A Study on the Shrink Fits and Internal Clearance Variation for Ball Bearing of Machine Tool using FEM
A Study on the Shrink Fits and Internal Clearance Variation for Ball Bearing of Machine Tool using FEM
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通讯作者：
W. Kim;C. M. Lee;Y. Hwang
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作者：
W. Kim;C. M. Lee;Y. Hwang
机床系统的刚性是极其重要的，因为在载荷作用下的挠度大小决定了加工精度。轴承刚度是影响系统刚度的主要因素。因此，需要增加轴承预紧力，以提高系统的刚性和运行精度。轴承预紧力可视为负内部游隙。为了加强主轴的支撑，需要适量的负轴承游隙。然而，不适当的负轴承游隙会导致过大的滚动接触应力，并最终导致轴承卡住。因此，必须选择适当的内部游隙，以防止轴承卡住，提高轴承刚度。轴承间隙在运行过程中受到紧配合和热膨胀的影响。设计人员必须考虑安装后过盈配合间隙的减小，并且必须考虑热膨胀。本研究的目的是通过有限元分析，掌握与轴承疲劳寿命和主轴性能密切相关的轴承内部游隙的变化和行为。根据热力条件和转速的变化情况，利用商用有限元分析软件Ansys进行了有限元分析。根据工作时的温度，提出了正确的负内间隙。此外，为了在主轴系统中保持足够的接触力，还提出了热膨胀和热收缩之间的相互关系。研究了离心力和轴承内部游隙变化对工作转速的影响。
System rigidity in machine tool is extremely important because the magnitude of deflection under load determines machining accuracy. The bearing stiffness is main factor that influence system rigidity. Therefore, bearing preload is needed to enhance system rigidity and to increase running accuracy. Bearing preload can be regarded as negative internal clearance. A proper amount of negative bearing clearance is desirable in order to stiffen the support of the spindle. However, inappropriate negative bearing clearance can cause excessive rolling contact stresses and eventually lead to bearing seizure. Therefore, Proper internal clearance have to be selected in order to prevent bearing seizure and to improve bearing stiffness. The bearing clearance is influenced by tight fit and thermal expansion during operation. The designer must take into account the reduction of clearance after installation to the interference fits, and thermal expansion must be considered. The purpose of this study is to grasp the internal clearance variation and behavior of a bearing which is a deep connected with fatigue life of bearing and performance of spindle through FEM(Finite Element Method). Finite element analysis is performed by using commercial code ANSYS according to variation of thermal condition and rotational speeds. This paper presents correct negative internal clearance according to temperature during operation. Furthermore, interrelation between thermal expansion and contraction are presented to maintain adequate contact force in spindle system. The influence of the centrifugal force and Internal clearance variation of bearing is studied to operating rotational speed.