- It belongs to cutting CNC machine tool
Corresponding to the traditional turning, milling, drilling, grinding and gear processing, CNC lathes, CNC milling machines, CNC drilling machines, CNC grinding machines, CNC gear processing machines, etc. Although there are great differences in the processing methods of these CNC machine tools, and the specific control methods are also different, the actions and movements of the machine tools are digital control, with high productivity and automation.
- CNC machine tools for plate processing
- CNC machine tools for special machining
In addition to cutting CNC machine tools, CNC technology is also widely used in CNC WEDM machine tools, CNC EDM forming machines, CNC plasma arc cutting machines, CNC flame cutting machines, CNC laser machining machines, mold accessories processing, etc.
The common CNC machine tools used in sheet metal processing include CNC press, CNC shear and CNC bending machine.
In recent years, CNC technology has been widely used in other mechanical equipment, such as CNC multi coordinate measuring machine, automatic drawing machine and industrial robot.
2、 Classification by control trajectory
- Point control CNC machine tool
Accurate positioning of the position, no processing is carried out in the process of moving and positioning. The CNC system only controls the coordinates of the end of the stroke, and does not control the trajectory between the points, so there is no relationship between the movements of several coordinate axes. Several coordinates can move to the target point at the same time, or each coordinate can move in turn.
This kind of CNC machine tools mainly include CNC coordinate boring machine, CNC drilling machine, CNC punching machine, CNC spot welding machine, etc. The numerical control device of point position control CNC machine tool is called point position numerical control device.
- Linear control CNC machine tool
The linear control CNC machine tool can control the tool or worktable to move and cut along the direction parallel to the coordinate axis with appropriate feed rate. The feed rate can change in a certain range according to the cutting conditions.
Linear control of the simple CNC lathe, only two coordinate axes, can process step axis. CNC milling machine with linear control has three coordinate axes, which can be used for plane milling. Modern modular machine tool adopts CNC feed servo system to drive the axial feed of power head with multiple axle boxes for drilling and boring. It can also be regarded as a kind of linear control CNC machine tool.
- Contour control CNC machine tool
The contour control CNC machine tool can continuously control the displacement and speed of two or more motions, so that the resultant planar or spatial motion trajectory can meet the requirements of the part contour. It can not only control the coordinates of the starting point and the end point of the moving parts of the machine tool, but also control the speed and displacement of each point of the whole machining contour, so that the workpiece can be processed into the required contour shape.
3、 Classification according to characteristics of driving device
- Open loop control CNC machine tool
The control system of this kind of CNC machine tool has no position detecting element, and the servo driving parts are usually reaction stepping motor or hybrid servo stepping motor. When the CNC system sends out a feed command, after the power amplification of the driving circuit, the stepping motor is driven to rotate for an angle, and then the screw is driven to rotate by the gear reducer, which is converted into the linear displacement of the moving parts through the screw nut mechanism. The velocity and displacement of moving parts are determined by the frequency and number of input pulses. The information flow of this kind of CNC machine tool is unidirectional, that is, after the feed pulse is sent out, the actual moving value is no longer fed back, so it is called open-loop control CNC machine tool.
- Closed loop control of CNC machine tools
Then the actual displacement of the worktable is detected, the measured actual displacement value is fed back to the numerical control device, and compared with the input command displacement value, the difference value is used to control the machine tool, so that the moving parts move according to the actual displacement required, and finally realize the accurate movement and positioning of the moving parts. Theoretically speaking, the motion accuracy of the closed-loop system mainly depends on the detection accuracy of the detection device, and has nothing to do with the error of the transmission chain, so its control accuracy is high. Figure 1-3 shows the system block diagram of closed-loop control CNC machine tool. In the figure, a is speed sensor and C is linear displacement sensor. When the displacement command value is sent to the position comparison circuit, if the table does not move, there is no feedback. The command value makes the servo motor rotate. The speed feedback signal is sent to the speed control circuit through a, and the actual displacement of the workbench is fed back through C. the position comparison circuit is compared with the displacement command value, and the difference value obtained after comparison is used for position control Until the difference is zero. This kind of control CNC machine tool is called closed-loop control CNC machine tool because the machine table is included in the control link.
The lubrication system of CNC machine tool is intermittent oil supply mode. Therefore, the pressure in the lubrication system is checked regularly, that is, after each operation of the lubricating pump. If there is a fault, such as oil leakage, oil pump failure, oil pipeline blockage, the pressure in the lubrication system will suddenly drop or rise. At this time, the machine tool should be forced to stop running immediately for inspection, so as to avoid the expansion of the situation. The conventional way to deal with the low oil level is to classify the “low oil level” signal and the “abnormal pressure” alarm signal as an emergency stop signal. Once the PMC system receives the above signal, the machine tool will enter the emergency stop state immediately, and the servo system will be powered off at the same time. However, the lubrication system is caused by blockage or oil leakage“
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