What are the principles for selecting milling cutters in CNC machining centers? How to deal with overcutting problems in CNC machining centers?
Milling cutters are used to process planes, steps, grooves, forming surfaces and cutting workpieces on CNC machining center milling machines, which have a great impact on the quality of workpieces, so how to choose a suitable milling cutter? What are the principles?
The milling cutter used on the CNC machining center should be made of solid carbide, and the general milling machine should be made of white steel. The hardness of the white steel milling cutter and the carbide milling cutter is softer. Carbide milling cutters have good thermal hardness and wear resistance, but have poor impact resistance. The blade will be broken if you drop it at will. Cemented carbide is a material made by powder metallurgy. The hardness can reach about 90HRA, and the thermal property can reach about 900-1000 degrees.
1. Number of teeth of milling cutter
When choosing a milling cutter, consider its number of teeth. For example, a coarse-tooth milling cutter with a diameter of 100mm only needs 6 teeth, while a fine-tooth milling cutter with a diameter of 100mm can have 8 teeth. The size of the tooth pitch will determine the number of teeth that participate in cutting at the same time during milling, which affects the stability of cutting and the requirements for the cutting rate of the machine tool.
2. Chip flutes
Coarse-tooth milling cutters are mostly used for roughing operations because they have larger chip pockets. Assuming that the chip flute is not large enough, it will cause difficulty in chip rolling or increase the conflict between the chip and the cutter body and the workpiece. At the same feed rate, the cutting load per tooth of the coarse-tooth milling cutter is larger than that of the dense-tooth milling cutter.
3. Cutting depth
When finishing milling, the cutting depth is shallow, generally 0.25-0.64mm. The cutting load of each tooth is small (about 0.05-0.15mm), and the required power is not large. The dense-tooth milling cutter can be selected, and a larger feed rate can be selected.
4. Application of rough milling
Excessive cutting forces can cause chattering in less rigid machines during heavy roughing. This chatter can lead to chipping of carbide inserts, which in turn reduces tool life. The choice of coarse-tooth milling cutters can reduce the power requirements of the machine tool.
The milling cutter used in the CNC machining center is relatively expensive. The price of a face milling cutter body with a diameter of 100mm may cost three or four thousand yuan, so it should be selected prudently. Many people who have operated CNC machining centers have encountered overcutting problems, so how to deal with this situation?
The workpiece processing process of cnc machining center is no longer like traditional processing equipment, which requires continuous control of the machine tool to complete, control the various functional components of the machine tool to perform complex and precise movements, and then complete the processing process with high precision and efficiency. The preparation of the workpiece processing program is the key to the workpiece processing of the machining center. However, if the programming is unreasonable or the parameters are set improperly, it will seriously affect the machining accuracy and machining efficiency of the workpiece, such as overcutting. Overcutting is a serious problem in workpiece processing, which can lead to the scrapping of the workpiece when severe. For some reason, the front-line processing personnel have compiled a processing program that is sure to cause overcutting during CNC programming. The system can announce an alarm signal in advance during the work process, which can avoid the occurrence of overcutting accidents. How to judge the cause of the overcut phenomenon in the CNC machining center?
1. Overcut during arc machining in machining center
When the machining center performs internal arc machining, if the selected tool radius rD is too large, overcutting is likely to occur when the radius R of the arc required for machining is exceeded. The CNC machining programs are compiled according to the actual generalized orbit of the workpiece, regardless of the movement orbit of the tool during the actual machining process. Because the existence of the tool radius makes the actual tool path coarse and does not coincide with the programmed path, in order to obtain a correct workpiece surface overview, it is necessary to set the tool radius compensation command between the tool path and the programmed path. Otherwise the workpiece overcut will be inevitable.
2. Judgment of overcut during straight line processing
When machining a workpiece composed of straight line segments in a CNC machining center, if the tool radius is too large, it is very likely that overcut will occur, and then the workpiece will be scrapped. It can be judged by the positive or negative of the scalar product of the programming vector and its corresponding correction vector.