CNC machining technology(2)

What is CNC
Traditional mechanical processing is performed by manual operation of ordinary machine tools. During processing, the mechanical tool is shaken by hand to cut metal, and the accuracy of the product is measured by the eye with tools such as calipers. Modern industry has already used computer digitally controlled machine tools for operations. CNC machine tools can automatically process any products and parts directly in accordance with the procedures programmed by technicians in advance. This is what we call "CNC machining". Numerical control processing is widely used in any field of all mechanical processing, and it is the development trend and important and necessary technical means of mold processing.
"CNC" is the abbreviation of Computerized Numerical Control in English.
The CNC machine tool automatically processes the processed parts according to the pre-programmed processing program. We put the part's machining process route, process parameters, tool motion trajectory, displacement, cutting parameters (spindle revolutions, feed, back tooling, etc.) and auxiliary functions (tool change, spindle forward, reverse, etc.) Cutting fluid on, off, etc.), according to the instruction code and program format specified by the CNC machine tool, write a processing program list, and then record the content of the program list on the control medium (such as punched paper tape, magnetic tape, disk, magnetic bubble memory) ), and then input into the numerical control device of the numerical control machine tool to command the machine tool to volley the parts.
This whole process from the analysis of the part drawing to the preparation of the control medium is called the compilation of the NC program. The difference between CNC machine tools and ordinary machine tools processing parts is that CNC machine tools automatically process parts according to the program, while ordinary machine tools must be operated by humans. We can achieve the purpose of processing different parts by changing the program that controls the motion of the machine tool. Therefore, CNC machine tools are particularly suitable for processing small batches of parts with complex shapes and high precision requirements.
Since the CNC machine tool must process the parts according to the program, after the programmer has compiled the program, it is input into the CNC device to command the work of the machine tool. The input of the program is through the control medium.
development trend:
The application of numerical control technology has not only brought revolutionary changes to the traditional manufacturing industry, and made the manufacturing industry a symbol of industrialization, but also with the continuous development of numerical control technology and the expansion of application fields, it is important to the international people`s livelihood in some important industries such as national defense, automobile, etc. The development of these industries is playing an increasingly important role. The digitization of equipment in these industries has become a major trend of modern development, such as: bridge-type three- and five-axis high-speed CNC gantry milling machines, gantry mobile five-coordinate AC swing-angle CNC gantry milling machines, gantry mobile Type three-coordinate CNC gantry milling machine, etc.
Rapid development
With the progress of the core processor of the numerical control system, the current high-speed machining center feed speed can reach up to 80m/min, and the dry running speed can reach about 100m/min. Many automobile factories in the world, including my country's Shanghai General Motors Corporation, have already replaced modular machine tools with production lines composed of high-speed machining centers. The HyperMach machine tool of American CINCINNATI has a maximum feed rate of 60m/min, a rapid rate of 100m/min, an acceleration of 2g, and a spindle speed of 60000r/min. It only takes 30 minutes to process a thin-walled aircraft part, while the same part needs 3 hours to process on a general high-speed milling machine and 8 hours to process on a general milling machine.
Due to the specialization of the division of labor of the various components of the mechanism, under the development of professional spindle factories, the high-speed spindles are becoming more and more popular. In the past, the models used only for high-speed automotive industry (models with more than 15,000 revolutions per minute) have become essential mechanical product requirements.
Precision development
With the advancement of servo control technology and sensor technology, under the control of the CNC system, the machine tool can perform sub-micron precise motion. In terms of machining accuracy, the machining accuracy of ordinary CNC machine tools has been increased from 10μm to 5μm, and the precision machining center has increased from 3~5μm to 1~1.5μm, and the ultra-precision machining accuracy has begun to enter the nanometer level (0.01μm) .
