The feedback device, which consists of a measuring element and a corresponding circuit, detects the speed and displacement and feeds back the information to form a closed-loop control. Some of the requirements for precision are not very high.CNC machine toolsIf there is no feedback device, then it is called an open-loop system.
5、Machine tool body
The entity of a CNC machine tool is the machine body, which belongs to the part of the machine that carries out the actual cutting process, which covers the bed, as well as the base, and then the table, in addition to the bed saddle, to the spindle and so on.
CNC machiningCharacteristics of the process
digital controlProcessingCNC, also following the laws of machining cutting, and general machine tool processing technology is generally similar. It is the use of computer control technology to the automation of machining processing, with high processing efficiency, high precision features, has a unique processing technology, the process is more complex, step by step arrangement is very meticulous and thoughtful.
Tool selection, cutting parameters to determine the process route as well as the design of the knife, etc., all belong to the CNC CNC machining process category. CNC CNC machining process is both the core foundation of CNC programming, as long as to do a reasonable process will be programmed out of the quality and high output efficiency and fast CNC program. Minimum machining time, minimal tool loss, the best workpiece machining results, these are the measure of the standard of excellence of the CNC programme.
The overall machining process of the workpiece covers the CNC machining part of the process, or even a separate process, which needs to be coordinated with other processes before and after each other, in order to ultimately fit the overall machine or mould assembly requirements, so as to be able to process the parts in accordance with the standard.
The process of CNC machining is usually divided into a roughing step, a medium roughing step, a semi-finishing step, and a finishing step.
CNC programming for CNC
CNC programming covers the entire process of obtaining a CNC machining programme based on the part drawing, the main task of which is to calculate the tool point for machining the tool travelling situation, also known as point referred to as CL point, which is usually chosen to be the intersection of the tool axis and the tool surface, and in the case of multi-axis machining, the tool axis vector must also be given.
There exists a type of machine tool, known as a CNC machine tool, which operates according to the requirements given in the workpiece drawing and the corresponding specific machining process. For this operating behaviour, there are a series of operations, including the placement of the tool used, as well as the amount and speed of movement of the various components, as well as the sequence in which the actions are carried out, the spindle speed, the direction of rotation of the spindle, the clamping of the cutterhead, the loosening of the cutterhead and the cooling of the cutterhead are all listed here. These operations should be in the form of a prescribed CNC code, written as a programme sheet, and then entered into the machine tool computer. After the input, the CNC system will be based on the input instructions to start compiling, arithmetic and logic processing operation. When the processing action is completed, it will output various signals and instructions, which can control various parts of the machine tool, so that under the instructions corresponding to the specified displacement, and in accordance with the sequential action requirements, and ultimately process a variety of different shapes of the workpiece. Therefore, in view of the operation process, the programming has a great influence on the performance of CNC machine tools.
First of all, in CNC machine tools, instruction codes representing different functions are entered into the CNC control in the form of programmes. Then, these instruction codes are processed by the CNC. Afterwards, the CNC sends out pulse signals to control the operation of the moving parts of the CNC machine. The end result is that the part is machined.
Nowadays, there are two standards for CNC programmes, one of which is the ISO of the International Organisation for Standardisation and the other is the EIA of the Electronic Industries Association of the United States of America, and it is the ISO code that is used in our country.
As technology advances, manual programming is rarely used in 3D CNC programming, and commercial CAD/CAM software is used instead.
The core of the computer-aided programming system is CAD/CAM, which has a number of major functions: it has, data input/output function; at the same time, it can also be carried out, machining trajectory calculation and editing operations; in addition to setting up, process parameters; you can run, machining simulation process; it also includes, CNC programme post-processing work; and contains, data management and other content.
At this moment, in our country popular users 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
Analyse the drawing of the part to know the general situation of the workpiece, which includes the geometry, know the material of the workpiece, and understand its 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, the program into the machine, then do graphical simulation, and then verify whether the programming is correct.
6, to carry out machining operations on the workpiece, (good process control can be extremely effective in saving time and at the same time improve the quality of processing).
