During rough milling, the milling should be done layer by layer according to the allowance given by the machined surface with an end mill. This rough milling is efficient, and the surface after rough milling is similar to the terraced fields on the hillside. The height of the steps depends on the rough milling accuracy.
The purpose of semi-finishing milling is to mill off the “terraced fields” steps left during rough machining, so that the machined surface is closer to the theoretical surface. When using a ball end mill, a machining allowance of about 0.5000mm is generally reserved for the finishing process. The line spacing and step spacing of semi-finishing can be larger than those of finishing.
Finishing finally produces the theoretical surface. When finishing a surface with a ball nose end mill, the line cutting method is generally used. For part surfaces with better openness, the turning point of the line cutting should be selected outside the curve table, that is, when programming, the surface should be extended outward. For part surfaces with poor openness, due to the change in cutting speed during the turning back, it is easy to leave tool marks caused by pauses and vibrations on the machined surface and the blocking surface.
Therefore, when processing and programming, first, the evolution speed should be reduced when turning back; second, when programming, the turning point of the processed surface should be slightly away from the blocking surface, and a separate root cleaning program should be performed for the intersection line between the surface and the blocking surface, so that the processed surface and the blocking surface are smoothly connected without causing large cuts.
When the ball nose milling cutter is milling a curved surface, the cutting speed at the tip of the cutter is very low. If the ball cutter is used to mill a relatively flat curved surface perpendicular to the processed surface, the surface quality cut by the tip of the ball cutter is relatively poor, so the spindle speed should be appropriately increased, and cutting with the tip of the cutter should also be avoided.
Avoid vertical cutting. There are two types of flat-bottomed cylindrical milling cutters: one is that the end face has a top hole, and its end blade does not pass the center. The other is that the end face has no top hole, and the end blades are connected and retracted past the center. When milling a curved surface, the end mill with a top hole must never feed vertically downward like a drill bit, unless a process hole is drilled in advance, otherwise the milling cutter will be broken.
If a flat cutter without a top hole is used, the cutter can be fed vertically downward, but since the cutting edge angle is too small and the axial force is large, it should be avoided as much as possible. The best way is to feed the cutter obliquely downward, and then use the side edge to cut horizontally after a certain distance. When milling the groove surface, the process hole can be pre-drilled for cutting. Although the effect of vertical feeding with a ball-end milling cutter is better than that of a flat-bottomed end milling cutter, it is best not to use this cutting method because the axial force is too large and affects the cutting effect.
When milling curved surface parts, if it is found that the part material is not well heat treated, there are cracks, uneven structure, etc., the processing should be stopped in time to avoid wasting working hours.
When processing free-form surfaces, since the cutting speed of the ball tool tip is zero, in order to ensure the processing accuracy, the cutting line spacing is generally very small, so ball end mills are often used for finishing of curved surfaces. Flat tools are superior to ball tools in terms of surface processing quality and cutting efficiency. Therefore, as long as it is guaranteed not to overcut, flat tools should be given priority for both rough processing and finishing of curved surfaces.
