다물체 동역학을 이용한 고속 회전체로 구성된 기계 시스템의 수치 해석 및 측정

Abstract

Chatter vibration is detrimental to the quality of the metal strip in the rolling process. A numerical model was proposed to investigate the vibration characteristics. A rolling mill that includes the driving system was modeled by the multibody dynamics to investigate the cause and characteristics of the chatter vibration. The proposed numerical model was validated by the theoretical analysis and experiment that was carried out during manufacturing. It was observed in the analysis that the gear mesh frequency generated by the helical gear was transmitted to the work roll. Amplitudes of the gear mesh and chatter frequencies became high when the rolling force was high, but the chatter frequency did not occur when there was no rolling force. To date, a variety of analytical and mathematical dynamic models of the rolling mill have been developed, but they were simplified models involving the vertical vibration of the rolls and were not enough to be compatible with the actual chatter vibration. In this research, a mathematical model of the cold rolling mill including the driving system is proposed. The model is reliable enough to be compatible with the experimental and theoretical analysis. Not only the vertical, but also the horizontal vibration was investigated to study the added effect of the horizontal rolling force, frictional forces, and joint forces. The horizontal chatter vibration had a strong effect on the dynamic characteristics, although the chatter frequency was generated both in the vertical and horizontal directions. To investigate the effect of unbalanced mass, the work roll was modeled by a rigid rotor with eccentricity. Effect of the eccentricity in the horizontal direction can be used to predict eccentricity, because the amplitude variation of the chatter frequency was very sensitive to eccentricity. The eccentricity was predicted by comparing the amplitude obtained in the experiment with the numerical analysis. Predicted eccentricity was reliable enough because its value was confirmed at a different rotational speed, and the effect of higher eccentricity on the gear mesh and chatter frequencies was investigated. The effect of the rotational speed on the frequencies was also investigated, and the frequency responses in the vertical and horizontal directions were compared. The phenomenon of increase in the amplitude of vibration frequency with increasing rotational speed is well explained by the proposed mathematical model considering the unbalanced mass.