In recent years, in order to meet the needs of the market, many vocational and technical schools have successively set up numerical control technology majors. Last year, our school also purchased two economical CNC lathes and a CNC lathe bed milling machine, and equipped with Huaxing CNC simulation software (the CNC system of the machine tool is Nanjing Huaxing CNC operating system) to meet the requirements of CNC teaching. Through several semesters of teaching practice, I deeply feel that it is very important to do a good job in the operation of CNC machine tools and the preparation before machining parts.
A, parts processing program writing and calibration
When machining parts on a CNC machine tool, no matter what operating system the CNC machine tool uses, there must be a CNC machining program suitable for the CNC machine tool. First of all, students make their own processing program according to the part drawing given by the teacher. When writing a machining program, first analyze the part drawing, analyze the machining process route according to the technical requirements of the part drawing, determine the machining steps, reasonably select the cutting tools to be used in each process and the cutting parameters in machining, and carry out mathematical processing related to the NC machining program. There will be some complicated coordinate calculation problems in mathematical processing. In order to simplify the calculation and shorten the calculation time, we let students draw the part drawing with AutoCAD software in the computer simulation room, and then use the query command of AutoCAD software to solve and record the data. Through process analysis and mathematical calculation, the program is written according to the determined process route and parts processing steps. After the NC machining program is compiled, the NC simulation teaching software provided by the NC machine tool manufacturer is used for repeated calibration and simulation in the computer simulation room to check the correctness of the program. At the same time, the parameters such as coordinate value, feed speed and tool compensation value are further processed to meet the actual processing needs.
Why are you doing this? Due to the limitation of funds and other reasons, the number of CNC machine tools in general vocational and technical schools is small, so it is impossible for students to assess CNC machine tools at the same time, and the long delay is not conducive to teaching. On the other hand, through verification, students can be familiar with the use of CNC machining software and the operation panel of CNC machine tools before operating CNC machine tools, laying a good foundation for the next operation of CNC machine tools. Finally, the teacher conducted a comprehensive and detailed review of the processing program written by each student to determine the final processing program. The contents of the teacher's audit are mainly the rationality of program structure, feed route, spindle speed, feed speed, cutting depth and tool selection. At the same time, the teacher gives students constructive suggestions to let them know why they need to make such changes and what will happen if they don't. After the scheme is determined, they should write it down in time for operation.
Second, the preparation of processing materials, tools and fixtures
Program preparation is only the first step. After the scheme is verified, the next step is the preparation of processing materials, tools and fixtures. How this step is done will directly affect the final effect of CNC operation and students' interest in learning, so we should do it seriously.
At present, the main materials used in the teaching of CNC machine tool operation in vocational and technical schools are aluminum, nylon rods, steel, paraffin, hardwood chopping boards and so on. The selected materials should meet the requirements of NC operation teaching to the maximum extent, and at the same time, economy should be considered. According to the actual situation of our school, we choose aluminum and paraffin as processing materials for lathes and milling machines. The choice of cutting tool should be based on the surface shape and material of the processed material. Because the hardness of the material we choose is not high, there is no special requirement for the cutter, just ordinary cutter. However, due to the different shapes and technical requirements of parts, different types of tools should be selected for machining, such as triangular thread turning tools for machining triangular threads and arcs or sharp knives for machining arcs. Reasonable selection of machining tools is the basic guarantee for machining parts well. The choice of fixture is relatively simple, such as machining aluminum rod and paraffin rod on CNC lathe, and directly clamping aluminum rod and paraffin rod with three-jaw self-centering chuck; When machining on a milling machine, as long as the aluminum plate or paraffin plate is fixed on the workbench with a pressure plate or clamped by a machine with flat pliers according to the requirements of a common milling machine, it is necessary to control the clamping force so that the workpiece does not move during machining.
However, in the practical application of CNC machine tools, it is necessary to comprehensively consider the technical requirements of CNC machine tools, the characteristics of fixtures, the properties of workpiece materials, machining procedures, cutting parameters and other related factors to correctly select tools and fixtures. In the learning process, students are required to process paraffin materials as metal materials, use the cutting parameters of the processed metal materials to process paraffin materials, reasonably distribute the machining allowance during the machining process, and distinguish between rough machining and fine machining. Through the above practice, the processed workpiece meets the requirements of the drawings, and the effect is good, achieving the purpose of NC machine tool operation.
Third, the adjustment and tool alignment of CNC machine tools
After the NC machining program is written, the parts and materials are prepared, and the appropriate tools are selected, the NC machine tool should be adjusted, lubricated and checked to ensure the performance of the NC machine tool. Then, the tool alignment is carried out, so that the tool position of each tool on the CNC machine tool coincides with the same point after the tool rest is indexed or changed. After the tool alignment is completed, the parts will be trial-machined to check the accuracy of the program and tool alignment. If the dimensional accuracy and geometric tolerance of the trial-machined parts do not meet the requirements of the drawings, the tool deviation will be slightly adjusted, and then the trial machining will be carried out until the machined parts meet the requirements of the drawings. After trial processing, the parts can be processed in batches. Whether a NC machining part is qualified or not, the tool setting of NC machine tool plays a key role, that is to say, the basic guarantee for whether the machined part is qualified is accurate tool setting.
Fourth, the safety education work
Always keep in mind safety and the purpose of safety first. According to the characteristics of machining, it is very important to carry out safety education before operation. Students are required to strictly abide by the management system of CNC laboratory and the safety operation procedures of CNC machine tools. At the same time, we also use some typical cases of casualties caused by violation of operating procedures to educate students, requiring them to be serious, earnest and careful in the operation process, so as to enhance their safety awareness. Before getting on the computer, we will also distribute the operation steps of CNC machine tools to students in the form of handouts, asking them to understand and master them carefully. Students must follow the requirements of operating procedures during the operation of CNC machine tools to ensure that no safety accidents occur.
As long as teachers make good preparations before the operation of CNC machine tools and carefully organize and guide them in the operation teaching of CNC machine tools, they will certainly receive good teaching results.
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