CNC machine tools can be divided into three categories according to their control trajectory: point control CNC machine tools, linear control CNC machine tools, contour control CNC machine tools.
1. Point control CNC machine tool point control The feature of CNC machine tools is that they only control the exact positioning of moving parts from one position to another. Regardless of the middle movement trajectory, no machining is performed during the movement, and between two points There are no strict requirements on the speed of movement and trajectory. However, generally, in order to increase the efficiency of T addition, it is generally quick to move first and then slowly approach the end point.
Point-controlled CNC machine tools are mainly used in the plane of the hole system, mainly CNC drilling machine, CNC coordinate boring machine, CNC punch and so on. With the development of numerical control technology and the decrease of the price of numerical control systems, numerical control systems used for point control are rare.
2. Linear control CNC machine tools Linear control CNC machine tools not only have accurate positioning functions between the control points and points, but also ensure the linear movement between two points for cutting. The trajectory of the tool relative to the workpiece is parallel to the coordinates of the machine tool. The straight line or two axes of the shaft move at the same time to form an oblique line of 45°.
Linear control of CNC machine tools mainly include simple CNC lathes, CNC milling machines, machining centers, and CNC grinders. The CNC system of this machine tool is also called a linear control system. Similarly, numerical control machine tools that are used only for linear control are rare.
3. Contour control CNC machine tool contour control The CNC machine tool can continuously control two or more coordinate axes. It not only controls the starting point and end point coordinates of the moving parts of the machine tool, but also controls the speed of each point in the whole machining process. Displacement, that is, the trajectory that controls the movement of the tool, to produce a curve or surface with arbitrary slashes, arcs, parabolas, and other functional relationships. Such CNC machine tools mainly include CNC lathes, CNC milling machines, CNC wire EDM machines and machining centers. The corresponding numerical control device is called the contour control numerical control system. According to the different linkage coordinate axes it controls, it can be divided into the following several forms;
1 two-axis linkage: mainly used for CNC lathe processing rotary surface or CNC milling machine processing curve cylinder.
2 two-axis semi-linkage: mainly used for the control of three-axis machine tools, two of which can be linked, while the other axis can do periodic point or linear control. In this way, two-dimensional control within the three coordinate axes X, y, and Z is realized.
3 three-axis linkage: generally divided into two categories, one is the simultaneous control of X, Y, z three linear coordinate axis linkage, more for CNC milling machine, such as the center, etc., with a ball-end milling cutter three-dimensional space Surface. The other is that in addition to controlling two linear coordinates in x, y, and z at the same time, the rotating axis that rotates around one of the linear axes is also controlled at the same time. Such as turning plus T center, in addition to its vertical (z axis), horizontal (x axis) two linear coordinate axis linkage, but also need to control the rotation around the z axis (C axis) linkage. 4 four-axis linkage: refers to the simultaneous control of X, y, Z three linear coordinate axes and a rotation coordinate axis linkage.
5 five-axis linkage: refers to the simultaneous control of the x, y, zj linear coordinate axes, but also control the two coordinate axes in the A, B, and c coordinate axes that rotate around these linear coordinate axes to form simultaneous control Five axis linkage. At this time, the tool can be given in any direction of space. For example, controlling the tool while swinging around the x-axis and y-axis in two directions makes the tool always maintain the normal direction of the machined contour surface at its cutting point to ensure the smoothness of the machined surface and improve its machining accuracy and accuracy. _T efficiency, reduce the roughness of the surface being processed, it is particularly suitable for the processing of more complex space curved surfaces such as transparent blades, wings.
Numerical control flame cutting machines, EDM machines, and numerical control plotters also use contour control systems. The structure of the contour control system is more complex than that of the point/linear control system. In the machining process, it is necessary to continuously perform interpolation operations, and then perform corresponding speed and displacement control.
Now the control functions of the computer numerical control device are all realized by software. Increasing the numerical control machine tool contour control function will not bring about an increase in cost. Therefore, except for a few dedicated control systems, modern computer numerical control devices have contour control functions.
