The feedback device, which consists of measuring elements and corresponding circuits, has the function of detecting the speed and displacement and feeding back this information to form a closed-loop control system. Some of the precision requirements are not very high in theCNC machine toolsBecause there is no feedback device, it is called an open-loop system.
5、Machine tool body
The body of the machine tool, as the entity of the CNC machine tool, is the part of the mechanical aspect used to complete the actual cutting process, which covers the bed, including the base, and the table, as well as the bed saddle, in addition to spindles and so on.
CNC machiningCharacteristics of the process
CNC numerical controlProcessingWill be based on the laws of machining cutting to perform, and ordinary machine tool processing technology is basically similar, it is the use of computer control technology to mechanical processing in the automated processing mode, so has a high processing efficiency, high precision and so on, the characteristics of its processing technology there are unique places, the process is relatively complex, step by step arrangement of a more detailed and thorough.
The selection of tools, the determination of cutting parameters, and the design of toolpaths are all included in the CNC machining process, which is the basis and core of CNC programming, and only with a reasonable process can a high-efficiency and high-quality CNC programme be produced. The criteria for measuring the quality of a CNC programme are minimum machining time, minimum tool wear and the best possible results.
CNC machining process belongs to the workpiece as part of the overall process, but also one of the processes, it needs to work with other processes before and after each other, so as to ultimately meet the overall machine or mould assembly requirements, and then be able to process a qualified part.
The CNC machining process is usually divided into roughing, as well as during the medium roughing, semi-finishing and finishing operations.
CNC programming for CNC
CNC programming, is a complete process from the beginning of the part drawing, until the final acquisition of CNC machining programme, its main task is to calculate the machining process of the tool point, referred to as the CL point, the tool point is usually selected for the intersection of the tool axis and the tool surface, in multi-axis machining, but also need to give the tool axis vector.
The required digital control of the machine tool is based on the requirements given in the workpiece drawing and the specific process of the machining process, the amount of movement of the tool used and the various components, speed, and the sequence of actions associated with the order, spindle speed, direction of spindle rotation, head clamping action, head release action, and cooling, etc., by virtue of the prescribed form of numerical control code written as a programme sheet, placed into the machine tool dedicated computer. Computer. After that, the CNC system in accordance with the input of this instruction actually compiled, participate in computing and carry out logical processing, output all kinds of different signals and corresponding instructions, control the parts in accordance with the specified displacement and have the sequence of action, so as to process and manufacture a variety of different shapes of the workpiece. Therefore, the compilation of the programme has a huge impact on the success of the performance of the CNC machine tool.
CNC machine tools, need to represent a variety of different functions of the instruction code, in the form of a programme, input CNC device, CNC device will be calculated and processed, and then send out pulse signals to control the operation of the various moving parts of the CNC machine tools, so that, to complete the parts of the cutting process.
Nowadays, there are two standards for CNC procedures, one of which is ISO, established by the International Organisation for Standardisation, and the other is EIA, established by the Electronic Industries Association of the United States of America, which, as far as our country is concerned, adopts the ISO code.
Because of technological advances, 3D CNC programming is usually rarely done manually, so to speak, but rather using commercial CAD/CAM software.
The computer system used to assist programming, the core of which is CAD/CAM, involves a variety of functions, including data input and output, the calculation and editing of machining trajectories, including the setting of process parameters, with the function of machining simulation, but also involves the post-processing of CNC programmes and data management.
Nowadays, in our country, there are software with powerful CNC programming functions that are popular among users, such as UG, CAXA, etc. Each software has roughly the same principle about CNC programming but has its own characteristics. Each software about the principle of CNC programming, graphics processing and machining methods, roughly the same but each has its own characteristics.
Steps for CNC machining parts
1, analysis of parts drawings, know the general situation of the workpiece, such as geometry, and then understand the workpiece material material, and finally grasp the process requirements of such cases.
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, good process control, can be very good to save time, can be very good to improve the quality of processing of the workpiece.
7, workpiece acceptance, for workpiece inspection, if qualified will flow into the next process, if not qualified, with the help of quality analysis to explore the causes of errors and the corresponding corrective measures, but also for quality error analysis.
History of CNC machine tools
After the end of the Second World War, most of the production of manufacturing industry is to rely on manual operation, workers in the understanding of the drawings, through the manual operation of machine tools, and then processing parts, using this way to produce products, and this way of high cost, low efficiency, and quality can not be guaranteed.
Towards the end of the 1940s, there was an engineer in the United States named Parsons (John), who came up with a way to represent the geometry of the parts to be machined by punching holes in a cardboard card, with the help of which to control the movement of the machine, which was just an idea at that time.
In 1948, Parsons showed his idea to the U.S. Air Force, the U.S. Air Force looked over, expressed great interest, because the U.S. Air Force was looking for an advanced processing method, expect to solve the problem of aircraft prototype processing, given the complex shape of the prototype, high precision requirements, general equipment is difficult to adapt, the U.S. Air Force immediately commissioned and sponsored the Massachusetts Institute of Technology (MIT) to research and develop this machine tool controlled by cardboard, finally in 1952, MIT and Parsons collaborated to successfully develop the first demonstration machine. (MIT) to carry out research, the development of this machine tool controlled by the hard cardboard, finally in 1952, MIT and Parsons cooperation, successfully developed the first demonstration machine, to the 1960's simpler and more economical point control drilling machine, as well as linear control of CNC milling machine has gained rapid development, resulting in the gradual promotion of CNC machine tools in various sectors of the manufacturing industry.
