Song, School of Mechanical Engineering, Beihang University
The fierce second national numerical control skill competition has ended. It can really be said that "the smoke disappears and the prize is returned to the original owner." When everyone is talking about their achievements and taking stock of their rankings happily, I, as one of the main proposers of the theoretical test paper and the referee of the practice competition, feel that this competition deserves our careful summary and aftertaste.
The proposition group of this theoretical competition consists of several professors, senior engineers, senior technicians and senior lecturers. They are not only the proposers of the numerical control contest, but also the proposers of the distance education examination for numerical control technicians of the Ministry of Labor and Social Security. According to the proposition experience of numerical control technicians, these experts began to brew this test question after the first national numerical control skill competition. By summing up the experience of the examination proposition of CNC technicians and the theoretical examination proposition of the first CNC skill competition, combined with the newly promulgated national professional standards for CNC operators, after two years of repeated discussions, the final draft was finally formed and approved by the organizing Committee of the competition.
The proposition principles of the test questions in this theoretical competition are: following the principles stipulated by professional standards; The principle of integrating theory with practice; Focus on the principle of basic knowledge of NC machining; The principle of making up for the deficiency of practical examination.
First, follow the principle of professional standards.
On the theoretical test questions, strictly follow the knowledge scope and proposition required by professional standards. Students follow the requirements of senior workers, and workers and teachers follow the requirements of technicians.
The range of proposition is the basis of examination paper. It is also the basis of all players' learning theory. If the examination questions exceed the requirements of professional standards. Then the proposition will fail and the test results will be meaningless. Therefore, in the future, all vocational colleges should seriously study the professional standards and carry out and implement the requirements of professional standards in NC teaching practice.
Second, the principle of integrating theory with practice.
In this theoretical contest, the biggest feature is to integrate theory with practice. Many problems come from production practice. The content of these topics is very theoretical, but they all ask questions according to the phenomena in production and processing, so that players can make choices or make answers.
For example, the following contest topics:
In metal cutting, the chip color can reflect the temperature in the cutting process, which is helpful to judge whether the cutting parameters are reasonable. When processing carbon steel, the chip color is dark brown, which indicates that ().
A. the cutting speed is appropriate
B. High cutting speed
C if the cutting temperature is too high, the cutting speed should be reduced.
D. Low cutting speed
A: A.
This problem comes directly from the actual treatment. Many experienced operators can judge whether the selection of cutting parameters at that time is appropriate by observing the color of chips. The cutting amount is a theoretical problem, but the topic does not let the player calculate the cutting amount, but let the player observe it. Let players know how important it is to accumulate experience through the exam on this topic. In the usual production and processing, we must learn to use our brains and be a serious and responsible person in order to become an excellent skilled worker. Don't many contemporary model workers make important technological innovations through usual observation and experience accumulation, and thus embark on the road to success?
For example, the following contest topics:
Sometimes, after pressing the button to release the tool handle of the machine tool spindle, the tool handle still cannot be removed from the spindle. The reason for this phenomenon may be ()
A. The nail is slightly short or the tension spring is pressed too tightly.
Cold welding occurs between the tool holder and the spindle.
C. the position of releasing the cylinder is at the back.
D. All the above reasons are possible.
Answer: d
This problem is often encountered in machine tool operation. If we can ask more questions and read more materials when this phenomenon occurs, we will certainly be able to master the structural knowledge of machine tools very firmly.
The above two questions can't be found directly in the book. Only by in-depth study of theory and production practice can we answer questions accurately. Topics like this account for a considerable proportion in this theoretical examination. After this problem is put forward, teachers engaged in theoretical teaching in vocational colleges will face new challenges and bring new development direction, that is, our theoretical teachers must have rich experience in production and processing, and must be "double-qualified" talents, both teachers and technicians, in order to cultivate good students. In 2005 and 2006, the Ministry of Labor and Social Security held two classes of CNC technicians for teachers in vocational colleges, aiming to make more teachers have the level and qualification of technicians.
Third, focus on the basic knowledge of the principle of NC machining.
