High Speed Machine Tool Spindle Research Articles

A Review on High-speed Electric Spindle Dynamics Modeling and Vibration Response Research

Background: One of the main directions of modern technology in the field of precision machining is high-speed operation. The spindle system is commonly utilized in this kind of operation, and the electric spindle is the main preference among high-speed machine tool spindles. Objective: High-speed electric spindle vibration characteristics affect the machining accuracy of the machine tool and the quality of the workpiece, so the research on high-speed electric spindle vibration characteristics has important engineering practical significance. Methods: The research status of high-speed electrospindle at home and abroad has been summarized in this paper. Combined with the patents related to the dynamics modelling of electrospindle, the research on the dynamics modelling of high-speed electrospindle is analyzed. On this basis, the computational and analytical methods for the vibration modelling of the electrospindle, including the transfer matrix method and the finite element method, are investigated, the theoretical foundations of these methods are discussed in depth, and the advantages and disadvantages of the methods are evaluated. The applicability and limitations of the two methods are also compared. Results: The analysis has shown that the current research on the vibration characteristics of highspeed electrospindle is mainly based on mechanical modal analysis and electromagnetic analysis. At present, the dynamic modeling of the electrospindle mainly includes bearing modeling, shaft bearing modeling, spindle-case modeling, electrospindle electromechanical coupling modeling, electrospindle thermal coupling modeling, etc. The correctness of the modelling theory is verified through experimental and simulation results. Although these models tend to be perfected, they are still insufficient in the case of multiple influencing factors coupling and need further development. Conclusion: Finally, through the analysis of the patent and dynamic characteristics related to the high-speed electric spindle, thermal deformation, magnetic tension, material, and other factors should be considered comprehensively, and these factors should be coupled to establish an overall dynamics model for the vibration characteristics analysis. The dynamic modelling, vibration modelling method, and vibration characteristics of the high-speed electric spindle have been summarized in this study, and the outlook is presented.

Transient formation theory of air-microbubble oil and testing its oil-spraying mechanism

In oil–air lubrication systems, large numbers of air microbubbles are often included in the oil phase. However, the principles of microbubble formation in oil–air annular flow and their influencing factors remain uncertain, and previous conclusions regarding the effects of microbubbles on the viscosity properties of the lubricant oil are inconsistent. Thus, there is an urgent need for experimental verification. In this paper, a transient force balance model is established and used to ascertain the formation of air microbubbles in oil (AB-oil) for an oil–air annular flow. The stability of these microbubbles is analyzed using the Rayleigh–Plesset equation. Theoretical analysis shows that the microbubble radius is the key factor affecting the force balance and stability of microbubbles in oil. Experiments are conducted based on this theoretical analysis, and the void fraction of AB-oil is determined through image analysis to verify the principles and influencing factors of AB-oil formation in oil–air lubrication systems. The viscosity properties of AB-oil are then tested using a rheometer. The experimental results indicate that the formation of AB-oil is affected by oil viscosity, pipe range, oil feeding rate, and air pressure. AB-oil exhibit different viscosity properties at different shear rates and void fractions. Finally, the relationship between the void fraction and viscosity at different shear rates is determined from the experimental data. The outcomes of this research provide insights into the characteristics of oil–air lubrication systems for high-speed machine tool spindles.

Online Dynamic Balance Technology for High Speed Spindle Based on Gain Parameter Adaption and Scheduling Control

Unbalance vibration is one of the main vibration forms of a high speed machine tool spindle. The overlarge unbalance vibration will have some adverse effects on the working life of the spindle system and the surface quality of the work-piece. In order to reduce the unbalance of a high speed spindle system, a pneumatic online dynamic balance device and its control system are presented in the paper. To improve the balance accuracy and adaptation of the balance system, the gain parameter adaption and scheduling control method are proposed first, and then the different balance effects of the influence coefficient method and the gain scheduling control method are compared through many dynamic balance experiments of the high speed spindle. The experimental results indicate that the gain parameters can be changed timely according to the transformation of the speed and kinetic parameters of the spindle system. The balance accuracy can be improved for a high speed spindle with time-varying characteristics, based on the adaptive gain scheduling control method.

