DYNAMICS OF CUTTING TOOL TEMPERATURES DURING CUTTING PROCESS

An experimental study is performed to measure temperature variation of a carbide insert during metal cutting by means of fine thermocouples connected to a data acquisition system. A semiempiriad equation is developed based on transient conduction solutions combined with experimental data to predict temperature-time history in the cutting tool during operation. The governing parameters in the equation are derived, using AISI 1045 steel as the workpiece, to be the cutting speed, feed rate, and depth of cut at fixed rake and lead angles. Emphasis is placed on analyzing effects of the important factors on the cutting process, such as frictional heat generated at the tool-workpiece interface and wear of the tool. Dynamic behavior of the metal cutting process as predicted by the direct thermocouple measurement agreed with phenomenological observations reported in the existing literature.     

Condition monitoring of turning process using infrared thermography technique – An experimental approach

In metal cutting machining, major factors that affect the cutting tool life are machine tool vibrations, tool tip/chip temperature and surface roughness along with machining parameters like cutting speed, feed rate, depth of cut, tool geometry, etc., so it becomes important for the manufacturing industry to find the suitable levels of process parameters for obtaining maintaining tool life. Heat generation in cutting was always a main topic to be studied in machining. Recent advancement in signal processing and information technology has resulted in the use of multiple sensors for development of the effective monitoring of tool condition monitoring systems with improved accuracy. From a process improvement point of view, it is definitely more advantageous to proactively monitor quality directly in the process instead of the product, so that the consequences of a defective part can be minimized or even eliminated.In the present work, a real time process monitoring method is explored using multiple sensors. It focuses on the development of a test bed for monitoring the tool condition in turning of AISI 316L steel by using both coated and uncoated carbide inserts. Proposed tool condition monitoring (TCM) is evaluated in the high speed turning using multiple sensors such as Laser Doppler vibrometer and infrared thermography technique. The results indicate the feasibility of using the dominant frequency of the vibration signals for the monitoring of high speed turning operations along with temperatures gradient. A possible correlation is identified in both regular and irregular cutting tool wear. While cutting speed and feed rate proved to be influential parameter on the depicted temperatures and depth of cut to be less influential. Generally, it is observed that lower heat and temperatures are generated when coated inserts are employed. It is found that cutting temperatures are gradually increased as edge wear and deformation developed.     

Quasicontinuum analysis of the effect of tool geometry on nanometric cutting of single crystal copper

A dynamic multiscale simulation based on quasicontinuum method (QC) has been conducted to study the effect of tool geometry in nanometric cutting process of single crystal copper. In the simulation, the many-body EAM potential is used for the interactions between copper atoms in of the workpiece. The simulation captures the atomistic behaviors of material removal mechanisms from the free surface and the mobility of dislocations and their interactions with the computational cost of local atomistic simulation method. Simulations are performed on single crystal copper to study the atomistic details of material removal, chip formation, sub-surface deformation, and machining mechanism. The simulation results demonstrate that tool edge radius has significant effect on chip formation and subsurface deformation, because the effective rake angle varies with the tool edge radius. In addition, different effective rake angles result in different stress states and smoother surface can be obtained under bigger clearance angle. The variations of tangential force, normal force as well as the ratio of normal force to tangential force are obtained to analyze the effects of tool edge radius, rake angle and clearance angle in quantitative way.     

Ultrasonically assisted turning of aviation materials: simulations and experimental study

Ultrasonically assisted turning of modern aviation materials is conducted with ultrasonic vibration (frequency f approximately 20 kHz, amplitude a approximately 15 microm) superimposed on the cutting tool movement. An autoresonant control system is used to maintain the stable nonlinear resonant mode of vibration throughout the cutting process. Experimental comparison of roughness and roundness for workpieces machined conventionally and with the superimposed ultrasonic vibration, results of high-speed filming of the turning process and nanoindentation analyses of the microstructure of the machined material are presented. The suggested finite-element model provides numerical comparison between conventional and ultrasonic turning of Inconel 718 in terms of stress/strain state, cutting forces and contact conditions at the workpiece/tool interface.     

A METHOD TO ESTIMATE THE AVERAGE TEMPERATURE ON THE CUTTING EDGE OF TOOLS: APPLICATION ON THE MILLING PROCESS

In this work we present an experimental technique for the estimation of the average temperature on the cutting edge of each insert in a milling tool. The experimental device used thermistors, one per insert, and a rotational collector in order to ensure the transmission of the signals between the rotating tool and the acquisition device. Each thermistor is located at a point in the tool close to the tip of each insert. The average temperature on the cutting edge of each insert is estimated from the temperature at the nearest sensor and a model expressing these two temperatures. This model is achieved from the noninteger system identification method.     

