Investigating the dynamic characteristics of the hydrostatic bearing spindle system with active piezoelectric restrictors

Studies show that active control technology can improve system performance and meet the increasing industrial demand in diverse applications. In the present study, the dynamic characteristics of the bearing-spindle system based on active piezoelectric (PZT) restrictors, including the amplitude-frequency and phase-frequency characteristics are analyzed theoretically and experimentally. In the analysis, the influence of the pipeline model on the system characteristics is studied. Then the feasibility and effectiveness of the active control method are verified through experiments. It is demonstrated that the theoretical and experimental results are consistent. The present study is expected to provide a guideline for further investigations on the structural optimization and control law design for active hydrostatic oil-film bearing spindle systems.

Effect of Spinning Triangle and Production Speed of Hollow-Spindle System on the Bouclé Yarn Structure

This study aims to show the impact of both the width of the base of the spinning triangle and the production speeds of hollow-spindle spinning machines on the structure of ultimate multiple-thread-structure bouclé yarns and similar fancy yarns. A hollow-spindle spinning machine was used and bouclé yarns were made of a core thread, an effect thread and a (multifilament) binder. Initially, five bouclé yarns were made by setting the widths of the base of the spinning triangle at five levels, i.e. 4.5 mm, 7.5 mm, 10 mm, 13 mm and 16 mm. A further six bouclé yarns were made to show the changes that occur to the spinning triangle at various production speeds. The resulting fancy bouclé yarns were assessed by measuring the size, number and circularity ratio of bouclé profiles. It was found that at low production speeds, i.e. at start-up, that the spinning triangle was unstable, which adversely affected the structure of the final bouclé yarns. However, at production speeds higher than 17 m/min, the spinning triangle became stable, though such a stable spinning triangle had no impact on the structure of the resulting fancy bouclé yarns. The results of this study may help fancy yarn manufacturers to avoid making defective fancy yarns.

An Improved Thermal Performance Modeling for High-speed Spindle of Machine Tool Based on Thermal Contact Resistance Analysis

The distribution of the temperature field has a great influence on structural performance, thermal deformation, thermal error compensation. To improve the prediction accuracy of the temperature distribution of the spindle system, a comprehensive model considering the contact thermal resistance (TCR) of the interfaces was established to analyze the thermal performance of high-speed spindle system in the present work. An elastoplastic contact model was used to calculate the contacting areas and loads of interfaces, which were employed to establish the contact thermal resistance model of the main interfaces of spindle, such as bearing rings and tool holders. Basing on the TCR parameters, a Finite Element Analysis (FEA) model was proposed to analyze the temperature distribution of the spindle system. And a temperature test experiment was set up to verify the accuracy of the FEA model. The results show that the relative error of representative test points was all less than 5%, which means the established model can appropriately reflect the temperature field distribution of the spindle.

Determination of the Natural Frequency of the Model Spindle System with Active Regulation of the Initial Tension of the Bearings

This article presents a test stand with a model high-speed spindle equipped with a system of active control of the preload of the bearings. This preload was changed by means of three piezo actuators. The work presents the results of tests during which the commercial Abacus measuring equipment from Data Physics was used. Its application has shown that the spindle system with angular contact ball bearings is responsive to changes in the preload value of these bearings. The change preload resulted in a change in the value of the resonant frequency of the system and its amplitude. This article presents the dependence between the variable value of the preload of the bearings and the corresponding values of the resonance frequency and amplitude of the spindle system. The use of the Abacus measuring equipment for testing allowed for the preparation of a model showing the dynamic behavior of the spindle. The system was forced by a signal with known parameters, and the response to this excitation was recorded at eleven points located on the surface of the entire spindle.

