In CNC machining, the residual height refers to the height of the remaining unprocessed area between adjacent tool paths. The residual height determines the surface roughness of the machined surface and the subsequent polishing workload. It is an important index to evaluate the machining quality. In the process of NC programming with CAD / CAM software, the control of the residual height is the main basis for the calculation of the tool path row spacing. Under the premise of controlling the residual height, it is the high efficiency goal of NC machining to generate NC tool path with the maximum row spacing.
In the process of CNC machining [cnclathing.com], the cavity and core of plastic mold, the matching cone or inclined plane is often encountered. After NC machining, it may be found that the end face of cone and the end face of taper hole do not fit together. After polishing, it is still not in place until the tool mark disappears completely. Although manual polishing can achieve a certain surface roughness standard, it will also cause the loss of accuracy. Therefore, it is necessary to analyze the contact condition between NC tool and NC machining surface, and control the cutting depth or step distance, so as to ensure the enough accuracy and surface roughness standard.
When using flat bottomed cutter for NC machining of inclined plane or contour machining of curved surface, residual height will be left between the two layers; The residual height will be left when the ball end milling cutter is used for surface or plane NC machining; The residual height will be left when using the flat bottom cutter to cut the inclined plane or curved surface. This kind of residual height is similar to the plane milling with ball end milling cutter.
Residual height control in machining plane or inclined plane with ball end milling cutter. When using CAD / CAM software for NC programming, it is necessary to set either the line spacing or the residual height, and the relationship between them is determined by the above formula. The plane where the same row of tool path is located is called the section plane, and the row spacing of tool path is actually the distance between the section planes. For surface machining, in most cases, there is a certain angle between the machined surface and the section plane, and there are different angles in different areas of the surface.
Because the existing CAD / CAM software calculates the line spacing in the simplest way, and can't adjust the line spacing according to the different conditions of different areas of the surface, it can't really control the residual height (i.e. in-plane line spacing). At this time, programmers should adjust flexibly according to the specific situation of different NC machining areas. For the surface finishing, the residual height is controlled by changing the tool path form and adjusting the line spacing. One is the oblique cutting method, that is, the section plane and the coordinate plane have a certain angle (usually 45 °)， The advantage of this method is that it is simple and fast, but it has the disadvantage of not wide adaptability. It is not suitable for some products with complex angles. The other is the partition method, that is, the machined surface is divided into different areas for NC machining. In this method, different tool path forms or cutting directions are used in different areas, and different row spacing can be used. The correction method can be carried out according to the above formula. This method has high efficiency and good adaptability, but the programming is relatively complex.
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