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The application of numerical control technology has caused a qualitative change

Jan 05 , 2021

The application of numerical control technology has caused a qualitative change in the traditional manufacturing industry, especially in recent years. The development of microelectronic technology and computer technology has brought new vitality to numerical control technology. Numerical control technology and numerical control equipment are important foundations of industrial modernization in various countries.

CNC machine tools are the mainstream equipment of modern manufacturing industry. It is essential equipment for precision machining. It is an important symbol that reflects the technological level of modern machine tools and the technological level of modern machinery manufacturing. It is a strategic material related to the national economy, people's livelihood, and national defense. Therefore, all industrialized countries in the world have taken major measures to develop their own CNC technology and industries.

CNC machining

CNC is the abbreviation of English Computer Numberical Control, which means "computer data control", or simply "numerical control processing". In the Pearl River Delta region, people call it "computer gong".

Numerical control processing is an advanced processing technology in today's machinery manufacturing, and it is an automated processing method with high efficiency, high precision and high flexibility. It is to input the NC program of the workpiece to be processed to the machine tool, and the machine tool automatically processes the workpiece that meets people's wishes under the control of these data to produce wonderful products.

CNC machining technology can effectively solve the complex, precise, small batch and changeable machining problems like molds, and fully meet the needs of modern production. Vigorously developing numerical control processing technology has become an important way for my country to accelerate economic development and improve independent innovation capabilities. At present, the use of CNC machine tools in my country is becoming more and more common, and being able to master CNC machine tool programming is an important way to give full play to its functions.

CNC machine tool is a typical mechatronics product. It integrates many advanced technologies such as microelectronics technology, computer technology, measurement technology, sensor technology, automatic control technology and artificial intelligence technology, and is closely integrated with mechanical processing technology. A generation of machinery manufacturing technology and equipment.

The composition of CNC machine tools

CNC machine tools are automated equipment that integrates machine tools, computers, motors, and drag, motion control, and detection technologies. The basic composition of CNC machine tools includes control medium, CNC device, servo system, feedback device and machine tool body, as shown in the figure

1. Control medium

The control medium is the medium that stores the position information of all the action tools required by the CNC machining relative to the workpiece. It records the machining program of the part. Therefore, the control medium refers to the information carrier that transmits the machining information of the part to the CNC device. There are many forms of control media, which vary with the types of numerical control devices. Commonly used are punched tape, punched cards, magnetic tapes, and disks. With the development of numerical control technology, punched tapes and punched cards tend to be eliminated, and the use of CAD/CAM software to program in the computer, and then communicate with the numerical control system through the computer, the method of directly transmitting the program and data to the numerical control device is more and more widely used .

2. Numerical control device

The numerical control device is the core of the numerical control machine tool, and it is called the "central system". Modern CNC machine tools use computer numerical control device CNC. The numerical control device includes an input device, a central processing unit (CPU), and an output device. The numerical control device can complete information input, storage, transformation, interpolation, and realize various control functions.

3. Servo system

The servo system is a drive component that receives instructions from the numerical control device and drives the actuator of the machine tool. Including spindle drive unit, feed drive unit, spindle motor and feed motor, etc. When working, the servo system accepts the command information of the CNC system and compares it with the position and speed feedback signals according to the requirements of the command information, drives the moving parts of the machine tool or executes the actions of the parts, and processes the parts that meet the requirements of the drawings.

4. Feedback device

The feedback device is composed of measuring components and corresponding circuits. Its function is to detect speed and displacement, and feedback the information to form a closed-loop control. Some CNC machine tools with low precision requirements without feedback devices are called open-loop systems.

5. Machine tool body

The main body of the machine tool is the entity of the CNC machine tool, and is the mechanical part that completes the actual cutting process. It includes the bed, base, table, saddle, spindle, etc.

Features of CNC machining process

CNC machining technology also obeys the laws of machining and cutting, which is roughly the same as that of ordinary machine tools. Because it is an automatic processing that applies computer control technology to mechanical processing, it has the characteristics of high processing efficiency and high precision. The processing technology has its own unique features, the process is more complicated, and the work step arrangement is more detailed and thorough.

The CNC machining process includes the selection of cutting tools, the determination of cutting parameters, and the design of cutting process routes. CNC machining technology is the foundation and core of CNC programming. Only with reasonable technology can we compile high-efficiency and high-quality CNC programs. The criteria for measuring the quality of a CNC program are: the least processing time, the least tool loss, and the workpiece with the best results.

