The application of CNC technology has made a qualitative change in the traditional manufacturing industry, especially in recent years. The development of microelectronics technology and computer technology has brought new vigour to CNC technology. CNC technology and CNC equipment is an important foundation for the modernisation of industry in various countries.

CNC machine tool is the mainstream of modern manufacturing equipment, precision machining of the necessary equipment, is the embodiment of modern machine tool technology level, the modern mechanical manufacturing process level of important symbols, is the relationship between national economy and people's livelihood, cutting-edge national defence construction of strategic materials. Therefore, the world's industrially developed countries have taken significant measures to develop their own CNC technology and its industry.

CNC numerical control machining

CNC is the abbreviation of English Computer Numberical Control, meaning "computer data control", simply put, "numerical control machining", in the Pearl River Delta region, people are called In the Pearl River Delta region, it is known as "computer gong".

CNC machining is an advanced processing technology in today's machinery manufacturing, is an automated processing method with high efficiency, high precision and high flexibility. It is the CNC programme of the workpiece to be processed is input to the machine tool, and the machine tool under the control of these data automatically processes the workpiece that meets people's wishes to make wonderful products.

CNC machining technology can effectively solve complex, precise, small batch variable processing problems like moulds, fully adapted to the needs of modern production. Vigorously develop CNC machining technology has become an important way to accelerate the development of China's economy and improve the ability of independent innovation. At present, the use of CNC machine tools in China is becoming more and more common, can master CNC machine tool programming, is an important way to give full play to its functions.

CNC machine tool is a typical mechatronics products, it is a combination of microelectronics technology, computer technology, measurement technology, sensor technology, automatic control technology and artificial intelligence technology and other advanced technologies in one, and closely integrated with the machining process, is a new generation of machinery manufacturing technology and equipment.

Composition of CNC machine tools

CNC machine tools set machine tools, computers, motors and drag, dynamic control, testing and other technologies as one of the automation equipment. The basic composition of CNC machine tools, including control media, CNC devices, servo systems, feedback devices and machine tool body, as shown in the figure below

1, control media

Control media is the storage of CNC machining required for all the action of the tool relative to the position of the workpiece information medium, which records the parts of the machining process, therefore, the control media is the parts of the machining information transmitted to the CNC device to the information carrier. Control media has a variety of forms, it is different with the type of CNC device, commonly used perforated tape, perforated card, tape, disk and so on. With the development of CNC technology, perforated tape, perforated card tends to be eliminated, and the use of CAD/CAM software in the computer programming, and then through the computer and the CNC system communication, the program and data transmitted directly to the CNC device is more and more widely used method.

2, CNC device

CNC device is the core of the CNC machine tools, people referred to as the "central system". Modern CNC machine tools use computer numerical control device CNC. numerical control device including input devices and central processing unit (CPU) and output devices, etc. constitutes the numerical control device can complete the information input, storage, transformation, interpolation algorithms, as well as to achieve a variety of control functions.

3、Servo system

Servo system is to receive instructions from the CNC device, drive the machine tool actuator drive components. Including spindle drive unit, feed drive unit, spindle motor and feed motor. When working, the servo system accepts the instruction information of the numerical control system, and compares the position and speed feedback signals with the instruction information, drives the moving parts of the machine tool or the action of the execution parts, and processes the parts in accordance with the requirements of the drawings.

4、Feedback device

Feedback device is composed of measuring elements and the corresponding circuit, its role is to detect the speed and displacement, and will be the information back to form a closed-loop control. Some of the precision requirements of the CNC machine tools, no feedback device, is called open loop system.

5、Machine body

Machine tool body is the entity of the CNC machine tool, is to complete the actual cutting and processing of mechanical parts, which includes the bed, base, table, bed saddle, spindle, etc..

CNC machining process characteristics

CNC numerical control machining process also comply with the laws of machining cutting, and the general machine tool machining process is largely the same. Because it is the application of computer control technology in mechanical processing in a kind of automated processing, and thus has a high processing efficiency, high precision and so on, the processing technology has its own unique features, the process is more complex, step by step arrangement is more detailed and thorough.

CNC CNC machining process including tool selection, cutting parameters and the determination of the design of the tool route, etc. CNC CNC machining process is the basis and core of CNC programming, only reasonable process, in order to compile a high-efficiency and high-quality CNC programme. Measure the standard of CNC programme is good or bad: the minimum processing time, minimum tool loss and processing the best results of the workpiece.

