The processing of curved parts also follows the processing rules of the CNC machining center, that is, rough machining (roughing)-semi-finishing-finishing-detail processing. Because free-form curves and surfaces cannot be clearly expressed by geometric drawing and mechanical drawing, it has become the primary problem to be solved in the roughing stage of the machining center.
Rough
In order to improve the efficiency of milling when the rough parts of the curved surface parts are preliminary processed, according to the margin given by the surface to be processed, an end mill can be used to mill them layer by layer according to the contour surface. After rough milling, the shape of the curved surface will appear hierarchical distribution, and the height of the steps depends on the rough milling accuracy. During rough machining, due to the large machining allowance and cutting amount, a large amount of cutting heat is generated during the cutting process, which is easy to make the tool wear quickly. At this time, the temperature of the cutting area should be lowered, and the cutting fluid should be applied at this stage. Lubrication and cooling effect.
Semi-roughing
Semi-rough machining is indispensable. This is an important stage from roughing to finishing. Its purpose is to mill away the excess part left in the rough milling step. Semi-finish milling should be carried out with a ball-end milling cutter, and its line and step distance should be larger than that of fine milling. It should be noted that semi-finishing milling should leave a machining allowance of about 0.5 mm for the subsequent finishing milling process. After this process, the shape of the processed surface is close to the theoretical curved surface.
Finishing
Finishing is the process of finally processing the theoretical surface. Ball-end milling cutters are the first choice for finishing tools, and line cutting is usually used. Attention should be paid to the selection of the turning point and the determination of the feed speed during programming. For parts with better openness, the turning point should be selected outside the curve table, that is to say, the curved surface should be properly extended outwards during programming.
For parts with poor openness, since the cutting speed will change during the turning process, it is easy to leave tool marks on the machined surface and the blocking surface caused by pauses and vibrations, so the programming method just now is not applicable. The turning point should be selected at a position away from the blocking surface, and the feed speed should be reduced when turning back. The intersecting line of the curved surface and the blocking surface should be processed separately by a root removal program, so as to ensure the smooth connection of the processed curved surface and the blocking surface, and avoid obvious knife marks.
The tools for processing curved workpieces are mainly ball-end milling cutters
Ball end mill
Ball-end milling cutters are mostly made of high-speed steel. Due to the structure and movement mode, the cutting speed of ball-end milling cutters at the tool tip is very low. When using a ball-end milling cutter to mill a relatively smooth curved surface perpendicular to the machined surface, the surface quality cut by the tool tip will be relatively poor. Therefore, the cutting edge should not be used as much as possible, and the spindle speed should be appropriately increased.
The processing of complex curved surfaces and heterogeneous parts is an important manifestation of the degree of numerical control, and it is also a standard for testing the processing performance of machining centers.