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Main features of various types of CNC machine tools and classification criteria
From:Taian Haishu Machinery Co.,Ltd. Updatetime:2016-8-12 8:52:16 Views:
CNC machine tools, CNC machine tool manufacturers, CNC machine tools price

First, the processing method according to classification

1. Metal cutting class CNC machine tools
With the traditional turning, milling, drilling, grinding, gear cutting corresponding CNC machine tools CNC lathes, CNC milling, CNC drilling machine, CNC grinding machines, CNC gear cutting machine tools. Although these CNC machine tools there is a big difference in the processing method, the specific control methods vary, but the machine movements and movements are digitally controlled, with high productivity and automation.
In general the installation of a CNC machine tool magazine and tool changer has become CNC machining centers. Machining centers to further improve the degree of automation and production efficiency ordinary CNC machine tools. Such as milling, boring, drilling and machining centers, CNC milling machine which is based on the addition of a large capacity magazine and automatic tool changer formed after clamping a workpiece can be part of the box four or five faces big part processing steps performed milling, boring, drilling, expanding, multi-step process hinges and tapping, etc., especially suitable for machining box-type parts. Machining centers can effectively avoid the positioning error due to the workpiece caused by multiple installations, reducing the number of units and the machine footprint, shorten the auxiliary time, greatly improving production efficiency and processing quality.
2. Special working class CNC machine tools
In addition to cutting CNC machine tools, numerical control technology is also used extensively for CNC WEDM, CNC EDM machines, CNC plasma arc cutting machine, CNC flame cutting machine tools and CNC laser processing machine tools.
3. Class sheet metal processing CNC machine tools
Commonly used in sheet metal processing CNC machine tools are CNC press, CNC cutting and CNC bending machines.
In recent years, other machinery and equipment also uses a lot of digital technology, such as CNC multi-coordinate measuring machine, automatic drawing machines and industrial robots.
Second, according to the control trajectory classification
1. Point control of CNC machine tools
Point control of CNC machine tools is characterized by the machine moving parts can only be achieved from one location to another precise positioning, moving and positioning process without any processing. CNC system controls only the coordinate values ​​of the end of travel, does not control the trajectory between points, so the movement of several axes without any contact between. Some may point to the target coordinate at the same time movement to be followed by each individual coordinate movement.
Such major CNC machine tool CNC coordinate boring machine, CNC drilling machine, CNC punch, CNC spot welding. Point control of CNC machine tools NC device called NC device point.
2. Linear control of CNC machine tools
Linear control of CNC machine tools tool or table can be controlled in an appropriate feed rate along a direction parallel to the axis moves straight and cutting feed rate according to the cutting conditions can be varied within a certain range.
Simple linear CNC lathe control, only two axes, machine axis opportunities. Linear control of CNC milling machine, three axes, the plane can be used for milling. Modern Modular Machine Tool CNC feed servo system, drive power headband multiple axle box axial feed conduct drilling boring, it can be regarded as a linear control CNC machine tools.
CNC boring and milling machines, machining centers and other machine tools, the speed of the feed movement of its various coordinate directions can be adjusted within a certain range, and a little bit straight-line control and processing functions, such machines should be called Point / Line Control CNC machine tools.
3. Contour control CNC machine tools
Contour control CNC machine tools capable of displacement and speed of two or more continuous motion related control, so that the trajectory of the plane or space synthesis to meet the requirements of part contour. It not only can control the starting point and end point coordinates of the moving parts of the machine, and can control the entire contour of each point velocity and displacement, the contour of the workpiece as required.
Commonly used CNC lathes, milling machines, CNC grinding machine is a typical contour control CNC machine tools. CNC flame cutting machines, EDM and CNC plotter, also uses the outline control system. Structure than point contouring control system / linear control system is more complex, in the process requires constant interpolation operation, and then make the appropriate speed and position control.
Now computer numerical control function by means of software, Increase Increase contour control function will not bring the capital. Thus, in addition to a small number of dedicated control system, modern computer numerical control device has a contour control.
Third, according to the characteristics of the drive free
1. Open-loop control of CNC machine tools