Acceleration-Dependent Analysis of Vertical Ball Screw Feed System without Counterweight

The distinguishing feature of a vertical ball screw feed system without counterweight is that the spindle system weight directly acts on the kinematic joints. Research into the dynamic characteristics under acceleration and deceleration is an important step in improving the structural performance of vertical milling machines. The magnitude and direction of the inertial force change significantly when the spindle system accelerates and decelerates. Therefore, the kinematic joint contact stiffness changes under the action of the inertial force and the spindle system weight. Thus, the system transmission stiffness also varies and affects the dynamics. In this study, a variable-coefficient lumped parameter dynamic model that considers the changes in the spindle system weight and the magnitude and direction of the inertial force is established for a ball screw feed system without counterweight. In addition, a calculation method for the system stiffness is provided. Experiments on a vertical ball screw feed system under acceleration and deceleration with different accelerations are also performed to verify the proposed dynamic model. Finally, the influence of the spindle system position, the rated dynamic load of the screw-nut joint, and the screw tension force on the natural frequency of the vertical ball screw feed system under acceleration and deceleration are studied. The results show that the vertical ball screw feed system has obviously different variable dynamics under acceleration and deceleration. The influence of the rated dynamic load and the spindle system position on the natural frequency under acceleration and deceleration is much greater than that of the screw tension force.

Numerical and experimental modal analysis of machine tool spindle systems

The need for air transportation has increased drastically over the last few decades, to cope with these increasing demands manufacturing companies are trying to improve and speed up their machining processes. High precision in surface finish is required in aerospace industry. To achieve higher production rates, the cycle time (time required for a part or component to be machined) should be reduced. However, chatter often poses a limiting factor on the achievable productivity. One of the major parameters contributing to chatter is the fundamental frequency of the machining system. The system consists of cutting tool, tool-holder, and machine-tool spindle. Impact test is commonly used to determine frequency response function (FRF), which in turn is utilized to acquire the natural frequencies of the system. Impact testing at each stage of machining is impractical, as it will hinder production. Therefore, the study conducted in this report introduces Finite Element Analysis (using ANSYS®) to create an accurate model, which predicts the natural frequencies of the system. A calibrated FEM model of the spindle system, where the bearings are modelled as linear spring elements, is introduced. The spring constants are then varied such that the FEM natural frequencies match the theoretical/experimental ones. This technique is extremely useful as it reduces the downtime of the machine due to impact testing. An experimental setup of the spindle system was designed and fabricated. Impact tests were conducted on the spindle-setup and the results were used to validate the model. The proposed method could be ultimately used to incorporate the bearings degradation/aging effects into the dedicated calibrated FEM model, and to predict the system frequencies in terms of spindle age, i.e., number of in-service hours.

Numerical and experimental modal analysis of machine tool spindle systems

The need for air transportation has increased drastically over the last few decades, to cope with these increasing demands manufacturing companies are trying to improve and speed up their machining processes. High precision in surface finish is required in aerospace industry. To achieve higher production rates, the cycle time (time required for a part or component to be machined) should be reduced. However, chatter often poses a limiting factor on the achievable productivity. One of the major parameters contributing to chatter is the fundamental frequency of the machining system. The system consists of cutting tool, tool-holder, and machine-tool spindle. Impact test is commonly used to determine frequency response function (FRF), which in turn is utilized to acquire the natural frequencies of the system. Impact testing at each stage of machining is impractical, as it will hinder production. Therefore, the study conducted in this report introduces Finite Element Analysis (using ANSYS®) to create an accurate model, which predicts the natural frequencies of the system. A calibrated FEM model of the spindle system, where the bearings are modelled as linear spring elements, is introduced. The spring constants are then varied such that the FEM natural frequencies match the theoretical/experimental ones. This technique is extremely useful as it reduces the downtime of the machine due to impact testing. An experimental setup of the spindle system was designed and fabricated. Impact tests were conducted on the spindle-setup and the results were used to validate the model. The proposed method could be ultimately used to incorporate the bearings degradation/aging effects into the dedicated calibrated FEM model, and to predict the system frequencies in terms of spindle age, i.e., number of in-service hours.