Measuring elements and the corresponding circuitry together constitute a feedback device, which has the function of detecting speed and displacement, but also able to feed back the information, and then constructed into a closed-loop control. There are some precision requirements are not very highCNC machine toolsThey do not have a feedback device, so they are called open-loop systems.
5、Machine tool body
Among the many machine tools, the CNC machine tool body is the physical part of the machine, which is the part of the machine specifically designed to complete the actual cutting process, which covers the bed, as well as the base, as well as the table, in addition to the bed saddle, and even the spindle and other components.
CNC machiningCharacteristics of the process
CNC CNC machining process, also follow the laws of machining cutting, and ordinary machine tool machining process, generally the same. Only because it belongs to the computer control technology, the use of mechanical processing in a kind of automated processing, so with high processing efficiency, high precision of these characteristics, and the existence of a unique place of its machining process, the process is relatively more complex, step by step arrangement is more detailed and thorough.
CNC CNC machining process covers the selection of tools, cutting parameters clear, take the knife process route planning, etc. CNC CNC machining process is the foundation of CNC programming and the key to the only appropriate process, can be compiled with high effectiveness and high quality of the CNC programme. Measure the advantages and disadvantages of the CNC programme guidelines are: minimum time, minimum tool loss, and the best results of the workpiece.
The overall machining process of the workpiece includes CNC machining process, which belongs to one part, or even counted as a process, it needs to work with other processes before and after each other, in order to ultimately meet the requirements of the overall assembly of machines or moulds, so as to process the qualified parts.
The CNC machining process 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 from the start of the part drawing until the acquisition of the CNC machining programme, the main task is to calculate the tool position during the machining of the tool travelling point, that is, point referred to as the content of the CL point, the tool position point is usually selected for the tool axis and the intersection of the tool surface, the multi-axis machining also need to be given in the tool axis vector.
CNC machine tools used to process various workpieces of different shapes are based on the requirements given in the workpiece drawings and the process of machining, and a series of operations such as the amount of movement of the tools and parts used, the speed and sequence of movements, the spindle speed, the direction of rotation of the spindle, the clamping of the cutterhead, the release of the cutterhead, and the cooling of the cutterhead, etc., are compiled into a programme sheet in the form of the prescribed CNC code and entered into the machine tool special-purpose computer. Then, the CNC system compiles, calculates and logically processes according to the input instructions, outputs various signals and instructions, and controls various parts to rely on the specified displacement and sequential action, so as to process a variety of different shapes of workpieces. Therefore, the preparation of the programme has a great impact on the performance of the CNC machine tool.
CNC machine to represent the various types of different functions of the instruction code, in the form of a programme input to the CNC device, the CNC device will carry out arithmetic processing, and then send out pulse signals, in order to control the operation of the various moving parts of the CNC machine tool to complete the cutting process of the parts.
At present, there are two standards for CNC programmes: ISO (International Organisation for Standardisation) and EIA (Electronic Industries Association), and the ISO code is used in our country.
As science and technology move forward, CNC programming for digital 3D is usually done with minimal manual programming, and commercial computer-aided design and manufacturing software is used instead.
CAD/CAM is the core of the computer-aided programming system, which has data input and output functions, machining trajectory calculation and editing functions, process parameter setting functions, machining simulation functions, CNC programme post-processing functions, and data management functions.
Nowadays, in our country is popular with users, with powerful CNC programming software exists, UG,, CAXA and so on. Each software for CNC programming principles, graphics processing and processing methods are generally the same, but each has its own characteristics.
Steps for CNC machining parts
The first step is to analyse the part drawing to get a general idea of the workpiece, which covers the geometry, the material 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. Enter the programme into the machine, then carry out graphical simulation to verify that the programming is correct, this is the programme verification.
6. Start machining operations on the workpiece (good process control can be extremely effective in saving time and can significantly improve 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 error analysis to find out the cause of the error as well as ways to correct, this is the workpiece acceptance process.
History of CNC machine tools
After the Second World War, most of the manufacturing industry is operated by manual labour, workers read the drawings, through the manual operation of machine tools, and then processing parts, using such a way to produce products, the cost is high, the efficiency is very low, and the quality can not be guaranteed, as well.
At the end of the 1940s, there was an engineer in the United States, Parsons (John), he conceived a way to punch holes in a cardboard card to indicate the geometry of the parts to be machined, and then use this card to control the action of the machine tool, which, at that time, was just an idea.
In 1948, Parsons presented his idea to the U.S. Air Force, the U.S. Air Force after viewing, revealed a great interest, only because the U.S. Air Force was looking for an advanced processing methods, hoping to overcome the aircraft prototype processing problems, in view of the prototype shape of the complexity of the precision requirements are quite high, unusual equipment is difficult to adapt to, the U.S. Air Force immediately entrusted and financed by the Massachusetts Institute of Technology (MIT) to be the research to develop this hard cardboard manipulation machine, finally in 1952, MIT and Parsons worked together to successfully develop the first demonstration machine. (MIT) to be research, to develop this machine tool controlled by cardboard, finally in 1952, MIT and Parsons, Inc. to work together to successfully research and manufacture the introduction of the first demonstration machine, to the 1960's, the simpler and more economical point control drilling machine, as well as linear control of the CNC milling machine to be faster development, prompting the gradual promotion of numerical control machine tools in the manufacturing industry in all sectors.
The course of CNC machining, has been up to more than half a century of time, NC numerical control system, from the initial analogue signal circuit for control, the development of an extremely complex integrated machining system, programming, from the manual way, the development of the evolution of intelligent and powerful CAD / CAM integrated system.
