationship between the main courses and teaching links involved in this knowledge module is shown in Figure 1.

2. Integrate course content

Starting from the need to foster students' large engineering awareness, re-examine the syllabus of CNC machine tools and metal cutting principles and tools, study the contents of the textbook, optimize the original knowledge structure, and integrate the two courses into one The course name is adjusted to CNC machine tools and tool systems, forming a new comprehensive course that focuses on the mechanical structure of CNC machine tools, including metal cutting principles and CNC machine tool systems.

The integrated course system includes three parts: the mechanical structure part of the CNC machine tool, the metal cutting principle part and the CNC machine tool system part. After the integration of the first part, the content includes the introduction of CNC machine tools, the structure of CNC lathes, the structure of CNC milling machines, the structure of CNC machining centers (including turning centers, machining centers, etc.), the structure of CNC special processing machine tools and the accuracy inspection of CNC machine tools. Delete the original content The small ordinary machine tool structure and the difficult machine tool design part content, at the same time appropriately increase the current more advanced content, such as electric spindle and linear motor, etc., add more comprehensive content, such as CNC machine tool accuracy inspection and test machine, etc. . The second part of the teaching content has deleted the parts of the basic theory of the cutting process that are more difficult to understand or the mechanism is not yet clear, highlighting the basic concepts and practical applications. The third part of the teaching content deletes the tool angle conversion and non-standard tool design, and adds advanced tool selection and application examples and CNC machine tool system parts (including CNC lathe tool systems and CNC boring and milling machine tool systems).

3. Practical teaching link arrangement

In the practical teaching, the mechanical structure part of the CNC machine tool arranged a week-long CNC machine tool surveying and mapping practice before the course. Through the understanding and mapping of the specific CNC machine tool, the students already have a certain sensibility to the main mechanical structure components of the CNC machine tool. After the course, a mechanical assembly internship is arranged. It is the only important practical teaching activity for students of this major to participate in production in enterprises. Through a week of internship and life in the enterprise, understand the entire production process of CNC machine tool mechanical parts from casting to assembly, personally learn and learn CNC machine tool mechanical assembly, including scraping, hole matching, bearing and ball screw installation, adjustment and measurement accuracy, etc. It will enable students to have a deeper understanding of the mechanical structure and accuracy inspection and acceptance of the main components of CNC machine tools, as well as master certain assembly skills, which will lay a solid foundation for CNC machining and maintenance work after graduation.

In addition, two in-class experiments are arranged. One is the machine tool accuracy correction experiment. In the practice workshop, students can choose a CNC machine tool at will, use the laser interferometer to detect the machine tool accuracy, and analyze it. The other is the tool geometry angle experiment. The goniometer measures the geometric angle of commonly used tools and has an intuitive understanding of the commonly used tools on CNC machine tools. Through these two experiments, students can improve their hands-on ability and cultivate their ability to solve analytical problems.

4. Overall solution

After the above adjustments, it conforms to the general teaching laws, which is conducive to students' understanding and learning, and at the same time strengthens the practical content. In terms of class hours, due to the deletion of a large number of chapters with little relevance and difficult to understand theories, the total amount of theoretical class hours after the integration was greatly reduced. The original two courses totaled 96 hours, and the integration was 48 hours, which further eased The contradiction between more theoretical teaching content and less class hours. The integrated curriculum knowledge structure is shown in Figure 2.

3. Using modern teaching methods to improve teaching quality

Curriculum teaching reform should also focus on the reform of teaching methods and methods. Using modern teaching methods is a necessary guarantee to improve the teaching quality of the course. The reform should be conducive to strengthening the cultivation of students 'self-learning ability, analyzing problems and solving problems, and the cultivation of students' innovative thinking and innovative ability. Teaching has methods, but there is no fixed method. It is also one of the main contents of the curriculum reform to continuously explore teaching methods that are conducive to improving teaching effects and quality.