CNC machining process is part of the overall workpiece machining process, or even a process. It has to cooperate with other processes before and after, in order to ultimately meet the overall machine or mould assembly requirements, so as to process qualified parts.

CNC machining process is generally divided into roughing, medium roughness clear angle machining, semi-finishing and finishing steps.

CNC programming

CNC programming is from the part drawing to obtain the whole process of CNC machining procedures. Its main task is to calculate the machining tool in the point (cutter location point CL point). The tool location point is generally taken as the tool axis and the intersection of the tool surface, multi-axis machining, but also to give the tool axis vector.

CNC machine tool is based on the requirements of the workpiece drawing and machining process, the tool and components used in the amount of movement, speed and sequence of action, spindle speed, spindle rotation direction, head clamping, head release and cooling and other operations, in the form of a prescribed CNC code programmed into a single, dedicated to the machine tool computer input. Then, the CNC system according to the input instructions for compilation, arithmetic and logic processing, the output of a variety of signals and instructions to control the various parts of the prescribed displacement and sequential action, processing a variety of different shapes of the workpiece. Therefore, the preparation of the programme has a great impact on the performance of the CNC machine tool.

CNC machine tools must represent a variety of different functions of the instruction code in the form of a programme into the CNC device, by the CNC device for computing and processing, and then send out pulse signals to control the operation of the CNC machine tools of the various moving parts, so as to complete the parts of the cutting process.

At present, there are two standards for CNC programmes: ISO of the International Organisation for Standardisation and EIA of the Electronic Industries Association of the U.S.A. ISO code is adopted in China.

With the progress of technology, 3D CNC programming is generally rarely used manual programming, and the use of commercial CAD/CAM software.

CAD/CAM is the core of the computer-aided programming system, the main functions of data input / output, machining trajectory calculation and editing, process parameter settings, machining simulation, post-processing of CNC programmes and data management.

At present, in our country by the users like, CNC programming powerful software Mastercam, UG, Cimatron, PowerMILL, CAXA and so on. The principle of the software for CNC programming, graphics processing methods and processing methods are similar, but each has its own characteristics.

CNC CNC machining parts of the steps

1, analysis of parts drawings, to understand the general situation of the workpiece (geometry, workpiece materials, process requirements, etc.)

2, to determine the parts of the CNC machining process (processing content, processing route)

3, the necessary numerical calculations (base point, node coordinates calculation)

4, the preparation of the programme (different machines will vary, comply with the manual)

5, programme verification (enter the programme into the machine, and graphical simulation, to verify the correctness of the programming)

6, machining the workpiece (good process control can be very good to save time and improve the quality of machining)

7, workpiece acceptance and quality error analysis (the workpiece inspection, qualified into the next. Unqualified through the quality analysis to find out the causes of errors and corrective methods).

The history of the development of CNC machine tools

After World War II, most of the manufacturing production is dependent on manual operation, workers read the drawings, manual operation of machine tools, processing parts, with this way of producing products, high cost, low efficiency, quality is not guaranteed.

In the late 1940s, the United States has an engineer Parsons (John Parsons) conceived a method, punched holes in a cardboard card to indicate the geometry of the parts to be processed, using a cardboard card to control the action of the machine tool, at the time, this is just an idea.

In 1948, Parsons to the U.S. Air Force to show him this idea, the U.S. Air Force look after, expressed great interest, because the U.S. Air Force is looking for an advanced processing method, hoping to solve the problem of aircraft prototype processing, due to the complexity of the shape of the prototype, the precision requirements of the general equipment is difficult to adapt to, the U.S. Air Force immediately commissioned and sponsored by the United States of America, the Massachusetts Institute of Technology (MIT) to carry out research, the development of this cardboard to control the action of machine tools. The development of this hard cardboard to control the machine tool, finally in 1952, the Massachusetts Institute of Technology and Parsons, Inc. cooperation, the successful development of the first demonstration machine, to the 1960's more simple and economical point control drilling machine, and linear control CNC milling machine has been the rapid development of CNC machine tools in the manufacturing sector gradually gained popularity.

CNC processing history has been experienced for more than half a century, NC numerical control system from the earliest analogue signal circuit control for the development of extremely complex integrated processing systems, programming methods have also developed manually into an intelligent, powerful CAD/CAM integrated system.

As far as our country is concerned, the development of CNC technology is relatively slow, for most of the domestic workshop. Equipment is relatively backward, the technical level of personnel and the concept of backwardness is manifested in processing quality and processing efficiency is low, often delayed delivery.

