A study of materials swelling and recovery in single-point diamond turning of ductile materials

This paper presents an investigation of the effect of materials swelling in ultra-precision machining of ductile materials. The combined influence of materials swelling and recovery was found to affect the surface roughness in single-point diamond turning. It is interesting to note that the effect of materials swelling for ductile materials would be overwhelmed by the impact of recovery when the depth of cut is extremely small and the front clearance is small. In addition, radically different surface roughness profiles were found for different materials even though they are machined under the same cutting conditions. The difference in the machining behaviour could not be accounted by the elastic recovery alone but by the plastic deformation induced in the machined layer. The findings in the present study provide an important means for improving the surface roughness in ultra-precision machining.     

A theoretical and experimental investigation of surface roughness formation in ultra-precision diamond turning

In this paper, a model-based simulation system is presented for the analysis of surface roughness generation in ultra-precision diamond turning. The system is based on a surface roughness model which takes into account the effect of tool geometry, process parameters and relative tool-work vibration. It is evaluated through a series of cutting experiments. The results indicate that the system can predict well the surface roughness profile and the roughness parameters of a diamond turned surface under various cutting conditions. With the use of the spectrum analysis techniques, the system can also help to analyze the effect of vibration on the surface quality of workpiece and to diagnose the machine faults. The potential application of the system in process optimization is also discussed in the text.     

Orientation changes of aluminium single crystals in ultra-precision diamond turning

In this paper, the effects of cutting speed on the variation of surface texture and lattice rotation of diamond-turned surfaces were investigated. The {1 1 1} pole figures were determined at various locations by the X-ray diffraction method. The local lattice rotation at various locations on a machined groove by the electron back-scatter diffraction (EBSD) method was also obtained. A simulation of the orientation change was performed and the theoretical prediction was compared with the experimental results.     

A theoretical and experimental investigation into multimode tool vibration with surface generation in ultra-precision diamond turning

In ultra-precision diamond turning (UPDT), tool's high frequency vibration is natural mechanism influencing nanometric surface roughness of machined components. Its first mode high frequency vibration has been overemphasized. However, its multimode high frequency vibration (MHFTV) has not been reported. In the paper, the MHFTV and its effects on surface generation in UPDT are firstly studied. The experimental and theoretical results verify that (i) diamond tool naturally possesses multimode high frequencies, i.e. one sub-high frequency (SHF) for the tool shank tip, one high frequency (HF) for the tool tip, and one ultrahigh frequency (UHF) for the diamond tip; (ii) dampers cause the variation of tool's multimode high frequencies, under which the MHFTV together produces non-uniform zebra-stripe-like patterns at a machined surface; and (iii) cutting force has a linear relationship with and tool's stiffness has a reverse proportion to the amplitude of the MHFTV to influence surface generation, which can be used to improve surface quality.     

Conservation law of surface roughness in single point diamond turning

In this work, a comprehensive model is established to predict the surface roughness achieved by single point diamond turning. In addition to the calculation of the roughness components in relation to the kinematics and minimum undeformed chip thickness, the newly developed model also takes the effects of plastic side flow and elastic recovery of materials as machined into account. Moreover, the ‘size effect’ has also been successfully integrated into the model, i.e. an inflection point appears in the trend line of predicted surface roughness as the ratio of maximal undeformed chip thickness to cutting edge radius (h_Dmax/r_n) is equal to one unit. Face turning experiments validate that the maximal prediction error is only 13.35%. As the ratio of h_Dmax/r_n is higher than one unit, both the prediction and experiments reveal that a conservation law exists in diamond turned surface roughness, owing to the competitive effects of kinematics, minimum undeformed chip thickness, plastic side flow and elastic recovery of materials on surface formation. Under the conservation law, the freedom control for an invariable surface roughness can be fulfilled in response to a quantitative ratio of h_Dmax/r_n, either through an accurate configuration of feed rate and depth of cut with fixed tool nose radius and cutting edge radius, or by a reasonable selection of tool nose radius and controlled cutting edge radius with designed feed rate and depth of cut.     

