The chatter of CNC machine tool refers to the phenomenon that in the process of CNC milling, turning, drilling, and other processing, the unnecessary vibration generated in the process of cutting operation makes the surface of the machined parts fluctuate. This happens when the workpiece and tool vibrate at different frequencies and can be triggered by many process conditions: tool holder, tool, part fixture, and machine conditions.
How to deal with the vibration of CNC machine tool
The chatter in the machining process will lead to an unqualified surface finish and shorten tool life. Vibration marks appear on the machined surface, which is usually wavy or regular marks. The continuous vibration of the CNC machine tool will lead to uneven wear and even damage of the tool. The vibration of CNC machine tools can usually be heard. Experienced machinists will be able to recognize when chatter occurs through the unique sound of machine tool vibration.
Usually, 100 μ M was used as the criterion to judge whether the tremor was appropriate or not. If the vibration amplitude of cutting exceeds 100 μ m. It may cause the tool or workpiece to be loose and unable to continue operation. When the vibration is less than 100 μ M, although it can be machined, there will be obvious vibration scratch on the surface of the parts, which is not allowed on the surface of the finished product. Therefore, the machining vibration should be limited to a reasonable range.
How to deal with the vibration of CNC machine tool
1. Determine the correct tool path: This is a very important step in the cutting process. When the traditional tool path is used in CNC machine tools, the degree of tool engagement will be different. This may cause excessive force to be applied to the tool at some 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 a CNC milling machine uses a slender end mill to mill a deep cavity, insert milling is usually used, in which the milling cutter is fed axially like a drill bit. When milling a deep cavity, the overhanging amount of a long rod is usually more than 3 times the diameter of the cutter rod. Only when the cutting vibration is not serious, adjusting the cutting parameters is effective. Conventional adjustment method: reduce the speed of the tool or workpiece, reduce the cutting depth, and increase the cutting amount per revolution. In addition, the blades with a large rake angle and caster angle are used together with a light chip breaker. The cutting wedge angle of the blade is the smallest in milling.
3. Choose the right cutting tool: tool can greatly affect the vibration. Considerations include the correct substrate, geometry, coating, and aspect ratio. Programmers generally tend to use larger tools that can hold, but this may not be the ideal tool size. Long and thin tools are easier to shake (and deflect) than short and thick tools. Therefore, a tool with a larger diameter should be selected. Try to reduce the number of tools protruding from the tool holder, and ensure that they are firmly fixed with high jumping accuracy. It is an effective way to reduce the vibration of the tool by combining a variety of tools with variable groove shapes.
4. Correct tool holder: ordinary tool handles (double angle chuck and standard Er chuck) cannot provide the accuracy or stiffness required for high-performance machining. A better option is to combine the end face and taper contact of the tool holder to provide high accuracy and high rigidity. This type of cage makes contact with the taper while engaging with the precision ground surface of the spindle, providing the additional stiffness required and contributing to damping. By evaluating the balance of the tool, the surface quality can be improved even at lower speeds.