cnc machine tools are generally not classified, but classified. The common classification is: the classification of CNC machine tools
The Classification according to processing method and process use
1.Ordinary CNC machine tools
Ordinary CNC machine tools generally refer to automated machine tools that realize digital control in a process in the processing process, such as CNC milling machines, CNC lathes, CNC drilling machines, CNC grinding machines, and CNC gear processing machine tools. Ordinary CNC machine tools are not fully automated in terms of automation, and the replacement of tools and the clamping of parts still need to be completed manually.
The machining center is a CNC machine tool with a tool magazine and an automatic tool changer. It combines the functions of a CNC milling machine, a CNC boring machine, and a CNC drilling machine. After a part is clamped, most of its machining surfaces can be milled and bored. , Drilling, expanding, reaming, tapping and other multi-process processing. Since the machining center can effectively avoid positioning errors caused by multiple installations, it is suitable for products with frequent product replacement, complicated parts shapes, high precision requirements, small production batches and short production cycles.
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1.Point control CNC machine tools
Point position control is that the index control system only controls the accurate positioning of the tool or worktable from one point to another, and then performs fixed-point processing, and the path between points does not need to be controlled. There are CNC drilling machines, CNC boring machines and CNC jig boring machines that use this type of control.
2.Point linear control CNC machine tool
Point linear control is that the index control system not only controls the accurate positioning of the start and end points of the linear path, but also controls the linear cutting between these two points at a specified feed rate. There are CNC milling machines, CNC lathes and CNC grinders that use this type of control.
3. Contour control CNC machine tools
is also known as continuous trajectory control, which can continuously control the joint movement of two or more coordinate directions. In order to enable the tool to process the curve contour of the workpiece according to the specified path, the numerical control device has the function of interpolation calculation, so that the motion path of the tool approximates the specified contour curve with the smallest error, and coordinates the motion speed of each coordinate direction to facilitate the cutting process The specified feed rate is always maintained during the process. There are CNC milling machines, CNC lathes, CNC grinders and machining centers that use this type of control.
The Classified according to control method
1.Open loop control system
Open loop control system refers to the control system without feedback device, which is composed of stepper motor drive circuit and stepper motor, as shown in Figure 1-4. The numerical control device sends out pulse signals through control calculations, and each pulse signal makes the stepping motor rotate a certain angle, and the ball screw pushes the worktable to move a certain distance.
This kind of servo mechanism is relatively simple, stable in work, easy to master and use, but the improvement of accuracy and speed is limited.
2.Semi-closed loop control system
The semi-closed-loop control system is equipped with an angular displacement detection device in the servo mechanism of the open-loop control system. The displacement of the moving parts is indirectly detected by detecting the ball screw angle of the servo mechanism, and then fed back to the comparator of the numerical control device. The command displacement value is compared, and the compared difference is used for control, so that the moving part complements the displacement until the difference is eliminated.
The accuracy, speed and dynamic characteristics that this kind of servo mechanism can achieve are better than open loop servo mechanism, which is adopted by most small and medium-sized CNC machine tools.
3.Closed loop control system
The closed-loop control system is directly equipped with a linear position detection device on the position of the moving parts of the machine tool, and the actual displacement detected is fed back to the comparator of the numerical control device, and compared with the input original command displacement value, and the compared difference is used for control The moving parts make supplementary displacement and stop moving until the difference is eliminated, achieving an accurate positioning control system.
The positioning accuracy of the closed-loop control system is higher than that of the semi-closed-loop control, but the structure is more complicated, and it is more difficult to debug and maintain. It is often used for high-precision and large-scale CNC machine tools.
The Classification by the number of linkage axes
The numerical control system controls several coordinate axes to coordinate movement at the same time according to the required functional relationship, which is called coordinate linkage, which can be divided into:
The CNC machine tool can simultaneously control the linkage of two coordinate axes, which is suitable for CNC lathe processing of rotating surfaces or CNC milling machine for milling plane contours.
The movement of Z axis is added on the basis of two axes. When the X and Y axes of the machine tool coordinate system are fixed, the Z axis can do periodic feed. Two-axis semi-linked machining can realize layered machining.
The CNC machine tool can control the linkage of three coordinate axes at the same time, which is used for the processing of general curved surfaces. General cavity molds can be processed by three-axis processing.
CNC machine tools can control the linkage of more than four coordinate axes at the same time. Multi-coordinate CNC machine tools have complex structure, high precision requirements, and complex programming, which are suitable for processing parts with complex shapes, such as impeller blades.
Usually a three-axis machine tool can realize two-axis, two-axis half and three-axis machining; a five-axis machine tool can also only use three-axis linkage processing, while the other two axes are not linked.
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