In the national professional standards for operators of CNC lathes, CNC milling machines and machining centers, professional basic knowledge accounts for a large proportion.
Then, according to this requirement, the most relevant content of NC machining is selected to make the test questions more NC.
For example, the following contest topics:
If the English message "CHECK LUBURACATION" appears in the CNC system during machining, the following operations should be performed ().
A. adjust the hydraulic pressure of the hydraulic system
B. Adjust the pressure of compressed air
C. Add coolant
D. Add lubricating oil for guide rail
Answer: d
This topic includes both professional English and CNC machine tool maintenance. On the surface, it is an English vocabulary, but in fact it is knowledge of machine tool maintenance.
We don't require every operator to read foreign language materials in detail, but require the operator to basically understand foreign language words that often appear in CNC systems, and even regard these words as a symbol. The ultimate goal is to require every operator to be familiar with the machine tools he uses, so as to better master and maintain them.
For example, the following contest topics:
In the open-loop control servo system, the stepping motor is connected with the lead screw through a pair of gears. The power-on mode of stepping motor is three-phase six-beat mode, and the number of teeth of motor rotor is 40. Given that the pulse equivalent is 0.0 1mm and the basic lead of the ball screw is 6mm, the transmission ratio of the pair of gears is ().
A.5/3
B.3/5
C.2/5
D.5/2
Answer: c
This topic is a comprehensive reflection of several basic knowledge related to CNC machine tools. Including stepping motor knowledge, pulse equivalent knowledge, ball screw knowledge of CNC machine tools and gear transmission ratio knowledge of mechanical parts.
Although it is only a simple multiple-choice question, you can still learn a lot if you carefully ponder the meaning. As a proposer, I really hope that players can really grasp the knowledge points in this problem, rather than simply choose.
For example, the following contest topics:
When FANUC system or Siemens system executes N30 statement in the following program, the actual moving distance of the tool is ().
(Siemens) (FANUC)
… …
n 10 G54 G90 G00 X0 Y0； n 10 G54 G90 G00 X0 Y0；
N20 Roth RPL = 30；; N20 G68 X0 Y0 R30.0
n30g 1g 9 1 x 80.0 F500； n30g 1g 9 1 x 80.0 F500；
… …
A.x moves 56.569 and y moves 56.569.
B.x moves 80.000 and y moves 0.000.
C.x moves 40.000, and Y moves 69.282.
D.x moves 69.282, and Y moves 40.000.
Answer: d
This problem is ostensibly a numerical control programming problem, but it also includes simple trigonometric function calculation. Players should first know the instruction meaning of coordinate rotation in N20 statement, then look at the coordinate position of N30 statement, and finally calculate the moving distance by using trigonometric function of special angle. Most of the theoretical questions in this contest have multiple meanings like this. The proposer just wants to convey more information and investigate more knowledge points with limited space.
The above topics are the most basic contents required by the basic knowledge of CNC specialty. Players should build an idea by playing games or learning these topics, that is:
(1) Most of the competition topics are based on basic knowledge, with a wide range, but not very profound. Players will never learn well if they want to study hard before the game. Even if you learn by rote to cope with the competition, it is only temporary. It will be forgotten soon after the game. So players should pay special attention to their usual study and knowledge accumulation.
(2) The contest topic is not to ask you a knowledge point directly, but to ask you a variety of knowledge comprehensively.
Fourth, make up for the principle of practical examination.
Due to the limitation of venue, equipment and funds, it is impossible to assess all knowledge points in any numerical control skill competition. In order for me to
The content of our competition is richer and the test sites are more comprehensive, and the principle that the theoretical examination should be supplemented by the practical examination is put forward. Proposition experts believe that theoretical examination should be an extension of practical examination and a sublimation of practical examination. The aim of literary works is "from life, above life". Then our theoretical competition questions, like literary works, should come from actual production, but they are different from actual production. It should be a supplement to the practical competition, and reflect the key points, tricks and essence of the practical competition in a form suitable for the examination. The test questions of this theoretical competition include the following contents:
The concept of (1) high-speed machining
(2) Four-axis and five-axis machining concepts.
