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 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.     

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.     

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.     

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.     

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。     

A study on the effects of vibrations on the surface finish using a surface topography simulation model for turning

In this paper, a surface topography simulation model is established to simulate the surface finish profile generated after a turning operation. The surface topography simulation model incorporates the effects of the relative motion between the cutting tool and the workpiece with the effects of tool geometry to simulate the resultant surface geometry. It is experimentally shown that the surface topography simulation model can properly simulate the surface profile generated by turning operations. The surface topography simulation model is used to study the effects of vibrations on the surface finish profile. It is found that the vibration frequency ratio is a more important vibration parameter than the vibration frequency on the characterization of the surface finish profile. The vibration frequency ratio is the ratio between the vibration frequency and the spindle rotational speed.     

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.     

Machinability study of tungsten carbide using PCD tools under ultrasonic elliptical vibration cutting

Sintered tungsten carbide (WC) is an extremely hard and brittle material extensively used in tool manufacturing industries. However, the current cutting technologies for shaping this typical hard-to-machine material are still cost ineffective. In this study, polycrystalline diamond (PCD) tools are used to study the machinability of sintered WC (~15% Co) by applying the ultrasonic elliptical vibration cutting (UEVC) technique. Firstly, it presents the UEVC principle and the effects of speed ratio (i.e. the ratio of the nominal cutting speed to the maximum tool vibration speed in the cutting direction) on the tool–workpiece relative motion as the cutting speed greatly influences the UEVC performance. Then UEVC experiments are carried out to analyze the cutting force, tool-wear progression, chip formation and surface quality against the cutting time at different speed ratios. The results show that when the speed ratio decreases, the resultant cutting force and the tool flank wear decrease while the surface finish improves. Average surface roughness, R_a, in a range between 0.030 and 0.050 μm is achieved at speed ratios less than 0.107. The experimental findings suggest that the commercial PCD tools can be used to machine sintered WC to achieve ultraprecision surface by applying the UEVC technique, which will be cost effective for miniature cutting technologies in future.     

Modelling vibration transmission in the mechanical and control system of a precision machine

The relative vibration between tool and workpiece factors significantly to the performance of a precision machine. This paper develops a model for predicting the vibration transmission from two major excitation sources, ground vibration and fluid bearing force, to the tool and the workpiece position through the mechanical and control system of a precision machine. We synthesised the frequency response functions obtained from a finite element analysis of the machine to create transmissibility matrices that define the dynamic behaviours of the electromechanical system. The validity of the developed model was checked by comparing the measured relative vibrations to the results calculated from the measured excitations.     

A study of the diamond tool wear suppression mechanism in vibration-assisted machining of steel

Inability of machining steel strongly inhibits the application of diamond machining in manufacturing industry, especially in the fields of ultra-precision and micro machining. In recent years, vibration-assisted machining (VAM) has been proved to be capable of efficiently suppressing the diamond tool wear in cutting steel. Currently, the prevailing speculation claimed by most researchers for such suppression is that the tool–workpiece flash temperature was reduced in VAM, which would slow the chemical reaction between iron on steel and carbon on diamond. However, the correctness of this speculation has not been proved by any experimental or theoretical research. In this paper, in order to understand the true wear suppression mechanism of diamond tools in VAM of steel, a study is conducted by measuring the workpiece temperatures and modeling the cutting energy consumption in both VAM and conventional cutting (CC). Based on the comparison results, it is concluded that the cutting temperature and energy consumption in VAM are not smaller than in CC, and hence the reduced diamond tool wear in VAM should not be caused by the claimed reduced temperature, especially when the material removal rate is very small. Finally, based on the EDS analysis and the comparison of experimental results under different air pressure, two probable reasons are proposed for the significantly reduced diamond tool wear in VAM of steel: (i) increase of gas pressure at the tool–workpiece interface and (ii) generation of an oxide layer on the freshly machined surface.     

Investigation of Cutting Characteristics in Side-milling a Multi-thread Worm Shaft on Automatic Lathe

This paper investigates the cutting characteristics of side-milling which is proposed as a more efficient way to manufacture worms of higher accuracy than form-threading and planetary milling. A tool-tip trajectory based on the tool-workpiece interaction is modelled in terms of matrix transformation. Chip thickness, cutting force and surface roughness are simulated using the calculated tool-tip trajectories. The effects of various errors in the real cutting such as run-out errors of a tool axis, tool setup errors and workpiece deflection due to cutting forces are investigated. The simulation results are verified through numerous experiments on an automatic lathe.     

Dimensional errors in longitudinal turning based on the unified generalized mechanics of cutting approach.: Part I: Three-dimensional theory

During the machining of a part, a new surface is generated together with its dimensional deviations. These deviations are due to the presence of several phenomena (workpiece deflection under strong cutting forces, vibration of the machine tool, material spring-back, and so on) that occur during machining. Each elementary phenomenon results in an elementary machining error. Consequently, the accuracy of the manufactured workpiece depends on the precision of the manufacturing process, which it may be controlled or predicted.The first part of this work presents a new model to evaluate machining accuracy and part dimensional errors in bar turning. A model to simulate workpiece dimensional errors in longitudinal turning due to deflection of the tool, workpiece holder and workpiece is shown. The proposed model calculates the real cutting force according to the Unified Generalized Mechanics of Cutting approach proposed by Armarego, which allows one to take into account the three-dimensional nature (3D) of the cutting mechanism. Therefore, the model developed takes advantage of the real workpiece deflection, which does not lie in a plane parallel to the tool reference plane, and of the real 3D cutting force, which varies along the tool path due to change in the real depth of cut. In the first part of the work the general theory of the proposed approach is presented and discussed for 3D features. In the second part the proposed approach is applied to real cases that are mostly used in practice. Moreover, some experimental tests are carried out in order to validate the developed model: good agreement between numerical and experimental results is found.     

