Classified characteristics and processing characteristics of CNC lathe

Classified characteristics and processing characteristics of CNC lathe

CNC machine tools has been basically complete varieties, many specifications, according to incomplete statistics, there are more than 400 varieties specifications. It can be classified according to various principles. But to sum up, based on the following four common ways to classify.

1, according to technology use classification
(1) general CNC machine tools. Such a traditional general machine tools and the same species, CNC turning, milling, boring, drilling, grinding, etc., and there are many varieties of each, such as CNC milling machine in there Milling, horizontal milling, milling tools, gantry milling. Process the possibility of such machines and general machine similar, the difference is that it can process complex shape parts.
(2) CNC machine center CNC machine tools. Such tools are developed on the basis of the general CNC machine tools. It is the installation of a magazine in the general CNC machine tools (multi-tool can accommodate 10-100) and the automatic tool changer constituted CNC machine tools (also known as multi-process CNC boring and milling machine or a device with automatic tool changer machining Center, customarily referred to as the machining center --Machining Center), making CNC machine tools and automation to further develop efficient direction.
Difference CNC machining centers and CNC machine tools in general are: the workpiece by a fixture, machine tool numerical control device can control the automatic tool change continuously each machined surface of the workpiece automatically complete milling (car), boring, drilling, reaming and tapping and other machining processes. Such is the most boring and milling machine-based, mainly used for processing housing parts. It is generally CNC machine tools compared with the following advantages:
① reduce the number of machine units, easy to manage, as long as the parts for the multi-step one machine will be able to complete all the processing, and can reduce the amount of inventory of semi-finished products;
② As long as a workpiece clamping, thus reducing the positioning error caused due to multiple installation, you can rely on the accuracy of the machine to the quality assurance process;
③ process focused, reducing the auxiliary time and improve productivity;
④ Since the parts in a single setup on one machine will be able to complete the multi-channel processing, so greatly reducing the number of special tooling, and further shorten the production preparation time.
Because of the advantages of CNC machining centers, many, welcomed by users, and therefore plays an important role in the production of CNC machine tools.
There is also a class of machining centers, lathes are developed on the basis, as the main shaft of the object. In addition to available for turning, boring, but also can be any part of face and peripheral surface drilling, milling and tapping. Such machining center also has a tool magazine, the tool can be installed 4-12, he said on customary tools such as turning centers (TC: Turning Center).
            
1 five-axis CNC machining Figure
(3) multi-axis CNC machine tools. Some parts of complex shape with CMM or CNC machine tools can not be processed, such as a propeller, aircraft surface parts processing, it requires more than three coordinates can be processed resultant motion the desired shape. So there is a multi-axis CNC machine tools, which is characterized by a number of axis CNC control means more, the machine structure is relatively complex, which usually depends on the number of axes machining parts of the process requirements. Now commonly used CNC machine tools 4,5,6 coordinates. Figure 1 is a schematic diagram of five-axis NC machining. In this case, x, y, z coordinates and three rotary turret, the tool can swing linkage to other types of processing wing parts.
2, according to the trajectory of CNC machine tools Classification
In accordance with the trajectory between the tool and the workpiece can be controlled relative motion, CNC machine tools can be divided into point position control of CNC machine tools, CNC machine tool control point and a straight line, contour control CNC machine tools. It is described below:
(1) position control of CNC machine tools. Such machine tool numerical control device can control precisely moving parts move from one location (point) to another location (point), which controls only the coordinate values of the end of travel, during the move without any cutting, as two moving speed and route between related points depends on productivity. In order to pinpoint on the basis of the highest possible productivity, the mobile between the first two points related to the fast-moving close to the new location, and then slow down 1-3 to make it slow approaching the anchor point to ensure positioning accuracy.
Such machine tool CNC coordinate boring machine, CNC drilling machine, CNC punch press and CNC measuring machine, with its corresponding numerical control device called the point position control apparatus.
(2) point linear control CNC machine tools. When these machines work, not only to control the position of the two relevant points (ie, distance), but also control two related points between movement speed and route (ie, track). By its general route and straight line segments parallel to the axis of the respective components. It and position control of CNC machine tools difference: When the machine's moving parts moving, can (cutting in general to be 45 ° diagonal direction, but not along any slope of the straight line cutting) in the direction of an axis cutting processing, and its accessibility than the position control of CNC machine tools and more, for example, to increase the spindle speed control loop feed machining, tool selection and other functions.
Such machines are mainly simple CNC lathes, CNC milling machine and CNC machining centers. Appropriate NC device called linear control point devices.
(3) contour control CNC machine tools. Such machine control device capable of simultaneously two or more axes continuous control. Not only to control the processing start and end points, but also to control the entire process speed and position of each point, so that machining of complex shaped parts to meet requirements of the drawings. Its accessibility is also more complete.
Such machines are mainly CNC lathes, milling machines, CNC grinding machines and EDM machine tools. The corresponding numerical control device called the contour control device (or continuous control devices).
3, according to the control mode servo system classification
CNC machine tool is controlled according to the amount of feedback device presence detection can be divided into two kinds of open-loop and closed-loop. In a closed loop system, according to the measuring device sited and can be divided into two semi-closed loop and closed loop. In the open-loop system, based on the further development of an open loop compensation CNC system.
(1) open-loop control of CNC machine tools. In open-loop control, the machine is not detected feedback device (see Figure 2).
               
