Types of chatter in CNC machine tool chatter and workpiece chatter: There are two types of chatter that need attention: tool chatter and workpiece chatter. With tool chatter, the vibration generated by the CNC machine tool will be transmitted to the workpiece, which will cause the workpiece to have serious defects, which can directly cause the processed workpiece to be scrapped.
Flutter is a problem that every CNC machine operator must deal with from time to time. Processing vibration is a common problem in CNC manufacturing. Milling, turning, or drilling can cause parts to suffer this kind of torture. The vibration of the CNC machine tool will affect the quality and efficiency of the processing, will cause the smoothness of the parts to decrease, and will damage the vertical tool and significantly shorten its life.
What is the vibration knife of CNC machine tools?
The vibration of CNC machine tools refers to the phenomenon that the surface of the processed part fluctuates due to the unwanted vibration generated during the cutting operation during the machining process of CNC milling, turning, drilling, etc. This happens when the workpiece and tool vibrate at different frequencies and can be triggered by many process conditions: tool holders, tools, part fixtures, and machine conditions.
Chatter during machining can cause unacceptable surface finishes and shorten tool life. Vibration marks will appear on the machined surface, usually in the form of wave patterns or regular marks. The continuous vibration of the CNC machine tool will cause uneven wear and even damage to the tool. The vibration of CNC machine tools can usually be heard. Experienced mechanics will be able to recognize when chattering occurs through the unique sound of machine vibration.
Usually, 100μm is used as the criterion for judging whether the chatter is appropriate. If the vibration amplitude of cutting exceeds 100μm, it may cause the tool or the workpiece to loosen, and the operation cannot be continued. When the vibration is less than 100μm, although machining can be performed, there will be obvious vibration scratches on the surface of the part, which is not allowed on the surface of the finished product. Therefore, processing vibration should be limited within a reasonable range.
1. Determine the correct tool path: This is a very important step in the cutting process. When using traditional tool paths on CNC machine tools, the degree of engagement of the tools will be different. This may cause excessive force to be applied to the tool at certain points in the tool path, resulting in vibration. Using a constant meshing tool path or reducing the depth of the cut can help alleviate this situation.
2. Correct cutting: When the CNC milling machine uses a slender end mill to mill a deep cavity, plunge milling is usually used, in which the milling cutter feeds axially like a drill. When milling deep cavities, the overhang of the long rod is usually more than 3 times the diameter of the tool rod. Only when the cutting vibration is not serious, the adjustment of the cutting parameters is effective. Conventional adjustment methods: reduce the speed of the tool or workpiece, reduce the depth of cut, and increase the amount of cut per revolution. In addition, blades with large forward and backward inclination angles are used with light chip breakers. The cutting wedge angle of the insert is the smallest in milling.
3. Choose the right cutting tool: Knife tools can greatly affect vibration. Considerations include the correct substrate, geometry, coating, and aspect ratio. Programmers usually tend to use larger tools that can accommodate, but this may not be the ideal tool size. Long, thin tools are more likely to be shaken (and deflected) than short and thick tools. Therefore, a tool with a larger diameter should be selected. Minimize the number of tools protruding from the tool holder, and ensure that they are firmly fixed and have high runout accuracy. Combining a variety of tools with variable groove shapes is an effective way to reduce tool vibration.
How to deal with the vibration of the CNC machine tool
4. Correct tool holder: Ordinary tool holders (double-angle chuck and standard ER chuck) cannot provide the precision or rigidity required for high-performance machining. A better choice is to combine the end face and taper contact tool holder to provide high precision and high rigidity. This type of cage engages with the precision ground surface of the spindle while in contact with the taper, thereby providing the required additional stiffness and helping to damp. By evaluating the balance of the tool, the surface quality can be improved even at lower speeds.