The CNC machining process is a part of the overall processing technology of the workpiece, even a process. It must cooperate with other front and back processes to finally meet the assembly requirements of the overall machine or mold, so that qualified parts can be processed.

The CNC machining process is generally divided into rough machining, medium and rough corner clearing, semi-finishing and finishing

CNC programming

Numerical control programming is the whole process from part drawing to obtaining numerical control processing program. Its main task is to calculate the cutter location point (CL point for short) in the machining pass. The tool location point is generally taken as the intersection of the tool axis and the tool surface, and the tool axis vector is also given in multi-axis machining.

According to the requirements of the workpiece pattern and the processing process, the CNC machine tool operates the movement, speed and sequence of actions, spindle speed, spindle rotation direction, tool head clamping, tool head loosening and cooling of the used tools and various components to operate. The prescribed numerical control code form is compiled into a program list and input into the special computer of the machine tool. Then, the numerical control system compiles, calculates, and logically processes the input instructions, outputs various signals and instructions, and controls each part to process various workpieces with different shapes according to the prescribed displacement and sequential actions. Therefore, programming has a great influence on the effectiveness of CNC machine tools.

The CNC machine tool must input the instruction codes representing various functions into the CNC device in the form of a program, which is processed by the CNC device, and then sends out pulse signals to control the operation of the various moving parts of the CNC machine tool to complete the cutting process of the parts.

There are currently two standards for CNC programs: ISO from the International Organization for Standardization and EIA from the American Electronics Industry Association. my country adopts the ISO code.

With the advancement of technology, 3D CNC programming generally rarely uses manual programming, but uses commercial CAD/CAM software.

CAD/CAM is the core of the computer-aided programming system. Its main functions include data input/output, calculation and editing of processing trajectories, process parameter settings, processing simulation, post-processing of numerical control programs, and data management.

At present, in our country, the software with powerful CNC programming function that is loved by users includes Mastercam, UG, Cimatron, PowerMILL, CAXA, etc. The principles, graphics processing methods and processing methods of various softwares are similar, but each has its own characteristics.

Steps of CNC machining parts

1. Analyze the part drawing and understand the general situation of the workpiece (geometric shape, workpiece material, process requirements, etc.)

2. Determine the numerical control processing technology of the part (processing content, processing route)

3. Perform necessary numerical calculations (calculation of base point and node coordinates)

4. Write the program list (different machine tools will be different, follow the manual)

5. Program verification (input the program into the machine tool and perform graphic simulation to verify that the programming is correct)

6. Process the workpiece (good process control can save time and improve processing quality)

7. Workpiece acceptance and quality error analysis (inspect the work piece, and pass it to the next one. If it fails, find out the cause of the error and corrective method through quality analysis).

The development history of CNC machine tools

After the Second World War, most of the production in the manufacturing industry relied on manual operations. After the workers understood the drawings, they manually operated the machine tools and processed the parts. The production of products in this way resulted in high cost, low efficiency, and quality assurance.

In the late 1940s, an American engineer, John Parsons, conceived a method of punching holes in a hard paper card to indicate the geometry of the parts to be processed, using a hard card to Controlling the movement of the machine tool was just an idea at the time.

In 1948, Parsons showed his idea to the U.S. Air Force. After seeing it, the U.S. Air Force expressed great interest, because the U.S. Air Force was looking for an advanced processing method, hoping to solve the problem of processing aircraft appearance templates. Due to the complex shape of the prototype, high precision requirements, and difficulty in adapting to general equipment, the US Air Force immediately commissioned and sponsored the Massachusetts Institute of Technology (MIT) to conduct research and develop this hard cardboard-controlled machine tool. Finally, in 1952, Massachusetts In cooperation with Parsons, the Polytechnic Institute successfully developed the first demonstration machine. In 1960, the relatively simple and economical point control drilling machine and the linear control CNC milling machine had been developed rapidly, making CNC machine tools in the manufacturing industry. Various departments are gradually being promoted.

The history of CNC machining has gone through more than half a century. The NC numerical control system has also developed from the earliest analog signal circuit control to an extremely complex integrated processing system. The programming method has also been developed manually into an intelligent and powerful CAD/CAM integrated system. .