Open development
Due to the standardization and modularization of computer hardware and software modularization, open technology has become increasingly mature, and it has begun to enter the stage of openness. The open CNC technology system has better versatility, flexibility, adaptability and scalability. The United States, the European Community, Japan and other countries have implemented strategic development plans, and carried out the research and formulation of open system system CNC system specifications (OMAC, OSACA, OSEC). The three largest economies in the world have carried out almost the same in a short period of time. The formulation of the scientific plan and technical specifications heralded the advent of a new period of change in CNC technology. In 2000, my country also began to study and formulate the normative framework of China's ONC CNC system.
Compound development
With the complexity of the product appearance curve, the mold processing technology must be continuously upgraded, which puts forward new demands on the numerical control system. The five-axis machining and six-axis machining of machine tools have become increasingly popular, and the compounding of machine tool processing has become an inevitable development trend. New Nihon Koki's 5-sided machining machine adopts a composite spindle head, which can realize the machining of 4 vertical planes and the machining of any angle, so that 5-face machining and 5-axis machining can be realized on the same machine tool, and it can also realize inclined surface and Machining of inverted taper holes. German DMG company exhibited the DMUVoution series machining center, which can process 5-sides and 5-axis linkage processing in one clamping, and can be controlled by CNC system or CAD/CAM directly or indirectly.
Selection of CNC lathe
CNC lathes, also known as CNC lathes, are computer numerically controlled lathes. They are currently the most widely used and covered CNC machine tools in China, accounting for about 25% of the total number of CNC machine tools. CNC machine tools are mechatronics products that integrate multiple technologies such as machinery, electricity, hydraulics, pneumatics, microelectronics, and information. It is a working mother machine with the advantages of high precision, high efficiency, high automation, high flexibility, stable and reliable processing quality in mechanical manufacturing equipment. The technical level of CNC machine tools and their percentage of machine tool output and total ownership is one of the important indicators to measure the overall level of a country's national economic development and industrial manufacturing. CNC lathe is one of the main varieties of CNC machine tools. It occupies a very important position in CNC machine tools. For decades, it has been widely valued by countries all over the world and has been rapidly developed.
CNC lathes and turning centers are high-precision and high-efficiency automated machine tools. It has a wide range of machining performance, and can process straight cylinders, oblique cylinders, arcs and various threads. It has various compensation functions of linear interpolation and circular interpolation, and has played a good economic effect in the mass production of complex parts. Reasonable selection of CNC lathes should follow the following principles:
Selection principle
1. Preparation
Determine the process requirements of typical parts and the batch of processed workpieces. The function that the CNC lathe should have is to make preparations and the prerequisites for reasonable selection of CNC lathes. Meet the process requirements of typical parts
The process requirements of typical parts are mainly the structural size, processing range and accuracy requirements of the parts. According to the accuracy requirements, that is, the dimensional accuracy, positioning accuracy and surface roughness of the workpiece, the control accuracy of the CNC lathe is selected. Choose based on reliability. Reliability is a guarantee for improving product quality and production efficiency. The reliability of a CNC machine tool means that the machine tool runs stably for a long time without failure when it performs its functions under specified conditions. That is, the mean time between failures is long, even if there is a failure, it can be restored in a short time and put into use again. Choose machine tools with reasonable structure, well-manufactured, and mass-produced machines. Generally, the more users, the higher the reliability of the CNC system.
2. Purchase
Machine tool accessories, spare parts and their supply capacity, cutting tools, are very important for CNC lathes and turning centers that have been put into production. When choosing a machine tool, carefully consider the compatibility of tools and accessories.
3. Focus on the identity of the control system
Manufacturers generally choose products from the same manufacturer, and at least buy the control system of the same manufacturer, which brings great convenience to the maintenance work. Teaching units require students to be knowledgeable and knowledgeable, so it is a wise choice to choose different systems and to equip them with various simulation software.
4. Choose according to the performance-price ratio
Make sure that the functions and accuracy are not idle, not wasted, and do not choose functions that have nothing to do with your own needs.
5. Protection of machine tools
When needed, the machine tool can be equipped with fully enclosed or semi-enclosed protective devices and automatic chip removal devices.
When choosing CNC lathes and turning centers, the above principles should be considered comprehensively.