Detailed explanation of CNC CNC machining technology features and operation steps

CNC machine tools are the mainstream equipment of modern manufacturing industry. The necessary equipment for precision machining is an important symbol reflecting the level of modern machine tools and the level of modern machinery manufacturing. It is a strategic material that relates to the national economy and the people's livelihood and the cutting-edge construction of national defense. Therefore, all industrialized countries in the world have taken major measures to develop their own numerical control technology and its industry.

CNC machining

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

CNC machining is an advanced machining technology in today's machinery manufacturing, and it is an automated processing method with high efficiency, high precision and high flexibility. It is a CNC program that processes the workpiece to the machine tool. Under the control of these data, the machine automatically processes the workpiece according to people's wishes to create a wonderful product.

CNC machining technology can effectively solve complex, precise and small batches of processing problems like molds, fully adapting to the needs of modern production. Vigorously developing CNC machining technology has become an important way for China to accelerate its economic development and enhance its independent innovation capability. At present, the use of CNC machine tools in China is becoming more and more common, and it is an important way to fully utilize the functions of CNC machine tools.

CNC machine tools are typical mechatronic products. It integrates various advanced technologies such as microelectronics technology, computer technology, measurement technology, sensor technology, automatic control technology and artificial intelligence technology, and is closely integrated with the machining process. It is new. A generation of mechanical manufacturing technology and equipment.

The composition of CNC machine tools

CNC machine tools integrate machine tools, computers, motors and drag, motion control, detection and other technologies into one automation equipment. The basic components of CNC machine tools include control media, numerical control devices, servo systems, feedback devices, and machine tools.

1, control medium

The control medium is a medium for storing all the action tools required for numerical control machining with respect to the workpiece position information, and it records the machining program of the parts. Therefore, the control medium refers to the information carrier that transmits the part processing information to the numerical control device. There are many forms of control media, which vary with the type of numerical control device. Commonly used are perforated tapes, punched cards, magnetic tapes, magnetic disks, and the like. With the development of numerical control technology, the perforated tape and punched card tend to be eliminated, and the method of using CAD/CAM software in computer programming, and then communicating with the numerical control system through computer, the program and data are directly transmitted 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 people call it the “central system”. Modern CNC machine tools use CNC numerical control devices CNC. The numerical control device includes an input device, a central processing unit (CPU), and an output device, and the like, and the numerical control device can complete information input, storage, conversion, interpolation operation, and realize various control functions.

3, servo system

The servo system is a drive unit that receives commands from the numerical control device and drives the movement of the machine tool actuator. Including spindle drive unit, feed drive unit, spindle motor and feed motor. During operation, the servo system accepts the command information of the numerical control system, and compares with the position and speed feedback signals according to the requirements of the command information, then drives the moving parts or the executing parts of the machine tool to process the parts that meet the requirements of the drawings.

4, feedback device

The feedback device consists of a measuring component and a corresponding circuit that detects the velocity and displacement and feeds back the information to form a closed loop control. Some CNC machines with low precision requirements, without feedback devices, are called open loop systems.

5, machine body

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

The characteristics of CNC machining process

CNC machining processes also follow the machining rules of machining, which is roughly the same as that of ordinary machine tools. Because it is an automatic processing that applies computer control technology to machining, 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 steps are more detailed and detailed.

The CNC machining process includes the selection of the tool, the determination of the cutting parameters and the design of the cutting process route. The CNC machining process is the basis and core of CNC programming. Only when the process is reasonable, can we program high-efficiency and high-quality NC programs. The criteria for measuring the quality of a CNC program are: minimum machining time, minimum tool loss, and workpieces that produce the best results.

The CNC machining process is part of the overall machining process of the workpiece, or even a process. It has to work 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.

CNC machining processes are generally divided into rough machining, medium coarse and clear machining, semi-finishing and finishing.

CNC programming of CNC

CNC programming is the whole process from part drawing to obtaining CNC machining program. Its main task is to calculate the cutter location point (CL point). The tool 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 machining process, the CNC machine tool will operate the tool and the movement amount, speed and sequence of the various components, the spindle speed, the spindle rotation direction, the cutter head clamping, the cutter head release and cooling, etc. The specified numerical control code format is programmed into a program-specific computer and input to a machine-specific computer. Then, after the CNC system compiles, calculates, and logically processes according to the input instructions, it outputs various signals and commands, and controls each part to process workpieces of various shapes according to the specified displacement and sequential actions. Therefore, the programming of the program has a great impact on the performance of CNC machine tools.

The numerical control machine tool must input the instruction codes representing various functions into the numerical control device in the form of a program, perform numerical processing by the numerical control device, and then issue a pulse signal to control the operation of each moving part of the numerical control machine tool, thereby completing the cutting process of the parts.

The current CNC program has two standards: the ISO of the International Organization for Standardization and the EIA of the American Electronics Industry Association. China uses ISO code.

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

CAD/CAM is the core of computer-aided programming system. The main functions include data input/output, calculation and editing of machining trajectory, process parameter setting, machining simulation, NC program post-processing and data management.

At present, the powerful software for CNC programming in China is Mastercam, UG, Cimatron, PowerMILL, CAXA and so on. Each software is similar to the principle of CNC programming, graphics processing methods and processing methods, but each has its own characteristics.

CNC machining parts steps

1. Analyze the part drawing to understand the general situation of the workpiece (geometry, workpiece material, process requirements, etc.)

2. Determine the CNC machining process of the part (processing content, processing route)

3. Perform necessary numerical calculations (base point, coordinate calculation of nodes)

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

5, program verification (put the program into the machine, and perform a graphical simulation to verify the correct programming)

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

7. Workpiece acceptance and quality error analysis (test the workpiece and pass the test to the next one. If it fails, the quality analysis will be used to find out the cause of the error and the corrective method).

