The feedback device, which consists of measuring elements and corresponding circuits, plays a role in detecting the speed and displacement, and feeds back the relevant information to form a closed-loop control. There are some precision requirements are not very highCNC machine toolsIn the case where there is no feedback device, the situation is known as an open-loop system.
5、Machine tool body
Machine tool body as the physical presence of CNC machine tools, is to undertake the actual cutting and machining operations of the mechanical parts, which covers the bed, there is a base, equipped with a table, contains the bed saddle, but also includes the spindle and so on.
CNC machiningCharacteristics of the process
It obeys the laws of machining and cutting, which are the laws of ordinary machine tools.ProcessingAlso largely follow, it is the application of computer control technology in machining automation processing, so there is a high processing efficiency, high precision features, it has a unique processing process, the process is more complex, step by step arrangement of exhaustive and thorough.
The CNC machining process involves the selection of tools, the determination of cutting parameters, and the design of toolpaths, etc. The CNC machining process is the basis and core of CNC programming, and only when the process is reasonable can a highly efficient and high-quality CNC programme be produced. Measure the CNC programme is good or bad with the standard, that is, the minimum processing time, minimum tool loss, and machining with the best results of the workpiece.
CNC machining process belongs to the overall processing of the workpiece process category, but also one of the processes, this process needs to be with the other before and after the process with each other, and then can ultimately fit the overall machine or mould assembly requirements, and only in this way, can be processed to meet the standards of the parts.
The CNC machining process is usually divided into steps such as roughing, and medium roughing, plus semi-finishing, and finishing.
CNC programming for CNC
CNC programming becomes the whole process from the part drawing to the acquisition of CNC machining programme, the main task is to calculate the machining tool point, the tool point is referred to as the CL point, the tool point is usually selected for the tool axis and the tool surface of the intersection of the tool, in the multi-axis machining needs to be given to the tool axis vector.
CNC machine tools should be based on the requirements of the workpiece drawings and machining process, the tool used, as well as the amount of movement of the components, speed, action sequence, spindle speed, spindle rotation direction, head clamping, loosening, and cooling and other operations, in accordance with the provisions of the form of the CNC code compiled into the programme, and then input to the machine tool special computer. Then, the CNC system in accordance with the input instructions for compilation, arithmetic and logic processing, the output of a variety of signals and instructions to control the various parts in accordance with the specified displacement and sequential 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.
On behalf of a variety of different functions of the instruction code, to the form of the programme input to the CNC machine tool CNC device, the CNC device will be calculated and processed, and then send out a pulse signal, by virtue of the signal to control the operation of those moving parts of the CNC machine tool, and ultimately complete the cutting and processing of the parts.
Currently, there are two standards for CNC programmes, ISO, developed by the International Organisation for Standardisation, and EIA, the Electronic Industries Association of the U.S.A. The ISO code is the one used in our country.
As a result of technological advances, CNC programming for 3D is often rarely hand programmed, but rather commercialised CAD/CAM software is used.
The core of the computer-aided programming system is CAD/CAM, whose main functions include data input and output, as well as the calculation and editing of machining trajectories, process parameter setting, machining simulation, and post-processing of CNC programmes, as well as data management and so on.
Nowadays, in our country, the user's favourite, with powerful CNC programming software exists, UG,, CAXA and so on. The principle of each software for CNC programming, graphics processing and machining are more or less the same, but each has its own characteristics.
Steps for CNC machining parts
1, analysis of parts drawings, know the approximate condition of the workpiece, involving aspects of geometry, and workpiece materials, as well as 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. Programme verification (input the programme into the machine tool and carry out graphical simulation to verify the correctness of the programming)
6. Carry out machining operations on workpieces (good process control can be extremely effective in saving time and improving the quality of machining).
7, to carry out inspection of the workpiece, if qualified will flow into the next process, if not qualified, with the help of quality analysis to find out the causes of errors and the corresponding corrective methods, this is the acceptance of the workpiece and quality error analysis.