(3) Measurement of parts
(4) Calculation of fixture error
(5) programming with the fourth axis instruction.
(6) the writing method of the thesis
These contents cannot be carried out in this practical examination. Then it will be realized in the theoretical exam. Fortunately, this theoretical test was very successful.
It echoes and complements the software test and practice test, making the test questions of this contest more complete and comprehensive.
For example, as shown in figure-1, the positioning error of each process size is calculated in the test questions of NC milling center.
As shown in Figure -2, the calculation method of taper size in the theoretical contest of CNC lathe.
These questions are all from the actual production, and they can't be assessed in this competition. The most important thing is that these topics are often used in production and processing.
Basic skills and knowledge points used.
The game is over. Look at the theoretical contest topics of the second CNC Skills Competition, and summarize the following characteristics:
(1) Knowledge is comprehensive and focused.
The test questions cover most of the contents of the corresponding grades of CNC operators in the national professional standards. At the same time, the characteristics of numerical control operation are highlighted. Do more without confusion, and summarize incisively.
(2) Connecting with practice, the topic is flexible
The test questions come from actual production and don't copy books. Some content is not in the book at all. Only by mastering practical methods can we answer the questions correctly. In addition, the test questions have great flexibility. For example, some candidates can use macro programming or subroutine programming. The theme of the thesis of CNC milling center is thread processing method. Players can discuss the methods of tapping and milling threads with taps on this topic.
(3) color printing, with clear meaning.
Although the cost of color printing is many times higher than that of monochrome printing, the organizing Committee still insists on color printing. This not only makes the theoretical examination paper beautiful, but also embodies the elegance of the national first-class competition. More importantly, color pictures make the meaning of the theme clearer and more accurate. A problem that could not be solved in the past.
(4) Combination of difficulty and difficulty, each taking what he needs.
A considerable number of theoretical questions in this competition are very simple basic questions. But there are also some difficult topics. Even if it is a difficult topic, there are quite simple scoring points. In the competition, players can answer questions according to the scope and degree of their knowledge. The idea of the proposition is that every question can have the hope and point of scoring, but it still needs a high theoretical level to do it correctly. This will not dampen the enthusiasm of the players, nor will it make the players score easily and lead to negligence.
Through this competition, proposition experts believe that the level of players has been significantly improved compared with the last competition. Their knowledge is more accurate. But experts have also found many problems worthy of serious consideration by players and teachers engaged in CNC teaching. The contestants' questions are as follows:
(1) Incomplete basic knowledge;
(2) Teachers and students know little about new technology and equipment;
(3) Lack of practical multi-axis machining technology;
(4) weak general computing ability;
(5) The ability to use programming instructions flexibly is not enough;
(6) the language expression ability is not enough;
(7) Workers and teachers lack experience in writing technical papers or summarizing;
(8) The examination skills are not well mastered.
Due to the limitation of space in this paper, it is impossible to analyze these problems in detail. I hope to discuss it with the contestants in detail in the future exam review book or in the forum of the competition.
Although the second national numerical control skill competition is over, its influence is far from over. Its influence is far-reaching, and it will still play its guiding and leading role for a long time. This role will last until the third competition, even several years. It is still too early to discuss the style of the theoretical competition questions in the third numerical control skill competition. But it can be said with certainty that experts will gradually explore and establish themselves in the examination of CNC technicians in the past two years.
Through the promotion of the competition, experts found that a number of outstanding experts in numerical control operation technology emerged in China. They have a high level of technology and theory. This is of great and positive significance to the improvement of CNC operation technology in China. At the same time, passing this theoretical competition exam also sets a direction for the teaching of CNC operation theory in vocational and technical colleges in the future, that is, we must integrate theory with practice. Theory comes from practice, and then refined to guide practice. As a numerical control operator, you must have a solid theoretical foundation, which plays a very important role in improving the technical level in the future.
Finally, I hope the contestants, students majoring in numerical control, teachers and workers engaged in numerical control operation will study hard, keep forging ahead and strive for the modernization of China! Make our due contribution to the NC cause in China!