CNC machining technology for high-end precision manufacturing

The feedback device, which consists of a measuring element and a corresponding circuit, has the function of detecting the amount of speed, detecting the amount of displacement, and feeding back the relevant information to form a closed-loop control situation. Some precision requirements are not highCNC machine toolsIt is called, open loop system because there is no feedback device.

5、Machine tool body

The entity of the CNC machine tool is the body of the machine tool, which is the mechanical part to complete the actual cutting process, the bed belongs to it, the base also belongs to it, the table also belongs to it, the bed saddle is also a part of it, and even the main spindle is still attributed to it.

CNC machiningCharacteristics of the process

CNC numerical controlProcessingIt follows the laws of machining and cutting, and is roughly the same as ordinary machine tool processing technology. It will be used in computer control technology for machining, belonging to the automated processing, so it has the characteristics of high processing efficiency and high precision. Its processing technology has a unique place, the process is more complex, step by step arrangement of detailed and thorough.

The selection of tools, the determination of cutting parameters and the design of tool routing are all included in the CNC machining process, which is the core and foundation of CNC programming, and only when the process is reasonable can a CNC programme be compiled that achieves high efficiency and quality. The criteria for measuring the quality of a CNC programme are: minimum machining time, minimum tool wear and the ability to produce the best possible results.

CNC machining process is part of the overall processing of the workpiece, and is one of the processes, it needs to be with the front and back of the other processes with each other, in order to ultimately achieve the overall assembly requirements of the machine or mould, so as to be able to process the parts in line with the standard.

CNC machining process, usually divided into some of these steps part, there is roughing, there is the middle roughing clear angle processing, in addition to including semi-finishing, and then finishing and so on.

CNC programming for CNC

CNC programming is a complete process that starts from the part drawing and continues until the final CNC machining programme is acquired. The main task is to calculate the tool position point during the machining process, which is referred to as the CL point. The tool position point is usually chosen as the point where the tool axis intersects the tool surface, and in the case of multi-axis machining, the tool axis vector must also be given.

In accordance with the requirements of the drawing of the workpiece and the flow of the machining process, the tool to be used, as well as the amount and speed of the movement of each part, the sequence of each action, the speed of the spindle, the direction of the spindle, the action of the cutterhead clamping, cutterhead loosening action, and cooling and other types of operations are written in the form of the prescribed CNC code into a programme sheet, which is entered into the machine tool's specially equipped computer. After that, the CNC system based on the input instructions to carry out compilation, arithmetic and logic processing, so as to output all kinds of signals and instructions to control each part in accordance with the specified displacement and orderly action, so as to process 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.

A variety of different functions of the instruction code, to the form of the program input to the CNC machine tool CNC device, CNC device followed by arithmetic processing, and then send out a pulse signal, which controls the operation of the various moving parts of the CNC machine tool, and ultimately complete the cutting and processing of parts.

Currently, there are two standards for CNC procedures, one of which is ISO (International Organisation for Standardisation) and the other is EIA (Electronic Industries Association), which is the ISO code adopted in China.

As technology advances, 3D CNC programming is often rarely done manually, and commercial CAD/CAM software is used instead.

The core of the computer-aided programming system is CAD/CAM, which has the function of data input/output, but also can carry out the calculation of the machining trajectory, as well as the editing of the trajectory, which can be set up to process parameters, can achieve the machining simulation, can carry out the post-processing of CNC programmes, and has the function of data management.

Nowadays, in China's popular users, with powerful CNC programming software exists, UG,, CAXA and so on. Each software for the principle of CNC programming, graphic processing and machining methods are more or less the same, but each has its own characteristics.

Steps for CNC machining parts

Firstly, the part drawing is analysed, and then the general situation of the workpiece is known, which covers the geometry, but also the material of the workpiece and the process requirements.

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

3. Perform the necessary numerical calculations (calculation of coordinates of base points and nodes)

4、Prepare the programme sheet (it will be different for different machine tools, comply with the user manual)

5, program verification, the program into the machine, followed by graphical simulation, in order to verify that the programming is correct.

When machining workpieces, good process control can be extremely effective in saving time and significantly improving the quality of the workpieces.

7, to carry out acceptance of the workpiece, while the quality of error analysis, the first workpiece to be inspected, if qualified to flow into the next process, if not, then with the help of quality analysis to find out the causes of errors and the corresponding corrective methods.

