THE EFFECT OF MATERIAL MICROSTRUCTURE ON MICROCUTTING PROCESSES

In the machining of mirror-like surfaces, a typical cutting depth of a few micrometers is common. With such a small depth of cut, chip formation takes place within individual grains of polycrystalline materials. In this article, orthogonal cutting of single copper crystals was performed in order to investigate the dependency of cutting deformation and surface quality on the crystallographic orientation of the substrate material. The experimental results show that the crystallographic orientation of the workpiece exerts a significant influence on the shear angle and the machined surface roughness. Cutting force variation with crystallographic orientation was analyzed on the basis of a microplasticity model. The trend in the variation of theoretical values of an effective Taylor factor (the shear strength) compares well with that of published experimental data on cutting forces.     

Anisotropy of surface roughness in diamond turning of brittle single crystals

This paper deals with an investigation of the effect of crystallographic orientation and process parameters on the surface roughness of brittle silicon single crystals in ultraprecision diamond turning. The process parameters involve the depth of cut, feed rate, and spindle speed. Experimental results indicate that anisotropy in surface finish occurs when the cutting direction relative to the crystal orientation varies. There exists a periodic variation of surface roughness per workpiece revolution, which is closely related to the crystallographic orientation of the crystals being cut. Such an anisotropy of surface roughness can be minimized with an appropriate selection of the feed rate, spindle speed, and depth of cut. The findings provide a means for the optimization of the surface quality in diamond turning of brittle silicon single crystals.     

A PARAMETRIC ANALYSIS OF CUTTING FORCES IN SINGLE-POINT DIAMOND TURNING OF Al6061/SiCp METAL MATRIX COMPOSITES (MMCs)

A detailed parametric analysis of cutting forces in diamond turning of Al6061/15SiC_p composite is presented. Spectrum analysis was used to analyze the features of cutting force variation. It was found that the presence of SiC particles led to a large fluctuation in the cutting and thrust forces. The magnitude and frequency of the variation were found to be closely related to the cutting conditions. The use of higher feed rate, lower spindle speed, and smaller depth of cut significantly reduced both the magnitude and frequency of the cutting force variation. Compared with diamond turning of ductile materials, a much greater ratio of the thrust and cutting forces was obtained under various cutting conditions. Empirical cutting force equations are presented based on a nonlinear multiple regression analysis method. A good correlation between the actual and the predicted results was found. These findings can provide guidelines for the selection of optimal cutting conditions in minimizing the fluctuation of cutting forces.     

The influence of cutting force on surface machining quality

Appropriately controlled cutting forces can contribute not only to the safety and efficiency of machining but also to the quality of machined surfaces. It is even more important when hardened material is cut. The correlation between the cutting force and the surface quality in ball-end milling operations has been investigated by machining P20 steel (HRC 30) work-pieces using solid carbide ball-end cutters. Plane surfaces with different depth of cut were machined using two different cutting strategies. The first strategy cut the test-piece using a cutting force model, whereas the other machined with a feed rate optimization product, which uses the removal rate as an analogue of cutting force to control the feed rate. The test results show that constant surface quality is possible when the cutting forces are controlled through feed rate adjustment. Conversely, a desired surface quality can also be maintained by controlling the cutting force in a predetermined manner.     

Investigation on diamond tool wear in ultrasonic vibration-assisted turning die steels

This paper presents comprehensive theoretical analyses and experimental investigations for evaluating the ultrasonic vibration-assisted turning (UVAT) of die steels with single-crystal diamond tools. The diamond tool wear was found to rely heavily on the feed rate and the cutting speed while being insensitive to the depth of cut and the tool relief angle under the cutting conditions used in the tests. The tool wear characteristics were further studied based on the observation of wear zone using Raman spectral analysis and energy-dispersive X-ray (EDX) analysis. The detection results of the tool worn topography, the phase transformation and the carbon diffusion of diamond crystals revealed that tool wear mainly occurred on the tool flank face due to the graphitization and the diffusion of the diamond tool. Analytical results of the function mechanisms of the ultrasonic turning indicated that the friction force between the tool flank face and the machined surface, which depended mainly on the ratio of the cutting speed and the vibration speed, could be effectively reduced in ultrasonic turning process. The analytical and experimental results indicated that compared with conventional turning (CT), the cutting performance, in terms of the tool life, was markedly improved by applying ultrasonic vibration to the cutting tool.     

