Figure 1 Cutting force diagram
Figure 2 shows the system schematic for determining tool wear and breakage based on changes in cutting forces.
Figure 2 Tool state diagram with cutting force detection
When the tool wears during the cutting process, the cutting force will increase, and if the tool is chipped or broken, the cutting force will drastically decrease. In the system, due to factors such as uneven workpiece machining allowance, the cutting force may also be changed. In order to avoid misjudgment, the ratio of the cutting force component and the rate of change of the ratio are taken as the characteristic quantities to be discriminated, ie three cuttings are measured online. The corresponding electrical signals of the component FX, FY, and FZ are input to the divider after amplification, and the component ratios FX/FZ and FY/FZ are obtained, and the differentiator is input to obtain d(FX/FY)/dt and d(FY/FZ). )/dt. This data is then input into the corresponding comparator and compared with the set value. This setpoint is obtained after a series of tests to indicate that the tool is still working or has worn or broken thresholds. When each parameter exceeds the set value, the comparator outputs a high-level signal, and these signals are input to a discriminator composed of a logic circuit. The discriminator can conclude whether it is worn or damaged based on the level of the input level. Load cells (eg strain gages) are best placed on the shank, but because the tool often needs to be replaced, it is structurally difficult to implement. Therefore, the load cell is placed on the outer ring of the front end bearing of the main shaft. On the one hand, it is not affected by the tool change; on the other hand, it is close to the tool cutting workpiece, which is sensitive to the direct monitoring of the change of the cutting force. It is continuous. This detection method has good real-time performance and certain anti-jamming ability, but it needs to determine the threshold of tool wear and breakage through experiments.