1. Multimedia teaching

In the course teaching, the use of multimedia teaching methods, make full use of teaching methods such as models, objects, slides, videos, multimedia, etc. to visualize and vividize some abstract concepts in the teaching content, solving the teaching that is difficult to explain directly in words and language content. For example, when teaching the concept of tool geometry angle, students are generally more difficult to understand because of the abstraction. They can explain each terminology and concept through a scaled-up wooden model. Pro / E three-dimensional software can also be used to draw the three-dimensional graphics of the tool, so that the tool structure can be displayed in multiple directions, and the labeling of each geometric angle of the tool can be displayed intuitively and accurately through the cross-sectional view. When teaching a variety of multi-tooth tools (such as drills, milling cutters) and other more complex tool structures, the use of usually taken physical photos and processing videos and the use of three-dimensional software designed three-dimensional graphics of the tool to assist teaching, greatly improving the students' learning Interest also makes more complex content intuitive and simple, easy for students to accept, and the teaching effect is significantly improved.

2. Adopt virtual reality technology to assist teaching

Virtual Reality Technology (VRT), which has developed rapidly in the past 20 years, is a computer system that can create and experience virtual worlds. The virtual world here is also called a virtual environment, which refers to a three-dimensional figure with a sense of reality. It can be a real reproduction of a specific real world, or it can be a purely imagined world. With some special equipment, the operator can interact with it naturally through sight, hearing, touch, etc., thereby creating a sense of immersion.
In the teaching of CNC machine tool mechanical structure, there are more theoretical studies and fewer practical operation opportunities; CNC machine tools with the opportunity to see the mechanical structure is complex and bulky, and the product details and internal structure cannot be observed, which also brings to the understanding of its content. Certain difficulties, the teaching effect is not obvious.

To this end, make full use of the software installed in the laboratory to create a virtual reality environment to assist teaching, systematically establish a realistic three-dimensional interactive machine tool model, and simulate the visual effects of the machine tool from all angles (including the display of internal structure principles) ). For example, each component and assembly process of a CNC machine tool is dynamically displayed, so that students can proficiently understand the internal structure of the machine tool and can skillfully complete the disassembly and assembly of the machine; fully simulate the dynamic process of the operation of the CNC machine tool and demonstrate the operation , Students want to observe which part of the machine tool can clearly see which part, in the first time to understand the working principle of the machine tool. Students have such a personal experience, so that the complex and abstract CNC machine tool structure becomes intuitive and easy to understand, and the teaching effect is significantly improved. The operation interface of Chuangyi virtual machine is shown in Figure 3.

3. Assist teaching by establishing teaching websites

After all, classroom teaching time is limited. In order to give students more learning opportunities, a teaching website can be established to allow students to study online after class. Teachers can also put teaching resources such as the curriculum syllabus, courseware and related auxiliary materials on the school curriculum teaching webpage. Students can download and watch at any time, and establish forums. Teachers can answer students ’questions in time, thus forming a benign interactive situation.

4. Conclusion

Through the optimization and integration of CNC machine tools and metal cutting principles and the content of tool courses, the relationship between the course contents is straightened out, and the teaching efficiency is improved. The use of advanced teaching methods has enhanced students' interest in learning about CNC machine tool knowledge modules and greatly improved the quality of teaching. During the implementation process, I also encountered some specific problems, such as the reduction in the amount of class hours after integration, but the necessary teaching content cannot be deleted, and the teaching requirements cannot be reduced. This requires teachers to be able to make a reasonable teaching plan and effectively complete the teaching within the specified time task. Secondly, the teaching experiment conditions must keep up. This is the basic guarantee for learning this course well. If the CNC machine tool experimental equipment is insufficient, it will cause students to fail to achieve the expected results in the teaching practice.

References [1] Wang Mulan, Zhu Xiaochun, Liu Kun, etc. Case Teaching to Cultivate Major Engineering Awareness of Automation Majors [J]. China Modern Education Equipment, 2008, 12: 165 ～ 167
[2] Wang Xuefeng, Cao Rong. Large engineering concept and higher engineering education reform [J]. Higher Engineering Education Research, 2006, 4: 19 ～ 22
[3] Zhang Junsheng. Metal cutting machine tools and CNC machine tools [M]. Beijing: Mechanical Industry Press, 1996
[4] Lu Jianzhong, Sun Jianing. Metal Cutting Principles and Tools (Fourth Edition) [M]. Beijing: Machinery Industry Press, 2005

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