Optimization of High Speed Machine Tool Spindle to Minimize Thermal Distortion

Thermal errors contribute significantly to the dimensional error on machined components. Various machine design and operating factors are responsible for the thermal error. In the present work, experiments are performed to understand the effect of spindle rotational speed and the chiller unit setting on the temperature distribution in the spindle and consequently the thermal distortion of the Tool Center Point (TCP). A metrology fixture is fabricated and calibrated to measure TCP displacements as a precursor to experimentation. In addition, multiple temperature sensors are affixed at critical points within the spindle. It is seen that the temperature distribution across the outer race of front bearings is non-uniform (> 2.5°C) which in turn indicates that the heat extraction is not uniform across the spindle. Concurrently, significant tilt (yaw and pitch angles of the order of 50μ radian) is visible at speeds greater than 5000rpm. In the second part of the paper, a thermal compensation model is developed in a linear regression framework. To improve robustness of the model and reduce redundancy, only five out of eighteen temperature sensors (two near front bearing, one each near rear bearing and motor coil and an ambient temperature) are chosen through Principal Component Analysis (PCA) and k-means clustering. The predictions of the model agrees well with the measurements taken from a different set of experiments.

Effect of recess configuration on the performances of high-speed hybrid journal bearing

Purpose The purpose of this paper is to study the influences of recess configurations on the performances of high-speed hybrid journal bearing. Hybrid journal bearing earns increasing attention in high-speed machine tool spindle owing to its intrinsic outstanding performances of low temperature rise and high stability. Design/methodology/approach To investigate the coupled effects of temperature, turbulence and the interaction between lubricant and journal/bearing bush, a thermal fluid-structure interaction approach is presented and validated by the experimental results. Findings Ladder-type recess has excellent tribological characteristics in decreasing temperature rise, improving stability and inhibiting cavitation, which are all beneficial to improve the performances of high-speed spindle system. Originality/value This work can be a valuable guide for the future high-speed hybrid journal bearing design.

Dynamic Stability of a Motorized High Speed Machine Tool Spindle Supported on Bearings

Dynamic behaviour of spindle system influences chatter stability of machine tool considerably. Self-excited vibrations of the tool results in unstable cutting process which leads to the chatter on the work surface and it reduces the productivity. In this paper, a system of coupled spindle bearing system is employed by considering the angular contact ball bearing forces on stability of machining. Using Timoshenko beam element formulation, the spindle unit is analyzed by including the gyroscopic and centrifugal terms. Frequency response functions at the tool-tip are obtained from the dynamic spindle model. In the second phase, solid model of the system is developed and its dynamic response is obtained from three dimensional finite element analysis. The works on analysis of the stability of milling processes focus on calculating the stability boundary of the machining parameters based on the dynamic models characterizing the milling processes. The stability lobe diagrams are generated from frequency response functions (FRF’s) lead to an stability limit prediction for the system at high speed ranges.

고속스핀들의 고무압을 이용한 가변예압장치 실용화를 위한 기초연구

One of the most important element technologies for achieving high-precision in machine tool spindle systems is preload technology for the bearing of spindle systems. Fixed position preload, constant pressure preload, conversion preload and variable preload methods have been applied for the spindle systems. In this study, a new variable preload method using centrifugal force and rubber pressure is used for reducing installation costs through simplifying its structure. The main objective of the work is the verification of the operability in a preload device using the rubber pressure by the finite element analysis. It is shown that the variable preload device proposed in this study is applicable to high speed machine tool spindles.

FSI 해석법을 이용한 고속 주축계의 열특성 해석

FSI (Fluid Structure Interaction) method, in this study, has been applied to analyzing thermal characteristics of a high speed machine tool spindle system. The spindle is composed of angular contact ceramic ball bearings, a high speed built-in motor, a cooling jacket, and so on. The cooling jacket has three inlets and outlets. Using the FSI method, temperature distributions and thermal displacements of the spindle system were computed considering the heating of the front and rear bearings and the built-in motor. The results computed using the FSI method were compared with those determined by experiment and using the conventional numerical approach. The results determined using the FSI method were similar to those from the conventional numerical approach but showed better agreement with the experimental results. Therefore, it is concluded that the FSI method is useful for analyzing the thermal characteristics of high speed spindles and can be applied to the design of high speed spindles.

A new double-face online dynamic balance device and its control system for high speed machine tool spindle

Dynamic balance technology is one of the basic questions that must be considered during the high speed, high-precision machine tool’s design and production course, and its function has a great impact on the working performance, efficiency and life of the machine tool. A new double-face online dynamic balance device with a pneumatic driving system is designed in the paper. Compared with similar balance devices, the dynamic balance device has many advantages: the mechanism structure is simple, the body dimension (the axial dimension in particular) is small, the practical application in the machine tool is easy to realize etc. In order to accurately separate the unbalance vibration component from the vibration measuring signal, the least square algorithm is adopted to fit the fundamental frequency signal. The method has a theoretical advantage compared with the traditional fast Fourier transform algorithm. Based on the influence coefficient principle, the implementation steps of the double-face online dynamic balance are designed. Based on these steps, the location experiments are done to test the position correcting error of the balance discs, the test weight experiments are done to estimate the influence coefficient, and the balance correction experiments are done to examine the online dynamic balance effect. The experimental results indicate that the online dynamic balance device and its control system have the advantage that the system is stable and reliable, the location of the balance disc is accurate and the dynamic balance precision is high.

