CNC machine tool is developed on the basis of ordinary machine tools. It has been widely used in the machinery manufacturing industry because of its good flexibility, high machining accuracy and stability, being able to process complex parts, reducing labor intensity of workers and easy to realize modern management.
In 1946, the world was born by front-end computer, which made human enter the information society. Six years later, computer technology was used on machine tools. Since then, the traditional machine tools have changed in essence. Half a century later, CNC machine tools have gone through two stages and six generations of development. Especially in 1970, the general small computer industry began to develop, and the computing speed was greatly improved. So it was transplanted to the core parts of the CNC system, and then entered the CNC stage, and it has been to the sixth generation of the present CNC machine tools based on PC.
With the development of computer technology, CNC machine tool technology has been developed accordingly. With the continuous adoption of computer and control theory, its performance is improving and its application field is becoming more and more extensive. In order to meet the new market demand and new demand, the world numerical control technology and its equipment are developing towards the following characteristics:
1) High speed, high efficiency, high precision and reliability development. The high speed is reflected in the high speed of the spindle,
High feed speed, high operation speed and high tool change speed. 2) Modularization, intelligence, flexibility and integration. 3) Openness. 4) New generation NC machining technology and equipment.
At present, the United States, Japan and Germany are the countries with advanced technology and rich experience in the research, design, manufacture and use of CNC machine tools in the world. Because of their different social conditions, each has its own characteristics. The United States government attaches importance to the development of machine tool industry. The Department of defense and other parts of the United States constantly propose the development direction and scientific research task of machine tools due to their military needs, and provide sufficient funds, talents in the network world, pay attention to efficiency and innovation, and computer technology advanced, so it is leading the machine tool manufacturing industry all the way; German government has always attached importance to the important strategy of machine tool industry The status is to be strongly supported in many aspects, especially the combination of theory and practical application, the emphasis on basic research and applied technology research, the close combination of enterprises and scientific research departments, in-depth research on the common and characteristic problems of CNC machine tools, and the improvement in quality. The quality and performance of the numerical control machine tools in Germany are good, advanced and applicable, and the goods are real and are exported to the world, especially Siemens company, which is famous in the world; Japan studies Germany in the respect of talents and the matching of machine tool components, and studies the United States in quality management and numerical control technology, and the results are better than blue in some aspects; China has no difference with the western developed countries in terms of CNC machine tools Since 2002, China has become the top country in machine tool consumption and import in the world for three years. We need to see the situation, fully understand the absence of domestic CNC machine tools, and strive to develop advanced technology and equipment to narrow the gap with developed countries.
CNC machine tools are usually composed of program carrier, CNC device, servo system, detection and feedback device, auxiliary device and machine body. Program carrier is a device for accessing part processing program, which can store the processing program in a certain format and code on the carrier, and the program carrier can be disk, tape, hard disk and flash card;
CNC device is the core of automatic machining of machine tool, and the soul of the whole CNC machine tool. The main control system is mainly composed of CPU, memory, controller, etc. The main control objects of NC system are position, angle, speed and other mechanical quantities, as well as temperature, pressure, flow and other physical quantities. The control mode can be divided into two categories: data processing control and sequential logic control. The challenge compensation module in the main controller is to carry out the corresponding tool path interpolation operation according to the part program read in, after decoding and compiling, and then control the displacement of each coordinate axis of the machine tool by comparing with the position and speed feedback signals of each coordinate servo system;
Servo system is the electrical transmission link between CNC system and machine tool body. It is mainly composed of servo motor, drive control system and position detection and feedback device. Servo motor is the executive component of the system, and the driving control system is the power source of servo motor
The command signal sent out by the CNC system is compared with the position feedback signal and then used as the displacement command. After the power amplification of the drive system, the motor is driven to run, and the working table or tool holder is moved by the mechanical transmission device.
The detection and feedback device is helpful to improve the machining accuracy of CNC machine tools. The parameters of the moving track of guide rail and spindle are detected. The digital signals of Centennial city are fed back to the CNC device, and the correction is carried out according to the feedback information.
The main function of auxiliary control device is to receive the switch quantity command signal output by the numerical control device, and then drive the corresponding electrical appliances after compiling, logic discrimination and movement, and then drive the corresponding electrical appliances after power amplification, and drive the mechanical, hydraulic, pneumatic and other auxiliary devices of the machine tool to complete the switch action specified in the instruction. These controls include the change of speed, reversing and start stop commands of spindle moving parts, the selection and exchange of tools, the start and stop of cooling and lubrication devices, the release and clamping of workpieces and machine parts, and the auxiliary actions of the switches such as indexing table rotation indexing.
The machine body of NC machine tool is similar to traditional machine tool, which consists of spindle drive, feed transmission device, bed, working table and auxiliary movement device, hydraulic pneumatic system, lubrication system and cooling device. But the whole layout, appearance, transmission system, tool system structure and operating mechanism of CNC machine tools have changed greatly. The purpose of the change is to meet the requirements of CNC machine tools and give full play to the characteristics of CNC machines.