As far as my country is concerned, the development of CNC technology is relatively slow, for most workshops in China. The equipment is relatively backward, and the technical level and concept of the personnel are backward, which is manifested by low processing quality and processing efficiency, and often delays the delivery date.

1. The first-generation NC system was introduced in 1951, and its control unit is mainly composed of various valves and analog circuits. In 1952, the first CNC machine tool was born. It has developed from a milling machine or a lathe to a machining center, becoming a modern manufacturing Key equipment for the industry.

2. The second-generation NC system was produced in 1959, which is mainly composed of a single transistor and other components.

3. The third-generation NC system was introduced in 1965, and the integrated circuit board was used for the first time.

4. In fact, in 1964, the fourth-generation NC system was developed, that is, the computer digital control system (CNC control system) that we are very familiar with.

5. In 1975, the NC system adopted a powerful microprocessor, which was the fifth-generation NC system.

6. The sixth-generation NC system adopts the current integrated manufacturing system (MIS) + DNC + flexible processing system (FMS)

The development trend of CNC machine tools

1. High speed

With the rapid development of industries such as automobiles, national defense, aviation, aerospace, and the application of new materials such as aluminum alloys, the requirements for high-speed machining of CNC machine tools are getting higher and higher.

a. Spindle speed: The machine tool adopts an electric spindle (built-in spindle motor), and the maximum spindle speed is up to 200,000r/min;

b. Feed rate: When the resolution is 0.01µm, the maximum feed rate reaches 240m/min and complex precision machining can be obtained;

c. Operation speed: The rapid development of microprocessors provides a guarantee for the development of CNC systems in the direction of high speed and high precision. The development of CPUs has developed to 32-bit and 64-bit CNC systems, and the frequency has been increased to several hundreds of megahertz and above gigahertz. . Due to the greatly improved calculation speed, the feed speed of up to 24~240m/min can be obtained when the resolution is 0.1µm and 0.01µm;

d. Tool change speed: At present, the tool change time of foreign advanced machining centers has generally been around 1s, and the high has reached 0.5s. The German Chiron company designed the tool magazine into a basket style, with the spindle as the axis, and the tools arranged on the circumference. The tool change time from tool to tool is only 0.9s.

2. High precision

The accuracy requirements of CNC machine tools are now not limited to static geometric accuracy. The motion accuracy, thermal deformation, and vibration monitoring and compensation of machine tools are getting more and more attention.

a. Improve the control accuracy of CNC system: adopt high-speed interpolation technology, realize continuous feed with tiny program segments, make CNC control unit refined, and adopt high-resolution position detection device to improve position detection accuracy, and position servo system adopts feedforward Control and nonlinear control methods;

b. Adopt error compensation technology: adopt backlash compensation, screw pitch error compensation and tool error compensation technology to comprehensively compensate the thermal deformation error and space error of the equipment.

c. Use a grid decoder to check and improve the accuracy of the motion trajectory of the machining center: predict the machining accuracy of the machine tool through simulation to ensure the positioning accuracy and repetitive positioning accuracy of the machine tool, so that its performance is stable for a long time, and it can complete multiple operations under different operating conditions. Kind of processing tasks, and to ensure the processing quality of parts.

3. Functional composite

The meaning of the compound machine tool is to realize or complete the processing of multiple elements from the rough to the finished product on a machine tool. According to its structural characteristics, it can be divided into two types: process compound type and process compound type. The machining center can complete various processes such as turning, milling, drilling, gear hobbing, grinding, and laser heat treatment, and can complete all the processing of complex parts. With the continuous improvement of modern machining requirements, 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 development needs of manufacturing flexibility and manufacturing automation, the degree of intelligence of CNC machine tools is constantly improving. It is embodied in the following aspects:

a. Adaptive control technology for processing;

b. Intelligent optimization and selection of processing parameters;

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

d. Intelligent fault playback and fault simulation technology;

e. Intelligent AC servo drive device;

f. Intelligent 4M Numerical Control System: In the manufacturing process, the four aspects of measurement, modeling, processing, and machine operation (ie 4M) are integrated into one system.

5. Open system

a. Open to future technology: As the software and hardware interfaces follow the recognized standard protocol, the new generation of general software and hardware can be adopted, absorbed and compatible.

b. Open to users' special requirements: update products, expand functions, and provide various combinations of hardware and software products to meet special application requirements;

c. Establishment of CNC standards

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