Such control of CNC machine tools is its control system is not the position detection device, the servo drive member is generally reactive stepping motor or hybrid stepping motor servo. NC system each send a feed command, the drive circuit after power amplifier to drive a stepper motor rotation angle, through a gear reduction drive screw rotation is converted to linear displacement of the movable member through the screw nut mechanism. Moving speed and amount of displacement of the movable member is determined by the input pulse frequency and the number of pulses of the decision. Such information flow is one-way CNC machine tools, namely the feed back pulse emitted, the actual movement values ​​are no longer fed back, so called open-loop control of CNC machine tools.
CNC machine tool structure is simple open-loop control system, the lower the cost. However, the system of actual displacement of the movable member is not monitored, error correction can not be performed. Thus, loss of stepping motor step, step angle error, and other gear and screw transmission error will affect the accuracy of machined parts. Open-loop control system is only applicable to the processing accuracy is not very high for small and medium CNC machine tools, especially simple economical CNC machine tools.
2. Closed-loop control of CNC machine tools
Closed-loop control of CNC machine tools is directly mounted linear displacement detecting device on the machine moving parts directly to the actual displacement table to detect the actual value of the displacement measurement is fed back to the numerical control apparatus, and the displacement command value input is compared with the difference between the machine tool control, the moving parts in accordance with the actual needs of the motion displacement, the ultimate realization of precise movement and positioning of moving parts. In theory, the movement precision closed-loop system depends primarily on the detection accuracy of the detection device, has nothing to do with the chain of transmission error, so the control accuracy. CNC machine tools for the closed-loop control system block diagram shown in Figure 1-3. Figure A is a speed sensor, C is the linear displacement transducer. When the shift position command value is sent to the comparator circuit, if the table does not move, there is no feedback, so that the servo motor rotates command value by the A speed feedback signal to the speed control circuit, the C table by actual displacement feedback go back, compared to the value at the position comparison circuit and displacement instruction, position control comparison was the difference, until the difference is zero. Such control of CNC machine tools, because the machine table incorporated into the control link, it is called closed-loop control of CNC machine tools.
Closed-loop control of CNC machine tools, high positioning accuracy, but are more difficult to debug and maintenance, system complexity, high cost.
3. Semi-closed loop control of CNC machine tools
Semi-closed loop control of CNC machine tools are provided with angular displacement current detecting device (such as a photoelectric encoder, etc.) on the servo motor shaft or drive CNC machine screw, to detect the actual displacement of the mobile member indirectly by detecting the angle of the screw, then feed to the numerical control device to, and error correction. By speed component A and B optical encoder disk can be indirectly detected by the servo motor speed to calculate the actual amount of displacement of the table, this value is compared with the command value, with the difference to achieve control. Since the table is not included in the control loop, so called semi-closed loop control of CNC machine tools.
Semi-closed loop numerical control system debugging more convenient, and has good stability. Currently most of the angle detection device and a servo motor designs into one, so make the structure more compact.
4. Hybrid control of CNC machine tools
The above three types of CNC machine features combine to form a hybrid control CNC machine tools. Hybrid control of CNC machine tools is particularly suitable for large or heavy-duty CNC machine tools, due to the large or heavy-duty CNC machine tools requires a higher feed rate and a very high precision, the transmission chain inertia and torque, if only with full closed-loop control, machine drive chain and the tables are all placed in a closed-loop control, closed-loop debugging more complex. Hybrid control system is divided into two forms:
(1) open loop compensated. Its basic selection of stepping motor control open loop servo mechanism, in addition attach a correction circuit. Mounted with linear displacement error table measuring element feedback signal correction of the mechanical system.
(2) semi-closed loop compensated. It is made with a semi-closed loop control precision control, and then packed in linear displacement measurement workbench components to achieve closed-loop correction to get the same high speed and high accuracy. Where A is the speed measuring device (such as a tachometer generator), B is the angle measurement element, C is a linear displacement measuring device

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