The dynamic performance of a new high-speed spindle supported by water-lubricated hybrid bearings is experimentally studied on a test rig. The present design allows the speed of the spindle up to 30,000 rpm, with a bearing internal diameter of 40 mm, which makes it possible to simulate many actual machining processes. Some experiments have been presented to study the mechanical and thermal behaviors of the spindle and its supporting hybrid bearings. The maximum temperature rise is less than 15°C with a speed of 30,000 rpm and a water supply pressure of 2.5 MPa. The spindle radial run-out of the rotational frequency is about 1
High-speed machining has been widely used in the automobile, aeronautic, shipping, and mold industries for its advantage of high efficiency. Increased cutting speeds are needed for milling and grinding processes. High-speed spindles and supporting bearings, as the key components of machining centers, directly affect machining productivity and the surface quality of work-pieces [
A basic feature of high-speed spindle design is the strategy for selecting supporting bearings. Ceramic bearings are the most widely used types in high-speed spindles, but these bearings usually fail to serve for an extended period at high rotational speeds and heavy loads. Spindles supported by air bearings can operate at ultrahigh speeds and have a theoretically infinite life span. However, air bearings are not widely used in heavy-load industrial applications because of their low stiffness and instability.
Fluid-film hybrid/hydrostatic spindles have been used in precision machines because of their low wear and friction, low noise, low contamination, and high precision [
One method for overcoming these problems is to use water-lubricated hybrid journal bearings with high load carrying capability, high stiffness, high precision, and low temperature rise. Some studies have been conducted to investigate the performance of water-lubricated high-speed bearings, which are used in gas turbines, rocket engines, and spindles. Nakano et al. [
The static characteristics of high-speed hybrid bearings used for high-speed spindles have been studied experimentally and theoretically. Yoshimoto et al. [
However, few studies investigate the dynamic performance of high-speed spindles supported by water-lubricated hybrid journal bearings. Besides, more friction power loss is generated with the increase of the high-speed spindle rotational speed, and then the temperature rise becomes a barrier to the improvement of spindle speed and accuracy [
The test rig of the new high-speed spindle is shown in Figure
Schematic of high-speed spindle system test rig.
The hybrid bearing has a diameter of 40 mm with an L/D ratio of one. The hybrid bearing consists of four stepped recesses and two symmetric circumferential grooves, as shown in Figure
Geometry and coordinate system of the hybrid bearing (a) cross section view and (b) developed view of the bearing surface.
The displacement response of the spindle in the horizontal (
The experiments were conducted according to the following steps. The supply pressure was increased to 2.5 MPa. The rotor was activated at 9,000, 12,000, 15,000, 18,000, 21,000, and 24,000 rpm. The corresponding displacement after the vibrations were recorded until the temperature became stable. The supply pressure was kept constant. Imbalance mass The supply pressure was kept constant. Imbalance mass
The temperature rise of water linearly increases with rotational speed as shown in Figure
Exit temperature rise versus rotational speed at a supply pressure of 2.5 Mpa.
Figure
Flow rate versus rotational speed at a supply pressure of 2.5 MPa.
Figure
Vibration amplitude versus rotational speed in time domain and frequency domain.
To investigate the effect of speed on dynamic performance, the experiment procedure in Section
The orbits near two supporting bearings are recorded at different imbalance forces and rotational speeds. Figures
Orbits of the front bearing without attached unbalance mass.
9000 rpm
12000 rpm
15000 rpm
18000 rpm
21000 rpm
24000 rpm
Orbits of the front bearing with an attached unbalance mass
9000 rpm
12000 rpm
15000 rpm
18000 rpm
21000 rpm
24000 rpm
Orbits of the front bearing with an attached unbalance mass
9000 rpm
12000 rpm
15000 rpm
18000 rpm
21000 rpm
24000 rpm
A new high-speed spindle supported by water-lubricated hybrid journal bearings was developed. Experiments were conducted to study the dynamic performance of the water-lubricated high-speed spindle system. The results indicate that the maximum temperature rise is less than 15°C at a speed of 30,000 rpm and a supply pressure of 2.5 MPa. The radial run-out of the rotational frequency is approximately 1
The authors declare that there is no conflict of interests regarding the publication of this paper.
The work included in this paper was supported by the National Natural Science Fund of China (no. 51505384 and no. 51575421) and the Fundamental Research Funds for the Central Universities (no. 3102015JCS05007).