NEW BEARING STEEL FOR HIGH-SPEED APPLICATIONS

The requirements for speed suitability and fatigue strength of motor spindle bearings are constantly increasing. These challenges can be met by further developing the spindle bearings, e.g. by using higher-performance bearing steels. In the following, the experimental investigation results of a spindle bearing made of a new raceway steel tested on a high-speed rolling bearing test rig are presented. Spindle bearings of the type 7008 (hybrid execution) were tested in an endurance run at a rotational speed of 46 krpm and 3 kN axial load. The operating behaviour was validated based on the bearing outer ring temperature and the vibration behaviour. Microscope analysis of the raceways after the test shows that the new steel has good resistance to micropitting and surface fatigue. The calculated contact pressures, wear parameter and lifetime for the bearings in the tests show that the performance limits of spindle bearings are significantly higher than initially assumed.

Monitoring and Control System for Heat Experimental Equipment of High-Speed Vertical Spindle Bearings

High speed of spindle for high-speed machining is the mission and development trend of today's machine tools. However, improper lubrication can cause a large temperature difference on the bearings, causing thermal deformation that affects the accuracy of the spindle. Heat experimental equipment for high-speed vertical spindle bearing is necessary. This paper presents a design and manufacture of control and monitoring system of heat experimental equipment for high-speed vertical spindle bearing based on PLC, WinCC and Webserver. This experimental device with supervisory control solution allows easy implementation of the test mode and data collection to plan out the appropriate lubrication mode. The system includes motor control and monitoring, observing of sensors, alarm and reporting at local and on site remotely. This solution can be applied to other industrial equipment to meet the needs of Industry 4.0.

Multi-body Dynamic Modelling and Error Analysis of Planar Flexible Multilink Mechanism Considering Clearance and Thermal-mechanical Coupling Effect of the Crankshaft-bearing Structure

In order to study the dynamic position accuracy of bottom dead point (BDP) for multilink high-speed precision presses (MHSPPs), it’s essential to develop a dynamic model of planar multilink mechanism with clearance and spindle-bearing structure. Traditional models always neglect the effect of thermal characteristics of spindle-bearing structure, which reduces the prediction accuracy of dynamic model for multilink transmission mechanisms. To overcome the shortcomings of the previous models, a thermal network model (TNM) of the crankshaft-bearing system is established firstly considering the effects of thermal contact resistance and variable stiffness of bearing concerning the temperature rise. Then, dynamic model of the crankshaft-bearing system is built through the finite element method, which includes rigid disk, Timoshenko beam and quasi-statics model of ACBB. On this basis, an improved dynamic model of planar flexible multilink mechanism with clearance considering the thermal-mechanical coupling effect of the crankshaft-bearing structure is developed and the corresponding dynamic error dimension chain between slider and crankshaft is constructed in this work. Compared to the simulation from traditional models, the simulated slider’s BPD position error from the improved model agrees better with experimental data, which verifies the correctness of the proposed model. It’s demonstrated that the punching force and thermally induced variable stiffness of bearing lead to a significant increase of slider’s BDP position error, which reduces the machining precision of MHSPP. Furthermore, the influence of crankshaft speed, contact angle of bearing and clearance size on the slider’s BDP position error is also investigated.

Research on Thermal Stiffness of Machine Tool Spindle Bearing under Different Initial Preload and Speed Based on FBG Sensors

As a key parameter, stiffness determines the dynamic characteristics of the bearing and the spindle unit. However, the interaction of the spindle speed, initial preload, and cutting force will change the bearing stiffness characteristics during the running process cause the thermal expansion of spindle unit components. Aiming at real-time online monitoring of the thermal characteristics of machine tool spindle bearing stiffness, this paper proposed a fiber Bragg grating (FBG) sensors network. And under different axial loads, combined axial and specific radial load, the bearing temperature rise, thermally induced preload, and thermal stiffness are studied. The results show that the thermal stiffness of the bearing decreases with the increase of the spindle speed, and there is an optimal initial preload at the speed to maximize the thermal stiffness of the bearing, and the thermally induced preload has an additional pre-tightening effect on the bearing.

Dynamic modeling and vibration response analysis of a synchronous motorized spindle with inclined eccentricity

The air-gap eccentricity will produce unbalanced magnetic pull and cause vibrations and noises in a motor. In this study, the dynamic behavior of a synchronous motorized spindle with inclined eccentricity is investigated. A semi-analytical method is proposed to model the unbalanced magnetic pull and the electromagnetic torque of a rotor with inclined eccentricity, and the semi-analytical method is verified by the finite element method. The dynamic model of a spindle-bearing system is built by taking the centrifugal force and gyroscopic effects into account. Then, the vibration response of dynamic displacement eccentricity, inclined eccentricity including displacement eccentricity and angle eccentricity, rotating speed, and unbalanced mass eccentricity in both time domain and frequency domain are simulated and analyzed. The results show that the eccentricities can lead to fluctuations in amplitudes of the dynamic displacement response and the angle response. The frequency components of the dynamic responses are the combination of rotating frequency, VC frequency, and power frequency. It is indicated that the coupling interactions of bearing forces, unbalanced mass force, and unbalanced magnetic pull have an obvious effect on the spindle-bearing system.