单晶金刚石刀具后刀面沟槽磨损的石墨化生成过程分析

单晶金刚石刀具切削单晶硅时后刀面会发生剧烈沟槽磨损,严重影响零件加工质量和刀具寿命。为了从金刚石石墨化转变角度揭示沟槽磨损生长扩展机制,建立了金刚石刀具后刀面具有初始沟槽的分子动力学模型,模拟了切削单晶硅时初始沟槽处的工件材料流动行为与金刚石刀具晶体结构变化情况。结果表明,初始沟槽的存在改变了工件材料的流动状态;并且这种材料流动引起了刀具初始沟槽附近温度和能量的变化,温度升高了8%,势能提高了1.4%;通过分析金刚石刀具晶体结构发现,初始沟槽处的刀具材料发生了石墨化转变,并通过计算采样点处原子间键角,得到了石墨化转化率随着切削的进行不断升高,并最终趋于恒定的规律,当切削进入到稳定切削阶段时,石墨化转化率约为6%。     

Evaluation of the tool life and fracture toughness of cutting tools boronized by the paste boriding process

The present study evaluates the tool life and the fracture toughness of AISI M2 steel cutting tools boronized by the paste boriding process. The treatment was done in selective form on the tool tips of the steels. The temperatures were set at 1173 and 1273 K with 4 h of exposure time and modifying the boron carbide paste thicknesses in 3 and 4 mm. Microindentation fracture toughness method was used on the borided tool at the temperature of 1273 K and a 4 mm paste thickness, with a 100 g load at different distances from the surface. Also, the borided cutting tools were worn by the turning process that implied the machining of AISI 1018 steel increasing the nominal cutting speed, of 55 m/min, in 10 and 25% and maintaining the feed and the depth cut constants. The tool life was evaluated by the Taylor's equation that shows the dependence of the experimental parameters of the boriding process.     

Study on critical rake angle in nanometric cutting

Molecular dynamics (MD) simulations of nanometric-cutting copper are conducted to study the critical rake angle during the cutting process. A new approach based on the maximum displacement of atoms in cutting direction is proposed to estimate the chip formation in MD simulation. It is found that the minimum rake angle for chip formation is ?65^°–(?70^°) and the subsurface deformations of copper are mostly the dislocation and stacking faults. Three-dimensional simulation results show that the effective rake angle of stagnation region is constant with the same depth of cut. According to the limited depth of cut of copper can be achieved, the available minimum tool edge radius is suggested to be not less than 10?nm.     

Methods for reducing cutting temperature in ultrasonic cutting of bone

Ultrasonic cutting is widely used in food processing applications to produce a clean and accurate cut. However, it is yet to be adopted as an instrument of choice in orthopaedic applications, mainly due to the high temperatures that can be generated at the cut site and the consequent requirement to use additional cooling. For example, if cutting temperatures above 55-60 degrees C are reached, particularly for sustained periods, bone necrosis can occur, compromising post-operative recovery. A recent study by the authors has shown that the thermal response in natural materials, such as wood and bone, is affected by the absorption of ultrasonic energy and conduction of heat from the cut site. In this paper the dependency of cutting parameters, such as blade tip vibration velocity, applied load, tuned frequency and coupling contact conditions, on the thermal response are reported and results show that it is possible to maintain cutting temperatures within safety limits by controlling the cutting parameters. A novel cutting blade design is proposed that reduces frictional heat generated at the cut site. Through a series of experimental investigations using fresh bovine femur it is demonstrated that the cutting temperature, and hence thermal damage, can be reduced by selecting appropriate cutting parameters and blade profile.     

Effect of different downstream temperatures on the performance of a two-layer porous burner

The influence of considering different downstream temperatures on the performance of a two-layer porous burner is studied numerically. A 3D numerical model based on a unit cell was implemented to correctly predict the momentum, heat and mass transfer at the interface of the two layers. Two operating modes are simulated corresponding to the burner radiating to cold and hot environments. When the burner radiates to a hot environment, its radiative heat losses are lower and, as a consequence, the temperatures and pollutants emissions are higher. Additionally, the flame front moves upstream and stabilizes nearer the interface of the two layers.     

