With the development of science and technology, people's requirement for parts processing quality is becoming higher and higher. At the same time, product modification is frequent. In general mechanical processing, single and small batch products account for an increasing proportion. In order to ensure product quality, improve productivity and reduce costs, machine tools are required not only to have good versatility and flexibility, but also to have a high degree of automation in the process of processing. NC machining technology is a kind of high-efficiency and flexible automatic processing technology developed under this environment, which is controlled by digital information of NC machine tools. It is suitable for high-precision, complex parts and small and medium-sized batch production.
CNC machine tool is an efficient and flexible mechanical-electrical integration equipment which integrates computer technology, modern control technology, sensor detection technology, information processing technology, network communication technology, hydraulic pneumatic technology, optical and mechanical technology, and it is the basis of modern manufacturing technology.
1. Composition of NC Machine Tool and NC Machining Process
CNC machine tools refer to the machine tools that use digital information recorded in the media to control the machine tools through the CNC device, so that it can automatically implement the specified processing process.
1) Composition of CNC Machine Tools
NC machine tools automatically process workpieces according to pre-programmed processing procedures. CNC machine tools are usually composed of machine body, servo system, CNC device and control medium, as shown in Figure 2-61.
Figure 2-61 Composition of CNC Machine Tool
Control medium. Control medium, also known as information carrier, is an intermediate medium which conveys the operation intention of human to CNC machine tools. It contains all the information necessary to process a part. Commonly used control media are perforated tape, magnetic tape, disk and other carriers that can store instruction information. For the short NC processing program, the NC device can be input directly through the keyboard on the NC operation panel.
NC device. CNC device is the center of CNC machine tool. It receives the information from control medium, and converts it into pulse signal to control machine tool action.
Servo system. Servo system is a device which connects the moving parts of machine tool with CNC system, including servo drive mechanism and movable parts of machine tool. It is the executive part of CNC system of machine tool. It transforms the impulse signal from CNC device into the movement of machine tool parts, so that the worktable or tool holder can be positioned accurately or moved strictly according to the expected trajectory, and the parts meeting the requirements of the drawings can be machined.
Machine tool. Machine tool is the mechanical part of NC machine tool. Besides the general parts such as main drive device, feed drive device, bed, worktable and auxiliary part, there are also special parts, such as tool storehouse, automatic tool changer and rotary worktable.
NC Machine Parts Processing Process
The NC machine tool parts processing process is that the operator first changes it into the content of manufacturing process according to the processing pattern. On the basis of familiarity with the processing technology, the processing program is compiled, and the human will is transformed into the acceptable information of CNC machine tools with the prescribed code and program format. Record information on control media (such as punched tape, tape or disk) to make it an instruction for controlling machine tools. After the input information is processed by the NC device, the command pulse is sent to the servo system of the coordinate axes of the machine tool to drive the corresponding moving parts of the machine tool, and other actions such as speed change, tool change and machine shutdown are controlled to automatically process the workpiece that meets the requirements of the drawings.
Classification of 2 NC Machine Tools
CNC machine tools can be classified according to process use, locus of motion, control mode and so on. This paper only introduces the classification according to process use. CNC machine tools are classified according to their processing characteristics or main processing procedures. They are mainly CNC lathes (including turning centers), CNC milling machines (including milling centers), CNC boring machines, CNC machining centers, CNC grinding machines (including grinding centers), CNC drilling machines (including drilling centers), CNC broaching machines, CNC planer, CNC cutting machine, CNC gear processing machine and CNC EDM machine (including EDM center, etc.). Figure 2-62 shows the appearance of CK50 NC lathe. Its processing range is the same as that of ordinary lathe. It mainly processes rotational parts such as shafts and discs. Figure 2-63 shows the appearance of XJK125 NC milling machine. It is especially suitable for the processing of complex parts. It can complete milling, drilling and boring.
Figure 2-62 CK50 CNC lathe appearance chart
Figure 2-63 XJK125 CNC Milling Machine Appearance Diagram
Machining center (MC) is a kind of NC machine tool for multi-process machining of workpiece. It has a tool library and an automatic tool changer (ATC). After the workpiece is clamped once, under the control of the NC system, the machining center can automatically select and change the cutting tools according to different processes; automatically change the spindle speed, feed rate and the movement track of the tool relative to the workpiece and other auxiliary functions; sequentially complete the multi-process processing on several surfaces of the workpiece. Therefore, it reduces the time of workpiece clamping, measuring and machine adjustment, shortens the time of workpiece storage and handling, improves productivity and machine tool utilization, and it is an important development direction of CNC machine tools. Figure 2-64 shows the layout of JCS-018 machining center. Its shape is similar to that of vertical milling machine. There is a sliding seat 2 on the bed 1, and it moves horizontally (y axis direction). Workbench 3 moves longitudinally on the slide seat (x-axis direction). There are frame pillars 5 at the back of the machine tool. The spindle box 9 makes vertical lifting motion (z axis direction) on the column guide rail. The left and right parts of the column are the NC device 6, the left front part is equipped with the tool storehouse 7 and the automatic tool changing manipulator 8, and the left lower part is equipped with the lubrication device 4. There are 16 cutters in the tool library, which can complete all kinds of hole processing and milling. There are 16 cutters in the tool library, which can complete all kinds of hole processing and milling. The NC operation panel 10 is suspended in front of the operator's right for easy operation. The working state of the machine tool is displayed on the panel. Machining centers are usually divided into horizontal, vertical and universal machining centers according to the spatial position of the spindle during processing.
Figure 2-64 JCS-018 Machining Center Layout
machine tool body; 2-slide seat; 3-worktable; 4-lubrication device; 5-pillar; 6-NC device; 7-tool library; 8-tool changing manipulator; 9-spindle box; 10-operation panel
The so-called programming means that the process, process parameters, tool movement and direction and other auxiliary actions (tool changing, cooling, clamping, etc.) of parts are compiled into tables according to the sequence of movement and the instruction code and program format given by the NC machine tools used. This form is called "parts processing program sheet", or simply "procedure sheet". Then, all the contents of the program sheet are recorded on the control medium (such as perforated tape, tape, etc.), and then transmitted to the NC device to direct the NC machine tool processing. The whole process from the analysis of part drawings to the production of control media for NC machine tools is called programming.
Generally speaking, the steps of NC programming are: process design