The working principle of CNC machine tool. When machining parts by CNC machine factory, firstly, the geometric information and process information of the processed parts shall be woven into processing procedures. Input devices shall be sent to the CNC system. After the processing, calculation and components of each coordinate axis, the machine is sent to the drive circuit of each axis. After amplification, servo motor is driven to drive the movement of each axis and the movement of each axis is carried out Feedback control, so that the tool, workpiece and other devices strictly in accordance with the order, track and parameters specified in the processing procedure orderly work, so as to process the whole contour of the parts.
CNC machine tool has been more and more used in modern manufacturing industry, and has played an incomparable advantage of ordinary machine tools. CNC machine tools have the following characteristics: 1) the transmission chain is short, compared with the ordinary machine tool, the spindle drive is no longer motor speed change, but the transverse and longitudinal feed are driven by two servo motors. 2) High rigidity, in order to match with the high precision of the CNC system, the rigidity of CNC machine tool is high, so as to meet the requirements of high precision machining. 3) Light drag, tool frame movement adopts ball screw pair, small friction, portable movement. The pressure angle of the special bearing with support type at both ends of the screw is larger than that of the ordinary bearing, and it is selected and matched well when leaving the factory; the lubrication part of the CNC machine tool adopts oil mist automatic lubrication, which makes the CNC machine move easily.
The machining characteristics of CNC machine tools: 1) high degree of automation, which can reduce the manual labor intensity of the operator. The NC machining process is completed automatically according to the input procedure. The operator only needs to start the tool alignment, loading and unloading the workpiece and changing the tool. During the process, the main purpose is to observe and supervise the operation of the machine tool. However, because of the high technology content of CNC machine tool, the operator's mental labor is improved accordingly. 2) The precision of the processed parts is high and the quality is stable. The positioning accuracy and repeated positioning accuracy of CNC machine tools are very high, which is easy to ensure the consistency of a batch of parts size. As long as the process design and procedures are correct and reasonable, and careful operation, the parts can be ensured to obtain high machining accuracy and quality control in the process of machining. 3) High production efficiency. NC machine tool processing can process multiple machining surfaces in clamping again, generally only the first piece is detected. Therefore, many intermediate processes, such as marking dimension detection, can be used in the processing of ordinary machine tools in the province, which reduces the auxiliary time. Moreover, the quality of parts processed by NC is stable, which brings convenience to the subsequent process, and its comprehensive efficiency is obviously improved. 4) It is convenient for new product development and modification. NC machining generally does not need many complex process equipment. By programming the processing program, parts with complex shape and high precision can be processed. When the product is changed and the design is changed, the procedure is changed instead of the redesign of tooling. Therefore, NC machining can greatly shorten the product development cycle, and provide a shortcut for the development of new products and the improvement and modification of products.
The parts suitable for NC machine tool processing: 1) more suitable for many kinds of small and medium-sized parts. With the gradual decline of manufacturing cost of CNC machine tools, the processing of large quantities of parts has also appeared both at home and abroad. When processing small batch and single piece production, it can be selected if it can shorten the debugging time of the program and the preparation time of tooling. 2) Parts with high precision requirements. It has the advantages of good rigidity, high manufacturing precision, accurate tool, convenient dimension compensation, so it can process parts with high dimensional accuracy requirements. 3) Parts with small surface roughness value. Under the condition that the material, machining allowance and tool angle of workpiece and tool are certain, the surface roughness depends on the constant speed of cutting speed and feed speed. The different cutting speed of diameter is different. For example, CNC lathe has the function of constant linear cutting. When the end face and the outer circle of different diameter are used, the surface roughness value can be small and consistent. When machining different surface roughness, the surface with small roughness selects small feed speed, and the surface with high roughness selects a larger feed speed, which is very changeable. This is difficult to achieve in ordinary machine tools. 4) Parts with complex outline shapes. Any plane curve can be approximated by straight line or arc. CNC machine tool has the function of arc interpolation, and can process various parts with complex contour.
Conclusion: for the CNC industry in China, we must make the domestic CNC system advanced and reliable, pay close attention to the quality of products and supporting parts, and lay a good technical foundation. In the near future, we should lay emphasis on laying the foundation, building credibility, expanding the market share of domestic CNC machine tools, and seeking to catch up with the advanced level of the world in the long term and stride to the world market; we must pay close attention to the fundamental, adhere to the "people-oriented", accelerate the improvement of personnel quality and train various experts and talents, and fundamentally change the current low efficiency and backward state. People are the foundation of success or failure of all undertakings. At all levels, we should pay attention to "cultivating, selecting and using talents", establishing learning enterprises, establishing corporate culture, accelerating the cultivation of new people and training on-the-job personnel.
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