2 open-loop control system block diagram
NC device sends a signal flow is unidirectional, there is no stability problems. It is due to the one-way flow of signals, the actual position of the moving parts of the machine it is not for examination, so the machining accuracy is not high, its accuracy depends on the performance of the servo system. Working process: data input through the NC device operation command pulse dispensed by the servo (servo element often a stepping motor) the controlled table movement.
This machine work more stable, responsive, easy to debug, simple maintenance, but its control accuracy is limited. It applies to the general requirements of medium and small CNC machine tools.
(2) closed-loop control of CNC machine tools. Because of the open-loop control accuracy of less than precision machine tools and large machine requirements, so it is necessary to detect the actual operating position, for detecting an increase in the open-loop control feedback means on CNC machine tools, processing time in the position to detect moving machine parts position, and make it conform to the requirements of the NC device, in order to achieve high precision.
Closed-loop control system block diagram shown in Figure 3. A figure measuring element is speed, C for the location measuring element. When the command value is sent to the position comparator circuit, at this time if the table does not move, there is no feedback, so that the servo motor instruction value by A speed feedback signal to the speed control circuit, by C the actual amount of displacement of the table fed back in the circuit with a command position comparison value, controlled by comparing the difference, up to the time difference is eliminated, and ultimately to achieve precise positioning of the table. Advantages of these machines are high precision, speed, but commissioning and maintenance more complex. The key is the stability of the system, so the design must be given enough attention to stability.
              
3 closed-loop control system block diagram of FIG.
(3) can be common. Thus flexibility and adaptability, but also facilitate mass production, modular hardware and software to improve the quality and reliability of the system. Therefore, the modern CNC machine tools are used CNC equipment. Semi-closed loop control of CNC machine tools. Semi-closed loop control system components shown in Figure 4.
               
4 semi-closed loop control system block diagram
This control of the actual position of the table without checking measurements, but with the servo motor connected measuring element, such as a tachometer generator A and optical encoder disk B (or resolver) and other indirect servo motor rotation angle detected , calculate the actual displacement table, 4 semi-closed loop control system block diagram using this value and the command value, with the difference to achieve control. As can be seen from Figure 5, since the table is not fully included in the control loop, so it is called semi-closed loop control. This control between open-loop and closed-loop, closed-loop accuracy is not high, debugging and convenient than the closed-loop.
(4) open loop compensated CNC machine tools. The characteristics of the three control modes are selectively together, can form a hybrid control. This is the subject of research for many years people in large CNC machine tools, has now become a reality. Because large CNC machine tools, require a much higher feed rate and return rate, but also requires a fairly high accuracy. If only closed loop control, machine drive chain and the table placed in the control of all aspects of the factors are very complex, although installation through more twists and turns, is still difficult. To avoid these conflicts, you can use mixed control. In a particular aspect it can be divided into two forms: one is the open loop compensated; one semi-closed loop compensated. Here only the open loop compensated control of CNC machine tools to be introduced.
Figure 5 is a block diagram of the open loop compensated control mode. It is characterized by: a basic choice of stepper motor control open loop servo control, attach a corrected servo circuit. Feedback signal mounted on the table linear displacement measuring element to correct errors of the mechanical system.
             
5 open loop compensated control block
4, according to the NC device classification
If their CNC machine tools NC NC logic function control device points, hard line (member) NC NC and two cords (member).
(1) hard-line NC (numerical control, said the general, that NC). Such input NC system, interpolation calculation, control and other functions by devices such as integrated circuits or discrete components to achieve. In general, different CNC machine tools, the control circuit is different, so the poor versatility of the system, because all the hardware, the functionality and flexibility is also poor. Such systems 70 years ago was more widely applied.

(2) soft line NC (also known as CNC or computer numerical control, or CNC namely MNC). The use of such systems in large-scale and ultra large scale integrated circuits CNC device, consisting of a microcomputer or a dedicated integrated chip, its main CNC functions almost entirely implemented by software, for different CNC machine tools, only the preparation of different software It can be achieved, and the hardware is almost universal. Thus flexibility and adaptability, but also facilitate mass production, modular hardware and software to improve the quality and reliability of the system. Therefore, the modern CNC machine tools are used CNC equipment.

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