Stiffness Of Spindle Research Articles

Stiffness increase in main spindles by using tapered roller bearings for aluminum cutting tests

Due to increasing demands regarding higher manufacturing accuracy and the machining of high-strength materials, the stiffness and load-carrying capacity of main spindles must be enhanced. One approach is to replace the conventionally used angular contact ball bearings, so called spindle bearings, with tapered roller bearings of the same size, which have a higher stiffness and load carrying capacity due to their larger rolling contact. In case the speed requirement is below a speed parameter n·dm=0.9×106\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$n\\cdot d_{m}=0.9\ imes 10^{6}$$\\end{document} mm/min, the poorer speed parameter of tapered roller bearings can be compensated by a sufficiently high lubrication quantity. However, the stiffness increase by using this bearing type in main spindles has not yet been quantified in field tests. Therefore, the aim of this paper is to demonstrate the stiffness advantage of a spindle with an elastically arranged tapered roller bearing compared to a conventional spindle with angular contact ball bearings by machining tests. First, the radial load displacement characteristic of the newly developed tapered roller bearing spindle is tested in advance on an isolated test rig. In machine cutting tests, full slots are milled in an aluminum block. During the tests, the axial and radial displacements of the spindle shaft relative to the housing are measured and evaluated in radial and axial direction. These tests are repeated and compared with the conventional spindle. By varying the process parameters such as cutting depth, feed rate or rotational speed, the increased stiffness of the tapered roller bearing spindle compared to the conventional spindle is illustrated based on the measured displacements. Moreover, frequency response measurements at different speeds underpin the improved damping of the tapered roller bearing spindle. Assuming that the speed requirements are not too high and the tapered roller bearing is sufficiently lubricated, the use of this type of bearing can significantly increase the stiffness and thus the manufacturing precision in the long term for main spindles.

Notice of Retraction: Reliability Sensitivity Analysis for Dynamic Stiffness of Motor Spindles in a Machining Center

Notice of Retraction: Reliability Sensitivity Analysis for Dynamic Stiffness of Motor Spindles in a Machining Center

Factors determining the resection ability of snares in cold snare polypectomy: Construction of an ex vivo model for accurately evaluating resection ability.

Cold snare polypectomy (CSP)-dedicated snares (DSs) may have a higher resection ability than conventional snares. However, a model that can accurately and objectively evaluate and compare the resection ability of each snare has yet to be determined, and characteristics of snare parts that increase resection ability remain unknown. Therefore, we elucidated DSs' resection ability and all characteristics of the parts required for acquiring high resection ability. An ex vivo model for evaluating resection ability was generated using human colons obtained from forensic autopsy specimens. The force required to resect a 15 mm wide human colonic mucosa (FRR) was measured using this model; if the FRR is small, the resection ability is high. Next, after measuring the stiffness of each snare part, the correlation between the stiffness and resection ability was analyzed. The force required to resect using SnareMaster Plus, Micro-Tech Cold Snare, Captivator Cold, Exacto Cold Snare, or Captivator II was 13.6 ± 1.0, 12.5 ± 1.2, 7.4 ± 1.2, 6.5 ± 1.0, and 28.7 ± 3.7 N, respectively. All DSs had significantly lower FRR than the conventional snare (Captivator II) and had higher resection ability (P < 0.001). A negative correlation was found between FRR and sheath or wire spindle stiffness, with correlation coefficients of 0.72 (P = 0.042) or 0.94 (P < 0.001), respectively. Moreover, 1 × 7 type wire rings had significantly higher friction coefficients than 1 × 3 type wire rings (P < 0.002). Sheath and wire spindle stiffness should be increased to increase resection ability; 1 × 7 type wire rings may be suitable for CSP-snare parts.

Static Characteristics of Water-Lubricated Hydrodynamic Spiral-Groove Journal and Thrust Bearings for Motorized Spindle

Abstract Oil-lubricated hydrodynamic bearing is a typical support for motorized spindle. However, a motorized spindle supported by the oil-lubricated hydrodynamic bearing has disadvantages regarding high-temperature rise and low rotational speed. To overcome this problem, this technical brief proposes novel water-lubricated hydrodynamic spiral groove bearings for the motorized spindle. A rotor-bearing static model for the motorized spindle was established considering the external loads and the tilting effect of bearings. An experimental prototype for the motorized spindle was developed, and the theoretical calculation and experimental research on the bearing static characteristics were carried out. The result shows that the water-lubricated hydrodynamic spiral groove bearings have significant advantages in terms of low-temperature rise, good high-speed performance, and moderate spindle stiffness, together with the inherent low manufacture cost and high rotation accuracy of the bearings, and the proposed bearings can be a potential alternative to the fluid bearing for the high-speed motorized spindle.

