The concept of tool compensation (offset) in CNC machining center is widely used in our life. For example, when driving a car around a stone, the driver will let the car go around the stone on the side of the stone.
Considering that the car has a certain width, the driver should keep the center line of the car at least half the width of the car away from the stone. In the 1960s and 1970s, there was no concept of compensation in NC machining, so programmers had to program around the relative relationship between the theoretical route and the actual route of the tool, which was easy to make mistakes. The concept of compensation has greatly improved the efficiency of programming.
There are three kinds of compensation in NC machining: tool radius compensation, tool length compensation and fixture compensation. This paper mainly introduces the principle of tool radius compensation:
Purpose of tool radius compensation. When contour machining is carried out on the milling machine because the milling cutter has a certain radius, the tool center (tool center) path does not coincide with the workpiece contour. If the numerical control device does not have the function of tool radius automatic compensation, it can only program according to the tool center path (dotted line in Fig. 1). Sometimes its numerical calculation is quite complex, especially when the tool diameter changes due to tool wear, regrinding and tool replacement, it is necessary to recalculate the tool center path and modify the program, which is cumbersome and difficult to ensure the machining accuracy. When the CNC system has the function of tool radius compensation, the programming only needs to be carried out according to the contour line of the workpiece (thick solid line in Fig. 2). The CNC system will automatically calculate the tool center path coordinates to make the tool deviate from the contour of the workpiece by a radius value, that is, radius compensation.
Method of tool radius compensation. CNC tool radius compensation is that the process of tool center path is executed by CNC system. When programming, it is assumed that the radius of the tool is zero, and programming is carried out directly according to the contour shape of the part, while the actual tool radius is stored in a programmable tool radius offset register, The NC system automatically calculates the tool center path according to the part program and tool radius to complete the machining of the part. When the tool radius changes, there is no need to modify the part program, just modify the radius value stored in the tool radius offset register or select the tool corresponding to the tool radius in another tool radius offset register.