New Finite Element Modeling Approach of a Propagating Shaft Crack

Transverse shaft cracks are one of the most dangerous malfunctions of the rotating machines, including turbo- and hydrogenerators, high-speed machine tool spindles, etc. The undetected crack may grow slowly and not disturb normal machine operation. However, if it extends to a critical depth, the immediate shaft fracture may completely damage the machine, resulting in a catastrophic accident. Therefore, in-depth knowledge of the crack propagation process is essential to ensure reliable and safe operation of rotating machinery. The article introduces a new model of the propagating shaft crack. The approach is based on the rigid finite element (RFE) method, which has previously proven its effectiveness in the dynamical analysis of numerous complicated machines and structures. The crack is modeled using several dozen spring-damping elements (SDEs), connecting the faces of the cracked section of the shaft. By controlling the exact behavior of individual SDEs, not only the breathing mechanism, but also the crack propagation process can be simply introduced. In order to accomplish this, the stress intensity factors (SIFs) along the crack edge are calculated using the novel approach based on the modified virtual crack closure technique (VCCT). Based on the SIF values, the crack propagation rate is calculated from the Paris law. If the number of load cycles is greater than the constantly updated threshold number, then the crack edge is shifted by a small increment. This way, starting from the first initially cracked SDE, the crack is extended little by little, continuously changing its shape. The approach is illustrated with numerical results, demonstrating the changes in the rotor vibration response and in the crack shape and also explaining some issues about the breathing mechanism due to the propagating shaft crack. The increasing amplitude of the 2X harmonic component is recognized as an evident propagating crack signature. The numerical results correspond well with the data reported in the literature. The RFE model of the rotor is validated by comparing the vibration responses obtained experimentally and numerically. A good agreement between these data confirms the correctness and accuracy of the proposed model. The suggested approach may be utilized for a more reliable dynamic analysis of the rotating shafts, having the potential to experience propagating transverse cracks.

Dynamic Performance Test and Analysis of Spindle System of High Speed Grinding Machine Tools

The high speed machine tool spindle plays an important role in machining operations. Based on modal test techniques and rotating machinery signature techniques, the research focused on the test and analysis of the dynamic characteristics of spindle system of high speed grinder. First, an experimental modal analysis (EMA) is performed in the spindle system; then, the frequency response characteristics and the FRFs of the system should be considered. Furthermore, rotating machinery signature techniques are used to analyze the dynamic behavior of the spindle system in process due to the limitation of modal test techniques, and the theoretical proof is given to explain the spindle system order. The results show that it requires the machine tool to avoid the use of vibration-sensitive speed in the production process and the machine production process, especially bearing manufacturing to improve its accuracy.

Estimation for Bearing Preload of Machine Tool Spindle Based on Vibration Signal

A significant source of noise and vibration in high speed machine tool spindle is bearing induced vibration, which is caused by geometrical characteristics and interactions between rolling members with surface irregularities. In this paper, analytical approach was proposed to calculate the bearing internal load distribution of spindle, with consideration of the operating conditions. The influences of operating conditions to internal load distribution, contact angles were analyzed. Furthermore, the estimation of power spectral density (PSD) method was used to analyze determination of bearing frequencies. The bearing preload of machine tool spindle was estimated according to the change of ball bearing frequencies. Experiments were carried out in a spindle bearing test rig to verify the validity of the presented analytical method. The method described in this paper can achieve the estimation for bearing preload of machine tool spindle.

Optimization of Thermal Performance of Hybrid Journal Bearings for High Speed Machine Tool Spindle with Small Diameter

Multi-array hole-entry hybrid journal bearings have been widely applied to support the high speed precision machine tool spindle with small diameter used in high efficient inner grinding, due to their prominent properties of high rotation accuracy, high dynamic stiffness, high vibration damping and long life. But the imperfection of the hybrid bearing is the significant temperature rising in the oil film on the condition of high speed operation, which brings about the sharp decreasing of load capacity and the larger thermal deformation of the bushing that cause the bearing failure immediately. In this paper, CFD analysis of the temperature fields of the multi-array hole-entry hybrid journal bearing with various bearing construction parameters and operation parameters are presented. According to the simulation results, the temperature rising in the oil film can be controlled efficiently by optimizing the matching of the bearing construction parameters and operation parameters and excellent characteristics of load capacity and static stiffness have been obtained simultaneously.

