An analysis of the surface generation mechanics of the elliptical vibration texturing process

The elliptical vibration texturing process is a vibration assisted machining method for the fast generation of micro structured surfaces. It adds a higher order motion component to the cutting tool that leads to periodic changes in the cutting depth during the machining process. This results in the creation of micro-dimples on the machined surface, whose shape is a function of the tool geometry and trajectory. This paper studies the surface generation mechanics of the elliptical vibration texturing process through experimentation and modeling. A surface generation algorithm is presented for this newly developed process. The model fully describes the motion and the 3D geometry of the cutting tool including its rake face, flank face, and the cutting edge, since all these tool features influence the topography of the generated surface. Since the process takes place in the micro/meso-scale cutting regime, the model includes the minimum chip thickness and elastic recovery effects. The experimental results are shown to validate the simulation model. The simulation model is used to characterize the influences of the process parameters on the texture patterns. The effects of the tool geometry on the process, including the cutting edge radius, are also analyzed.     

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.     

Predicting the effect of vibration on ultraprecision machining surface finish as described by surface finish lobes

Surface finish error resulting from unwanted relative tool/workpiece harmonic motion in the in-feed direction is studied for the ultraprecision face turning operation. Specifically consideration is given to the manifestation of this motion in the feed direction of the workpiece for a broad range of relative tool/workpiece motion disturbance frequencies. The concept of surface finish lobes is presented and is used to describe the feed direction surface finish error spatial frequency expected on a workpiece surface, for a given disturbance frequency. The surface finish lobes make it possible to know, for a broadband of disturbance frequencies, the resulting error on the workpiece surface in the feed direction. The surface finish lobe methodology is validated with experimental findings. Finally, potential applications of the surface finish lobes are discussed, including their use in shifting waviness errors to a very long wavelength, thus reducing the impact of unwanted relative tool/workpiece harmonic motion on ultraprecision machining quality.     

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.     

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.     

An improved cutting force and surface topography prediction model in end milling

During the milling operation, the cutting forces will induce vibration on the cutting tool, the workpiece, and the fixtures, which will affect the surface integrity of the final part and consequently the product's quality. In this paper, a generic and improved model is introduced to simultaneously predict the conventional cutting forces along with 3D surface topography during side milling operation. The model incorporates the effects of tool runout, tool deflection, system dynamics, flank face wear, and the tool tilting on the surface roughness. An improved technique to calculate the instantaneous chip thickness is also presented. The model predictions on cutting forces and surface roughness and topography agreed well with experimental results.     

Effect of the lubrication-cooling technique, insert technology and machine bed material on the workpart surface finish and tool wear in finish turning of AISI 420B

The paper is focussed on the effects produced by cutting operations on workpiece surface finish and tool wear. To this end, finish turning of AISI 420B stainless-steel was carried out under wet, minimum quantity of lubricant and dry cutting conditions, using both conventional and wiper technology inserts, on turning centres equipped with beds made in polymer concrete and cast iron. The workpiece surface finish and tool wear versus cutting volume were measured, and the results analysed and discussed in detail. The most significant results were: (i) the lubrication-cooling technique does not significantly affect the tool wear, whilst wet cutting produces the worst surface finish, (ii) the wiper inserts allow obtaining of the best surface finish, and (iii) the use of polymer concrete bed leads to an improved behaviour in terms of tool wear and surface roughness.     

基于振动传感器的车削加工表面粗糙度预测

文章通过深入研究车床精车外圆时刀具和工件存在相对振动的情况下,加工工件表面轮廓的形成机理,探索出一种建立表面粗糙度值预测模型的新方法。并结合传感器技术,搭建一个能用于测量振动信号的实验平台,通过比较表面粗糙度的预测值和实测值,证明预测模型有一定的准确度。     

Effect of plastic side flow on surface roughness in micro-turning process

Kinematic roughness-based surface finish prediction is known to often under-predict the measured surface roughness in turning process, especially at small (micron level) feed rates. It has also been observed that the surface roughness in micro-turning decreases with feed, reaches a minimum, and then increases with further reduction in feed. This paper presents a model for predicting the surface roughness in micro-turning of Al5083-H116 alloy that takes into account the effects of plastic side flow, tool geometry, and process parameters. The model combines these effects with more accurate estimation of the average flow stress of Al5083-H116 at micron scale of deformation with the help of a previously reported strain gradient-based finite element model. The surface roughness model is evaluated through a series of micro-turning experiments. The results show that the model can predict the surface roughness in micro-turning quite well. It is shown that the commonly observed discrepancy between the theoretical and measured surface roughness in micro-turning is mainly due to surface roughening caused by plastic side flow. Further, it is shown that the increase in roughness at low feed can be attributed to the increased side flow caused by strain gradient-induced strengthening of the material directly ahead of the tool.     

