A paper on mechanical systems

Mechanical drawing is a very important basic course for mechanical majors in higher vocational colleges, and the quality of mechanical drawing teaching directly affects students' career. The following is the content of the paper on mechanical drawing that I collected for you. Welcome to read the reference!

Mechanical Drawing Paper 1 Teaching Reform and Practice of Mechanical Drawing Surveying and Mapping

Mechanical drawing is of great significance in equipment maintenance, transformation, imitation of products and improvement of technical data, and it is a basic skill that engineers and technicians must master. Higher vocational colleges should strengthen training in this field. Part mapping is a process in which students comprehensively apply what they have learned to solve practical problems, which is of great significance for cultivating applied and skilled talents who can adapt to the front line of production. Based on many years' teaching practice of surveying and mapping, the author analyzes the problems existing in the teaching of mechanical drawing surveying and mapping, and puts forward some suggestions for improvement to improve the teaching effect of students' surveying and mapping training.

Keywords: mechanical drawing; Improve the teaching effect; Ability training

With the rapid development of China's social economy, the requirements for professional ability are gradually improved, and the comprehensive degree of requirements for employees' professional ability and social ability is also improved accordingly. Higher vocational colleges undertake the training of vocational skills practitioners in China at present. In order to meet the needs of society, higher vocational education should be employment-oriented and service-oriented, and cultivate strong practical skills and abilities. Go straight to work? Applied skilled talents.

Mechanical mapping is of great significance in equipment maintenance, transformation, imitation of products and improvement of technical data, and it is a basic skill that engineers and technicians must master. At present, many higher vocational colleges conduct spot checks on students' skills, and the drawing course mainly focuses on students' drawing and surveying and mapping abilities. Therefore, higher vocational colleges should strengthen this training. Based on many years of surveying and mapping teaching practice, the author talks about how to do a good job in mechanical drawing surveying and mapping teaching.

First, the current problems in surveying and mapping training

1. Drawing and survey guidance is too simple.

Our original surveying and mapping instruction mainly includes: the purpose and task of surveying and mapping, the content and requirements of surveying and mapping, the arrangement of surveying and mapping process, the schematic diagram of parts, the surveying and mapping methods and steps of main parts, and the assessment method. However, the use of surveying and mapping tools, the matching accuracy of parts, surface roughness, shape and position tolerance and technical requirements are not explained, and these contents are scattered in various chapters of surveying and mapping textbooks, so it is difficult for students to form a systematic understanding. Some students don't know how to use measuring tools and dimensions after sketching parts, and don't know how to formulate technical requirements for products.

2. Ignore the importance of sketches

Part sketch is the basis of drawing part drawing, and sometimes it is directly used to process urgently needed parts. Therefore, the sketch of the part is exactly the same as the part drawing except that it is hand-drawn and does not need to strictly abide by the proportional relationship. However, in surveying and mapping, some students always think that the part drawing and assembly drawing drawn with a ruler compass are important, while the hand-drawn part sketch is not important, just a sketch. Therefore, the selection of view expression scheme, the labeling of dimensions and the labeling of technical requirements are arbitrary, which affects the quality of assembly drawings and parts working drawings.

3. Incomplete and unreasonable size.

In surveying and mapping, whether students mark dimensions on assembly drawings or parts drawings, there will be missing or repeated labeling. In addition, the selection of dimension datum is unreasonable, the important dimensions are not given directly, and the dimensions of related parts are inconsistent.

4. Unreasonable labeling of technical requirements

In surveying and mapping major, it is often difficult for students to put forward reasonable technical requirements due to the lack of knowledge and practical experience in manufacturing and processing technology. The marked surface roughness, dimensional tolerance, shape and position tolerance, heat treatment, etc. often do not meet the requirements of parts function and assembly, and there are many errors.

5. Relevant manuals and materials are not in place.

In part surveying and mapping, students must consult manuals and materials after sketching parts by hand, and choose appropriate dimensional tolerance, shape and position tolerance, surface roughness and metal materials. When surveying and mapping common parts and standard parts, we should consult the relevant national standards and correctly determine the relevant dimensions and structural parameters of the parts. However, due to the limited teaching hours of the previous drawing class, the students' usual practice is insufficient, the standards and related parameters listed in the appendix of the textbook are limited, the students have not been fully exercised, and their ability to consult documents is not strong. As a result, some students download similar parts online and copy them directly without thinking, and some even copy them directly, which is extremely unfavorable for cultivating students' engineering concept and strengthening engineering literacy, and also fails to achieve the due teaching effect.

6. The roles of teachers and students are not in place.

In the past surveying and mapping practice, most teachers were still the leaders of surveying and mapping practice courses. In reality, teachers mainly lecture and guide, and students' participation is low. The atmosphere in the whole surveying and mapping process is rather dull, and students' plagiarism is serious, which is extremely unfavorable for cultivating students' practical ability and comprehensive analysis ability.