Influence of the Mechanism of Fluid-Structure Interaction on Stiffness of Static Pressure Spindles and Slides

The stiffness of static pressure spindles and slides is affected by the phenomenon of fluid-structure interaction (FSI). Many methods have been proposed to calculate the stiffness with FSI considered. However, the influence of FSI on stiffness is still unknown. This paper studies the lateral stiffness of an aerostatic slide. The relationship between the lateral stiffness of the aerostatic slide, the lateral bearings, and the solid structure is deduced. According to the relationship, this paper proposes a theory that reveals the influence mechanism of FSI on the stiffness of static pressure spindles and slides. The proposed theory is also valid for the normal stiffness of the aerostatic slide and the thrust stiffness of an aerostatic spindle.

Reliability evaluation of spindle stiffness of railway turnout ballast cleaning machine

The railway turnout ballast cleaning machine has a very complex working environment, where and the operational loads conditions are extremely harsh on the spindle. The spindle is one of the key parts that cause the malfunction of the ballast cleaning machine, and the failure form of the spindle is insufficient stiffness. So, the stochastic finite element method is applied to analyze the influence of the uncertainty of the structural size, material parameters and external load of the spindle on the stiffness reliability of the spindle, and evaluated the stiffness reliability in this paper. The finite element analysis model of the spindle is simulated by ANSYS software, and the spindle&apos;s stress, strain, natural frequency, and mode shape are analyzed. The spindle stiffness reliability model is established, and the stiffness reliability of the spindle is evaluated based on Six Sigma.

Research on the Effect of Spindle Speed on the Softening and Hardening Characteristics of the Axial Operating Stiffness of Machine Tool Spindle

Spindle stiffness is one of the most critical indicators for evaluating and measuring the service performance of spindles. The traditional static stiffness indexes only involve static analysis and rarely focus on the study of spindle-carrying capacity under operating conditions. In this paper, the explicit solution approach is used to develop a mechanical model of the spindle’s axial operating stiffness. This model was then used to explore the influence of rotational speed on the softening and hardening features of the spindle axial operating stiffness, and experimental verification was carried out. According to studies, the speed of a fixed-position preload spindle can lead its operating stiffness to exhibit a “stiffness-hardening” feature. However, when the axial displacement of the spindle is small, the operating stiffness curve of the spindle displays a noticeable “fluctuation” phenomenon for low-speed spindles. Furthermore, the speed-induced preload has a significant impact on the test results when testing spindle axial operating stiffness.

Fracture mechanism of transmission spindle system for high-speed tracked vehicle

According to the traits of engine output torque and vehicle longitudinal dynamic model, considering the influence of the vehicle, the dynamic model of the transmission spindle system is established by using the lumped mass model, and the Runge–Kutta is used to solve the model under sinusoidal excitation and step excitation in starting stage, the time–frequency of transmission spindle under two kinds of excitation is analyzed. Modal analysis is used to decouple differential equations and solve the response of a single-degree-of-freedom system. The analytical approach and numerical solution are compared to each other to verify the correctness of the analysis method, the impact of rotating shaft torsional stiffness on the natural characteristics and dynamic load are analyzed, and the fracture mechanism of transmission spindle is further explored. The analysis results show that when the spindle stiffness is asymmetric, the sinusoidal excitation causes the dynamic load on both sides of the spindle and the driving force on both sides of the vehicle track to be inconsistent, the step excitation induces the second-order low-frequency resonance. Under the small damping, the vibration attenuation is slow, the right end of the spindle is broken under two combined excitations. When the stiffness of the spindle is symmetrical, the influence of sinusoidal excitation on both sides of the spindle is undifferentiated, and the vibration caused by step excitation decays quickly. Finally, the theoretical analysis results were confirmed by crack morphology, vehicle test data.