7, the workpiece acceptance, but also for the quality of the error to be analysed (for the implementation of the workpiece inspection, if qualified to flow into the next process; if not qualified, then the quality of analysis with the help of the causes of error and corrective measures to find out).
History of CNC machine tools
After the end of the Second World War, most of the production of manufacturing industry is the use of manual operation, when the workers understand the relevant drawings, in order to manually operate the machine tools, and then to be processed parts, through such a way to produce products, but so the cost is higher, the efficiency is also very low, and the quality of the same can not be guaranteed.
At the end of the 1940s, John Parsons, an engineer in the United States, conceived the idea of punching holes in a cardboard card to represent the geometry of the part to be machined, and using that card to control the machine's movements, which was only a concept at that time.
In 1948, Parsons put his idea to the U.S. Air Force made a demonstration, the U.S. Air Force has seen, showed great interest, this is because the U.S. Air Force at that time is looking for an advanced processing methods, expect to solve the aircraft prototype processing problems, in view of the prototype shape of the complexity of the precision requirements of the 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 develop the hard cardboard to manipulate the machine tool. MIT) to carry out research to develop the machine tool manipulated by the hard cardboard, finally in 1952, MIT and Parsons collaborated to successfully develop the first demonstration machine, to the 1960's, the simpler and more economical point control drilling machine, as well as linear control of CNC milling machine has gained rapid development, prompting the gradual promotion of CNC machine tools in the manufacturing industry in all sectors.
The history of CNC machining has already lasted more than half a century, NC numerical control system from the initial analogue signal circuit control, developed into an extremely complex integrated machining system, programming from the manual development of intelligent and powerful CAD / CAM integrated system.
According to China's situation, the development of CNC technology is relatively slow, for most of the domestic workshop, the equipment is relatively old, the technical level of personnel and the concept of lagging behind the presentation of poor processing quality and processing efficiency is not high, often delayed delivery date.
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 circuit boards, the first CNC machine tool was born in 1952, it has evolved from a milling machine or lathe into a machining centre, which in turn has become the key equipment of 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.
First of all, the time came to 1964, when the fourth generation of NC system had been successfully developed, and this fourth generation of NC system was the kind of computer numerical control system, or CNC control system, that we are extremely familiar with.
After the fourth generation NC system, the NC system was adopted in 1975 with a powerful microprocessor, and this is the fifth generation NC system.
6, the sixth generation of the NC system, the use of the current integrated manufacturing system, that is, MIS, but also the use of DNC, and the use of flexible machining system, this system is FMS.
Trends in CNC machine tools
1. High-speed
Along with the rapid development of the automotive industry, the defence industry is also in the process of taking off, and a series of circumstances such as the continuous progress in the field of aviation and aerospace, as well as a variety of new materials including aluminium alloys are being put into use, and the demand for high speeds generated by CNC machine tooling is becoming increasingly high.
_a. Spindle speed: The machine utilises an electric spindle, i.e. the type with a built-in spindle motor, which can reach a maximum speed of / per minute.
b. Feed rate, with a maximum feed rate of 240m/min at a resolution of 0.01µm, and the ability to obtain accurate machining of complex shapes.
c. Operating speed: the rapid development of microprocessors, which for the CNC system towards high-speed, high-precision development of the direction to lay the foundation for the protection, and then developed the current CPU has been developed to 32-bit and 64-bit CNC system, the frequency has now been increased to hundreds of megahertz to the extent of the degree, and even on the gigahertz. Because of the greatly increased computing speed, feed rates of 24 to 240 m/min can be achieved with resolutions of 0.1 µm or 0.01 µm.
d. Tool change speed, nowadays the tool exchange time of advanced foreign machining centres is usually at the level of about 1s, and the higher level has already reached 0.5s. The German company designed the tool magazine into a basket like style, with the main spindle as the axis, and the tools are arranged in the circumferential position, and the tool change time from tool to tool is only 0.9s.
2. High precision
Nowadays, the requirements for the accuracy of CNC machine tools are no longer limited to static geometrical accuracy, but more and more attention is being paid to the motion accuracy of the machine tool, the thermal deformation of the machine tool as well as the monitoring and compensation of vibrations.
