Design of a five-axis ultra-precision micro-milling machine—UltraMill. Part 2: Integrated dynamic modelling, design optimisation and analysis

Using computer models to predict the dynamic performance of ultra-precision machine tools can help manufacturers to substantially reduce the lead time and cost of developing new machines. However, the use of electronic drives on such machines is becoming widespread, the machine dynamic performance depending not only on the mechanical structure and components but also on the control system and electronic drives. Bench-top ultra-precision machine tools are highly desirable for the micro-manufacturing of high-accuracy micro-mechanical components. However, the development is still at the nascent stage and hence lacks standardised guidelines. Part 2 of this two-part paper proposes an integrated approach, which permits analysis and optimisation of the entire machine dynamic performance at the early design stage. Based on the proposed approach, the modelling and simulation process of a novel five-axis bench-top ultra-precision micro-milling machine tool—UltraMill—is presented. The modelling and simulation cover the dynamics of the machine structure, the moving components, the control system and the machining process and are used to predict the entire machine performance of two typical configurations

A novel haptic model and environment for maxillofacial surgical operation planning and manipulation

This paper presents a practical method and a new haptic model to support manipulations of bones and their segments during the planning of a surgical operation in a virtual environment using a haptic interface. To perform an effective dental surgery it is important to have all the operation related information of the patient available beforehand in order to plan the operation and avoid any complications. A haptic interface with a virtual and accurate patient model to support the planning of bone cuts is therefore critical, useful and necessary for the surgeons. The system proposed uses DICOM images taken from a digital tomography scanner and creates a mesh model of the filtered skull, from which the jaw bone can be isolated for further use. A novel solution for cutting the bones has been developed and it uses the haptic tool to determine and define the bone-cutting plane in the bone, and this new approach creates three new meshes of the original model. Using this approach the computational power is optimized and a real time feedback can be achieved during all bone manipulations. During the movement of the mesh cutting, a novel friction profile is predefined in the haptical system to simulate the force feedback feel of different densities in the bone

A holistic integrated dynamic design and modelling approach applied to the development of ultraprecision micro-milling machines

Ultraprecision machines with small footprints or micro-machines are highly desirable for micro-manufacturing high-precision micro-mechanical components. However, the development of the machines is still at the nascent stage by working on an individual machine basis and hence lacks generic scientific approach and design guidelines. Using computer models to predict the dynamic performance of ultraprecision machine tools can help manufacturers substantially reduce the lead time and cost of developing new machines. Furthermore, the machine dynamic performance depends not only upon the mechanical structure and components but also the control system and electronic drives. This paper proposed a holistic integrated dynamic design and modelling approach, which supports analysis and optimization of the overall machine dynamic performance at the early design stage. Based on the proposed approach the modelling and simulation process on a novel 5-axis bench-top ultraprecision micro-milling machine tool – UltraMill – is presented. The modelling and simulation cover the dynamics of the machine structure, moving components, control system and the machining process, and are used to predict the overall machine performance of two typical configurations. Preliminary machining trials have been carried out and provided the evidence of the approach being helpful to assure the machine performing right at the first setup

Study of characteristic variations of high-speed spindles induced by centrifugal expansion deformations

High-speed machining has continuously pushed the demand of spindles with higher speed and higher reliability. In order to design, analyze, and test spindles in a virtual environment, accurate modeling of the spindle dynamics during the running state is essential. This paper investigates the variations of interference fit and bearing preload condition induced by centrifugal expansion deformations at high speed. Firstly, the elastic expansion deformations of the rotating parts due to centrifugal force are calculated based on mechanics of elasticity. It is found that the centrifugal expansion deformation of the bearing inner ring is much larger than the deformation of the shaft when the rotational speed increases, and therefore the amount of the interference between the shaft and the bearing decreases with the speed. Then, with consideration of the centrifugal expansion deformation, a dynamic model of high-speed rolling ball bearings is presented with experimental validation. With the proposed bearing model, centrifugal effects on the bearing preload condition are studied in detail. It is shown that the bearing contact angle decreases, while the contact load increases with the centrifugal expansion deformation of the bearing inner ring. The radial bearing stiffness increases, whereas the axial bearing stiffness decreases a little, due to the resultant effects of the decreased contact angle and the increased contact load. The preload condition of the spindle bearing is strengthened by the centrifugal expansion effect of the bearing inner ring

Applying Neural Network based on Fuzzy Cluster Pre-processing to Thermal Error Modeling for Coordinate Boring Machine

AbstractTo investigate the effect of the thermal characteristics of a motorized spindle system on the precision of a machine tool, a thermal error model for spindle axial expansion and radial thermal declination is proposed. With precision CNC coordinate boring machine as an object, using the five-point method to calibrate spindle system thermal errors by the eddy current sensors for axial thermal elongation and radial thermal tilted values, and temperatures of measurement points are obtained by the PT100. The relationships between the rotational speed and temperature field, thermal errors are analyzed. Then fuzzy clustering analysis method is used to group and optimize the temperature variables, selecting the variables for thermal error-sensitive. Finally the MIMO artificial neural network approach is established for the spindle axial thermal elongation and radial thermal drifts. The results indicated that the model prediction accuracy could reach 86% with perfect generalization ability under different cutting conditions, providing a theoretical model and thermal characteristic parameters for both thermal error compensation and thermal equilibrium design