1, the first generation of NC system was introduced in 1951, its control unit is mainly composed of a variety of valves and analog circuits, in 1952 the birth of the first numerical control machine tools have been developed from the milling machine or lathe to the machining centre, becoming the key equipment of modern manufacturing.

2, the second generation of NC systems produced in 1959, which is mainly composed of a single transistor and other components.

3. The third generation of NC systems was introduced in 1965, and for the first time, integrated circuit boards were used.

4, in fact, in 1964 has developed the fourth generation of NC system, that is, we are very familiar with the computer numerical control system (CNC control system).

5, 1975, the NC system uses a powerful microprocessor, which is the fifth generation of NC systems.

6, the sixth generation of NC systems using the current integrated manufacturing system (MIS) + DNC + flexible machining system (FMS)

The development trend of NC machine tools

High-speed

With the high-speed development of automobile, national defence, aviation, aerospace and other industries, as well as the application of aluminium alloys and other new materials, the high speed of CNC machine tool machining is increasingly demanding.

a. Spindle speed: the machine tool uses an electric spindle (internal spindle motor), the maximum spindle speed of 200000r/min;

b. Feed rate: the maximum feed rate reaches 240m/min when the resolution is 0.01µm, and it can get the precise machining of complex shape. c. Operation speed: the microprocessor can be used to operate the machine;

c. Operation speed: the rapid development of microprocessor provides guarantee for the development of CNC system in the direction of high-speed and high-precision, and the development of CPU has been developed to 32-bit and 64-bit CNC system, and the frequency has been increased to hundreds of megahertz and thousands of megahertz. Due to the great increase in computing speed, when the resolution of 0.1µm, 0.01µm can still be obtained when the resolution is 0.1µm, 0.01µm as high as 24 ~ 240m/min feed speed;

d. Tool change speed: at present, the tool change time of foreign advanced machining centres is generally around 1s, and the high one has reached 0.5s. German Chiron Company designs the tool magazine as a basket style, with the spindle as the axis and the tools arranged in the circle, and the tool change time from tool to tool is only 0.9s.

2. High precision

CNC machine tool accuracy requirements are now not limited to static geometric accuracy, machine tool motion accuracy, thermal deformation, as well as vibration monitoring and compensation is gaining more and more attention.

a. Improve the control accuracy of CNC system: adopt high-speed interpolation technology to achieve continuous feeding with tiny programme segments to refine the CNC control unit, and adopt high-resolution position detection device to improve the position detection accuracy, position servo system using feed-forward control and non-linear control and other methods;

b. Adopt error compensation technology: adopt reverse clearance compensation, screw pitch error compensation and tool error compensation and other technologies to comprehensively compensate for the thermal deformation error and spatial error of the equipment.

c. Adopt grid decoder to check and improve the motion trajectory accuracy of the machining centre: predict the machining accuracy of the machine tool through simulation to ensure the positioning accuracy and repetitive positioning accuracy of the machine tool, so as to make its performance stable for a long time, and to be able to complete a variety of machining tasks under different operating conditions and ensure the machining quality of the parts.

3. Functional composite

The meaning of composite machine tool is to achieve or as far as possible on a machine tool to complete a variety of elements from the blank to the finished product processing. According to its structural characteristics can be divided into process compound and process compound two types. Machining centres can complete turning, milling, drilling, hobbing, grinding, laser heat treatment and other processes, can complete all the processing of complex parts. With the continuous improvement of modern machining requirements, a large number of multi-axis CNC machine tools are more and more welcomed by major enterprises. 4.

4. Intelligent control

With the development of artificial intelligence technology, in order to meet the development needs of manufacturing production flexibility, manufacturing automation, the degree of intelligence of CNC machine tools is constantly improving. Specifically embodied in the following aspects:

a. Processing adaptive control technology;

b. Intelligent optimisation 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 measurement, modelling, machining and machine operation (i.e. 4M) are integrated in one system.

5. System openness

a. Open to future technologies: Since the hardware and software interfaces follow recognised standard protocols, they can be adopted, absorbed and compatible with a new generation of general-purpose hardware and software.

b. Open to the user's special requirements: update the product, expand functionality, provide a variety of combinations of hardware and software products to meet the requirements of special applications;

c. The establishment of numerical control standards: standardized programming language, both user-friendly, but also reduces and operating efficiency directly related to labour consumption.

6. Drive parallelisation

Can achieve multiple coordinates linkage CNC machining, assembly and measurement of a variety of functions, more to meet the complexity of the