Abstract
Recently, workpiece such as jet engine turbine case has been lightened and thinned for low fuel consumption. However, the parts such as jet engine turbine case reduce heat resistance for thinning. So it has been required thinning with heat resistance material. However, cutting heat resistance workpiece of low stiffness that thinning causes contributes chatter vibration. In order to understand chatter vibration characteristics, chatter vibration measurement was made in the circumferential direction using 24 displacement sensors. In order to clarify the relationship between the natural vibration and the generated chatter vibration, a striking vibration test was conducted. From the measurement results, it is anticipated that the chatter vibration model is a self-excited vibration oscillating by coupling two natural vibrations of the cosine mode and the sine mode by tool contact and demonstrated. Then, based on the magnitude of the open loop transfer function at the phase crossover frequency of the chatter vibration model, the occurrence of chatter vibration was predicted. In order to estimate the magnitude of the loop transfer function at the phase crossover frequency during cutting, first, a loop transfer function in the static state that is not affected by tool contact is obtained. Next, since the frequency near the phase intersection frequency is near the natural frequency of the workpiece, the magnitude of the open loop transfer function increases. This increase rate (gain amplification factor) is determined by the natural frequency difference between the cosine mode and the sine mode due to tool contact, and the workpiece attenuation. Assuming the case where chaotic vibration of the workpiece deformation type tends to occur most frequently, workpiece attenuation which does not surely generate chatter vibration is obtained. Therefore, it was found that occurrence prediction of chatter vibration of work piece is possible.
