We all know that when cnc machining parts on ordinary machine tools, the process personnel usually formulate the processing procedures of the parts in advance according to the design drawings. Work out the processing procedures, cutting amount, machine specifications, tools, fixtures, etc. of the parts in the process regulations. The operator operates the machine tool in accordance with the various steps of the process regulations and processes the parts with the given drawings. That is to say, the processing of parts is done by people. For example, driving, stopping, changing the spindle speed, changing the feed speed and direction, turning on and off the cutting fluid, etc. are all manually manipulated by workers.
When machining parts by cam-controlled automatic machine tools or profiling machine tools, although no human is required to operate it, the movement curve or profiling of the cam must be designed according to the characteristics of the part and the process requirements, and the cam and profiling Control the movement of the machine tool, and finally process the parts. In this machining process, although the operator avoids direct manipulation of the machine tool, each cam mechanism or profiling model can only process one type of part. When changing the processed parts, it is necessary to replace the cam and the master mold. Therefore, it can only be used in mass, specialized production.
CNC machine tools are different from the above two machine tools. It automatically processes the processed parts in accordance with the pre-programmed processing program. We put the part’s machining process route, process parameters, tool motion trajectory, displacement, cutting parameters (spindle revolutions, feed, back tooling, etc.), and auxiliary functions (tool change, spindle forward, reverse, etc.) Cutting fluid on, off, etc.), according to the instruction code and program format specified by the CNC machine tool, compile a cnc machining program list, and then record the content of the program list on the control medium (such as punched paper tape, magnetic tape, magnetic disk, magnetic bubble memory) ), and then input into the numerical control device of the numerical control machine tool to command the machine tool to process the parts.
Numerical control (English name: Numerical Control, abbreviated: NC) technology refers to a technology that uses digital instructions composed of numbers, characters and symbols to control the motion of one or more mechanical equipment. Numerical control generally uses general-purpose or special-purpose computers to realize digital program control, so numerical control is also called Computer Numerical Control (Computer Numerical Control), abbreviated as CNC, and generally called CNC abroad, and the concept of NC is rarely used.
What it controls is usually the position, angle, speed and other mechanical quantities and the switch quantity related to the flow of mechanical energy. The generation of numerical control relies on the emergence of data carriers and binary data operations. In 1908, a perforated sheet metal interchangeable data carrier came out; at the end of the 19th century, a control system with paper as a data carrier and auxiliary functions was invented; in 1938, Shannon conducted rapid data calculation and transmission at the Massachusetts Institute of Technology in the United States. Laid the foundation of modern computers, including computer digital control systems. Numerical control technology is developed in close combination with machine tool control. In 1952, the first CNC machining 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 computer numerical control technology (CNC, Compute Numerical Control), it is the technology that uses computer to realize digital program control. This technology uses a computer to execute the sequential logic control function of the movement track of the device and the operation of the peripherals according to the control program stored in advance. Because the computer is used to replace the original numerical control device composed of hardware logic circuits, the storage, processing, calculation, logical judgment and other control functions of the input operation instructions can be realized by computer software, and the micro-instructions generated by processing can be transmitted. Drive the motor or hydraulic actuators to the servo drive device to drive the equipment to run.
Numerical control technology is a technology that uses digital information to control mechanical movements and working processes. Numerical control equipment is a mechatronic product formed by the penetration of new technology represented by numerical control technology into traditional manufacturing industries and emerging manufacturing industries, which is the so-called digital equipment. , Such as CNC machine tools. Its technology involves multiple fields:
- (1) Machinery manufacturing technology;
- (2) Information processing, processing and transmission technology;
- (3) Automatic control technology;
- (4) Servo drive technology;
- (5) Sensor technology;
- (6) Software technology, etc.
Numerical control technology and equipment is the enabling technology and the most basic equipment for the development of emerging high-tech industries and cutting-edge industries. The information industry, biological industry, aviation, aerospace and other national defense industries in the world widely adopt numerical control technology to improve manufacturing capacity and level, and improve market adaptability and competitiveness. Industrial developed countries also list numerical control technology and numerical control equipment as national strategic materials, not only vigorously developing their own numerical control technology and its industry, but also imposing blockade and restrictive policies on my country’s “high-precision” key numerical control technology and equipment. Therefore, vigorously developing advanced manufacturing technology with numerical control technology as the core has become an important way for developed countries in the world to accelerate economic development and improve overall national strength and national status.
This whole process from the analysis of the part drawing to the preparation of the control medium is called the compilation of the numerical control program. It can be seen from the above analysis that the difference between CNC machine tools and ordinary machine tools processing parts is that the control machine tool automatically processes the parts according to the program, while the ordinary machine tool needs to be operated by humans. We only need to change the program that controls the motion of the machine tool to achieve the cnc machining of different parts. Purpose. Therefore, CNC machine tools are particularly suitable for processing small batches of parts with complex shapes and high precision requirements.
From the outside, CNC machine tools have CRT screens, and we can see the processing parameters and other content on the screen. From the perspective of internal structure, CNC machine tools do not have a gearbox, and the main movement and feed motion are all done by DC or AC stepless variable speed servo motors. In addition, CNC machine tools generally have a workpiece measurement system, which can reduce workpieces during processing. The number of manual measurements taken. Therefore, the use of CNC machine tools in various industries will become more popular in the future.
Since the CNC machine tool must process the parts according to the program, after the programmer has compiled the program, he enters the CNC device to direct the work of the machine tool. The input of the program is through the control medium. There are many specific methods, such as punched paper tape, data tape, floppy disk and manual input or MDI.
1. Punched paper tape
Most commonly used control media on CNC machine tools in my country are perforated paper tapes. It is to make the numerical control program into a perforated paper tape according to certain rules. The numerical control machine tool converts the code on the paper tape into an electrical signal that can be recognized by the numerical control device through the paper tape reading device, and then transmits it to the corresponding register after recognition and decoding. These instructions are used as the original basis for control and calculation. The controller controls the calculation and output devices according to the instructions to achieve the purpose of controlling the machine tool. Commonly used is eight-unit perforated paper tape.
2. Data tape
This method is to record the programmed program on the data tape, and then read the program from the data tape when processing the parts, so as to control the action of the machine tool.
3. floppy disk
With the rapid development of the computer industry, more and more computer floppy disks are used as program input control media. The programmer can use the automatic programming software to program on the computer, and then connect the computer with the RS-232 standard serial interface on the CNC machine tool to realize the communication between the computer and the machine tool (or use the floppy disk drive equipped on the CNC machine tool) . In this way, it is not necessary to make the program into a perforated paper tape, but through communication, the china cnc machining instructions are directly sent to the CNC system to direct the machine tool to process, thereby improving the reliability of the system and the efficiency of information transmission.
MDI is the manual data input method. It uses the keyboard on the operation panel of the numerical control machine tool to directly input the compiled program into the numerical control system, and the relevant content can be displayed on the display.
MDI is characterized by simple input, convenient inspection, verification, and modification, and is suitable for parts with simple shapes and short programs.