Machine tool spindle units

Bolted bearing connections are one of the most important connections in some industrial structures, and manufacturers are always looking for a quick calculation model for a safe design. In this context, all the analytical and numerical models reduce the global study to the study of the most critical sector. Therefore, the main inputs for these models are the maximal equivalent contact load and the corresponding contact angle. Thus, a load distribution calculation model that takes all the important parameters, such as the stiffness of the supporting structure and the variation in the contact angle, into consideration is needed. This paper presents a 3D finite element (FE) simplified analysis of load distribution and contact angle variation in a slewing ball bearing. The key element of this methodology, which is based on the Hertz theory, is modeling the rolling elements under compression by nonlinear traction springs between the centers of curvature of the raceways. The contact zones are modeled by rigid shells to avoid numerical singularities. Each raceway curvature center is coupled to the corresponding contact zone by rigid shells. The main contribution of this method is not only the evaluation of the contact loads with a relatively reduced calculation time but also the variation in the contact angle from the deformed coordinates of the curvature centers. Results are presented for several loading cases: axial loading, turnover moment, and a combined loading of axial force and turnover moment. The influence of the most important parameters such as the contact angle, the stiffness of the bearings, and the supporting structure is discussed. Finally, a preliminary experimental validation is conducted on a standard ball bearing. The results presented in this paper seem encouraging. The FE study shows an important influence of several parameters and a good correlation with experimental results. Consequently, this model can be extended to other types of slewing bearings such as roller bearings. Moreover, it can be implemented in complex industrial structures such as cranes and lifting devices to determine the corresponding load distributions and contact angles and, consequently, the most critical sector.

3D Simplified Finite Elements Analysis of Load and Contact Angle in a Slewing Ball Bearing

Modelling of angular contact ball bearings and axial displacements for high-speed spindles

Angular contact ball bearings are predominantly used for guiding high speed rotors such as machining spindles. For an accurate modelling, dynamic effects have to be considered, most notably in the bearings model. The paper is based on a dynamic model of angular contact ball bearings. Different kinematic hypotheses are discussed. A new method is proposed for the computation of the stiffness matrix: a complete analytical expression including dynamic effects is presented in order to ensure accuracy at high shaft speed. It is demonstrated that the new method leads to the exact solution, contrary to the previous ones. Besides, the computational cost is similar. The new method is then used to investigate the consequence of the kinematic hypotheses on bearing stiffness values. Last, the relevance of this work is illustrated through the computation of the dynamic behavior of a high speed milling spindle. The impact of this new computation method on the accuracy of a finite element spindle model is quantified.

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Complete Analytical Expression of the Stiffness Matrix of Angular Contact Ball Bearings

Nonlinear dynamic modeling of rotor system supported by angular contact ball bearings

In order to optimize the mechanical behavior of high speed rotors, it is useful to know the load-displacement law of the angular-contact ball bearing. The relationship between preload, speed, and contact angle is studied and a new analytical approach is proposed, giving explicitly and with good precision the contact angle versus preload and rotational speed for the special case of elastically preloaded high speed angular-contact ball bearing.

A. Molinari

Papers

A New Proposal for Explicit Angle Calculation in Angular Contact Ball Bearing