High Speed Machining Spindle Research Articles

Phenomenological model of preloaded spindle behavior at high speed

High-speed machining spindles are high-precision mechanisms with a complex and very sensitive behavior. Frequency response functions are required to avoid unstable cutting conditions that lead to premature failure of spindle and tool. However, FRFs are affected by stiffness loss of the bearings at high speed. Indeed, the rotor’s behavior is driven by its boundary conditions which are the preloaded bearings. In order to obtain an accurate model of the preloaded bearing system, this paper focuses on the axial spindle behavior. An analytical model that computes the equilibrium state of the shaft, rear sleeve, and bearing arrangement is presented. A model enrichment method is presented with several new physical phenomena: the macroscopic deformations of the shaft and bearing rings as well as the rear sleeve’s complex behavior. The significance of these phenomena is evaluated with a sensitivity analysis and used for the model updating to obtain a just accurate enough model. The contributions of these enrichments are presented for a case study performed on an industrial spindle. A good agreement between the simulation and the experimental results are achieved that validates the model updating strategy and the phenomenologically enriched model.

Monitoring of distributed defects on HSM spindle bearings

The High Speed Machining (HSM) spindle is one of the most critical bearing applications, because it requires both high speed and high power in order to obtain high quality and productivity. Therefore, bearing condition monitoring is important. Firstly, this paper presents a real and typical spindle life example. The vibration signals and their evolution are discussed in relation to the bearing failures that have been observed after the spindle disassembly. Cleavage notably occurred on the ceramic balls of the hybrid ball bearing. Damaged balls and their chippings then damaged uniformly the rings raceways on the whole circumference. As a consequence, a noise component increases in vibration signal due to the worsening of the ball-race contact during the rolling process. In a second section, the noise component produced by bearing condition is studied and characterized. The frequency spectrum distribution is briefly discussed in relation to a signal model. It is demonstrated by Pearson’s test that the distribution follows a Gaussian law all along the spindle life. Besides, it evolves with bearing condition. Thus, a new criterion, called SBN (Spindle Bearing Noise), is proposed for the monitoring of the uniformly distributed defect. A specific monitoring device was also developed in order to collect real industrial data during the spindle lifetime. Vibration signals are used in order to evaluate the criterion relevancy by comparison with the current best practices. The analyses through three required conditions for bearing condition monitoring and based on three spindles signals, have shown some good results.

Dynamic model of high speed machining spindle associated to a self-vibratory drilling head influence of drill torsional-axial coupling

The drilling of deep holes with small diameters remains an unsatisfactory technology, since its productivity is rather limited. The main limit to an increase in productivity is directly related to the poor chip evacuation, which induces frequent tool breakage and poor surface quality. Retreat cycles and lubrication are common industrial solutions, but they induce productivity and environmental drawbacks. An alternative response to the chip evacuation problem is the use of a vibratory drilling head, which enables the chips to be fragmented thanks to the axial self-excited vibration. Contrary to conventional machining processes, axial drilling instability is sought, thanks to an adjustment of head design parameters and appropriate conditions of use. In this paper, self-vibratory cutting conditions are established through a specific stability lobes diagram. A dynamic high-speed spindle/drilling head/tool system model is elaborated on the basis of rotor dynamics predictions. The model-based tool tip Frequency...

Rotor Model Updating and Validation for an Active Magnetic Bearing Based High-Speed Machining Spindle

This paper presents an experimentally driven model updating approach to address the dynamic inaccuracy of the nominal finite element (FE) rotor model of a machining spindle supported on active magnetic bearings. Modeling error is minimized through the application of a numerical optimization algorithm to adjust appropriately selected FE model parameters. Minimizing the error of both resonance and antiresonance frequencies simultaneously accounts for rotor natural frequencies as well as for their mode shapes. Antiresonance frequencies, which are shown to heavily influence the model’s dynamic properties, are commonly disregarded in structural modeling. Evaluation of the updated rotor model is performed through comparison of transfer functions measured at the cutting tool plane, which are independent of the experimental transfer function data used in model updating procedures. Final model validation is carried out with successful implementation of robust controller, which substantiates the effectiveness of the model updating methodology for model correction.

Rotor Model Validation for an Active Magnetic Bearing Machining Spindle Using Mu-Synthesis Approach

Model-based identification and μ-synthesis are employed for model updating of the rotor for a high-speed machining spindle supported on active magnetic bearings. The experimentally validated model is compared with a nominal engineering model to identify the unmodeled dynamics. The extracted missing dynamics from the nominal rotor model provides engineering insight into an effective model correction strategy. The corrected rotor model is validated by successful implementation of a number of μ-synthesized controllers, providing robust and stable levitation of the spindle over its entire operating speed range.

Modeling and performance evaluation of machining spindle with active magnetic bearings

Active magnetic bearings (AMBs) are increasingly employed in the machine tool industry to exploit their advantages over classical bearings such as high speed capability, rotation accuracy, high stiffness, and accurate displacement tracking capability. Furthermore, the possibility of on-line monitoring of the machining process (e.g., cutting force measurement, tool wear) makes AMB spindles very appealing to the High-Speed Machining (HSM) industry. Despite significant progress already reached in HSM technology, there remain numerous open challenges in modeling and control of magnetic bearings as applied to machining spindles. These include optimum control given AMB magnetic saturation levels, management of nonlinear effects, reduction of chatter, and rotor properties. This paper describes a five-degree-of-freedom, high-speed machining spindle supported on AMBs. The rotordynamic modeling and experimentally extracted transfer functions are presented and analyzed. The experimentally measured tool tip compliance is used to compare PID and mu-synthesis control schemes. The primary finding is that the achieved tool tip stiffness is substantially higher with the μ-synthesized controllers than with the best PID we were able to design.

μ Synthesis Applied to the Compliance Minimization of an Active Magnetic Bearing HSM Spindle's Thrust Axis

Many practical problems in magnetic bearing control concern essentially the minimization (maximization) of the dynamic compliance (stiffness) of the rotor. In this paper, the problem of minimizing the peak compliance of a high speed machining (HSM) spindle's thrust axis is examined. Experimental results are presented which demonstrate that μ synthesis provides an excellent tool for tackling this problem. Both complex μ and mixed μ synthesis are used to design controllers. The performance of the μ controllers is compared to that of an optimized PID controller. Under μ control, the dynamic stiffness of the system was increased by more than a factor of two over that obtained with the optimal PID controller. Careful attention was given to developing an accurate system model and uncertainty description, especially related to the transfer function of the magnetic actuators with solid stators and thrust disk.