A study of surface topography, friction and lubricants in metalforming

In this paper are presented the results of investigations concerning the relation between friction behaviour and surface topography using various lubricants and initial workpiece surface conditions in ring upsetting and rod extrusion processes. The tests were carried out using either a liquid lubricant or under clean dry conditions. Two types of workpiece surfaces, random and directional, were prepared by either shotblasting, or EDM or turning to different levels of surface finish. Not only has the friction effect of lubricant and initial surface been studied, but also the surface topography of the finished products has been examined in detail, to obtain a better understanding of the mechanism of lubrication and surface interaction. It was found that, for random surfaces, smoother ones could retain more lubricant and decrease friction resistance. The experimentation also demonstrated that turned surfaces were effective in reducing friction, but the final surface finish of the workpiece was not as good as that from random surfaces.     

Topography of the flank wear surface

In many applications, topography represents the main external features of a surface. This paper describes the topography of the flank wear surface and also presents the relationship between the maximum flank wear and the topography parameters (roughness parameters) of the flank wear surface during the turning operation. A modern CNC lathe machine (Okuma LH35-N) was used for the machine turning operation. Three-dimensional surface roughness parameters of the flank wear surface were measured by a surface texture instrument (from Talysurf series) using surface topography software (Talymap). Based on the resulting experimental data, it is found that as the flank wear increases, the roughness parameters (sR_a, sR_q, and sR_t) on the flank surface increase significantly. The greater the roughness value of the flank wear surface, the higher the friction of the tool on the workpiece and the greater the heat generation that will occur, thus ultimately causing tool failure. On the other hand, positive skewness (sR_sk) indicates the presence of a small number of spikes on the flank surface of the cutting tool, which could quickly wear off during the machining process.     

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.     

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.     

Influence of asymmetric cutting edge roundings on surface topography

For finishing operations in machining, hardened steel hard turning can compete with grinding operations by means of accuracy and productivity. In the past research focussed on the effect of process parameters and tool macro geometry on the resulting surface roughness. Recent investigations show, that the cutting edge micro geometry is an important factor to influence surface quality. The knowledge generated by new methods displays the importance of asymmetric cutting edge roundings on cutting forces, chip formation and tool life. It is known, that chip formation also affects the resulting surface quality. Therefore, this paper investigates the effect of asymmetric cutting edge roundings on the resulting surface roughness in hard turning of roller bearing inner rings. Cutting tests with differently shaped cutting edges and two different feed values are conducted. The resulting surface roughness is measured. The consequent surface quality is explained by geometric coherences between uncut chip thickness and stresses along the cutting edge and the effect of material side flow. It is found, that the cutting edge geometry and the resulting stress distribution around the cutting edge affects the generated surface quality.     

A study of back cutting surface finish from tool errors and machine tool deviations during face milling

The surface finish of mechanical components produced by face milling is given by factors such as cutting conditions, workpiece material, cutting geometry, tool errors and machine tool deviations. The contribution of the different tool teeth to imperfections in the machined surface is strongly influenced by tool errors such as radial and axial runouts. The surface profile of milled parts is not only affected by chip removal due to front cutting, but also by back cutting, which must be taken into account when predicting surface roughness. In the present work, the influence of back cutting on the surface finish obtained by face milling operations is studied. Final part surface roughness is modelled from tool runouts and height deviations that affect the surface marks provoked by back cutting. Round insert cutting tools and surface positions defined by cutter axis trajectory are considered, and milling experiments are developed for a spindle speed of 750 rpm, depth of cut of 0.5 mm and feeds from 0.4 to 1.0 mm/rev. Experimental observations are compared with the theoretical predictions provided by the surface roughness model, and good agreement is found between both results. Surface imperfections caused by front and back cutting are analysed, and discrepancies between experiments and numerical predictions are explained by undeformed chip thickness variations along the tool tooth cutting edge, the tearing of the workpiece material, and fluctuations in the feedrate and height deviation during machine tool axis displacement.     

