The application of CNC technology has brought about a qualitative change in the traditional manufacturing industry, especially in recent years. The development of microelectronics technology and computer technology has brought new vitality to CNC technology. CNC technology and CNC equipment are important foundations for industrial modernization in various countries.
CNC machine tools are mainstream equipment in modern manufacturing and essential equipment for precision machining. They are important symbols of the technical level of modern machine tools and the technological level of modern machinery manufacturing. They are strategic materials related to national economy, people's livelihood and cutting-edge national defense construction. Therefore, all industrially developed countries in the world have taken major measures to develop their own CNC technology and its industry.
CNC is the abbreviation of Computer Numberical Control in English, which means "computer data control". Simply put, it is "CNC machining". In the Pearl River Delta region, people call it "computer gong".
CNC machining is an advanced machining technology in today's mechanical manufacturing. It is an automated machining method with high efficiency, high precision and high flexibility. It is to input the CNC program of the workpiece to be machined into the machine tool. Under the control of these data, the machine tool automatically processes the workpiece that meets people's wishes to create wonderful products.
CNC machining technology can effectively solve complex, precise, small batch and variable machining problems like molds, and fully adapt to the needs of modern production. Vigorously developing CNC machining technology has become an important way for my country to accelerate economic development and improve its independent innovation capabilities. At present, CNC machine tools are becoming more and more common in my country. Being able to master CNC machine tool programming is an important way to give full play to its functions.
CNC machine tools are typical mechatronics products. They integrate a variety of advanced technologies such as microelectronics technology, computer technology, measurement technology, sensor technology, automatic control technology and artificial intelligence technology, and are closely integrated with mechanical processing technology. They are a new generation of mechanical manufacturing technology equipment.
CNC machine tools are automated equipment that integrates machine tools, computers, motors, and technologies such as drag, dynamic control, and detection. The basic components of CNC machine tools include control media, CNC devices, servo systems, feedback devices, and machine tool bodies.
The control medium is a medium that stores all the motion tool position information relative to the workpiece required for CNC machining. It records the machining program of the parts. Therefore, the control medium refers to the information carrier that transmits the part machining information to the CNC device. There are many forms of control media, which vary with the type of CNC device. Commonly used ones include punched tapes, punched cards, magnetic tapes, disks, etc. With the development of CNC technology, punched tapes and punched cards are becoming obsolete, and the method of using CAD/CAM software to program computers, and then communicating with the CNC system through the computer to directly transmit programs and data to the CNC device is becoming more and more widely used.
The CNC device is the core of CNC machine tools, and people refer to it as the "central system". Modern CNC machine tools all use computer numerical control devices CNC. The CNC device includes an input device and a central processing unit (CPU) and an output device, etc. The CNC device can complete the input, storage, transformation, interpolation calculation of information and realize various control functions.
The servo system is a driving component that receives instructions from the CNC device and drives the movement of the machine tool actuator. It includes a spindle drive unit, a feed drive unit, a spindle motor and a feed motor. When working, the servo system receives the command information from the CNC system, and after comparing the command information with the position and speed feedback signals, it drives the moving parts or executing parts of the machine tool to process parts that meet the requirements of the drawings.
The feedback device is composed of measuring elements and corresponding circuits. Its function is to detect speed and displacement and feedback the information to form a closed-loop control. Some CNC machine tools with low precision requirements do not have feedback devices, which are called open-loop systems.
The machine tool body is the entity of the CNC machine tool and the mechanical part that completes the actual cutting process. It includes the bed, base, workbench, saddle, spindle, etc.
The CNC processing technology also follows the cutting rules of mechanical processing, which is roughly the same as the processing technology of ordinary machine tools. Since it is an automated processing that applies computer control technology to mechanical processing, it has the characteristics of high processing efficiency and high precision. The processing technology has its own unique features, the process is relatively complex, and the work step arrangement is relatively detailed and careful.