7. The evaluation method of surveying and mapping results is unreasonable.

The traditional method of evaluating grades is mainly to give grades according to the quality of sketches, working drawings and drawings drawn by assemblers handed in by students. This kind of thinking, which only pays attention to the results and ignores the process, can't fully reflect the students' real engineering surveying and mapping ability, can't feedback the surveying and mapping effect, and also makes the plagiarists take advantage of the loopholes, causing students to complain about the negative psychology of unfair assessment and can't mobilize students' learning enthusiasm.

Second, measures to improve the teaching effect of mechanical drawing surveying and mapping week

1. Improve the teaching of drawing and surveying.

In order to cultivate students' ability to analyze and solve problems independently, and complete the task of component mapping on time with good quality and quantity. We revised the teaching of Drawing and Measurement, adding basic requirements, precautions, general principles of view selection, drawing steps, dimensioning methods, material selection, dimensional tolerance selection, surface roughness and shape and position tolerance selection, as well as common measuring tools, common methods of measuring parts, related tables, national standards and common mistakes, which is more convenient for students to check and correct by themselves and improve learning efficiency.

2. Strengthen students' ability to draw sketches of parts by hand.

In production practice, hand-drawn sketches are needed to discuss design schemes, technical exchanges, field visits and other occasions limited by site conditions or time. Hand-drawing is the basic skill for engineers and technicians to conceive and design.

Hand-drawing ability is of great benefit to cultivate students' graphic observation and thinking ability, especially to cultivate students' practical ability. Therefore, in the process of surveying and mapping, students should strengthen the training of freehand drawing, strictly control the quality of surveying and mapping, and incorporate the results of sketch into the final evaluation results, which will attract students' attention.

3. Pay attention to and strengthen the training of dimensioning.

Dimension marking is an important content and a difficult point in surveying and mapping teaching. Therefore, teachers should take advantage of the opportunity of surveying and mapping to explain the method of dimensioning parts to students in time, and focus on asking students to master the selection of dimension datum in surveying and mapping, understand the roundness of dimensions and the selection of tolerance, and learn to find relevant information and determine parameters. Teachers play a leading role in this link, guiding students to correctly mark dimensions on part drawings and assembly drawings.

The dimension of the part drawing should be correct, complete, clear and reasonable, and can meet the design requirements and process requirements. When dimensioning, students are required to do the following: ① Choose the appropriate dimension datum from the design requirements and process requirements, and don't label it as a closed dimension chain. (2) Dimensions should be marked as far as possible outside the view and between the two views. (3) The dimension datum of parts connected with two parts should be unified. (4) For standard structures, such as threads, unloading grooves and gears, the measurement results should be checked with the standards and the standard values should be adopted. ⑤ Important dimensions, such as fitting dimensions, positioning dimensions, dimensions to ensure working accuracy and performance, etc. , should be directly marked. ⑥ The dimensions should be easy to process and measure. The size of the assembly drawing is different from that of the part drawing. It is not used to directly process parts, so it is not necessary to write down all the dimensions of each part, only the dimensions related to assembly, inspection, installation and use requirements. Dimensions in the assembly drawing can be roughly divided into the following categories: performance (or specification) dimensions, assembly dimensions, installation dimensions, overall dimensions and other important dimensions. These five dimensions need to be marked according to the structure of the assembly, and not all assemblies have these five dimensions.

4. Reasonable selection of technical requirements

In part surveying and mapping, it is often difficult for students to formulate reasonable technical requirements because of their lack of practical experience in production and knowledge of machining technology. This requires teachers to guide students to observe and analyze interrelated parts in part mapping, so as to obtain the perceptual knowledge of common mechanical structures with true and correct representations. For example, in order to have interchangeability, it is necessary to give appropriate dimensional tolerance and surface roughness requirements for parts with matching relationship. Some parts are required to be both wear-resistant and impact-resistant, and heat treatment is often required. Correct selection of parts materials requires familiarity with the properties of commonly used metal materials, so teachers should guide students to correctly mark technical requirements from the following aspects:

(1) material selection.

The selection of parts materials can be determined according to the analysis of physical objects and related standards and manuals. Commonly used metal materials are carbon steel, cast iron, copper, lead, aluminum and their alloys. Refer to the materials of the same type of parts and determine by analogy.

(2) Selection of surface roughness.

The surface roughness grade of parts can be determined according to the working requirements and precision grade of each surface, and can be compared and determined by referring to the roughness requirements of similar parts or using roughness templates. Generally speaking, the surface roughness of contact surface, surface with relative motion, surface bearing periodic load, corrosion-resistant surface or surface requiring sealing is higher.

(3) Selection of shape and position tolerance.