The history of CNC machining has gone through a development process that lasts for an extremely long time and lasts for more than half a century. The NC numerical control system has evolved into an integrated machining system with an unimaginably complex structure and complexity, and the programming method has evolved into a powerful CAD/CAM integrated system with intelligent features from the stage of relying on the manual application of the relevant method. The programming method has evolved from a manual method to a powerful CAD/CAM integrated system with intelligent features.
For China, the development of CNC technology is relatively slow, most of the domestic workshop, equipment is more backward, the technical level of personnel is poor and lagging behind the concept, showing poor processing quality and processing efficiency is not high, often delaying the delivery date.
1, the first generation of the NC system, was introduced in 1951, its control unit, mainly by a variety of valves and analogue circuits are composed of, in 1952, the first CNC machine tools were born, it has developed from the milling machine or lathe to the machining centre, has become the key equipment for modern manufacturing.
2. The second generation of NC systems, which was produced in 1959, is 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 system has been developed, this system is also very familiar with the computer numerical control system, that is, CNC control system.
5. In 1975, a powerful microprocessor was introduced to the NC system, which was the fifth generation of the NC system.
6. The sixth-generation NC system takes an integrated manufacturing system (MIS) in operation, plus DNC, plus a flexible machining system (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, and with the application of new materials such as aluminium alloys, for the processing of CNC machine tools, the high-speed requirements are becoming more and more high.
a. The machine tool uses an electric spindle, that is, a built-in spindle motor, whose spindle has a maximum speed of up to 1 minute per minute, for / min, which is the spindle speed of the relevant situation.
b. Feed rate, with a resolution setting of 0.01µm, is capable of a maximum feed rate of 240m/min, which enables precise machining of complex shapes!
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 obtain feed speeds of up to 24 to 240m/min.
d. Tool replacement speed, now advanced foreign processing centre, tool exchange time required, generally speaking, has been in the range of about 1 second, the higher level has reached 0.5 seconds. German companies to the tool magazine designed as a basket style, the spindle as the axis, the tool in the circumferential direction for the arrangement of its from a tool replacement to another tool time is only 0.9 seconds.
2. High precision
Nowadays, the requirements for the accuracy of CNC machine tools are no longer limited to static geometrical accuracy, more attention is paid to the motion accuracy of the machine tool, thermal deformation is also getting more and more attention, and vibration monitoring and compensation are also getting more and more attention.
a. In order to improve the control accuracy of the CNC system, high-speed interpolation technology is used to achieve continuous feeding through tiny programme segments, which contributes to the refinement of the CNC control unit, and a high-resolution position detection device is also used to improve the position detection accuracy, and the position servo system applies feed-forward control and non-linear control methods.
b. Comprehensive compensation of thermal and spatial errors generated by the equipment through the use of specific technologies, such as backlash compensation, screw pitch error compensation, and tool error compensation.
c. The use of grid checking to improve the accuracy of the motion trajectory of the machining centre, the use of simulation to predict the machining accuracy of the machine tool, to ensure that the positioning accuracy and repeat positioning accuracy of the machine tool, so as to achieve long-term stability of its performance, so that it is able to complete a variety of machining tasks under different operating conditions, thus guaranteeing the machining quality of the parts.
3. Functional complexity
The meaning of the machine tool is to realise, or complete as far as possible, a variety of elements of processing from the blank to the finished product on a single machine tool, which is a composite machine tool. According to its structural characteristics, it can be divided into two categories: process compound and process compound. Machining centres are capable of turning, milling, drilling, hobbing, grinding, laser heat treatment and other processes, which in turn 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 increasingly welcomed by major enterprises.
4. Intelligent control
In view of the continuous development of artificial intelligence technology, in response to the development of manufacturing production flexibility and manufacturing automation needs, the degree of intelligence of CNC machine tools is continuing to improve, specifically 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. In the manufacturing process, measurement, modelling, machining and machine operation are integrated into one system, i.e. measurement, modelling, machining and machine operation (4M).
5. Openness of the system
a. Open the door to future technologies, given that software and hardware interfaces are based on widely recognised standard protocols that can be adopted and then assimilated and made compatible with a new generation of common software and hardware.
b. Openness to special user requirements, product updates, functionality expansion, and various combinations of hardware and software products to meet the needs of special applications.
c. The establishment of CNC standards and the existence of standardized programming languages, which are user-friendly and also reduce labour consumption directly related to operational efficiency.
6. Parallelisation of drives
Being able to achieve multi-coordinate linkage CNC machining, as well as assembly and measurement functions, and being able to meet the needs of complex special parts machining, parallel machine tools are regarded as “the most significant advancement in the machine tool industry since the invention of numerical control technology”, and as “the new generation of CNC machining equipment for the 21st century”. It 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, 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 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
Not only can it reach the sharing of network resources, but also can reach the remote monitoring of CNC machine tools, and can reach the remote control, as well as in addition can reach the remote diagnosis, in addition to reach the maintenance.
9. Greening of processes
In the past two years, the kind of coolant, or less coolant, and thus achieve dry cutting, semi-dry cutting, and has the characteristics of energy-saving and environmental protection machine tools, continue to present, green manufacturing trend, resulting in various types of energy-saving and environmental protection machine tools to accelerate the pace of 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, can reach a comprehensive and intelligent information processing, can be applied to real-time monitoring system, as well as production site equipment fault diagnosis, production process parameters monitoring, so there is a significant value of the application.
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