CNC machining process includes the selection of tools, determination of cutting parameters and design of tool path process route. CNC machining process is the foundation and core of CNC programming. Only with reasonable process can high-efficiency and high-quality CNC programs be compiled. The criteria for measuring the quality of CNC programs are: the least processing time, the smallest tool loss and the best workpiece.
CNC machining process is part of the overall machining process of the workpiece, or even a process. It must cooperate with other previous and subsequent processes to finally meet the assembly requirements of the overall machine or mold, so that qualified parts can be processed.
CNC machining processes are generally divided into rough machining, medium and rough corner cleaning, semi-finishing and finishing steps.
CNC programming is the whole process from part drawings to obtaining CNC machining programs. Its main task is to calculate the cutter location point (CL point for short) in the machining path. The cutter location point is generally taken as the intersection of the tool axis and the tool surface. The cutter axis vector must also be given in multi-axis machining.
According to the requirements of the workpiece drawing and the processing process, the CNC machine tool compiles the movement, speed and sequence of the tools and components used, the spindle speed, spindle rotation direction, tool head clamping, tool head loosening and cooling operations into a program sheet in the form of specified CNC code and inputs it into the dedicated computer of the machine tool. Then, the CNC system compiles, calculates and logically processes the input instructions, and outputs various signals and instructions to control each part according to the specified displacement and sequential actions to process various shapes of workpieces. Therefore, the compilation of the program has a great impact on the performance of CNC machine tools.
CNC machine tools must input the instruction codes representing various functions into the CNC device in the form of a program, which is then processed by the CNC device and then sends out pulse signals to control the operation of each moving part of the CNC machine tool to complete the cutting of parts.
At present, there are two standards for CNC programs: ISO of the International Organization for Standardization and EIA of the American Electronics Industry Association. my country adopts ISO code.
With the advancement of technology, 3D CNC programming generally rarely uses manual programming, but uses commercialized CAD/CAM software.
CAD/CAM is the core of computer-aided programming system, and its main functions include data input/output, calculation and editing of machining trajectories, process parameter setting, machining simulation, NC program post-processing and data management.
At present, the software with powerful NC programming functions that are popular among users in my country include Mastercam, UG, Cimatron, PowerMILL, CAXA, etc. The principles, graphics processing methods and machining methods of each software are similar, but each has its own characteristics.
1. Analyze the part drawing to understand the general situation of the workpiece (geometry, workpiece material, process requirements, etc.)
2. Determine the CNC machining process of the part (machining content, machining route)
3. Perform necessary numerical calculations (base point, node coordinate calculation)
4. Write a program sheet (different machine tools will be different, follow the user manual)
5. Program verification (input the program into the machine tool and perform graphic simulation to verify the correctness of the programming)
6. Process the workpiece (good process control can save time and improve processing quality)
7. Workpiece acceptance and quality error analysis (inspect the workpiece, and pass it to the next step. If it is unqualified, find out the cause of the error and the correction method through quality analysis).
With the rapid development of industries such as automobiles, national defense, aviation, and aerospace, as well as the application of new materials such as aluminum alloys, the requirements for high-speed CNC machine tool processing are getting higher and higher.
a. Spindle speed: The machine tool uses an electric spindle (built-in spindle motor), and the maximum spindle speed reaches 200,000r/min;
b. Feed rate: When the resolution is 0.01µm, the maximum feed rate reaches 240m/min and complex precision processing can be achieved;
c. Operation speed: The rapid development of microprocessors has provided a guarantee for the development of CNC systems in the direction of high speed and high precision. The CPU has been developed to 32-bit and 64-bit CNC systems, and the frequency has been increased to hundreds of megahertz and thousands of megahertz. Due to the great improvement in operation speed, when the resolution is 0.1µm and 0.01µm, the feed speed can still be as high as 24-240m/min;
d. Tool change speed: At present, the tool exchange time of advanced foreign machining centers is generally around 1s, and the highest has reached 0.5s. Chiron of Germany designed the tool magazine into a basket style, with the spindle as the axis and the tools arranged in a circle. The tool change time from tool to tool is only 0.9s.