To improve the control accuracy of the CNC system is to use high-speed interpolation technology to achieve continuous feeding through small segments of the programme, thus promoting the CNC control unit tends to be refined, and the use of high-resolution position detection devices to improve the accuracy of the position detection, position servo system using feed-forward control and non-linear control and other means.
b. The use of error compensation technology: the use of backlash compensation technology, the use of screw pitch error compensation technology, the use of tool error compensation and a series of related technologies, for the equipment exists in the thermal deformation error and spatial error to carry out a comprehensive and integrated compensation.
c. Use the grid **** to carry out checks to improve the accuracy of the machining centre's trajectory, and predict the machining accuracy of the machine tool with the help of simulation, so as to ensure that the machine tool's positioning accuracy and repetitive positioning accuracy, so that its performance will remain stable in the long term, so that it can complete a variety of machining tasks under different operating conditions, and to ensure that the machining quality of the parts is guaranteed.
3. Functional complexity
Compound machine tools are machines that can be used to achieve or cover as many elements as possible on a single machine, from the blank to the finished product. According to its structural characteristics, it can be divided into two categories: process compound and process compound. Machining centres can complete many processes such as turning, milling, drilling, hobbing, grinding, laser heat treatment, etc., and are capable of processing all complex parts. Along with modern machining requirements continue to improve, a large number of multi-axis CNC machine tools are more and more popular with various large enterprises.
4. Intelligent control
Following the development process of artificial intelligence that technology, in order to reach the development needs of manufacturing production flexibilisation and manufacturing automation, the degree of intelligence of CNC machine tools continues to improve, specifically in the following aspects, these aspects are:
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: In the manufacturing process, the integration of measurement operations, the integration of modelling behaviour, the integration of machining, and the integration of machine operations, all four of which are known as 4M, are integrated into a single system.
5. Openness of the system
a. Openness to future technologies: Given that software and hardware interfaces are based on recognised standard protocols, it is possible to adopt, assimilate, and be compatible with the new generation of commonly used software and hardware.
b. To be open to the special requirements of users, which includes updating products, including the expansion of functionality, and to provide a variety of combinations of hardware and software products to meet the requirements of special applications.
c. The construction of numerical control standards, standardised programming languages, which on the one hand facilitate the user's application, and on the other hand enable the reduction of labour consumption, which is closely linked to operational efficiency.
6. Parallelisation of drives
Multi-coordinate simultaneous CNC machining is possible, with such qualities as assembly, measurement and the ability to meet the needs of complex speciality parts. In this way, the parallel machine is considered “the most significant advance in the machine tool industry since the invention of numerical control technology”, and it is also regarded as “the new generation of numerical control 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 need for large-scale and good performance of CNC machine tools support, the development of aerospace, the need for large-scale and good performance of CNC machine tools support, energy and other basic industrial equipment for large-scale, the need for large-scale and good performance of CNC machine tools support. Rather, it is the 21st century strategic technology of ultra-precision machining technology, need to develop new manufacturing processes and equipment that can adapt to the micro-small size and micro-nanometer machining accuracy, is the 21st century strategic technology of micro-nanotechnology, 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
Both can reach the sharing of network resources, but also can reach the remote monitoring of CNC machine tools, but also can reach the remote control, and can reach the remote diagnosis and maintenance.
9. Greening of processes
These years, the kind of no or less coolant, to achieve dry cutting, semi-dry cutting, with energy-saving and environmentally friendly features of the machine tool, continue to emerge, the formation of green manufacturing trend, prompting various types of energy-saving and environmentally friendly machine tools, accelerated the pace of development.
10. Application of multimedia technologies
Multimedia technology combines computer, audio and video and communications technology, so that the computer has the ability to comprehensively process sound, text, images and video information, can reach the information processing with integrated, intelligent features, applied to real-time monitoring system, also applied to the production site equipment troubleshooting, but also applied to the production process parameter monitoring and other levels, so there is a significant application of the Value.
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