History of CNC machine tools

After the Second World War, the manufacturing industry is dependent on manual production, workers have to read the drawings, and then manually operate the machine tools, and then go to process the parts, by virtue of this way to produce products, the cost is relatively high, the efficiency is relatively low, and the quality of the same can not be guaranteed.

In the late 1940s, the United States, there is an engineer named Parsons (John), he conceived a way, this approach is in a cardboard card above the punch, through the punch to indicate the need to carry out machining of the geometry of the parts, and then use this card to control the action of the machine tool, and at that time at that time, this is only a kind of idea.

In 1948, Parsons told the U.S. Air Force their ideas, the U.S. Air Force heard, showed great interest, only because the U.S. Air Force at that time is looking for advanced machining methods, aimed at solving the problem of aircraft prototype machining, in view of the prototype shape is extremely complex, the precision requirements of the very high, the ordinary equipment is difficult to fit, 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, go to the R & D! This machine tool controlled by cardboard, and finally in 1952, MIT and Parsons joined forces to successfully develop the first demonstration machine, to the 1960's, the easier and more economical point control drilling machine, as well as linear control CNC milling machine to rapid development, prompting the gradual promotion of CNC machine tools in the manufacturing industry in all sectors.

CNC machining history, has been up to more than half a century, NC numerical control system, but also from the earliest analogue signal circuit control, the development of an extremely complex integrated processing system, programming methods, but also by hand, the development of intelligent, powerful CAD / CAM integrated system.

Speaking of the domestic situation, the development of CNC technology in China is relatively slow, for many domestic workshops, there is a relative backwardness of its equipment, personnel in the technical level and the concept of backwardness, which is reflected in the processing of poor quality and processing efficiency is not high, and often delayed delivery of the phenomenon of the deadline.

1, the first generation of NC system was introduced in 1951, its control unit is mainly composed of a variety of valves as well as analogue circuits, the first CNC machine tools were born in 1952, it has developed from milling machines or lathes to machining centres, becoming the key equipment for modern manufacturing.

2. The second generation of NC systems was produced in 1959, and it was mainly composed of individual transistors as well as other components.

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

In fact, in 1964, the fourth generation of NC system was developed, which is the computer numerical control system that we are extremely familiar with, that is, CNC control system.

5. In 1975, the NC system adopted a microprocessor with powerful functions, and this is known as the fifth generation of the NC system.

The sixth generation of NC systems, with the current Integrated Manufacturing System, or MIS, and the addition of DNC, as well as the Flexible Machining System, or FMS.

Trends in CNC machine tools

1. High-speed

High-speed development of the automotive industry, the high-speed development of the defence industry, the high-speed development of the aviation industry, the high-speed development of the aerospace industry, aluminium alloys and other new materials can be applied, in this case, for the high-speed CNC machine tool processing requirements are higher and higher.

a. Spindle speed: the machine tool using an electric spindle, that is, the spindle motor as the spindle power source, the spindle can achieve the maximum speed of how many revolutions per minute, the specific value of / min.

b. The feed rate is shown as follows, with a resolution of 0.01µm, the maximum feed rate can reach 240m/min, and it is also possible to obtain accurate machining of complex shapes, which is the case.

c. Operating speed: the rapid development of microprocessors, for the CNC system towards high-speed, high-precision direction to provide a guarantee, according to which the development of the CPU has been developed to 32-bit or 64-bit CNC system, its frequency increased to hundreds of megahertz and even thousands of megahertz. Because of this significant increase in computing speed, it is possible to obtain feed speeds of up to 24 to 240 m/min when the resolution is 0.1 µm or 0.01 µm.

d. Tool change speed: Nowadays, the tool exchange time in the heart of foreign advanced processing has usually been around 1s, and some are as high as 0.5s. The German company puts as a basket style in this case, the tool magazine is designed to be so, and with the spindle as the axis, and then there is a tool arrangement in the periphery of the knife to the knife to finally go through the knife change time is only 0.9s.

2. High precision

Nowadays, the requirements for the accuracy of CNC machine tools are no longer limited to static geometric accuracy, the motion accuracy of the machine tool is receiving more and more attention, thermal deformation is also receiving more and more attention, and vibration monitoring and compensation is also becoming more and more important.