Predictive modeling of surface roughness and tool wear in hard turning using regression and neural networks

In machining of parts, surface quality is one of the most specified customer requirements. Major indication of surface quality on machined parts is surface roughness. Finish hard turning using Cubic Boron Nitride (CBN) tools allows manufacturers to simplify their processes and still achieve the desired surface roughness. There are various machining parameters have an effect on the surface roughness, but those effects have not been adequately quantified. In order for manufacturers to maximize their gains from utilizing finish hard turning, accurate predictive models for surface roughness and tool wear must be constructed. This paper utilizes neural network modeling to predict surface roughness and tool flank wear over the machining time for variety of cutting conditions in finish hard turning. Regression models are also developed in order to capture process specific parameters. A set of sparse experimental data for finish turning of hardened AISI 52100 steel obtained from literature and the experimental data obtained from performed experiments in finish turning of hardened AISI H-13 steel have been utilized. The data sets from measured surface roughness and tool flank wear were employed to train the neural network models. Trained neural network models were used in predicting surface roughness and tool flank wear for other cutting conditions. A comparison of neural network models with regression models is also carried out. Predictive neural network models are found to be capable of better predictions for surface roughness and tool flank wear within the range that they had been trained.Predictive neural network modeling is also extended to predict tool wear and surface roughness patterns seen in finish hard turning processes. Decrease in the feed rate resulted in better surface roughness but slightly faster tool wear development, and increasing cutting speed resulted in significant increase in tool wear development but resulted in better surface roughness. Increase in the workpiece hardness resulted in better surface roughness but higher tool wear. Overall, CBN inserts with honed edge geometry performed better both in terms of surface roughness and tool wear development.     

Signal analysis of surface roughness in diamond turning of lens molds

Diamond turning of high-precision lens molds is an important production process. The surface roughness of the mold heavily affects the quality of lens. In diamond turning, the surface roughness obtained depends on the cutting tool, the cutting conditions, the machine characteristics, the surrounding vibrations and the work piece material. This work studies the surface roughness obtained from the diamond turning of a phosphor–bronze lens mold with various tool nose radii, spindle speeds, feed rates and cutting depths. The surface roughness was measured in the time domain using a Form Talysurf instrument (a stylus-type surface roughness meter) and then transformed into the frequency domain using the fast Fourier transform. Based on the magnitude of the intensity, the tool geometry, low-frequency vibration and the measuring instrument are identified as the main influencing factors of the generated surface roughness. The intensities associated with the latter two vary little with the cutting conditions and are thus considered constant. The intensity of the tool geometry varies with the feed rate, the spindle speed and the radius of the tool nose. A relationship between the root-mean-square summation of the surface roughness and cutting conditions was found. The model agrees well with the experimental results. The analysis also identified the critical feed rate that maximized machining productivity, below which the surface roughness was only slightly improved as the production rate fell sharply.     

A power spectrum analysis of effect of rolling texture on cutting forces in single-point diamond turning

In most of the existing metal cutting theories, the workpiece is assumed to be homogeneous and most continuum theories do not take into account the effect of crystallographic anisotropy that causes variations in the shear plane at the grain level and hence of the cutting force. As the depth of cut in single-point diamond turning (SPDT) is usually less than the average grain size of a polycrystalline aggregate, cutting is generally performed within a grain. At this scale, the difference in the individual grain properties cannot be integrated out and a continuum solution would be insufficient. As a result, this paper presents a power spectrum analysis of the periodic fluctuation of micro-cutting forces in SPDT of polycrystalline materials. The experimental results show that the features of the power spectra of the cutting forces can be well correlated with the change of rolling texture of the materials being cut. These findings help to explain quantitatively the fluctuation of micro-cutting forces and hence the effect of rolling texture in SPDT, which are not encountered in conventional machining.     

A theoretical and experimental investigation into five-DOF dynamic characteristics of an aerostatic bearing spindle in ultra-precision diamond turning

In ultra-precision diamond turning (UPDT), spindle vibration has great influence on machining precision of high precision optical components. However, the spindle-vibration mechanism has not been fully understood. In this study, mathematical solutions for a proposed five-degree-of-freedom (FDOF) dynamic model of an aerostatic bearing spindle are derived to explore natural mechanisms of spindle vibration. Thus, the potential benefits of the solutions are to be applied for the prediction and optimization of the effects of spindle vibration on surface generation. Its dynamic characteristics possess three translational frequencies along the radial and axial directions, a spindle rotational frequency (SRF), and a pair of coupled tilting frequencies (CTFs) around the radial directions influenced the SRF. The theoretical results are identified by the frequency characteristics of thrust cutting forces, and the periodic, concentric, spiral, radial and two-fold patterns (PCSRPs) of the machined and simulated surface topographies, respectively.     