切削参数对新型光学铝级金刚石车削刀具磨损的影响

光学器件和光学测量系统的关键部件主要通过超精密加工制造。铝合金具有很多优势,通常用于光子产业。光学领域对铝合金使用和需求的不断增加,促进了在铸造过程中采用快速凝固技术对铝合金等级重新改良的发展。优异的微观结构和改进的机械和物理性能是新型铝合金等级的特点。目前主要问题在于采用金刚石车削时,由于在切削性方面缺乏对铝合金性能的充分研究,导致机械加工数据库非常有限。本文通过改变金刚石的切削参数,测量切齿安装距超过4km时金刚石刀具的磨损,研究了快速凝固铝合金RSA 905的切削性能。改变的机械加工参数为切削速度、进给速度和切削深度。结果表明切削速度对金刚石刀具的磨损影响最大。主轴转速为500rpm、进给速度为25mm/min、切削深度为15μm时,刀具磨损达到最大值12.2μm;主轴转速为1750rpm、进给速度为5mm/min、切削深度为5μm时,刀具磨损达到最小值2.45μm。通常,较高的切削速度、较低的进给速度和较短的切削深度的组合可以减少金刚石刀具磨损。建立了模型统计以分析金刚石刀具磨损。通过该模型可以生成磨损图,从而确定切削参数产生最小磨损的区域。结果证明,快速凝固铝是更好的选择,为机械工程师使用这种材料提供了参考。     

单晶硅纳米切削中C–C键断裂对金刚石刀具磨损的影响

本文基于分子动力学方法模拟金刚石刀具纳米切削单晶硅, 从刀具的弹塑性变形、C–C键断裂对碳原子结构的影响以及金刚石刀具的石墨化磨损等方面对金刚石刀具的磨损进行分析, 采用配位数法和6元环法表征刀具上的磨损碳原子. 模拟结果表明: 在纳米切削过程中, 金刚石刀具表层C–C键的断裂使其两端碳原子由sp³杂化转变为sp²杂化, 同时, 表面上的杂化结构发生变化的碳原子与其第一近邻的sp²杂化碳原子所构成的区域发生平整, 由金刚石的立体网状结构转变为石墨的平面结构, 导致金刚石刀具发生磨损; 刀具表面低配位数碳原子的重构使其近邻区域产生扭曲变形, C–C键键能随之减弱, 在高温和高剪切应力的作用下, 极易发生断裂; 在切削刃的棱边上, 由于表面碳原子的配位严重不足, 断开较少的C–C键就可以使表面6 元环中碳原子的配位数都小于4, 导致金刚石刀具发生石墨化磨损.     

ESTIMATED TEMPERATURE ON A MACHINED SURFACE USING AN INVERSE APPROACH

An experiment devoted to the heat flux estimation in a workpiece during a machining process by turning is presented. The method is based on temperature measurement from thermocouples embedded in the workpiece, close to the heated surface. A model that expresses the heat flux according to the temperature at the sensors is developed. The stationary and linearity assumptions are used in order to decompose the three-dimensional original problem into two bi-dimensional problems. This decomposition can be realized given the difference between the cutting speed and feed velocity in two orthogonal directions. The temperature on the machined surface is calculated from the estimated heat flux and the heat transfer model in the workpiece. The application concerns hard steel machining, using a CBN insert tool. Three parameters are placed into evidence from this application: the temperature magnitude on the machined surface, the thermal gradient in the workpiece, and the `thermal persistence' that represent the heating time of the machined surface. This study leads to a better understanding of the influence of temperature during a hard steel turning process.     

Molecular dynamics simulation of subsurface deformed layers in AFM-based nanometric cutting process

Three-dimensional molecular dynamics simulations of AFM-based nanometric cutting monocrystalline copper with pin tool radius of 0.713 nm are performed to investigate the effect of uncut chip thicknesses (0.1805 nm, 0.361 nm, 0.5415 nm, 0.722 nm, 0.9025 nm, 1.0875 nm, and 1.268 nm) on the depth of subsurface deformed layers. The EAM potential and Morse potential are utilized respectively to compute the interactions between workpiece atoms, the interactions between workpiece atoms and tool atoms. The single-atom potential energy variations of the workpiece atoms within the subsurface regions during the cutting process are obtained and analyzed through a deformation criterion to determine the deformation behaviors of subsurface atoms. The simulation results reveal that the depth of subsurface deformed layers is affected by the AFM pin tool's rake angle. At each uncut chip thickness, the AFM pin tool presents different negative rake angles, consequently different degrees of deformation in the subsurface take place.     

Co元素对硬质合金基底金刚石涂层膜基界面结合强度的影响

采用基于密度泛函理论的第一性原理平面波赝势方法, 研究了硬质合金刀具基底黏结相Co元素对金刚石涂层膜基界面结合强度的影响机理. 借助Materials Studio软件建立了WC/Diamond膜基界面模型和WC-Co/Diamond膜基界面模型, 采用CASTEP仿真软件计算了WC/Diamond膜基界面模型和WC-Co/Diamond膜基界面模型的最优稳定结构. 通过仿真计算, 获得了WC/Diamond膜基界面模型和WC-Co/Diamond膜基界面模型的界面结合能、电荷密度图及Mulliken重叠布居数. 经对比分析后发现, 硬质合金基底中磁性元素Co的存在能转移金刚石涂层膜基界面处W元素及C元素的电荷, 从而使膜基界面处的原子因失电荷而相斥, 这直接导致了金刚石涂层膜基界面间距变大, 使得金刚石涂层膜基界面结合能降低.     