History of CNC machine tools
After the end of the Second World War, the manufacturing industry to carry out the production of most of the proportion is to operate with the help of manpower, when the workers will understand the drawings, in the form of manual operation of machine tools, and then parts to be processed, the use of such a way to produce products, the cost of the state in a high degree, the efficiency is relatively low, and the quality of the same can not be guaranteed.
At the end of the 1940s, the United States, an engineer called Parsons (John), he conceived a method, this method is punched in a cardboard card, through the holes to indicate the need for machining the geometry of the parts, and then use this card to control the action of the machine tool, and at that time, this is just an idea.
In 1948, Parsons showed his idea to the U.S. Air Force, the U.S. Air Force looked at, showed great interest, because the U.S. Air Force was looking for an advanced processing method, looking to solve the problem of aircraft prototype processing, in view of the complexity of the shape of the prototype, the precision requirements and high, the general equipment is difficult to adapt to the United States, the U.S. Air Force immediately commissioned and sponsored by the U.S. Massachusetts Institute of Technology (MIT) to carry out research, to develop this hard cardboard-controlled machine. To develop this machine tool controlled by hard cardboard, finally in 1952, MIT and Parsons collaborated to successfully develop the first demonstration machine, to 1960, the more simple and economical point control drilling machine, as well as linear control CNC milling machine to the rapid development, resulting in the gradual promotion of CNC machine tools in various sectors of the manufacturing industry.
After more than half a century, CNC machining has its own history, NC numerical control system from the initial analogue signal circuit for control, and gradually developed into an extremely complex integrated machining system, programming from manual programming, evolved into intelligent and powerful CAD / CAM integrated system.
For China, the development of CNC technology is relatively slow, for most of the domestic workshop, the equipment is relatively obsolete, the technical level of personnel and the concept of lagging behind to show for the poor quality of machining and processing efficiency is not high, often delayed delivery deadlines.
1, was introduced in 1951, the first generation of NC systems, its control unit consists of a variety of valves as well as analogue circuitry, the birth of the first CNC machine tools in 1952, it has developed from milling machines or lathes to machining centres, and then become the key equipment for modern manufacturing.
2. The second generation of NC systems, which was produced in 1959, 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.
4. In fact, in 1964, the fourth generation of NC systems was already developed, which is the computer numerical control system that we are very familiar with, i.e. the CNC control system.
5. In 1975, the NC system adopted a powerful microprocessor, which is the fifth generation of the NC system.
6. The sixth-generation NC system uses the current Integrated Manufacturing System, or MIS, as well as DNC, and a flexible machining system, or FMS.
Trends in CNC machine tools
1. High-speed
Along with the high-speed development of the automobile 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, as well as aluminium alloys and other new materials are applied, the high-speed requirements for CNC machine tool processing is higher and higher.
a. Spindle speed can be described in this way, the machine tool used is an electric spindle, that is, the kind of internal spindle motor, the spindle can achieve the maximum speed for how many revolutions per minute.
b. In terms of feed rate, the maximum feed rate is 240 metres per minute at a resolution of 0.01 microns, and it is possible to achieve complex types of precision machining.
c. In terms of operation speed, the rapid development of microprocessors has guaranteed the development of numerical control systems in the direction of high speed and high precision, which in turn has led to the development of numerical control systems with 32-bit and 64-bit CPUs, whose frequency has been increased to hundreds of megahertz and thousands of megahertz. Because of the significant increase in computing speed, when the resolution is 0.1µm or 0.01µm, it is still possible to get up to 24-240m/min feed speed.
d. Foreign advanced machining centres, tool exchange time, now generally in 1s or so, the high has reached 0.5s. German companies, the tool magazine design style, is a basket style, to the spindle as the axis, the tool circumferential arrangement, as well as its knife to the knife tool change time, only 0.9s.