Cutting performance of diamond tools during ultra-precision turning of electroless-nickel plated die materials

This study is an attempt (a) to observe the wear characteristic of diamond tool with 200 km cutting distance and to study the effects of wear on the surface roughness and cutting forces and (b) to optimize various cutting parameters such as depth of cut, feed rate, spindle speed and phosphorus content. The experimental results showed that tool wear was not so significant although some defects on rake face were observed after cutting 15.6 km. Further cutting showed that the surface roughness increases with cutting distance, and that the cutting forces were larger than thrust force at the beginning of cutting, but after cutting 130 km, thrust force became larger and increased rapidly. It was also observed that forces increase with the increase of depth of cut, spindle speed and feed rate, and decrease with the increase of phosphorus content of the plating. Depth of cut has no significant effect on surface roughness, while it increases with increase of feed rate and decreases with the increase of percentage of phosphorus content in the workpieces. In case of spindle speed, surface roughness decreases with the increase of spindle speed up to a certain value and then starts to increase with the increase of spindle speed.     

Statistical analysis of surface roughness and cutting forces using response surface methodology in hard turning of AISI 52100 bearing steel with CBN tool

The present work concerns an experimental study of hard turning with CBN tool of AISI 52100 bearing steel, hardened at 64 HRC. The main objectives are firstly focused on delimiting the hard turning domain and investigating tool wear and forces behaviour evolution versus variations of workpiece hardness and cutting speed. Secondly, the relationship between cutting parameters (cutting speed, feed rate and depth of cut) and machining output variables (surface roughness, cutting forces) through the response surface methodology (RSM) are analysed and modeled. The combined effects of the cutting parameters on machining output variables are investigated while employing the analysis of variance (ANOVA). The quadratic model of RSM associated with response optimization technique and composite desirability was used to find optimum values of machining parameters with respect to objectives (surface roughness and cutting force values). Results show how much surface roughness is mainly influenced by feed rate and cutting speed. Also, it is underlined that the thrust force is the highest of cutting force components, and it is highly sensitive to workpiece hardness, negative rake angle and tool wear evolution. Finally, the depth of cut exhibits maximum influence on cutting forces as compared to the feed rate and cutting speed.     

金刚石车刀自动研磨装置图像处理系统的开发

本研究开发了能够应用于圆弧刃金刚石车刀自动研磨的图像处理系统,在使用基于形状的模板匹配的方法对车刀进行初始安装的基础上,进行了切削刃形状信息和位置信息的亚微米精度测量。测量结果表明:开发的图像处理系统实现了圆弧刃半径分别为1mm,0.5mm,0.2mm的金刚石车刀测量,能够在线获得自动研磨所需的形状信息和位置信息,在精度和效率上为自动研磨系统的开发提供了保证。     

A comparison of dry and air-cooled turning of grey cast iron with mixed oxide ceramic tool

The present work compares the performance of a mixed oxide ceramic tool in dry and air-cooled turning of grey cast iron. First, the study was done in the range of process parameters where dry turning provided satisfactory performance. The contours of surface roughness and tool life were generated with the help of trained neural networks. A novel procedure of neural network training is used in this work. The study was extended to the range in which dry turning performed poorly in terms of tool life. Tool wear, surface roughness of the machined job and forces and vibration during the cutting were studied. It was observed that air-cooling significantly reduces the tool wear at high cutting speed. At higher cutting speeds, where the dry turning performs very poorly, the air-cooled turning provides an improved surface finish also apart from the reduction in tool wear. In all the cases, the cutting and feed forces get reduced in air-cooling. Thus, air-cooled turning of grey cast iron with mixed oxide ceramic tools offers a promising environment-friendly option.     