Ultrasonic excitation affects friction interactions between food materials and cutting tools

In the food industry, ultrasonic cutting is used to improve separation by a reduction of the cutting force. This reduction can be attributed to the modification of tool–workpiece interactions at the cutting edge and along the tool flanks because of the superposition of the cutting movement with ultrasonic vibration of the cutting tool. In this study, model experiments were used to analyze friction between the flanks of a cutting tool and the material to be cut. Friction force at a commercial cutting sonotrode was quantified using combined cutting–friction experiments, and sliding friction tests were carried out by adapting a standard draw-off assembly and using an ultrasonic welding sonotrode as sliding surface. The impact of material parameters, ultrasonic amplitude, and the texture of the contacting food surface on friction force was investigated. The results show that ultrasonic vibration significantly reduces the sliding friction force. While the amplitude showed no influence within the tested range, the texture of the contact surface of the food affects the intensity of ultrasonic transportation effects. These effects are a result of mechanical interactions and of changes in material properties of the contact layer, which are induced by the deformation of contact points, friction heating and absorption heating because of the dissipation of mechanical vibration energy.     

Measurement of thermal radiative and conductive properties of semitransparent materials using a photothermal crenel method

This paper deals with a theoretical and an experimental study allowing the measurement of the radiative and the conductive properties of semitransparent materials. The method consists of applying a crenel heat flux on the front face of a semitransparent sample and recording the temperature at the rear face using an open thermocouple junction.Parameter identification is performed by the minimization of the ordinary least-squares function comparing the measured and the calculated temperatures. This later is obtained from the thermal model describing the heat transfer by conduction and radiation in the medium. This model is built by the thermal quadrupole formalism.Measurements are reported on commercial glasses and plexiglass samples, and the used iterative algorithm is based on the Gauss-Newton method.     

Characterization of atomic layer deposition coated cutting tools by X-ray photoelectron spectroscopy and examination of cutting performance

Abstract

The performance of cutting tools was examined, involving synthesis of a 10?nm thin film of Aluminum oxide using atomic layer deposition. Characterization of coated and uncoated cutting tools was done by several methods. scanning electron microscopy was used and the images were compared with each other. Chemical characterization was performed by X-ray diffraction and X-ray photoelectron spectroscopy. Coated and uncoated cutting tools were tested with steel material in turning tests. After turning, it was observed that the adhesion effect was reduced to a large extent in turning with coated tool. It was observed that the coating showed stability at high temperatures during cutting and the cutting performance was increased. The main advantage of the coating was that the tools produced were more environmentally friendly, with a longer useful life and they were easier to recycle.     

Heat and mass transfer at adiabatic evaporation of binary zeotropic solutions

Results of numerical simulation of heat and mass transfer in a laminar flow of three-component gas at adiabatic evaporation of binary solutions from a flat plate are presented. The studies were carried out for the perfect solution of ethanol/methanol and zeotrope solutions of water/acetone, benzene/acetone, and ethanol/acetone. The liquid-vapor equilibrium is described by the Raoult law for the ideal solution and Carlson–Colburn model for real solutions. The effect of gas temperature and liquid composition on the heat and diffusion flows, and temperature of vapor-gas mixture at the interface is analyzed. The formula for calculating the temperature of the evaporation surface for the binary liquid mixtures using the similarity of heat and mass transfer was proposed. Data of numerical simulations are in a good agreement with the results of calculations based on the proposed dependence for all examined liquid mixtures in the considered range of temperatures and pressures.     

Problems of shock temperature measurements for metals by using optical radiometry method

Abstract

Several problems encountered in shock temperature measurements for metals using optical radiometry were discussed in detail. The influences of the driver/film gap upon the observed interface temperature history were formulated analytically, and the temperature relaxation behaviors at the film/window interface were also characterized. We found that the energy deposition at the driver/film gap would influence to varied degrees the film/window interface temperature profile unless the film deposited on the window can be regarded to have an infinite thickness. Modeling calculations showed that at shock pressures of a few megabars, the observed interface temperature of iron would be at least 300–600 K higher, relative to the prediction from the Grover model, provided that the gap and film were both 1 ～ 2 pm thick. Additionally, a metal-plate sample was used to measure a reliable shock temperature based on one-dimensional heat conduction model for the plate-sample(driver)/ pm-gap/window setup we proposed. Preliminary measured results for a meteoritic iron sample (kamacite, with Fe 93.65 wt.% and Ni 6.35 wt.%) using a disc sample showed that this method was practical and effective. Finally, the “heat-resistance model” proposed by Tang et al., and the experimental measurement of the heat conductivity for a transparent window (sapphire or LiF crystal) at megabar shock pressures were discussed and commented on as well.