The requirements for the accuracy of CNC machine tools are no longer limited to static geometric accuracy. The motion accuracy, thermal deformation and vibration monitoring and compensation of machine tools are increasingly valued.
a. Improve the control accuracy of the CNC system: adopt high-speed interpolation technology to achieve continuous feeding with small program segments, make the CNC control unit more refined, and adopt high-resolution position detection devices to improve the position detection accuracy. The position servo system adopts feedforward control and nonlinear control methods;
b. Adopt error compensation technology: adopt reverse clearance compensation, screw pitch error compensation and tool error compensation technologies to comprehensively compensate for the thermal deformation error and spatial error of the equipment.
c. Use grid decoders to check and improve the motion trajectory accuracy of the machining center: predict the machining accuracy of the machine tool through simulation to ensure the positioning accuracy and repeated positioning accuracy of the machine tool, so that its performance is stable for a long time, and it can complete a variety of machining tasks under different operating conditions and ensure the machining quality of parts.
3. Functional Complexity The meaning of a compound machine tool is to realize or complete as many elements as possible from the blank to the finished product on a single machine tool. According to its structural characteristics, it can be divided into two categories: process complex type and process complex type. The machining center can complete multiple processes such as turning, milling, drilling, gear hobbing, grinding, laser heat treatment, etc., and can complete all the processing of complex parts. With the continuous improvement of modern mechanical processing requirements, a large number of multi-axis linkage CNC machine tools are becoming more and more popular among major companies.
With the development of artificial intelligence technology, in order to meet the development needs of flexible production and manufacturing automation in the manufacturing industry, the intelligence level of CNC machine tools is constantly improving. It is specifically reflected in the following aspects: a. Processing process adaptive control technology; b. Intelligent optimization and selection of processing parameters; c. Intelligent fault self-diagnosis and self-repair technology; d. Intelligent fault playback and fault simulation technology; e. Intelligent AC servo drive device; f. Intelligent 4M CNC system: In the manufacturing process, the four elements of measurement, modeling, processing, and machine operation (i.e. 4M) are integrated into one system.
a. Open to future technologies: Since the software and hardware interfaces follow recognized standard protocols, the new generation of general software and hardware can be adopted, absorbed and compatible.
b. Open to special user requirements: update products, expand functions, and provide various combinations of hardware and software products to meet special application requirements;
c. Establishment of CNC standards: standardized programming languages are convenient for users to use and reduce labor consumption directly related to operating efficiency.
It can realize multi-coordinate linkage CNC machining, assembly and measurement functions, and can better meet the processing of complex special parts. Parallel machine tools are considered to be "the most meaningful progress in the machine tool industry since the invention of CNC technology" and "the new generation of CNC machining equipment in the 21st century."
The development of national defense, aviation, aerospace and the large-scale equipment of basic industries such as energy require the support of large and high-performance CNC machine tools. Ultra-precision machining technology and micro-nano technology are strategic technologies in the 21st century. It is necessary to develop new manufacturing processes and equipment that can adapt to micro-size and micro-nano machining precision.
It can not only realize network resource sharing, but also realize remote monitoring, control, remote diagnosis and maintenance of CNC machine tools.
In recent years, machine tools that do not use or use less coolant and realize dry cutting and semi-dry cutting for energy saving and environmental protection have continued to appear. The general trend of green manufacturing has accelerated the development of various energy-saving and environmentally friendly machine tools.
Multimedia technology integrates computer, audio and video and communication technology, enabling computers to have the ability to comprehensively process sound, text, image and video information. It can achieve integrated and intelligent information processing, and is applied to real-time monitoring systems and fault diagnosis of production site equipment, production process parameter monitoring, etc., so it has great application value.
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