CNC Machine

Definition

NC (Numerical Control): Represents the old and original CNC technology.

CNC (Computerized Numerical Control): Computer numerical control technology-new version, the preferred abbreviated form of numerical control.

NC may be CNC, but CNC is by no means old CNC technology.

The early numerical control system was composed of hardware circuits called hardware NC (Hard NC). After the 1970s, hardware circuit components were gradually replaced by special computers and called computer numerical control systems. Generally, special computers were used and equipped with interface circuits. It can control the movement of multiple types of CNC machine. Therefore, the current numerical control is generally CNC (computer numerical control), and the concept of NC is rarely used.

The traditional mechanical processing is performed by manually operating the ordinary machine tool. During the processing, the machine tool is shaken by hand to cut the metal, and the accuracy of the product is measured with a caliper and other tools by the eyes. The modern industry has long used computerized digitally controlled machine tools to perform operations. CNC machine tools can automatically process any products and parts directly according to the procedures pre-programmed by technicians. This is what we call "CNC machining". CNC machining is widely used in all fields of mechanical machining, and it is also the development trend and important and necessary technical means of mold machining.

"CNC" is the abbreviation of Computerized Numerical Control in English. The CNC machine tool automatically processes the parts to be processed according to the pre-programmed processing program. We put the processing route of the parts, process parameters, tool trajectory, displacement, cutting parameters (spindle rotation, feed, back-feeding, etc.) and auxiliary functions (tool change, spindle forward, reverse, cutting fluid on, off, etc.), according to the instruction code and program format specified by the CNC machine tool into a processing program list, and then record the contents of the program list on the control medium (such as perforated paper tape, magnetic tape, magnetic disk, bubble memory ), And then input into the numerical control device of the numerical control machine tool to direct the machine tool to process parts.

This entire process from the analysis of the part drawing to the production of the control medium is called the preparation of the NC program. The difference between CNC machine tools and ordinary machine tool parts is that CNC machine tools automatically process parts according to the program, and ordinary machine tools need to be operated by humans. We can achieve the purpose of processing different parts by changing the program that controls the movement of the machine tool. Therefore, CNC machine tools are particularly suitable for processing small batches and complex shapes requiring high precision parts.

Because the CNC machine tool needs to process the parts according to the program, after the programmer has compiled the program, it is input into the CNC device to direct the work of the machine tool. The input of the program comes through the control medium.

CNC Machine

History

It usually controls the mechanical quantities such as position, angle, speed, and the switch quantity related to the flow of mechanical energy. The production of numerical control depends on the emergence of data carriers and binary form data operations. In 1908, a perforated metal foil interchangeable data carrier came out; at the end of the 19th century, a control system that used paper as a data carrier and had auxiliary functions was invented; in 1938, Shannon performed fast data calculation and transmission at the Massachusetts Institute of Technology, Laid the foundation of modern computers, including computer digital control systems. CNC technology is developed in close combination with machine tool control. In 1952, the first CNC machine tool came out, which became an epoch-making event in the history of the world machinery industry and promoted the development of automation.

Now, numerical control technology is also called computerized numerical control (CNC, Computerized Numerical Control). At present, it is a technology that uses computers to realize digital program control. This technology uses a computer to execute a sequential logic control function of the device's movement trajectory and peripheral operation according to a control program stored in advance. Because the computer replaces the numerical control device originally composed of hardware logic circuits, the storage, processing, operation, logic judgment and other control functions of the input operation instructions can be realized by computer software, and the microinstructions generated by the processing are transmitted Drive the servo motor or hydraulic actuator to drive the equipment.

Spare Parts

The computer numerical control system is composed of hardware and software, and the understanding of the CNC system architecture should be carried out from both hardware and software aspects. Its core is the computer digital control device. It cooperates with the system hardware through the system control software, reasonably organizes and manages the input, data processing, interpolation and output information of the CNC system, controls the execution components, and enables the CNC machine tool to perform automatic processing according to the requirements of the operator. The CNC system uses a computer as a control component. Usually, some or all of the CNC functions are realized by the CNC system software resident in it, so as to control the movement of the machine tool in real-time. As long as the control software of the computer numerical control system is changed, a completely new control method can be realized. There are many types of CNC systems, including CNC systems such as lathes, milling machines, and machining centers.

The CNC system of various CNC machine tools generally includes the following parts: central processing unit CPU, memory (ROM / RAM), input and output devices (I / O), operation panel, display and keyboard, paper puncher, programmable control And so on.

With the rapid decrease in the cost-performance ratio of computer hardware and the popularization and application of graphic displays, modern numerical control systems no longer require perforated paper tapes and are directly controlled by computers. It uses a small general-purpose computer or personal computer to directly control a machine tool The control program of the machine tool is stored in the memory of the computer, it is easy to modify and expand the function, and the flexibility is good.

Functions

In order to give full play to the potential of computers, the functions of modern CNC systems are far more than just completing basic linear and circular interpolation calculations, but are equipped with a lot of special software that can complete many aspects of work, some of which are traditional NC is impossible or difficult. The following describes the main functions that modern CNC systems usually have.

1. Coordinate axis control can simultaneously control 3, 4, and 5 coordinate axes. It can achieve a higher cutting speed and processing quality.

2. Tool offset compensation Modern CNC systems often have a three-dimensional linear tool radius compensation function.

3. Programming function The system provides certain programming functions. Usually, the system's color graphics display terminal can be used to manually compile the processing program of plane contour parts composed of straight lines and arcs. The system is equipped with software to automatically calculate the intersection and tangent points of the contour.

4. Parallel operation The system can realize two working modes in parallel: machine tool controlled mode and programming mode.

When the machine tool is under the control of the system to process a part, the operator can use the keyboard to complete the above manual programming at the same time, or input external programs or edit and modify existing programs through the data transmission interface. When the machine tool is processing, the graphic display terminal can simultaneously simulate the execution of another processing program for inspection and editing.

5. Tool management and monitoring Modern CNC machine tools are developing towards the machining center. Usually, milling and boring machine tools have a tool magazine with dozens of tools, and the turning center often also has a tool magazine. The CNC system has the function of controlling and managing the tool magazine. The replacement of the tool is automatically controlled by the CNC system according to the program control tool change mechanism on the processing machine tool.

6. High and low-speed feed control The feed speed control performance of the system to the moving parts of the machine tool is an important performance index of the numerical control system. Modern CNC systems can control the cutting motion of the machine tool at a relatively high feed rate within a short distance. This is very beneficial for curved surface processing, which can greatly shorten the processing time, especially for the transition zone with a large curvature change, and still obtain good processing quality.

7. The electronic contact aligning system provides three-dimensional measuring contacts (similar to measuring probes), which is extremely convenient for aligning workpieces.

8. Physical measurement and automatic generation of processing program With the above three-dimensional electric probe, the physical object (sample to be copied) can be scanned and measured. The system automatically collects measurement point data. The distance between points is related to the scanning speed. The linear interpolation NC program is automatically generated and can be executed without any post-processing.

9. Execution of external programming and DNC operation The system is usually equipped with a standardized data communication interface, which can accept externally transmitted programs, such as the processing program output by the CAD / CAM system. Short programs can be stored and stored; long programs for processing complex surfaces can be input to the system in blocks and executed synchronously. This ensures that the system can adapt to the DNC operation mode controlled and managed by other computers.

10. A portable electronic manual control device system usually provides portable electronic manual control device. Operators can use it to sensitively adjust the movement of the moving parts of the machine tool in the clearest and convenient place to observe, and the control range is 0.02 ~ 20mm.