Vibration monitoring of high speed spindles using spectral analysis techniques

A significant source of noise and vibration in precision high speed machine tool spindles is bearing induced vibration, which is caused by inherent geometrical characteristics, as well as out-of-balance assembly and interactions between rolling mating members with surface irregularities. The multitude of causes often makes a diagnostic approach quite arduous, particularly due to insufficient information obtained from frequency domain analysis alone. Furthermore, the averaging nature of Fourier analysis and its poor frequency resolution make the task in complex vibration spectra more difficult. The paper presents a new approach in use of auto-correlation analysis with good frequency resolution, combined with windowing capability to isolate significant causes for subsequent remedial actions. The method is applied to a routing spindle with special reference to primary induced bearing frequencies.

Experimental and Computer Aided Analysis of High-Speed Spindle Assembly Behaviour

A methodology of experimental identification of machine tool spindle assembly behaviour has been developed at the Institute for Production Engineering in Novi Sad. The methodology allows analysis of the spindle assembly in terms of static, dynamic and thermal behaviour. This methodology is applied to high-speed machine tool spindle assembly analysis. To increase reliability of experimental results, the methodology is combined with computer aided modeling of static and dynamic behaviour, using software packages based on the finite elements method (l-DEAS, ALGOR, SAP-90, VRETENO). Special attention has been paid to the influence of the used bearing arrangement on the spindle assembly behaviour.

高速主軸のための直列形複合転がり軸受の試作

A hybrid bearing is proposed for high speed machine tool spindle. The bearing composed of two angular contact ball bearings in a series arrangement and has a middle race between double column rolling elements besides the inner and outer race. The third race rotates with keeping a balance of the inner and outer bearing's friction. The spindle rotates at the speed of the sum of the inner and outer bearing's speed. The friction torque of the proposed bearing is less than a conventional bearing's one. But the simulation showed that the bearing has an effective speed range due to the retainer speed and the centrifugal force of the balls. At the critical speed, the friction torque of the bearing coincides with a conventional bearing's one. The critical speed can be rised by use of ceramics balls or small steel balls and an optimum lubricant system. A preliminary experiment of the proposed bearing showed that the final temperature rise of outer race is three degrees C only at 10000 rpm. The experimental critical spindle speed was about 8000 rpm against theoretical 17500 rpm.

Review Lecture - Electromagnetic suspension and levitation techniques

Defying gravity seems to have fascinated scientists and philosophers through the ages. Electromagnetic suspension and levitation, following on from aircushion vehicles, such as the Tracked Hovercraft and the Aerotrain, has been the focus of attention and research for passenger-carrying vehicles since the 1970s. Two major demonstration systems are now in operation: one in Germany and one in Japan. Besides application to passenger-carrying vehicles, controlled DC electromagnet technology has been applied to produce frictionless magnetic bearings, conveyor systems, flow meters, etc. This is becoming a rapidly expanding area, moving out of the realms of academe into one of considerable industrial importance. The applications now include high-speed machine tool spindles, ultra-centrifuges, turbo-alternators, corrosive-liquid pumps, gas compressors and high-vacuum pumps, fly wheels for energy storage, handling components for protective coating and weighing balances. New developments in superconducting materials have also aroused fresh interest in the electrodynamic levitation schemes such as the Japanese one.

APPLICATION OF MAGNETIC BEARING TECHNOLOGY FOR VIBRATION FREE ROTATING MACHINERY

ABSTRACTBy levitating the rotor of a machine with an actively controlled magnetic field, friction is reduced to negligible values and wear is eliminated. By controlling the magnetic fields through a servo‐control system, the rotor position can be exactly maintained; in addition, automatic balancing and stator vibration control can be provided, producing essentially vibration‐free operation.Tests have been conducted utilizing magnetic bearings in an auxiliary turbine. These tests showed a reduction in vibration level of 25 decibels at the rotational speed when operating with magnetic bearings in place of conventional oil lubricated journal and thrust bearings.Revolutionary friction‐free magnetic bearings have been used in a wide variety of industrial applications including highspeed machine tool spindles, large turbine generators, and natural gas pipeline compressors up to 12,000 horsepower. Application of this technology could ultimately permit extremely quiet operation of rotating machinery without the severe penalties in space and weight required by present noise reduction techniques.

Rolling bearings in ultra-precision and high-speed machine tool spindles

Rolling bearings in ultra-precision and high-speed machine tool spindles