Rotordynamics of an Improved Face-Grinding Spindle: Rotational Stiffness of Thrust Bearing Increases Radial Stiffness of Spindle

Abstract The support is a key factor affecting performance of face-grinding spindle. However, advantage of traditional rolling element bearing is not highlighted when it is for large-size face grinding. This technical brief aims to develop a combined support for the face-grinding spindle consisting of a water-lubricated hydrostatic thrust bearing and two types of radial rolling bearings, and the flexible rotor dynamics of the spindle with the combined support is analyzed using the modified transfer matrix method. The results show that the rotational stiffness of water-lubricated hydrostatic thrust bearing can increase the radial stiffness of the face-grinding spindle, so the small-size rolling bearings can be utilized as the radial support for the spindle by aid of such rotational stiffness. A comparative study of comprehensive performance between the spindle supported by rolling bearings and the replacement spindle designed with our proposed combined support shows that the proposed one has technical advantage of large axial load-carrying capacity, low frictional power loss, low temperature rise, etc.

A steady modeling method to study the effect of fluid–structure interaction on the thrust stiffness of an aerostatic spindle

ABSTRACT Under support forces from static pressure bearings, the solid deformations of static pressure spindle or slide systems will affect their performance, especially for those with high load-carrying capacity and stiffness. This paper proposes a steady modeling method to study the effect of fluid–structure interaction (FSI) on the thrust stiffness of an H-shaped aerostatic spindle. The proposed method can be readily applied to different static pressure spindles or slides, and can save a lot of time compared with the transient method, which is generally used to consider the phenomenon of FSI. The method proposed in this study is more suitable for studying the performance of spindles and slides with high load-carrying capacity and stiffness, especially in the design phase. In this paper, solid deformations, pressure distributions and the thrust stiffness are all obtained based on this method. Moreover, the effects of the axial position of the spindle and the air film thickness on the thrust stiffness are studied. The proposed method is verified by experimental results. The calculation error of the proposed method is reduced by nearly 77% compared with the traditional method ignoring FSI.

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 both the bearing and the spindle unit. However, interactions between the spindle speed, initial preload, and cutting force caused by the thermal expansion of spindle unit components alter the bearing stiffness characteristics during the running process. Aiming to carry out real-time online monitoring of the thermal characteristics and their effect on the machine tool spindle bearing stiffness, a fiber Bragg grating (FBG) sensors network was proposed. Further, the effects were considered under various axial loads, combined axial, and specific radial load to study bearing temperature increase, thermally induced preload, and thermal stiffness. The results have shown that the bearing thermal stiffness of the bearing decreases with the increase of the spindle speed. Moreover, an optimal initial preload can be selected with respect to the speed to maximize the thermal stiffness. Finally, the thermally induced preload additionally pre-tightened the bearing.

Compact curved-edge displacement sensor-embedded spindle system for machining process monitoring

Abstract Spindle dynamic conditions such as stiffness, damping, runout, and resonance frequencies are the most important factors to determine the quality of the machined part. Thus, spindle dynamic characterization to in-situ identify the spindle behavior is crucial to achieve high dimensional accuracy during the machining. This paper presents a new class of dimensional sensors, the so-called curved-edge sensors (CES), capable of spindle dynamic characterization and in-situ spindle condition monitoring while machining. Unlike conventional dimensional sensors such as capacitive proves or eddy current probes whose sensitivities are sensitive to the curvature of the target surface and lateral motion of the spindle, CES is not sensitive to those effects that CES can be used for spindle metrology, providing more accurate dimensional information available for spindle dynamic characterization. In this study, two-axis CES were embedded inside the aerostatic spindle system not to disturb the spindle system while machining a part, even under working fluid conditions. The CES showed the sensitivity 0.301 and 0.304 V/μm along the X and Y axes, and the linearity was 0.06 % and 0.05 % in full scale, respectively. In addition to the calibration, bandwidth, noise level, and reliability of CES were characterized. Also, the spindle runouts at different speed conditions were characterized by CES, and the cutting forces were in-situ estimated by multiplying 3 × 3 spindle stiffness matrix and the measured displacement.

Qualitative research on the relationship between spindle vibration characteristics and bearing thermal load

The dynamic performance of machine tool is one of the most important factors affecting the machining accuracy. As the core part of machine tool, the dynamic performance of spindle directly determines the performance of machine tool. In this paper, the spindle of machine tool is taken as the research object, and the change of fit clearance between bearing inner and outer rings, rotating shaft and bearing seat caused by spindle bearing heat, and its influence on the stiffness of spindle system are analyzed. Based on Timoshenko beam theory and finite element method, this paper qualitatively analyzes the variation characteristics of spindle stiffness caused by bearing overheating and grease lubrication failure during high-speed machining.