Shape and position errors will affect the working accuracy, connection strength, motion stability, sealing and service life of machines or instruments, especially for parts that often work under high temperature, high pressure, high speed and heavy load conditions. For example, in the cooperation between the hole and the shaft, due to the shape error, the gap distribution will be uneven, and the local wear will be accelerated, thus reducing the life of the parts; For interference fit, the amount of interference is inconsistent everywhere. In general, if there is no special requirement, shape and position tolerances are not marked.

(4) Selection of dimensional tolerance and fit.

The choice of dimensional tolerance and fit is the design of dimensional accuracy when the basic dimensions have been determined, and it is a reasonable choice of reference system, tolerance grade and fit type. The principle of its selection is to obtain the best technical and economic benefits on the premise of meeting the requirements of use. We usually use analogy method in surveying and mapping, refer to the tolerance fit of similar parts, determine through analysis and comparison, and reasonably choose tolerance fit, which can promote interchangeable production, improve product quality and reduce production cost.

5. Cultivate students' ability to consult materials and manuals.

Students are future engineers and technicians, and their ability to consult materials and technical manuals should be cultivated. In surveying and mapping, students should not ask questions first, but should check and consult standards, textbooks and manuals first. For example, there are bolt connection, pin connection and gear transmission in gear oil pump. These structures require students to consult relevant manuals and determine relevant parameters to ensure the correctness of parts size and structure. This kind of training lays a foundation for students to take up their jobs and finish their work independently in the future.

6. Change the roles of teachers and students and take students as the center.

Drawing mapping is a practical link after studying the basic theory of mechanical drawing in an all-round way, in order to cultivate students' comprehensive application ability and practical ability in the course of mechanical drawing. Therefore, in the whole teaching and training process, we should always insist that students are in the main position, and teachers only play a guiding role. Don't cover everything from typesetting to drawing, so that students lose their initiative.

In surveying and mapping, teachers should make students do more, think more and explore more as far as possible, encourage students to find and solve problems by themselves, and teachers should give appropriate guidance. For example, how to disassemble parts and draw assembly sketches, how to measure dimensions, how to determine the expression scheme of parts, how to consult technical data, how to draw parts and assembly sketches better, etc. These contents are all organized and discussed by students themselves, analyzed and studied, consulted materials and completed by themselves, while teachers play a more important role in counseling, guiding, advising, finding mistakes and proposing suggestions for revision. This can cultivate students' practical ability, comprehensive analysis ability and teamwork spirit.

7. Reform the assessment methods of surveying and mapping training to improve the quality of surveying and mapping.

The purpose of surveying and mapping practice examination is to test students' mastery of the knowledge and skills they have learned, and also to evaluate the teaching effect of teachers. Teachers should change the practice of evaluating students only according to the drawing quality of assembly drawings and parts drawings, and adopt the method of combining process assessment with homework assessment to formulate a more scientific and reasonable surveying and mapping assessment system, which is very important to improve the practical training effect of students. The author believes that students can be evaluated from the following aspects:

(1) process evaluation. In the process of guiding surveying and mapping, teachers should make detailed records of students' learning attitude, surveying and mapping progress and attendance, and then give points in proportion.

(2) Ask questions for assessment. In the teaching process of each project, students' ability to master, understand and apply theoretical knowledge is examined through discussion and questioning, and records are made; Students use one-to-one scoring method for part sketches. By asking questions, students' ability to independently complete drawings and find information can be assessed. At the same time, it can also help students to check and fill gaps, effectively curb plagiarism and mobilize students' enthusiasm for learning.

(3) job evaluation. Mainly to review the assembly drawings and parts working drawings handed in by students. Teachers should list scientific and reasonable grading standards, give a fair evaluation of each student's labor, and fully affirm the students' labor achievements.

(4) National defense assessment. After surveying and mapping, professional teachers will form a defense team to give students a defense and comprehensive performance assessment, and ask students to describe the whole surveying and mapping process, talk about their own learning experience, and then answer some professional questions and answers. The teacher will give some grades according to the defense.

All-round assessment of students and evaluation of comprehensive scores can make drawing really effective.

8. Add some surveying and mapping training content.

For students with good grades and quick drawing, CAD can be used to draw working drawings of parts, which can keep their strong interest in learning and make the content of surveying and mapping practice more comprehensive.

By reforming traditional practices and optimizing surveying and mapping teaching, a good environment for students to integrate theory with practice has been created, which not only improves students' drawing ability, drawing reading ability, surveying and mapping ability and data access ability, but also cultivates students' work style of unity, cooperation, hard work, good analysis and meticulous work, laying a good foundation for future professional course study and production front-line work.

References:

Jiang Dayuan. New Theory of Vocational Education Research [M]. Beijing: Education Science Press, 2007.

[2] Ye Xiaoping, Hu Xiaoping. Strengthening the Teaching of Surveying and Mapping Week to Cultivate Students' Engineering Quality [J]. Journal of lishui university, 2009(5).

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