Views: 10 Author: Site Editor Publish Time: 2021-09-27 Origin: Site
The application of CNC precision machining technology has brought about a qualitative change in the traditional manufacturing industry, especially in recent years. The development of microelectronic technology and computer technology has brought new vitality to numerical control technology. Numerical control technology and numerical control equipment are important foundations of industrial modernization in various countries.
CNC machine tools are the mainstream equipment of modern manufacturing. CNC precision processing equipment is an important symbol that reflects the technological level of modern machine tools and the technological level of modern machinery manufacturing. It is a strategic material related to the national economy, the people's livelihood, and the cutting-edge construction of national defense. Therefore, all industrialized countries in the world have taken major measures to develop their own CNC technology and industries.
CNC is the abbreviation of Computer Numberical Control in English, meaning "computer data control", or simply "numerical control processing"
CNC precision machining is an advanced processing technology in today's machinery manufacturing, and it is an automated processing method with high efficiency, high precision and high flexibility. It is to input the NC program of the workpiece to be processed to the machine tool, and the machine tool automatically processes the workpiece according to people's wishes under the control of these data to produce wonderful products.
CNC precision machining technology can effectively solve the complex, precise, small batch and changeable processing problems like molds, and fully meet the needs of modern production. Vigorously developing CNC precision machining technology has become an important way for my country to accelerate economic development and improve independent innovation capabilities. At present, the use of CNC machine tools in our country is becoming more and more common, and 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. It integrates many advanced technologies such as microelectronics, computer technology, measurement technology, sensor technology, automatic control technology and artificial intelligence technology, and is closely integrated with mechanical processing technology. A generation of machinery manufacturing technology and equipment.
CNC machine tools are automated equipment that integrates machine tools, computers, motors, and drag, motion control, and detection technologies. The basic composition of CNC machine tools includes control medium, CNC device, servo system, feedback device and machine tool body, as shown in the figure
1. Control medium
The control medium is the medium that stores the position information of all the action tools required by the CNC machining relative to the workpiece. It records the machining program of the part. Therefore, the control medium refers to the information carrier that transmits the machining information of the part to the CNC device.
There are many forms of control media, which vary with the types of numerical control devices. Commonly used are punched tape, punched cards, magnetic tapes, and magnetic disks. With the development of numerical control technology, punched tapes and punched cards tend to be eliminated, and the use of CAD/CAM software to program in the computer, and then through the computer to communicate with the numerical control system, the method of directly transmitting the program and data to the numerical control device is more and more widely used .
2. Numerical control device
The numerical control device is the core of the numerical control machine tool, and it is called the "central system". Modern CNC machine tools use computer numerical control device CNC. The numerical control device includes an input device, a central processing unit (CPU), and an output device. The numerical control device can complete information input, storage, conversion, interpolation, and realize various control functions.
3. Servo system
The servo system is a drive component that receives instructions from the numerical control device and drives the actuators of the machine tool to move. Including spindle drive unit, feed drive unit, spindle motor and feed motor, etc.
When working, the servo system accepts the command information of the CNC system and compares it with the position and speed feedback signals according to the requirements of the command information, drives the moving parts of the machine tool or executes the actions of the parts, and processes the parts that meet the requirements of the drawings.
4. Feedback device
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 without feedback devices are called open-loop systems.
5. Machine tool body
The main body of the machine tool is the entity of the CNC machine tool, and is the mechanical part that completes the actual cutting process. It includes the bed, base, worktable, saddle, spindle and so on.
CNC precision machining technology also obeys the laws of machining and cutting, which is roughly the same as the machining process of ordinary machine tools. Because 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 more complicated, and the work step arrangement is more detailed and thorough.
CNC precision machining technology includes the selection of tools, the determination of cutting parameters, and the design of tool-traveling process routes. CNC machining technology is the foundation and core of CNC programming. Only with reasonable technology can we compile high-efficiency and high-quality CNC programs. The criteria for measuring the quality of a CNC program are: the smallest processing time, the smallest tool loss, and the best results.
CNC precision machining is a part of the overall machining process of the workpiece, even a process. It must cooperate with other front and back processes to finally meet the assembly requirements of the overall machine or mold, so that qualified parts can be processed.
The CNC machining process is generally divided into rough machining, medium and rough corner clearing, semi-finishing and finishing.
Numerical control programming is the whole process from part drawing to obtaining numerical control processing program. Its main task is to calculate the cutter location point (CL point for short) in the machining pass. The tool position point is generally taken as the intersection of the tool axis and the tool surface, and the tool axis vector is also given in multi-axis machining.
According to the requirements of the workpiece pattern and the processing process, the CNC machine tool operates the movement amount, speed and sequence of actions, spindle speed, spindle rotation direction, tool head clamping, tool head loosening and cooling of the used tools and various components to operate. The prescribed numerical control code form is compiled into a program list and input into the special computer of the machine tool.
Then, the numerical control system performs compilation, calculation and logic processing according to the input instructions, and outputs various signals and instructions, and controls each part to process various workpieces of different shapes according to the prescribed displacement and sequential actions. Therefore, the programming of the program has a great influence on the effectiveness of CNC machine tools.
The CNC machine tool must input the instruction codes representing various functions into the CNC device in the form of a program, and the CNC device performs arithmetic processing, and then sends out pulse signals to control the operation of the various moving parts of the CNC machine tool to complete the cutting process of the 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 the ISO code.
With the advancement of technology, 3D CNC programming generally rarely uses manual programming, but uses commercial CAD/CAM software.
CAD/CAM is the core of a computer-aided programming system. Its main functions include data input/output, calculation and editing of processing trajectories, process parameter settings, processing simulation, post-processing of numerical control programs, and data management.
