Precision CNC machine tools|Classification of CNC machine tools - classification according to the control trajectory of machine tool movement
Precision CNC machine tools(1) Point-controlled CNC machine tools
Point control only requires the accurate positioning of the moving parts of the machine tool from one point to another. The requirements for the movement path between points are not strict. No processing is performed during the movement process, and the movement between the coordinate axes is not strict. is irrelevant. In order to achieve both fast and accurate positioning, the movement of the displacement between two points generally moves quickly at first, and then approaches the positioning point at a slow speed to ensure the positioning accuracy.
The machine tools with point control function mainly include CNC drilling machines, CNC milling machines, CNC punching machines, etc. With the development of numerical control technology and the reduction of the price of numerical control systems, numerical control systems only used for point control are rare.
⑵ Linear control CNC machine tools
Linear control CNC machine tools, also known as parallel control CNC machine tools, are characterized by controlling the movement speed and route (track) between two related points in addition to the accurate positioning between the control points, but the movement route is only the same as the one. The machine tool coordinate axis moves in parallel, that is to say, there is only one coordinate axis controlled at the same time (that is, there is no need for interpolation operation function in the numerical control system). Rectangular, stepped parts.
The machine tools with linear control function mainly include relatively simple CNC lathes, CNC milling machines, and CNC grinding machines. The numerical control system of this machine tool is also called linear control numerical control system. Similarly, CNC machine tools that are purely used for linear control are rare.
⑶ contour control CNC machine tools
Contour control CNC machine tools, also known as continuous control CNC machine tools, are characterized by the ability to simultaneously control the displacement and speed of two or more moving coordinates.
In order to meet the requirements of the relative motion trajectory of the tool along the workpiece contour to meet the requirements of the workpiece machining contour, the displacement control and speed control of each coordinate movement must be precisely coordinated according to the specified proportional relationship.
Therefore, in this kind of control mode, the numerical control device is required to have the function of interpolation operation. The so-called interpolation is to describe the shape of the straight line or arc through the mathematical processing of the interpolation operator in the numerical control system according to the basic data input by the program (such as the end point coordinates of the line, the end point coordinates of the arc, and the center coordinates or radius). , that is, while calculating, assign pulses to each coordinate axis controller according to the calculation results, so as to control the linkage displacement of each coordinate axis to conform to the required contour. During the movement process, the tool continuously cuts the workpiece surface, and various Processing of straight lines, arcs and curves. Contour-controlled machining path.
Such machine tools mainly include CNC lathes, CNC milling machines, CNC wire cutting machines, machining centers, etc. The corresponding CNC devices are called contour control CNC systems, which can be divided into the following types according to the number of linkage axes it controls. form
① Two-axis linkage: It is mainly used for CNC lathes to process rotating surfaces or CNC milling machines to process curved cylindrical surfaces.
② Two-axis semi-linkage: It is mainly used for the control of machine tools with more than three axes, two of which can be linked, and the other axis can be used for cycle feed.
③ Three-axis linkage: generally divided into two categories, one is the linkage of X/Y/Z three linear coordinate axes, which are mostly used in CNC milling machines, machining centers, etc. The other type is that in addition to controlling the two linear coordinates in X/Y/Z at the same time, it also controls the rotating coordinate axis that rotates around one of the linear coordinate axes at the same time.
For example, in a turning machining center, in addition to the linkage of the longitudinal (Z-axis) and lateral (X-axis) linear coordinate axes, it also needs to control the linkage of the main shaft (C-axis) that rotates around the Z-axis at the same time.
④ Four-axis linkage: Simultaneously control the three linear coordinate axes of X/Y/Z to be linked with a rotating coordinate axis.
⑤ Five-axis linkage: In addition to simultaneously controlling the linkage of the three Yuxian coordinate axes of X/Y/Z. It also controls two of the A, B, and C coordinate axes that rotate around these linear coordinate axes at the same time, forming a five-axis linkage control at the same time. At this time, the tool can be set in any direction in space.
For example, control the tool to swing around the x-axis and the Y-axis at the same time, so that the tool always maintains the normal direction to the contour surface to be processed at its cutting point, so as to ensure the smoothness of the processed surface and improve its machining accuracy and machining. efficiency, reducing the roughness of the machined surface.