The "knife quantity"
In the machining of CNC, there is a method called "knife quantity". What does this mean? The size of the cutting tool is mainly limited by the rigidity of the machine tool, the work piece and the cutting tool. The selection principle is to choose the most large amount of knife to meet the requirements of the process and the rigidity of the process system, so as to improve the processing efficiency. In order to ensure the machining accuracy and surface roughness of CNC, the finishing allowance of 0.2~0.5mm should be left. In the rough machining, the remainder excision often uses the layer cutting method. In the CAM programming, the cutting depth and the maximum width of the step are set, and the actual step distance is often related to the shape of the work piece.
For the CNC precision machining, the selection of the cutting tool is related to the surface roughness. In the CAM software, two parameters are usually provided to control the surface roughness: the step width and the residual height (Scallop). When the step width is used to control surface roughness, the smaller the width of the step is, the smaller the surface roughness is, but the processing path and the processing time will be extended greatly, so the step width should not be set too small. In practice, the surface quality can be improved by changing the method of semi finishing and finishing the path of the cutter (the two is orthogonal). When the RC height is used to control the surface roughness, the step width will be automatically adjusted according to the shape of the work piece.
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