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.     

滚齿机床振动对齿轮几何精度的影响

滚齿机床切削加工过程中,刀刃成排轮流从切入到切出,切削力由小逐渐变大,再逐渐变小,在工件和刀具之间产生周期性的激振力,使刀刃和工件加工表面产生相对位移,对加工齿轮的几何精度产生影响。研究机床结构振动与被加工齿轮精度的关系,建立滚刀和工件加工表面产生的相对位移对齿轮几何精度影响的理论模型,定量推导出了由此相对位移产生的齿廓误差;通过大量实验,对滚刀和工件加工表面产生相对位移对应的齿轮齿廓误差进行在线精密测量;使用此齿廓误差减法运算新方法,对两组实验数据进行对比分析。结果表明:提出的运算新方法能够准确地处理数据,实验数据很好地验证了建立的理论模型的正确性,误差小于2%。     

Active vibration control for peripheral milling processes

In this paper, an active vibration control system is developed for peripheral milling processes. In this system, the workpiece is driven by a specially designed active stage to control the relative vibration between the tool and workpiece during milling processes. The stage is modeled as a control plant, and the cutting vibrations are treated as disturbances to the system. Robust mixed sensitivity method is employed in feedback controller synthesis to achieve robust disturbance rejection and stabilization. Numerical simulations and cutting experiments are carried out to validate the effectiveness of the control system. Results indicate the relative vibration between the workpiece and tool, as well as the rough of surface finish decrease significantly in the case of milling processes with the presented controller.     

Measurement of milling tool vibrations during cutting using laser vibrometry

Spindle and tool vibration measurements are of great importance in both the development and monitoring of high-speed milling. Measurements of cutting forces and vibrations on the stationary spindle head is the most used technique today. But since the milling results depend on the relative movement between the workpiece and the tool, it is desirable to measure on the rotating tool as close to the cutters as possible. In this paper the use of laser vibrometry (LDV) for milling tool vibration measurements during cutting is demonstrated. However, laser vibrometry measurements on rotating surfaces are not in general straight forward. Crosstalk between vibration velocity components and harmonic speckle noise generated from the repeating revolution of the surface topography are problems that must be considered. In order to overcome the mentioned issues, a cylindrical casing with a highly optically smooth surface was manufactured and mounted on the tool to be measured. The spindle vibrations, radial tool misalignment, and out-of-roundness of the measured surface were filtered out from the signal; hence, the vibrations of the cutting tool were resolved. Simultaneous measurements of cutting forces and spindle head vibrations were performed and comparisons between the signals were conducted. The results showed that vibration velocities or displacements of the tool can be obtained with high temporal resolution during cutting load and therefore the approach is proven to be feasible for analysing high-frequency milling tool vibrations.     

Effect of machining parameters in ultrasonic vibration cutting

The ultrasonic vibration cutting (UVC) method is an efficient cutting technique for difficult-to-machine materials. It is found that the UVC mechanism is influenced by three important parameters: tool vibration frequency, tool vibration amplitude and workpiece cutting speed that determine the cutting force. However, the relation between the cutting force and these three parameters in the UVC is not clearly established. This paper presents firstly the mechanism how these parameters effect the UVC. With theoretical studies, it is established that the tool–workpiece contact ratio (TWCR) plays a key role in the UVC process where the increase in both the tool vibration parameters and the decrease in the cutting speed reduce the TWCR, which in turn reduces both cutting force and tool wear, improves surface quality and prolongs tool life. This paper also experimentally investigates the effect of cutting parameters on cutting performances in the cutting of Inconel 718 by applying both the UVC and the conventional turning (CT) methods. It is observed that the UVC method promises better surface finish and improves tool life in hard cutting at low cutting speed as compared to the CT method. The experiments also show that the TWCR, when investigating the effect of cutting speed, has a significant effect on both the cutting force and the tool wear in the UVC method, which substantiates the theoretical findings.     

基于切削技术的金刚石刀具磨损特征分析

金刚石刀具的磨损情况决定其使用寿命。用金刚石PCD刀具切削6061-T6镁铝合金工件,通过不同切削速度、切削深度、振动频率、刀具后角时的切削力及切削温度变化,研究不同刀具前后角、进给量、切削转速时的工件表面粗糙度及刀具磨损面积。结果表明:金刚石刀具的切削力和切削温度随切削速度、切削深度的增加而增大,随振动频率的增加而减小;刀具后角增大,金刚石刀具的切削力呈先下降而后缓缓上升趋势,但对切削温度的影响很小。当刀具前角为10°,刀具后角为8°,切削速度为0.46?m/s,切削深度为28?μm,进给量为0.10?mm/r,切削转速为4100?r/min,振动频率为22?kHz,切削振幅为9?μm时,金刚石刀具的磨损面积最小,磨损程度最低,使用寿命最长,但工件的表面粗糙度稍高。      

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.