2. High precision
Currently, the search for accuracy of CNC machine tools is not limited to static geometric accuracy, machine tool motion accuracy, and thermal deformation, as well as for vibration monitoring and compensation, more and more attention.
a. Improve the control accuracy of CNC system, using high-speed interpolation technology, through a small programme segment to achieve continuous feeding, prompting the CNC control unit refinement, the use of high-resolution position detection device, improve the position detection accuracy, position servo system using feed-forward control and non-linear control methods.
b. Comprehensively compensate the thermal deformation error of the equipment and the spatial error of the equipment by applying the technology of backlash compensation, the technology of screw pitch error compensation, and the technology of tool error compensation.
c. The use of grid checking to improve the accuracy of the motion trajectory of the machining centre, with the help of simulation to predict the machining accuracy of the machine tool, and then ensure the positioning accuracy and repeat positioning accuracy of the machine tool, so that its performance can be maintained for a long time to ensure that its performance is stable, and that it is able to complete a variety of machining tasks under different operating conditions and to ensure that the machining quality of the parts.
3. Functional complexity
Compound machine tool means to achieve or as far as possible to complete a variety of elements of processing from the blank to the finished product on a single machine tool. According to its structural characteristics, it can be divided into two categories: process composite type and process composite type. Machining centre can complete turning, milling, drilling, hobbing, grinding, laser heat treatment and many other processes, can complete all the processing of complex parts. With the modern machining requirements continue to improve, a large number of multi-axis CNC machine tools more and more by the major enterprises.
4. Intelligent control
According to the evolution of artificial intelligence technology, in view of the need to meet the development needs of manufacturing production flexibility and manufacturing automation, CNC machine tools in the degree of intelligence continues to improve, specifically in the following levels:
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. smart manufacturingIn the process, there is a CNC system that integrates the measurement aspect with the modelling aspect, the machining aspect, and the machine operation aspect, which are all covered by the 4Ms, in the same system.
5. Openness of the system
a. Openness to future technologies, given that software and hardware interfaces are based on recognised standard protocols that can be adopted, assimilated and made compatible with a new generation of general-purpose software and hardware.
b. To be open to the special needs of users, to achieve product updates, to achieve functionality expansion, to provide various combinations of hardware and software products to meet the special application needs.
c. With regard to the construction of CNC standards, there are standardised programming languages that are user-friendly and allow for the reduction of labour consumption directly related to operational efficiency.
6. Parallelisation of drives
The parallel machine tool is regarded as “the most significant development in the machine tool industry since the invention of CNC technology” and “the new generation of 21st century CNC machining equipment”. 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, the same need for large-scale and good performance of CNC machine tools support, the development of aerospace industry, but also need to large-scale and good performance of CNC machine tools support, such as energy and other basic industrial equipment large-scale, but also the need for large-scale and good performance of CNC machine tools support. And, ultra-precision machining technology is the 21st century strategic technology, micro and nanotechnology is the 21st century strategic technology, so the need to develop new manufacturing processes and equipment to adapt to micro and small size, the need to develop new manufacturing processes and equipment to adapt to micro and nanometer processing accuracy.
8. Networking of information interactions
Not only to achieve the sharing of network resources, but also to achieve remote monitoring of CNC machine tools, as well as remote control, as well as remote diagnosis, and maintenance.
9. Greening of processes
In recent years, those who do not use coolant or less coolant, to reach the dry cutting and semi-dry cutting and energy-saving environmental protection characteristics of the machine tool, continue to appear, green manufacturing trend, prompting various types of energy-saving environmental protection machine tools to accelerate the development.
10. Application of multimedia technologies
Multimedia technology, the computer, audio and video and communications technology fusion together, so that the computer has the ability to comprehensively deal with sound, text, images and video information, it can reach a comprehensive and intelligent information processing, can be applied to real-time monitoring system, but also can be used in the production site equipment fault diagnosis, as well as the production process parameter monitoring, etc., so there is a significant value of the application.
Chinese 
Japanese 
English 
German 
Finnish 
No comments