The history of CNC machine tools

After the Second World War, most of the manufacturing industry relied on manual operation. After the workers understood the drawings, manually operated the machine tools and processed the parts, the products were produced in this way, with high cost, low efficiency and unguaranteed quality.

In the late 1940s, an engineer in the United States, John Parsons, conceived a method of punching a cardboard card to indicate the geometry of the part to be machined, using a hard card to control it. The action of the machine tool, at the time, was just a concept.

In 1948, Parsons showed his thoughts to the US Air Force. After watching the US Air Force, he expressed great interest because the US Air Force is looking for an advanced processing method and hopes to solve the processing problems of aircraft exterior models. Due to the complex shape of the model, high precision requirements, and the general equipment is difficult to adapt, the US Air Force immediately commissioned and sponsored the Massachusetts Institute of Technology (MIT) to conduct research to develop this hard-card-controlled machine tool, finally in 1952, Massachusetts. The Institute of Science and Technology and Parsons cooperated successfully to develop the first demonstration machine. By 1960, the simple and economical point-controlled drilling machine, and the linear control CNC milling machine developed rapidly, making CNC machine tools in the manufacturing industry. Various departments have gradually been promoted.

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

As far as China is concerned, the development of numerical control 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 due to the low processing quality and processing efficiency, and often delay the delivery period.

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

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

3. In 1965, the third-generation NC system was introduced, which used integrated circuit boards for the first time.

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

5. In 1975, the NC system used a powerful microprocessor, which is the fifth-generation NC system.

6, the sixth generation NC system uses the current integrated manufacturing system (MIS) + DNC + flexible processing system (FMS)

The development trend of CNC machine tools

High speed

With the rapid development of automobiles, defense, aviation, aerospace and other industries 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 adopts electric spindle (built-in spindle motor), the maximum speed of the spindle reaches 200000r/min;

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

c. Operation speed: The rapid development of the microprocessor provides guarantee for the development of the CNC system to high speed and high precision. The CPU has been developed to 32-bit and 64-bit CNC systems, and the frequency is increased to several hundred megahertz and upper gigahertz. . Due to the greatly improved operation speed, the feed rate of up to 24-240 m/min can still be obtained when the resolution is 0.1 μm and 0.01 μm;

d. Tool change speed: At present, the tool exchange time of foreign advanced machining centers is generally around 1s, and the high has reached 0.5s. Chiron of Germany designed the tool magazine into a basket style with the spindle as the axis and the tool in the circumference. The tool-to-knife tool change time is only 0.9s.

2. High precision

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

a. Improve the control accuracy of the CNC system: use high-speed interpolation technology to achieve continuous feed with small blocks, refine the CNC control unit, and use high-resolution position detection device to improve position detection accuracy. The position servo system adopts feedforward. Control and nonlinear control methods;

b. Using error compensation technology: using backlash compensation, screw pitch error compensation and tool error compensation technology to comprehensively compensate the thermal deformation error and spatial error of the equipment.

c. Use grid decoder to check and improve the accuracy of the machining center's motion track: Predict the machining accuracy of the machine tool by simulation to ensure the positioning accuracy and repeat positioning accuracy of the machine tool, so that its performance is stable for a long time, and it can be completed under different operating conditions. Processing tasks and guarantee the quality of the parts.

3. Functional composite

The meaning of a compound machine tool means that a plurality of elements from the blank to the finished product are processed on one machine or as much as possible. According to its structural characteristics, it can be divided into two types: process composite type and process composite type. The machining center can complete various processes such as turning, milling, drilling, hobbing, grinding, laser heat treatment, etc., and can complete the complete 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 companies.

4. Control intelligence

With the development of artificial intelligence technology, in order to meet the development needs of manufacturing production flexibility and manufacturing automation, the degree of intelligence of CNC machine tools is constantly improving. Specifically embodied in the following aspects:

a. Adaptive process control technology;

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;

f. Intelligent 4M CNC system: In the manufacturing process, the measurement, modeling, processing, and machine operation (ie 4M) are integrated into one system.

5. System openness

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

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

c. The establishment of numerical control standards: a standardized programming language that is convenient for users to use and reduces labor consumption directly related to operational efficiency.

6. Drive parallelization

It can realize multi-coordinate linkage CNC machining, assembly and measurement of various functions, and can better meet the processing of complex special parts. Parallel machine tools are considered to be "the most significant progress in the machine tool industry since the invention of numerical control technology" and "new 21st century" A generation of CNC machining equipment."

7. Extreme (large size and miniaturization)

The development of defense, aerospace, aerospace, and the expansion of basic industrial equipment such as energy require the support of large-scale and well-performing CNC machine tools. Ultra-precision machining technology and micro-nano technology are the strategic technologies of the 21st century, and it is necessary to develop new manufacturing processes and equipment that can adapt to micro-miniature size and micro-nano processing precision.

8. Information interaction networking

It can realize network resource sharing and realize remote monitoring, control, remote diagnosis and maintenance of CNC machine tools.

9. Greening of the process

In recent years, machine tools that do not use or use less coolant, achieve dry cutting, semi-dry cutting, energy saving and environmental protection have emerged. The trend of green manufacturing has accelerated the development of various energy-saving and environmentally-friendly machine tools.

10. Application of multimedia technology

Multimedia technology combines computer, audiovisual and communication technologies to give computers the ability to process sound, text, image and video information. It can realize information processing integration and intelligence, and is applied to fault diagnosis of real-time monitoring system and production field equipment, monitoring of production process parameters, etc., so it has great application value.

At present, the development of CNC machine tools is changing with each passing day. High-speed, high-precision, composite, intelligent, open, parallel-driven, networked, extreme, and green have become the development trend and direction of CNC machine tools.