Computational-experimental research of the stiffness of high-speed spindles

The stiffness indices of high-speed spindle units on angular contact ball bearings at high rotational speeds are investigated. It is found, that the spindle rotational speed, radial load, bearing temperature, type and magnitude of the preload in the bearings significantly affect the stiffness of the spindle unit. Keywords: high-speed spindle unit, angular contact ball bearing, elastic-deformation model. i.a.zverev@stankin.ru

Oil pressure and viscosity influence on stiffness of the hydrostatic spindle bearing of a medium-sized circular grinding machine

In surface finishing of a grinding machine, the dimension accuracy of the workpiece is most affected by the stiffness of the spindle. For the hydrostatic spindle of a medium-sized circular grinding machine, the primary factors affecting the oil film stiffness are bearing structure parameters, lubrication characteristics, and working conditions. In this study, the effects of lubricant pressure and oil viscosity on the stiffness of the hydrostatic spindle based on the working conditions were investigated. The oil viscosity affects the spindle by increasing the stiffness that corresponds to the increase in viscosity in the range of 0.001–0.002 Pa[Formula: see text]S, while the stiffness proportionally increases with pump pressure changing in the range of 3–5 MPa. Experimental results also indicate that based on the stiffness of the bearing, a viscosity of 0.002 Pa[Formula: see text]S, pump pressure of 5 MPa, and load range of 500–1000 N are the most feasible working conditions for hydrostatic spindle associated with the fine-machining process on a medium-sized external grinding machine.

Dynamic characteristics of spindle with water-lubricated hydrostatic bearings for ultra-precision machine tools

A key component of ultra-precision machine tools is the spindle. The motivation for this study was to improve machining accuracies in precision cutting and grinding by pursuing improvements in the spindle characteristics by designing a sophisticated spindle with water-lubricated hydrostatic bearings. The static bearing stiffness of the developed spindle was investigated in previous studies. In addition to the static bearing stiffness, the dynamic characteristics regarding bearing stiffness also affect significantly on the machining results. In this study, dynamic characteristics of the developed spindle with water-lubricated hydrostatic bearings were investigated via simulations and experiments. Not only bearing dynamics but also rotor dynamics were considered in this study.In the simulation studies, the spindle dynamic characteristics were analysed based on the transfer matrix method. A spindle rotor supported with hydrostatic bearings was represented by discrete sections of the rotor. The mathematical model of transverse linear vibrations of the spindle rotor was derived with distributed parameters for these discretized rotor sections. As a result of the analysis on the amplitude-frequency characteristic, radial displacements of the rotor due to bearing displacement and bending deformation were defined. Then, the frequency characteristics were represented with Nyquist plots. Resonant frequencies and amplitudes formation in the transverse vibration of the rotor were determined. The influence of rotor bending deformations on spindle compliance was assessed. Furthermore, the study examined the influences of the supply pressure of the lubricating fluid, radial clearance and journal diameter of the hydrostatic bearings on the amplitude of the rotor vibration, and the resonance frequency of the system.Furthermore, the dynamic characteristics of the spindle were examined experimentally. The simulation results were in good agreement with the actual spindle dynamics obtained experimentally. The influence of the structural parameters of the rotor and the operating parameters of the bearings on the spindle dynamic characteristics was also determined. It was verified that the amplitude of the vibration of the rotor overhang part was dominantly affected not by bearing stiffness but by bending stiffness of the bearing journal of the front bearing and the length of the rotor overhang.Then it was verified that the resultant displacement of the rotor in the radial direction due to the influence of the bearing characteristics and the structural effect of the rotor is significantly small. Practical recommendations to improve the spindle design in terms of the dynamic characteristics of the spindle with water-lubricated hydrostatic bearings were also derived.