截割厚度与截线距对镐型截齿破岩力学参数的影响

基于对一种砂岩的直线截割试验,研究截割厚度和截线距对镐型截齿破岩力学参数的影响。单因素回归表明:截割力、法向力与截割厚度成正比,线性拟合和幂函数拟合均能很好地描述它们之间的统计学关系;随着截割厚度的增加,法向力截割力比值呈线性减小;随着截线距的增加,截割力和法向力呈线性增加,法向力截割力比值呈幂函数减小。载荷波动性系数随着截线距与截割厚度比值的增大呈线性减小。多元线性回归表明:截割力、法向力与截割厚度和截线距之间有极强的统计学关系;载荷波动性系数与截割厚度及截线距之间存在显著的统计学关系,且与截割厚度成正比,与截线距成反比。对比发现,Evans的理论模型较Roxborouth等、Goktan的改进模型对截割力有更好的预测性能。     

Study of Factors Affecting the Surface Quality in Ultra-Precision Diamond Turning

This paper deals with an investigation of the process factors and the material factors affecting the surface roughness in ultra-precision diamond turning. The process factors involve cutting conditions, tool geometry, and relative tool-work vibration which are related to the cutting geometry and the dynamic characteristics of the cutting process. The material factors considered are material anisotropy, swelling, and crystallographic orientation of the work materials. Experimental results indicate that the influence due to the process factors can be minimized through a proper selection of operational settings and better control of dynamic characteristics of the machine. The material factors, on the other hand, exert consistent influence on the surface roughness which can not be minimized solely by an optimization of process parameters and machine design. Based on these findings, some suggestions are proposed for the optimization of the surface quality in ultra-precision diamond turning.     

brittle-ductile TRANSITION IN DIAMOND CUTTING OF SILICON SINGLE CRYSTALS

Silicon single crystals are not amenable to conventional machining operations because of their inherent low fracture toughness. This paper deals with an investigation of brittle-ductile transition in diamond cutting of silicon from the viewpoint of material response and tool geometry. Micro indentation and scribing tests were conducted in order to investigate the influence of applied loads on the deformation characteristics. The transition of material removal from brittle to ductile was observed by continuously changing the cutting depth. The effect of tool rake angle on the machined surface quality was studied by actual diamond turning. A mirror surface, with a roughness of 5 nm R_a, was produced using a tool with a -25° rake angle. The reason for the difference in the machined surface quality is discussed based on the analysis of stress distribution in the microcutting process.     

Experimental study on the meso-scale milling of tungsten carbide WC-17.5Co with PCD end mills

Tungsten carbide is a material that is very difficult to cut, mainly owing to its extreme wear resistance. Its high value of yield strength, accompanied by extreme brittleness, renders its machinability extremely poor, with most tools failing. Even when cutting with tool materials of the highest quality, its mode of cutting is mainly brittle and marred by material cracking. The ductile mode of cutting is possible only at micro levels of depth of cut and feed rate. This study aims to investigate the possibility of milling the carbide material at a meso-scale using polycrystalline diamond (PCD) end mills. A series of end milling experiments were performed to study the effects of cutting speed, feed per tooth, and axial depth of cut on performance measures such as cutting forces, surface roughness, and tool wear. To characterize the wear of PCD tools, a new approach to measuring the level of damage sustained by the faces of the cutter's teeth is presented. Analyses of the experimental data show that the effects of all the cutting parameters on the three performance measures are significant. The major damage mode of the PCD end mills is found to be the intermittent micro-chipping. The progress of tool damage saw a long, stable, and steady period sandwiched between two short, abrupt, and intermittent periods. Cutting forces and surface roughness are found to rise with increments in the three cutting parameters, although the latter shows signs of reduction during the initial increase in cutting speed only. The results of this study find that an acceptable surface quality (average roughness R_a<0.2 μm) and tool life (cutting length L>600 mm) can be obtained under the conditions of the given cutting parameters. It indicates that milling with PCD tools at a meso-scale is a suitable machining method for tungsten carbides.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-020-00298-y     

Optimizing feed force for turned parts through the Taguchi technique

The objective of the paper is to obtain an optimal setting of turning process parameters (cutting speed, feed rate and depth of cut) resulting in an optimal value of the feed force when machining EN24 steel with TiC-coated tungsten-carbide inserts. The effects of the selected turning process parameters on feed force and the subsequent optimal settings of the parameters have been accomplished using Taguchi’s parameter design approach. The results indicate that the selected process parameters significantly affect the selected machining characteristics. The results are confirmed by further experiments.     