A theoretical and experimental investigation of the tool-tip vibration and its influence upon surface generation in single-point diamond turning

This paper presents a theoretical and experimental investigation of the influence of tool-tip vibration on surface generation in single point diamond turning (SPDT). Although it is well known that the relative vibration between the tool and the workpiece plays an important role in the surface generation in single-point diamond turning, most of the prior work has been focused on studying the relative tool-work vibration in the infeed (thrust force) direction while the significant contribution of the effect of the tool-tip vibration in the cutting force direction has been overlooked. In the present study, two characteristic peaks (twin peaks) are identified and found to be corresponding to the tool-tip vibrations by power spectrum density (PSD) analyses. The vibrations possess the features of small amplitude but high frequency. A physical model is proposed to capture the dominant factor based on the characteristic and it reveals that the twin peaks are attributed by the impact between the tool tip and workpiece and the process damping effect. Hence, a geometric model of surface roughness is proposed to take account of tool-tip vibration and it is verified through a series of experiments. The simulation results have been found to agree well with the experimental results.     

Investigation in orthogonal turn-milling towards better surface finish

Turn-milling is a newly emerging machining process, which tends to make use of the advantages of both turning and milling, wherein both the work piece and the cutting tool are given rotary motion simultaneously. The objective of the present experimental work is to understand the phenomenon of orthogonal turn-milling especially in relation to the effects of work piece revolution, cutter diameter and depth of cut. Surface finish of the machined surface and the optimum work speed at which the surface roughness was minimum has been studied. It has been shown that surface quality obtained by turn-milling process is better than that of conventional milling process. The experiments have been conducted for orthogonal turn-milling of mild-steel work piece with high speed steel milling cutters using planning of experiments technique to study the surface finish achieved.     

Investigation on the influence of tool-tip vibration on surface roughness and its representative measurement in ultra-precision diamond turning

High frequency tool-tip vibration, in the cutting force direction, is an intrinsic feature of ultra-precision single point diamond turning (SPDT). This paper is dedicated to a study of the influence of the tool-tip vibration on surface roughness. The resulting periodic fluctuation of the surface profile is identified in a particular spatial frequency range by a tangential measurement method. The ISO standard provides merely a minimal, not an optimal requirement for surface measurement. Thus, in this paper, a more representative measurement method is proposed to better characterise the machined surface in SPDT. The conventional radial and aerial surface measurements yield a relatively biased result on surface roughness which cannot adequately reflect the detrimental effect of tool-tip vibration. Representative measurement takes account of the sample area ratios and is able to be used to objectively study the discrepancies in surface measurement. The proposed model for surface generation and representative measurement are applicable to the problems in surface generation in ultra-precision SPDT, such as the spiral turning marks and spatial errors in the radial profile measurement.     

A theoretical and experimental study of surface generation under spindle vibration in ultra-precision raster milling

In ultra-precision raster milling (UPRM), the impulse spindle vibration induced by the impulse-like cutting forces is intrinsic and special mechanism majorly influencing surface topography. It is fundamentally distinctive with the step spindle vibration induced by the step-like cutting forces in turning. However, no work has been conducted to study surface generation under the impulse spindle vibration in UPRM in depth. Consequently, this paper theoretically and experimentally elaborates that in UPRM, (i) the impulse spindle vibration includes the axial, radial and coupled-tilting spindle vibration with damping; (ii) the excitation frequency of the impulse-like cutting forces, i.e. spindle speed, determines the spindle vibration characteristics, i.e. synchronous or asynchronous spindle vibration; (iii) the coupled-tilting spindle vibration is a predominant factor influencing surface generation; and (iv) the irregular spindle-vibration waves induced by the impulse spindle vibration produce one of the irregular, lattice-like and stripe patterns or their hybrids at a milled surface.     

Characterisation of nanosurface generation in single-point diamond turning

This paper describes a parametric analysis of nanosurface generation in single-point diamond turning (SPDT). The properties of the surface roughness profiles were extracted and analysed using the power spectrum analysis method. A series of face cutting experiments was undertaken on an aluminium alloy under various cutting conditions. The results indicate that the power spectrum of a surface roughness profile is basically composed of several periodical components that can be correlated to different process parameters and mechanisms of surface generation. Moreover, it is found that the tool feed, tool geometry, spindle error motions and relative vibration between the tool and the workpiece are not the only dominant components contributing to the surface generation in SPDT. Materials swelling and tool interference are other important factors. Based on these findings, relationships are proposed to explain the influence of tool interference on the variation of the spectral components and process parameters. The implications of these findings on the optimisation of the surface quality in SPDT are also discussed.