The onset of chatter during machining is primarily a function of the variation in chip thickness that occurs due to vibration of the tool, workpiece, or both. The flexible tool engages the workpiece and, due to the cutting force, begins vibrating. This vibration is imprinted on the machined surface. In milling, the next tooth on the rotating cutter overcuts this wavy surface produced by the previous tooth. This wavy surface varies the instantaneous chip thickness which, in turn, modulates the cutting force and the cutter vibration (i.e., a feedback mechanism is produced that can lead to self-excited vibrations, or chatter). Depending on the relationship between the wavy surface left by the previous tooth and the current cutter vibration, the resulting deflections and forces can grow very large (chatter) or diminish (stable cutting). Excessive vibration and chatter costs manufacturers $100 Billion annually in lost productivity.
Vibration phenomena are not random, but rather they can be quantitatively measured and described. With the aid of advanced technology, it is now possible to scientifically quantify the vibration characteristics of a milling process, predict chatter, and make recommendations to eliminate it. However, it is important to recognize the degree of analysis that is required. Chatter has a direct impact on surface finish, tool life, cycle time, and cost. Understanding the priority of one or more of these variables in a given operation is crucial to successfully eliminating chatter and substantially optimizing specific milling operations.
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