After the Second World War, most of the manufacturing industry relied on manual operation. After the workers understood the drawings, manually operated the machine tools and processed the parts, the products were produced in this way, with high cost, low efficiency and unguaranteed quality.
In the late 1940s, an engineer in the United States, John Parsons, conceived a method of punching a cardboard card to indicate the geometry of the part to be machined, using a hard card to control it. The action of the machine tool, at the time, was just a concept.
In 1948, Parsons showed his thoughts to the US Air Force. After watching the US Air Force, he expressed great interest because the US Air Force is looking for an advanced processing method and hopes to solve the processing problems of aircraft exterior models. Due to the complex shape of the model, high precision requirements, and the general equipment is difficult to adapt, the US Air Force immediately commissioned and sponsored the Massachusetts Institute of Technology (MIT) to conduct research to develop this hard-card-controlled machine tool, finally in 1952, Massachusetts. The Institute of Science and Technology and Parsons cooperated successfully to develop the first demonstration machine. By 1960, the simple and economical point-controlled drilling machine, and the linear control CNC milling machine developed rapidly, making CNC machine tools in the manufacturing industry. Various departments have gradually been promoted.
The history of CNC machining has gone through more than half a century. The NC control system has also evolved from the earliest analog signal circuit control to an extremely complex integrated machining system. The programming method has also been developed manually into an intelligent and powerful CAD/CAM integrated system. .
As far as China is concerned, the development of numerical control technology is relatively slow, for most workshops in China. The equipment is relatively backward, and the technical level and concept of the personnel are backward due to the low processing quality and processing efficiency, and often delay the delivery period.
1. The first generation NC system was introduced in 1951. Its control unit is mainly composed of various valves and analog circuits. The first CNC machine tool was born in 1952. It has been developed from milling machine or lathe to machining center, becoming a modern manufacturing. Key equipment for the industry.
2. The second-generation NC system was produced in 1959 and consists mainly of a single transistor and other components.
3. In 1965, the third-generation NC system was introduced, which used integrated circuit boards for the first time.
4. In fact, in 1964, the fourth-generation NC system, the computer numerical control system (CNC control system) that we are very familiar with, has been developed.
5. In 1975, the NC system used a powerful microprocessor, which is the fifth-generation NC system.
6, the sixth generation NC system uses the current integrated manufacturing system (MIS) + DNC + flexible processing system (FMS)
The development trend of CNC machine tools
With the rapid development of automobiles, defense, aviation, aerospace and other industries and 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 adopts electric spindle (built-in spindle motor), the maximum speed of the spindle reaches 200000r/min;
b. Feed rate: When the resolution is 0.01μm, the maximum feed rate reaches 240m/min and the complicated precision machining can be obtained;
c. Operation speed: The rapid development of the microprocessor provides guarantee for the development of the CNC system to high speed and high precision. The CPU has been developed to 32-bit and 64-bit CNC systems, and the frequency is increased to several hundred megahertz and upper gigahertz. . Due to the greatly improved operation speed, the feed rate of up to 24-240 m/min can still be obtained when the resolution is 0.1 μm and 0.01 μm;
d. Tool change speed: At present, the tool exchange time of foreign advanced machining centers is generally around 1s, and the high has reached 0.5s. Chiron of Germany designed the tool magazine into a basket style with the spindle as the axis and the tool in the circumference. The tool-to-knife 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. Machine tool motion accuracy, thermal deformation and monitoring and compensation of vibration are gaining more and more attention.
a. Improve the control accuracy of the CNC system: use high-speed interpolation technology to achieve continuous feed with small blocks, refine the CNC control unit, and use high-resolution position detection device to improve position detection accuracy. The position servo system adopts feedforward. Control and nonlinear control methods;
b. Using error compensation technology: using backlash compensation, screw pitch error compensation and tool error compensation technology to comprehensively compensate the thermal deformation error and spatial error of the equipment.
c. Use grid decoder to check and improve the accuracy of the machining center’s motion track: Predict the machining accuracy of the machine tool by 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 be completed under different operating conditions. Processing tasks and guarantee the quality of the parts.
3. Functional composite
The meaning of a compound machine tool means that a plurality of elements from the blank to the finished product are processed on one machine or as much as possible. According to its structural characteristics, it can be divided into two types: process composite type and process composite type. The machining center can perform various processes such as turning, milling, drilling, hobbing, grinding, laser heat treatment, etc., and can complete the complete 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. Control intelligence
With the development of artificial intelligence technology, in order to meet the development needs of manufacturing production flexibility and manufacturing automation, the degree of intelligence of CNC machine tools is constantly improving. Specifically embodied in the following aspects:
a. Adaptive process 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;
f. Intelligent 4M CNC system: In the manufacturing process, the measurement, modeling, processing, and machine operation (ie 4M) are integrated into one system.
5. System openness
a. Open to future technologies: As hardware and software interfaces follow a recognized standard protocol, a new generation of general-purpose hardware and software can be adopted, absorbed and compatible.
b. Open to special requirements of users: update products, expand functions, and provide various combinations of hardware and software products to meet specific application requirements;
c. The establishment of numerical control standards: a standardized programming language that is convenient for users to use and reduces labor consumption directly related to operational efficiency.
6. Drive parallelization
It can realize multi-coordinate linkage CNC machining, assembly and measurement of various functions, and can better meet the processing of complex special parts. Parallel machine tools are considered to be “the most significant progress in the machine tool industry since the invention of numerical control technology” and “new 21st century” A generation of CNC machining equipment.”
7. Extreme (large size and miniaturization)
The development of defense, aerospace, aerospace, and the expansion of basic industrial equipment such as energy require the support of large-scale and well-performing CNC machine tools. Ultra-precision machining technology and micro-nano technology are the strategic technologies of the 21st century, and it is necessary to develop new manufacturing processes and equipment that can adapt to micro-miniature size and micro-nano processing precision.
8. Information interaction networking
It can realize network resource sharing and realize remote monitoring, control, remote diagnosis and maintenance of CNC machine tools.
9. Greening of the process
In recent years, machine tools that do not use or use less coolant, achieve dry cutting, semi-dry cutting, energy saving and environmental protection have emerged. The trend of green manufacturing has accelerated the development of various energy-saving and environmentally-friendly machine tools.
10. Application of multimedia technology
Multimedia technology combines computer, audiovisual and communication technologies to give computers the ability to process sound, text, image and video information. It can realize integrated and intelligent information processing, and is applied to fault diagnosis of real-time monitoring system and production field equipment, monitoring of production process parameters, etc., and therefore 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-driven, networked, extreme, and green have become the development trend and direction of CNC machine tools.