超精密车削工艺参数与表面质量关联性研究

为提高铝反射镜超精密加工的表面质量,介绍超精密切削的表面质量评价方法和影响表面质量的因素,分析各因素对表面质量的影响机制。采用单一变量法对Al6061进行不同工艺参数的单点金刚石车削实验,通过对比表面粗糙度和功率谱密度,研究各个工艺参数对表面质量的影响,并得出最佳工艺参数;最终加工出表面粗糙度为4.67 nm的光学表面。     

Dynamic modelling of shear band formation and tool-tip vibration in ultra-precision diamond turning

This paper proposes a dynamic model to correlate the two basic physical phenomena in ultra-precision diamond turning, i.e. the formation of adiabatic shear band (ASB) and high frequency tool-tip vibration (HFTTV). The conventional approach explains the former using a static model without consideration of the latter. In this paper, a dynamic model is developed to reflect how the ASB and the HFTTV interactively affect each other. To illustrate the validity of this model, a novel experimental method is proposed and the effect of HFTTV on cutting force, surface roughness and chip morphology of ASBs is discussed in terms of the variation of strain rates.     

Roughness and texture generation on end milled surfaces

Plane surface generation mechanism in flat end milling is studied in this research. The bottom of a flat end mill has an end cutting edge angle that plays an important role in surface texture. Surface texture is produced by superposition of conical surfaces generated by the end cutting edge rotation. The machined surface is cut once again by the trailing cutting edge. This back cutting phenomenon is frequently observed on surfaces after finishing. Tool run-out and tool setting error including tool tilting and eccentricity between tool center and spindle rotation center are considered together with tool deflection caused by cutting forces. Tool deflection affects magnitude of back cutting and the surface form accuracy. As a result, the finished surface possesses peaks and valleys with form waviness. Surface topography parameters such as RMS deviation, skewness and kurtosis are used for evaluating the generated surface texture characteristics. Through a set of cutting tests, it is confirmed that the presented model predicts the surface texture and roughness parameters precisely including back cutting effect.     

Study on the adaptability of thick film diamond tool to cutting composites

In order to explore the adaptability of a thick film diamond tool to the finish machining of composites, tool wear and its effect factors as well the machined surface roughness are investigated in this paper. The experimental results show that the thick film diamond tool has a low wear rate and the machined surface cut with the tool has a fine finish for the cutting of composites. The negative rake is beneficial for the tool standing wear and collision.     

Surface finish generated in hard turning of quenched alloy steel parts using conventional and wiper ceramic inserts

Significant progress has already been achieved in green manufacturing including dry and hard, often high-speed, machining technologies. For instance, the demand for higher productivity has resulted in the wider application of ceramic and PCBN tools with special multi-radii (wiper) geometry. This paper reports some important characteristics of the surface roughness produced in the turning of a hardened low-chromium alloy steel using mixed alumina–titanium carbon (TiC) ceramic cutting tools equipped with both conventional and wiper inserts. The characteristic geometrical features of surfaces obtained in both these turning operations have been assessed by means of representative two-dimensional (2D) surface roughness parameters, and some 3D visualizations, which allowed more complete characterization of the surface topography and prediction of its service properties. Results show that keeping equivalent feed rates, i.e. 0.1 mm/rev for conventional and 0.2 mm/rev for wiper tools, the surfaces obtained have similar 3D height roughness parameters, and comparable values of skew and kurtosis. At defined cutting parameters, surfaces produced by wiper tools contain blunt peaks with distinctly smaller slopes resulting in better bearing properties. Only marginal changes of Ra parameter were recorded during 15 min machining trials.     

State of the art in hard turning

Hard turning is gaining grounds for machining hardened steels as it has several benefits over grinding. There are several issues, which should be understood and dealt with, to achieve successful performance of the process. Researchers have worked upon several aspects related to hard turning. The present work is an effort to review some of these works and to understand the key issues related to process performance. The review shows that the type of tool material, cutting edge geometry and cutting parameters affect the process efficiencies in terms of tool forces, surface integrities integrity, and white layer. Adequate machine rigidity is a must essential to minimize the process inaccuracies. Also moreover, for finish hard turning, where the depth of cut is less than the nose radius of the tool, the forces deviate from the conventional trends as the radial force component is the maximum and axial force component becomes minimum. The present work finally lists down certain areas that can be taken up for further research in hard turning.