In China, the development of CNC technology is relatively slow, for most of the domestic workshop, the equipment is relatively old, the technical level of the personnel is poor and the concept of lagging behind to show the poor quality of machining and low machining efficiency, 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 as well as analogue circuits, the first CNC machine tools were introduced in 1952, has been developed from the milling machine or lathe to the machining centre, which has become the key equipment of modern manufacturing.
The second generation of NC systems was created in 1959, and it was largely made up 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 developed, which we know very well as computer numerical control systems (CNC control systems).
5. In 1975, the NC system adopted a powerful microprocessor, which resulted in the fifth generation of the NC system.
No. 6, the sixth generation of NC systems, uses, the current Integrated Manufacturing System, or MIS, plus DNC, plus the Flexible Machining System, or FMS .
Trends in CNC machine tools
1. High-speed
With the high-speed development of the automotive industry, with the high-speed development of the defence industry, with the high-speed development of the aviation industry, with the high-speed development of the aerospace industry, as well as aluminium alloys and other new materials have been applied to the processing of CNC machine tools, high-speed requirements have become increasingly high.
a. The maximum spindle speed that can be achieved is the number of revolutions per minute that can be achieved by a machine tool that uses the type of electrical spindle that incorporates a spindle motor inside the spindle.
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. Operational speed: the rapid development of microprocessors has ensured that CNC systems are developed in the direction of high speed and high accuracy, with the development of 32-bit and 64-bit CPUs and the increase in frequency to several hundred megahertz or a thousand megahertz. It is only because of the great increase in computing speed that feed speeds of up to 24-240m/min can still be obtained when the resolution is 0.1µm or 0.01µm.
d. Tool change speed: Nowadays, in advanced foreign machining centres, the time spent on tool exchange is generally in the range of about 1s, of which the higher level can reach 0.5s. The German company designed the tool magazine into a basket like style, with the spindle as the axis, the tool in the circumferential direction of the arrangement, it is from a tool to another tool change time is only 0.9s.
2. High precision
At this stage, the requirements for the accuracy of CNC machine tools are no longer limited to static geometrical accuracy, but also to the accuracy of the machine's movement, thermal deformation, and vibration monitoring and compensation, all of which are receiving increasing attention.
Adopting high-speed interpolation as a means to achieve uninterrupted feeding with the help of tiny programme segments, allowing the CNC control unit to move towards refinement, using high-resolution position detection devices to improve the accuracy of position detection, position servo systems using feed-forward control and the use of non-linear control of various approaches to improve the control accuracy of the CNC system, which is a practice involved.
b. Use of error compensation technology, use of backlash compensation technology, use of screw pitch error compensation technology, use of tool error compensation technology, etc., for the thermal deformation of the equipment to compensate for the error, for the equipment of the spatial error to compensate for the integrated.
c. A way to check and improve the accuracy of the machining centre's trajectory is to use a grid, how to improve it, by previewing the machine's machining accuracy through simulation, in order to ensure the machine's positioning accuracy and repeatability, so that it has the characteristics of a machine with stable performance over a long period of time, and is able to achieve a wide range of machining tasks in different operating conditions, and to guarantee the quality of the parts machined. quality.
3. Functional complexity
That which is called a compound machine tool means to achieve or complete as much as possible a variety of aspects of processing from the blank to the finished product on a single machine tool, which can be divided into two categories based on its own structural characteristics, namely, process compound and process compound. Machining centre can complete turning, milling, drilling this type of work, as well as hobbing, grinding, laser heat treatment and 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 are more and more popular with various large enterprises.
4. Intelligent control
Followed by the progress of artificial intelligence technology, in order to meet the progress of manufacturing production flexibility, manufacturing automation required, the intelligence level of CNC machine tools in the continuous improvement. Specifically shown 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 system: In the manufacturing process, the link of measurement, modelling, machining and machine operation, i.e. the 4Ms, are integrated into one system.
5. Openness of the system
(a) Openness to future technologies: Given that the interface between software and hardware is based on widely accepted standard protocols, it is possible to embrace, learn from and be compatible with a new generation of universally applicable software and hardware.
Firstly, a series of open responses to the special requirements of users: firstly, updating the products; secondly, expanding the functions; thirdly, providing various combinations of hardware and software products to meet the requirements of special applications.
c. Establishment of CNC standards: the existence of a standardised programming language facilitates access by users on the one hand, and reduces labour consumption directly linked to operational efficiency on the other.
6. Parallelisation of drives
Multi-coordinate linkage of CNC machining, assembly and measurement and other functions it can achieve, complex special parts processing it can meet, parallel machine tools are regarded as “since the invention of CNC technology in the machine tool industry's most significant progress,” is also regarded as “a new generation of the 21st century, CNC machining equipment! It is also regarded as ”the new generation of CNC machining equipment in 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. 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, 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
It can achieve the sharing of network resources, remote monitoring of CNC machine tools, remote control, remote diagnosis and maintenance.
9. Greening of processes
In recent years, machine tools continue to appear, these machine tools do not use coolant, or less coolant, can achieve dry cutting, semi-dry cutting, with energy saving and environmental protection features, and the general trend of green manufacturing prompted a variety of energy-saving ring machine tools to accelerate the development.
10. Application of multimedia technologies
Computer, audio and video and communications technology into one multimedia technology, so that computers have the ability to comprehensively process sound, text, images and video information, to achieve the integration of information processing and intelligence, used in real-time monitoring systems, production site equipment troubleshooting and production process parameter monitoring and other aspects of the production process, so there is a significant value of the application.
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