Vibration-Assisted Precision Machining of Steel with PCD Tools

This article presents experimental results of precision machining of steel alloys with polycrystalline diamond tools. Ultrasonic vibration-assisted cutting was tried out for expanding the application of diamond tools for high-precision and high-quality machining of ferrous materials. The experimental results show that compared with conventional turning, the cutting performance, in terms of cutting force, surface finish, and tool life, was improved by applying ultrasonic vibration to the cutting tool. The cutting forces and tool wear measured in vibration cutting are much lower than those in conventional cutting. The tool wear mechanism was discussed on the basis of the observation of wear zone.     

Cutting force behavior during a cutting tool entering and exiting a workpiece in turning silumins using tools with round polycrystalline diamond inserts

The pattern of variation of the cutting force components, resultant cutting force, and cut layer area at the stages of a tool entering and exiting a workpiece during the turning of silumins using round poly-crystalline diamond cutting inserts.     

单晶铜纳米切削过程的研究

采用分子动力学三维模型研究单晶铜纳米切削过程，工件原子间相互作用力和工件与刀具原子间相互作用力采用Morse势计算．通过分析切削过程中瞬间原子图像、切削力、单位切削力和轴向切削力与切向切削力比值。发现在整个切削过程中有位错产生，在加工表面发生弹性恢复，但未发生切屑体积的改变，切屑以原子团方式去除，单位切削力和轴向切削力与切向切削力的比值比传统切削时大得多．单晶铜纳米切削过程是位错在晶体中运动产生的塑性变形．     

具有力传感器的纳米加工探针的设计

给出了一种用于复杂表面形状精密纳米加工的探针装置．该探针由一个高速可控的金刚石切割单元（FTC单元）和一个高灵敏度的压电式力传感器组成．而FTC单元由一个单点金刚石切割工具和一个压电陶瓷晶体（PZT）驱动器构成．压电陶瓷晶体（PZT）驱动器可对与切削量相对应的金刚石工具的Z向位置进行高速控制,从而实现加工复杂表面形状的目的．加工中的切削力是反映切削进程的重要指标,可由联结于FTC单元的高灵敏度力传感器进行测量．比对了用于联结力传感器和FTC单元的两种设计方法．     

Integrated force measurement for on-line cutting geometryinspection

A novel on-line cutting geometry inspection technique based on the integrated force-sensing method has been developed. A piezoelectric force sensor, mounted at the back of a single crystal diamond tool, was used to measure the cutting forces encountered by the tool system as it plunge-cut parallel micro flow channels on copper foils about 125 μm in thickness. The force data were then converted by a software code which calculates the geometrical dimensions (depth and width) of the micro channels that had been cut. A series of experiments were conducted for four different feeds: 0.1, 0.3, 1.0, and 5.0 μm/rev., at a constant workpiece speed of 2,400 rpm. Error analysis showed that the maximum relative error of the measurement, as compared to the results from the theoretical analysis, is 9.8%. By incorporating this force sensing technique into the machine tool control system, a real-time control unit can be implemented which conducts on-line adjustment of the diamond cutting performance to improve manufacturing quality     

Investigating the Machinability of AISI 420 Stainless Steel Using Factorial Design

This work aims at studying the machining characteristics of high-strength materials using carbide cutting tool inserts at different cutting conditions. This is an essential step in building up an accurate machining information system. The tested material is high-strength stainless steel of the AISI 420 type. Machining tests were carried out using orthogonal cutting conducted to investigate the machining characteristics for high-strength stainless steel AISI 420 at different cutting conditions and tool rake angles. This assessment is achieved by investigating the effect of cutting parameters (cutting speed, feed, depth of cut, and tool geometry) on cutting forces, specific cutting energy, shear angle, coefficient of friction, shear stress, shear strain, and shear strain rate. Empirical equations and a correlation for the behavior of each of the output responses were investigated as a function of the independent variables. Main effect and interaction plot were presented for the most influential factors affecting the main cutting force and the power consumed.     

