Flutter is a costly and difficult problem in milling. The effects of flutter can be large enough to damage the tool, causing the workpiece to become scrapped or even damage the machine. To make matters worse, due to the risk of chattering, the machine operator may be too conservative in selecting the machining parameters, so that the machine capacity cannot be used to the best of its ability. Usually, the machining capacity of a machine tool is only one-half or a fraction. Flutter is a self-excited vibration, in which the energy input from the spindle Motor is converted into vibration by some mechanism. The main mechanism for machine tool flutter is "positive feedback amplification of vibration waves". In essence, the dynamic stiffness of the machining system (including tools and workpieces) is insufficient. When the cutter cuts the workpiece, it will cause vibration, and the vibrating cutter will form a ripple on the surface of the workpiece. When the next tooth is in contact with the corrugated surface, the surface ripple will cause the chip thickness to change, and the varying chip thickness will cause the cutting force to change, and the changing cutting force will cause the vibration. One way to eliminate the flutter mechanism is to test the dynamics of the processing system, use these test results to calculate a stable cutting area map, and select the cutting conditions within its stability interval. This pre-control range strategy relies on adjusting the tool vibration to match the corrugated surface. When the current back corrugation matches each Other, the chip thickness no longer changes and the vibration stops. When the number of vibration waves between adjacent teeth is exactly 1, 2 or an arbitrary integer, a stable interval appears on the stability sinusoidal graph. This machining strategy requires knowing the steady speed, maintaining a constant speed over the allowable spindle speed range, having evenly distributed teeth and precisely controlling the spindle speed. Another alternative strategy is to suppress the "positive feedback amplification of the vibration wave" mechanism by changing the pitch of the teeth. If the teeth have an asymmetrical (uneven) spacing, then the corrugated surface left by the previous tooth of each tooth has a different waveform, thereby suppressing vibration. Tools with unequal tooth pitches typically achieve a more stable axial depth of cut than tools with equally spaced teeth. However, to get such results, you need to make a careful estimate. Since the feed rate is constant, variations in the pitch of the teeth result in different feeds per tooth. This usually means that only one tooth can withstand the full chip load, while the remaining teeth are not fully loaded. For this reason, it is necessary to reduce the effective feed per revolution of the tool, and it is necessary to match the reduction in the feed amount by increasing the axial depth of cut until the teeth are just balanced. For example, let's examine the 4-edge end mill with evenly distributed teeth and the most stable axial depth of cut (10mm). The teeth are evenly distributed at 90°, and the orientations are 0°, 90°, 180°, and 270°, respectively. If the allowable chip load (feed per tooth) is 0.2 mm, the amount of tool per revolution will be 0.8 mm/rev. If only one of the teeth changes its orientation by 10°, the orientation of these teeth will be 0°, 100°, 190°, and 280°. Therefore, the pitch of the teeth is 100° (maximum pitch), 90°, 90°, and 80° (minimum pitch), respectively. Similarly, changing the spindle speed can also suppress the positive feedback amplification of the vibration wave, but the tooth pitch can also be effectively changed when the spindle rotates more than one revolution. However, since the feed rate is fixed, the maximum distance can still control the feed rate. Before any increase in metal removal rate is achieved, the change in spindle speed must allow for a doubling of the ratio of the stable axial depth of cut to the maximum pitch/equal spacing. Concerned about surprises Label: knife teeth chip flutter spindle speed cutting force Previous: Door and window hardware related to door and window sealing must not be ignored Next: Explain the standard specification of screws in the fastener industry Microcomputer temperature control Microcomputer Temperature Control,Microcomputer Temperature Controller,Electronic Temperature Control,Microprocessor Temperature Controller Ningbo Kyson Cool Electronic Technology Co., Ltd. , https://www.kysoncool.com
In order to maintain the feed per tooth at the maximum spacing not exceeding the permissible limit value, the maximum spacing is used as the control spacing. The feedrate must be reduced by the ratio of the equally spaced pitch to the maximum pitch (90°/100° in this example) based on the equally spaced pitch feed. Thus, the chip load corresponding to each pitch between the teeth is 0.2 mm, 0.18 mm, 0.18 mm, and 0.16 mm, respectively. The feed per revolution is 0.72 mm/rev. For this tool, the allowable stable axial depth of cut must be greater than the ratio of 100/90, which means that 11.1 mm is exactly the critical value of the metal removal rate. In general, when suppressing vibration wave positive feedback amplification by this method, in order to make the unequal pitch tool have application value, it is necessary to allow the axial depth of cut to be doubled than the maximum pitch/equal spacing. 