Selection of Lathe Spindle Material Based on Static and Dynamic Analyses Using Finite Element Method

Abstract Lathe spindle is considered as an essential component that makes material removal possible during the machining operation. The stiffness of spindle has an important role on productivity and surface finish of the work piece. Lathe tool spindle leads to unbalanced vibration and uneven tension in pulleys and belts. In the present study, three dimensional model of the spindle is prepared. Four different materials like AISI 1045 carbon steel, AISI 4140 alloy steel, AISI 304 stainless steel and grey cast iron are considered. Based on FEM, the static and dynamic analyses are done separately under cutting forces and during rotation. From dynamic analysis, modal shapes are obtained. Computational simulation is done in ANSYS 15.0 workbench and static structural analysis is performed with varied cutting force and speed. Total deformation, equivalent stresses and strains have been used in identifying the suitable material. AISI 1045 carbon steel is showing the minimum values of total deformation and equivalent stress in all the cases. Similar stress pattern is observed in all the materials with the position of the maximum stress also being same with varied magnitude. The value of maximum total deformation is observed at spindle face area and minimum at the spindle bearing part for all materials. In spindle, the maximum equivalent stress is induced in spindle housing area and minimum at tail end. Also, the maximum equivalent strain is observed at the spindle housing area and minimum at tail end region. The rotational speed has less effect on the development of stresses and strains in the spindle. With the help of Campbell diagram, critical velocity is also found for choosing the best material applicable. Thus, the present work discusses the static and dynamic analyses on lathe spindle for different materials

Stiffness modeling, identification, and measuring of a rotating spindle

The stiffness of a spindle at high speeds has a significant effect on the quality of the cutting surface and the machining accuracy. However, the spindle stiffness is difficult to be detected directly when the spindle is rotating, and the measured stiffness values are usually coupled with other parts of the spindle–tool system (such as toolholder, spindle–toolholder joint, tool). This paper presents a comprehensive method to deal with the stiffness modeling, identification, and measuring of a rotating spindle. Based on the deflection equation and the principle of superposition, the stiffness model is derived, for a spindle–tool system including a spindle, a specially manufactured toolholder, and a spindle–toolholder joint. A three-step identification algorithm is proposed to decouple and identify the actual spindle stiffness value. First, when the spindle is static, the stiffness values of the shaft, toolholder, and joint are obtained by using the least-squares method. Second, when the spindle is rotating, the stiffness values of the rear bearings and front bearings are identified based on the spindle error analysis method. Third, the stiffness values of the spindle under different rotating conditions are calculated based on the identification results from the previous two steps. Furthermore, the stiffness model and identification algorithm are verified experimentally on an instrumented spindle. The static stiffness value of the same spindle is also measured and compared with the stiffness value under rotating conditions subsequently. This work is useful and can be utilized as a guide for spindle stiffness testing and spindle performance evaluation to spindle manufacturers.

An Optimization Method for the Main Influence Factors on the Performance of Aerostatic Spindle

This paper proposes a novel optimization method to improve the performance of aerostatic spindle. The optimization process is based on the main factors affecting the load and stiffness of aerostatic spindle, which are determined by cross‐correlation analysis. The maximum values of load capacity and stiffness are obtained from the relationship between the optimization function and the main influence factors. After optimization, the corresponding natural frequency has been improved, which indicates that the optimization method proposed in this paper is more efficient and reliable in the field of precision machining. The results will enforce the industrial application of aerostatic spindle system.

Investigation on the influence of interference fit on the static and dynamic characteristics of spindle system

The performance of high-speed and high-precision machine tool spindle is quite sensitive to the variation of system parameters. How to accurately predict the influences of key parameters on spindle characteristics is important for designers to achieve required machining accuracy. In the assembly of spindle system, the interference fit, which is always used to connect bearing and shaft, affects the performances of spindle system directly. Therefore, the quantitative investigation on the effects of interference fit on spindle characteristics are of great practical significance. In this paper, the effect mechanism of interference fit on spindle bearing system is explored and used to modify the analytical spindle bearing model. Firstly, the internal geometric relationships among the assembly bearing parts and shaft is analyzed under the influence of assembly deformation and centrifugal expansion. Then, the static and dynamic characteristics of spindle bearing system, including the bearing stiffness, maximum loosing speed, spindle stiffness as well as modal characteristics, are predicted under different interference fit values based on the modified spindle bearing model. The results show that the interference fit will stiffen the bearing and spindle system and result in obvious increments on bearing stiffness, spindle stiffness as well as the natural frequencies. A specially designed spindle test rig is built to verify the simulation results, and the variation of spindle stiffness and natural frequencies are measured under different interference fit values. The maximum error of the system natural frequencies between the analytical results and the experimental data is 7.36%, which confirmed the accuracy of the proposed analytical model.