Comparison of experimental results obtained by designed dynamometer to fuzzy model for predicting cutting forces in turning

This paper presents a comparison of experimental results and consistent fuzzy rule-based model for estimating the cutting forces in turning. A dynamometer that can measure static and dynamic cutting forces by using strain gauge and piezo-electric accelerometer, respectively, was used for measuring the forces. AISI 1040 steel was used as the workpiece material. Feed force, thrust force and main cutting force were measured for three combinations of cutting speeds, feedrates and depth of cuts. The rake angle and approach angle of the cutting tool were kept constant throughout the experiments. The fuzzy model consists of 27 rules. In this research, a Mamdani max–min inference for inference mechanism and the centre of gravity (Centroid) defuzzifier formula method for defuzzification were used as these operators assure a linear interpolation of the output between the rules. It has a wide range of applications over many types of steels and turning conditions. It is also simple to implement, from a rule-chart mode to an intelligent on-line adaptive control mode. Experimental results were compared with the predicted fuzzy model. The difference between experimental and predicted results was obtained as around 99.6%.     

Studies of the ductile mode of cutting brittle materials (A review)

Theoretical and experimental studies of the ductile mode of cutting brittle materials (semiconductors, ceramics, and glass) have been considered. The ductile mode of cutting has been based on the implementation of high-pressure-induced phase transformations in a material machined that followed by a cutting of a transformed amorphous layer, which makes it possible to avoid cracking. Publications on studies of phase transitions in brittle materials in the course of the indentation, scratching, friction, and cutting have been reviewed. It has been shown that the cutting depth, cutting edge radius of a tool, chip thickness, tool cutting edge inclination, and crystallographic orientation of a material machined and diamond tool as well as a type of lubricoolant are the decisive factors in implementing the ductile mode of cutting     

Prediction of cutting force based on machining parameters on AL7075-T6 aluminum alloy by response surface methodology in end milling

Cutting forces modeling is the basic to understand the cutting process, which should be kept in minimum to reduce tool deflection, vibration, tool wear and optimize the process parameters in order to obtain a high quality product within minimum machining time. In this paper a statistical model has been developed to predict cutting force in terms of geometrical parameters such as rake angle, nose radius of cutting tool and machining parameters such as cutting speed, cutting feed and axial depth of cut. Response surface methodology experimental design was employed for conducting experiments. The work piece material is Aluminum (Al 7075-T6) and the tool used is high speed steel end mill cutter with different tool geometry. The cutting forces are measured using three axis milling tool dynamometer. The second order mathematical model in terms of machining parameters is developed for predicting cutting forces. The adequacy of the model is checked by employing ANOVA. The direct effect of the process parameter with cutting forces are analyzed, which helps to select process parameter in order to keep cutting forces minimum, which ensures the stability of end milling process. The study observed that feed rate has the highest statistical and physical influence on cutting force.     

Study of milling force variation in ultrasonic vibration-assisted end milling

Ultrasonic vibration cutting has been proved to be an effective cutting technology for its excellent cutting performance and has been widely applied in turning and drilling process. However, this kind of technology is rarely tried in milling process. In cutting process, cutting force is an important process parameter, which affects surface finish and tool wear. This paper investigates the milling force variation in ultrasonic vibration-assisted end milling process through a series of slot-milling experiments. The main research contents include two parts, one is the effect of the externally excited vibration on milling force in milling process, and the other is the influence of milling and vibrating parameters matching on milling force value. Experimental results show that ultrasonic vibration can change traditional milling conditions, realize separate-type milling, obtain similar pulse-like profiles of cutting forces, reduce average cutting force value; and the peak value of the feed direction cutting force can also be greatly decreased by adopting reasonable vibration amplitude, an optimal combination of machining parameters is of great benefit to achieving small cutting force. According to the experimental findings, ultrasonic vibration-assisted milling is a prospective technology to achieve precision milling of small part.