To improve the control accuracy of the CNC system, high-speed interpolation technology is used, through which continuous feeding is achieved with small programme segments to achieve the purpose of making the CNC control unit refined, and a high-resolution position detection device is used to improve the position detection accuracy, and the position servo system is used with feed-forward control and non-linear control methods.

Adoption of technologies such as backlash compensation, screw pitch error compensation, and tool error compensation, through which comprehensive compensation is made for the thermal deformation error and spatial error of the equipment, is the adoption of error compensation technology.

c. Checking with a grid to improve the accuracy of the machining centre's trajectory, predicting the machine's machining accuracy with the help of simulation, ensuring the machine's positioning accuracy and repetitive positioning accuracy, keeping its performance stable over time, enabling it to achieve a wide range of machining tasks under different operating conditions and ensuring the quality of the parts machined.

3. Functional complexity

To realise a variety of elements processing on one machine tool, or to complete the processing from blank to finished product as far as possible, this is the meaning of compound machine tool. It can be divided into two categories according to the structural characteristics of process compound and process compound. Machining centre can complete turning, milling, drilling, hobbing, grinding, laser heat treatment and other processes, but also to complete all the processing of complex parts. With the modern machining requirements continue to improve, 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 demand for manufacturing production flexibility, in order to meet the demand for the development of manufacturing automation, the degree of CNC machine tool intelligence continues to improve. Specifically embodied in the following aspects:

a. Process adaptive control technology;

b. Intelligent optimisation and selection of machining parameters;

c. Intelligent fault self-diagnosis and self-repair technology;

d. Intelligent fault playback and fault simulation techniques;

e. Intelligent AC servo drives;

f. Intelligent 4M CNC systems: In the manufacturing process, measurement, modelling, machining and machine operation are integrated into a single system, known as 4M.

5. Openness of the system

Because the hardware and software interfaces are based on recognised standard protocols, it is possible to adopt and assimilate as well as be compatible with a new generation of general-purpose hardware and software, which is a sign of openness to future technologies.

b. Openness to special user requirements, including updating of products, including expanded functionality, and the provision of various combinations of hardware and software products to meet special application requirements.

The establishment of CNC standards, with standardised programming languages, makes it easier for users to use them and also reduces the labour consumption directly related to operational efficiency.

6. Parallelisation of drives

Able to achieve multi-coordinate linkage CNC machining functions, but also has the assembly function, also has the measurement function, and more able to meet the needs of complex special parts processing, parallel machine tools are regarded as “since the invention of CNC technology in the machine tool industry's most significant progress”, but also regarded as “the 21st century new generation of CNC machining equipment”. The parallel machine is regarded as "the most significant advancement in the machine tool industry since the invention of CNC technology" and is also regarded as "the new generation of CNC machining equipment for the 21st century.

7. Polarisation (miniaturisation and miniaturisation)

The development of national defence, the need for large-scale and good performance of CNC machine tools support, the development of aviation, also need large-scale and good performance of CNC machine tools support, the development of aerospace industry, the same need for large-scale and good performance of CNC machine tools support, energy and other basic industrial equipment large-scale, or the need for large-scale and good performance of CNC machine tools support. Ultra-precision machining technology is a strategic technology of the 21st century, the need to develop new manufacturing processes and equipment that can adapt to the micro-small size and micro-nanometer machining accuracy, micro-nanotechnology is a strategic technology of the 21st century, but also the need to develop new manufacturing processes and equipment that can adapt to the micro-small size and micro-nanometer machining accuracy.

8. Networking of information interactions

That can achieve the common sharing of network resources, but also to achieve CNC machine tools in the case of remote monitoring, control, remote diagnosis and maintenance.

9. Greening of processes

In recent years, the emergence of a continuous no or less coolant, dry cutting, semi-dry cutting energy-saving and environmentally friendly machine tools, green manufacturing trend, so that a variety of energy-saving and environmentally friendly machine tools to accelerate the development forward.

10. Application of multimedia technologies

Let the computer has a comprehensive processing sound, text, image and video information ability of multimedia technology, is the computer, audio and video and communication technology integration as one of the technology, it can achieve these information processing integrated and intelligent, can be applied to real-time monitoring system, but also can be used in the production site equipment fault diagnosis and production process parameter monitoring and so on, so there is a significant value of the application.