At present, the software with powerful CNC programming function that is popular among users in China includes Mastercam, UG, Cimatron, PowerMILL, CAXA, etc. The principles of NC programming, graphics processing methods, and processing methods are similar for each software, but each has its own characteristics.
1. Analyze the part drawing and understand the general situation of the workpiece (geometric shape, workpiece material, process requirements, etc.)
2. Determine the numerical control processing technology of the part (processing content, processing route)
3. Perform necessary numerical calculations (calculation of base point and node coordinates)
4. Write the program list (different machine tools will be different, follow the manual)
5. Program verification (input the program into the machine tool and perform graphic simulation to verify that the programming is correct)
6. Process the workpiece (good process control can save time and improve processing quality)
7. Workpiece acceptance and quality error analysis (inspect the work piece, and pass it to the next one. If it fails, find out the cause of the error and corrective method through quality analysis).
1. Speed up
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 machining of CNC machine tools are getting higher and higher.
a. Spindle speed: The machine tool adopts an electric spindle (built-in spindle motor), and the maximum spindle speed is up to 200,000r/min;
b. Feed rate: When the resolution is 0.01µm, the maximum feed rate reaches 240m/min and complex precision machining can be obtained;
c. Operation speed: The rapid development of microprocessors provides a guarantee for the development of numerical control systems in the direction of high speed and high precision. The development of CPUs has developed to 32-bit and 64-bit numerical control systems, and the frequency has been increased to several hundreds of megahertz and above gigahertz. . Due to the greatly improved calculation speed, the feed speed of up to 24～240m/min can be obtained when the resolution is 0.1µm and 0.01µm;
d. Tool change speed: At present, the tool change time of foreign advanced machining centers has generally been around 1s, and the high has reached 0.5s. The German Chiron company designed the tool magazine into a basket style, with the spindle as the axis, and the tools arranged on the circumference. The tool-to-tool change time is only 0.9s.
2. High precision
The accuracy requirements of CNC machine tools are now not limited to static geometric accuracy. The motion accuracy, thermal deformation, and vibration monitoring and compensation of machine tools are getting more and more attention.
a. Improve the control accuracy of CNC system: adopt high-speed interpolation technology, realize continuous feed with small program segments, make CNC control unit refined, and adopt high-resolution position detection device to improve position detection accuracy, and position servo system adopts feed forward Control and nonlinear control methods;
b. Adopt error compensation technology: adopt backlash compensation, screw pitch error compensation and tool error compensation technology to comprehensively compensate the thermal deformation error and space error of the equipment.
c. Use a grid decoder to check and improve the accuracy of the machining center's motion trajectory: predict the machining accuracy of the machine tool through simulation to ensure the positioning accuracy and repeat positioning accuracy of the machine tool, so that its performance is stable for a long time, and it can complete multiple operations under different operating conditions. Kind of processing tasks, and to ensure the processing quality of parts.
3. Complex functions
The meaning of the compound machine tool is to realize or complete as much as possible the processing of multiple elements from the rough to the finished product on a machine tool. According to its structural characteristics, it can be divided into two types: process compound type and process compound type.
The machining center can complete various 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 machining requirements, a large number of multi-axis linkage CNC machine tools are increasingly welcomed by major enterprises.
4. Intelligent control
With the development of artificial intelligence technology, in order to meet the development needs of manufacturing flexibility and manufacturing automation, the degree of intelligence of CNC machine tools is constantly improving. It is embodied in the following aspects:
a. Adaptive control technology for processing;
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 Numerical Control System: In the manufacturing process, the four aspects of measurement, modeling, processing, and machine operation (ie 4M) are integrated into one system.
5. Open system
a. Open to future technology: Because the software and hardware interfaces follow the recognized standard protocol, it can adopt, absorb and be compatible with a new generation of general-purpose software and hardware.
b. Open to users' special requirements: update products, expand functions, and provide various combinations of hardware and software products to meet special application requirements;
c. The establishment of numerical control standards: standardized programming languages are not only convenient for users to use, but also reduce labor consumption directly related to operating efficiency.
6. Parallel drive
It can realize multiple functions of multi-coordinate CNC machining, assembly and measurement, and can better meet the processing of complex special parts. Parallel machine tools are regarded as "the most meaningful progress in the machine tool industry since the invention of CNC technology" and "new 21st century". A generation of CNC machining equipment".
7. Extreme (large and miniaturized)
The development of defense, aviation, and aerospace industries and the large-scale equipment of basic industries such as energy require the support of large-scale and good-performance CNC machine tools. Ultra-precision processing technology and micro-nano technology are strategic technologies in the 21st century, and it is necessary to develop new manufacturing processes and equipment that can adapt to micro-mini size and micro-nano processing precision.
8. Networking of Information Interaction
It can not only realize network resource sharing, but also realize remote monitoring, control, remote diagnosis and maintenance of CNC machine tools.
9. Green processing
In recent years, machine tools that do not use or use less coolant to achieve dry cutting and semi-dry cutting energy-saving and environmentally friendly machine tools continue to appear. The general trend of green manufacturing has accelerated the development of various energy-saving and environmentally-friendly machine tools.
10. Application of Multimedia Technology
Multimedia technology integrates computer, audio-visual and communication technology, so that the computer has the ability to comprehensively process sound, text, image and video information. Information processing can be integrated and intelligent, and it can be applied to real-time monitoring system and production site equipment fault diagnosis, production process parameter monitoring, etc., so it has great application value.
At present, the development of CNC machine tools is changing with each passing day. High-speed, high-precision, composite, intelligent, open, parallel drive, network, extreme, and green have become the trend and direction of the development of CNC machine tools. Contact our team.
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