Deformation of foamed rhyolites under internal and external stresses: an experimental investigation

The style of magma eruption depends strongly on the character of melt degassing and foaming. Depending on the kinetics of these processes the result can be either explosive or effusive volcanism. In this study the kinetics of foaming due to the internal stresses of gas expansion of two types of obsidian have been investigated in time series experiments (2 min-24 h) followed by quenching the samples. The volumetric gas-melt ratio has been estimated through the density measurements of foamed samples. The variation of gas volume (per unit or rhyolite melt volume) with time may be described by superposition of two exponentials responsible for gas generation and gas release processes respectively. An observed difference in foaming style in this study is interpreted as the result of variations in initial contents of microlites that serve as bubble nucleation centers during devolatilization of the melts. Quantitatively the values of the gas generation rate constants (k g) are more than an order of magnitude higher in microlite-rich obsidian than in microlite-free obsidian. Possible origins of differences in the degassing style of natural magmas are discussed in the light of bubble nucleation kinetics in melts during foaming. In a complementary set of experiments the mechanical response of vesicular melt to external shear stress has been determined in a concentric cylinder viscometer. The response of vesicular melt to the pulse of shear deformation depends on the volume fraction of bubbles. The obtained response function can be qualitatively described by a Burgers body model. The experimental shear stress response function for bubble-bearing melt has an overshoot due to the strain-dependent rheology of a twophase liquid with viscously deformable inclusions

Design and analysis of aerostatic spindle with high load characteristics for large ultra-precision drum lathe

Aerostatic spindles offer low heat generation and high rotation accuracy, which make them an ideal choice for ultra-precision drum lathe, where extremely high motional accuracy and thermal stability are required. However, the limitations such as insufficient load capacity and stiffness have restricted their permissible application range and make them not suitable for large ultra-precision machine tools including drum lathe. In order to improve the load capacity and stiffness, this paper presents a high load capacity aerostatic spindle with pocketed orifice-type restrictors. Fluent is adopted and three-dimensional simulation models of aerostatic spindle with orifice and feeding pocket are set up to analyze the load characteristics. The simulation results show that this restrictor can enhance the throttling effect of orifice and suppress the pressure drop away from the orifice. Moreover, for aerostatic journal bearing, when eccentricity ratio is in the range of 0.2–0.3 and gas supply pressure is 0.6 MPa, carrying capacity and stiffness can reach up to 9499.4 N and 2813.1 N/μm. Finally, a group of loading experiments are carried out which prove that the novel three-dimensional simulation method is feasible and accurate to calculate the load characteristics of aerostatic spindles

Sveobuhvatno mjerenje i evaluacija sustava visokobrzinskog pogonskog vretena

Reducing the manufacturing time is the trend of high precision manufacturing, and the precision of a work-piece is very important for the manufacturing industry. The high-speed motorized spindle is the most critical part and becoming more widely used in the machine tool at present, and its precision may affect the overall performance of high-speed cutting. Most of the studies on high-speed cutting are focused on the cutting force, the vibration of the spindle and effects of the spindle’s thermal deformations; hence, how to roundly measure and objectively evaluate a high-speed spindle is an inevitable question. Because the comprehensive dynamic properties and evaluation system of spindles directly affect the cutting ability of the whole machine tool before they are manufactured. This paper presents a comprehensive measurement and evaluation system of a high-speed motorized spindle, which reflect the overall performance of motorized spindle and bases on an international standard.Smanjenje proizvodnog vremena tendencija je u visoko preciznoj proizvodnji, pri čemu je preciznost radnog komada vrlo važna u proizvodnoj industriji. Pri tome je visokobrzinsko pogonsko vreteno jedan od najkritičnijih dijelova koji se naširoko koristi u alatnim strojevima, pa njegova preciznost predstavlja važnog čimbenika u sveukupnoj izvedbi visokobrzinskog rezanja. Mnoge studije o visokobrzinskom rezanju su fokusirane na sile rezanja, vibraciju vretena kao i na efekte toplinske deformacije vretena; stoga, kako propisno mjeriti i objektivno evaluirati visokobrzinsko vreteno jedno je od neizbježnih pitanja. Jer sveobuhvatna dinamička svojstva i evaluacija sustava vretena izravno utječu na rezna svojstva cjelokupnog alatnog stroja, prije no što je proizveden. Ovaj rad prikazuje sveobuhvatno mjerenje i evaluaciju visokobrzinskog pogonskog vretena, koja se odražavaju na sveukupne odlike pogonskog vretena, a koja se bazirana na međunarodnim standardima

Design and fabrication of prototype system for early warning of impending bearing failure

Ball bearing performance tests run on several identical ball bearings under a variety of load, speed, temperature, and lubrication conditions are reported. Bearing temperature, torque, vibration, noise, strain, cage speed, etc., were monitored to establish those measurements most suitable as indicators of ball bearing health. Tape records were made under steady-state conditions of a variety of speeds and loads. Sample sections were selected for narrowband spectral analysis with a real time analyzer. An artificial flow was created across the inner race surface of one bearing using an acid etch technique to produce the scratch. Tape records obtained before and after established a characteristic frequency response that identifies the presence of the flow. The signals found most useful as indicators of performance degradation were ultrasonic outputs