Surface integrity of finished turned Ti–6Al–4V alloy with PCD tools using conventional and high pressure coolant supplies

 Surfaces generated when machining Ti–6Al–4V alloy with PCD tools using conventional and high pressure coolant supplies was investigated. Longer tool life was recorded when machining Ti–6Al–4V with high-pressure coolant supplies and the recorded surface roughness R_a values were well below the tool rejection criterion (1.6 μm) for all cutting conditions investigated. The micro-structure of the machined surfaces were examined on a scanning electron microscope. Micrographs of the machined surfaces show that micro-pits and re-deposited work material were the main damages to the surfaces. Micro-hardness analysis showed hardening of the top machined surfaces when machining with conventional coolant while softening of the subsurface layer was observed when machining under high-pressure coolant supplies. The later is probably due to lower heat generated, with the consequent tempering action when machining with PCD tools with high-pressure coolant supplies. The microstructure below the machined surfaces had minimal or no plastic deformation when machining with conventional and high-pressure coolant supplies.     

Investigations of White Layer Formation During Machining of Powder Metallurgical Ni-Based ME 16 Superalloy

Surface integrity of machined parts made from the advanced Ni-based superalloys is important for modern manufacturing in the aerospace industry. Metallographic observations of the ME 16 alloy microstructure were made using optical metallography and a high-resolution scanning electron microscope with energy dispersive x-ray spectrometer (HR SEM/EDS). Tool life of cemented carbide inserts with TiAlN coating during machining (finishing turning operation) of ME 16 superalloy has been studied and wear patterns of the cutting tools were identified. Surface integrity of the machined part after completion of the turning operation was investigated. The morphology of machined parts has been examined and cross-sections of the machined surfaces have been analyzed. The formation of white layer on the surface of the machined part was studied for varied machining conditions. It was found that a 2-4 μm thick white layer forms during turning of the ME 16 superalloy. This layer was investigated using EDS and XRD. The studies show that the white layer is an oxygen-containing layer with a high amount of aluminum, enriched by chromium and tungsten. Under specific cutting conditions, the structure of white layer transforms into a γ-alumina. Formation of this thermal barrier ceramic white layer on the surface of the machined part negatively affects its surface integrity and cutting tool life.     

GH4169疲劳试样加工残余应力的表征及其对低周疲劳寿命的影响

为了探究GH4169合金低周疲劳试样加工过程中表面残余应力的变化及残余应力对低周疲劳性能的影响,采用X射线衍射法对“车 磨 抛”不同加工工艺的试样表面残余应力进行表征及对成品试样进行残余应力层深度测试,通过中子衍射法对试样内部进行残余应力测试。采用电液伺服万能试验机进行了低周疲劳试验。结果表明：GH4169合金低周疲劳试样加工表面残余应力随着切削量的增加由表面残余压应力变为残余拉应力。根据残余应力层深度测试,机加工对试样表面造成残余应力层深度小于0.01 mm,内部残余拉应力减小;根据疲劳试验结果,GH4169合金疲劳寿命与表面轴向残余压应力呈正相关关系。     

GH4169疲劳试样加工残余应力的表征及其对低周疲劳寿命的影响

为了探究GH4169合金低周疲劳试样加工过程中表面残余应力的变化及残余应力对低周疲劳性能的影响，采用X射线衍射法对“车 磨 抛”不同加工工艺的试样表面残余应力进行表征及对成品试样进行残余应力层深度测试，通过中子衍射法对试样内部进行残余应力测试。采用电液伺服万能试验机进行了低周疲劳试验。结果表明：GH4169合金低周疲劳试样加工表面残余应力随着切削量的增加由表面残余压应力变为残余拉应力。根据残余应力层深度测试，机加工对试样表面造成残余应力层深度小于0.01 mm，内部残余拉应力减小；根据疲劳试验结果，GH4169合金疲劳寿命与表面轴向残余压应力呈正相关关系。     

Dry machining of Inconel 718, workpiece surface integrity

In the machining of Inconel 718, nickel based heat resistant superalloy and classified difficult-to-cut material, the consumption of cooling lubricant is very important. To reduce the costs of production and to make the processes environmentally safe, the goal is to move toward dry cutting by eliminating cutting fluids. This goal can be achieved by using coated carbide tool and by increasing cutting speed.The present paper firstly reviews the main works on surface integrity and especially residual stresses when machining Inconel 718 superalloy. It focuses then on the effect of dry machining on surface integrity. Wet and dry turning tests were performed at various cutting speeds, with semi-finishing conditions (0.5 mm depth of cut and 0.1 mm/rev feed rate) and using a coated carbide tool. For each cutting test, cutting force was measured, machined surface was observed, and residual stress profiles were determined. An optimal cutting speed of 60 m/min was determined, and additional measurements and observations were performed. Microhardness increment and the microstructure alteration beneath the machined surface were analysed. It is demonstrated that dry machining with a coated carbide tool leads to potentially acceptable surface quality with residual stresses and microhardness values in the machining affected zone of the same order than those obtained in wet conditions when using the optimised cutting speed value; in addition, no severe microstructure alteration was depicted.     

Microscopic Observations on the Origin of Defects During Machining of Direct Aged (DA) Inconel 718 Superalloy

Surface quality of advanced superalloys after machining is one of the major issues in the aerospace industry because it directly affects service characteristics of the machined part. Tool life of cemented carbide inserts with the TiAlN coating during machining of direct aged DA 718 alloys under roughing and finishing conditions has been under study. The defect origin on the surface of the machined part was investigated. Metallographic observations of the DA 718 were made using optical metallography and SEM/EDS. To find out the origins of surface defect formation, the morphology of machined parts and cross sections of the machined surfaces have been investigated. Two major categories of defects were detected on the surface of the machined part: cracks and tears. The origin of the cracks on the machined surface is related to shearing of the primary complex TiC/NbC carbide revealed in a structure of DA 718 alloy. At the same time, Nb-rich regions of the primary complex carbide interact with the environment (oxygen from air) during machining with further formation of low strength oxide layer on the surface, forming tears.     

Surface integrity of dry machined titanium alloys

The study is focused on the machined surface integrity of titanium alloy under the dry milling process. Roughness, lay, defects, microhardness and microstructure alterations are investigated. The result of surface roughness shows that the CVD-coated carbide tool fails to produce better Ra value compared to the uncoated tool. Lay is found to be dependent on cutting speed and feed speed directions. Microhardness is altered down to 350 μm beneath the machined surface. The first 50 μm is the soft sub-surface caused by thermal softening in the ageing process. Down to 200 μm is the hard sub-surface caused by the cyclic internal work hardening and then it gradually decreased to the bulk material hardness. It was concluded that for titanium alloys, dry machining can be carried out with uncoated carbide tools as far as cutting condition is limited to finish and/or semi-finish operations.     

Effect of machining parameters and cutting edge geometry on surface integrity of high-speed turned Inconel 718

Stringent control on the quality of machined surface and sub-surface during high-speed machining of Inconel 718 is necessary so as to achieve components with greater reliability and longevity. This paper extends the present trend prevailing in the literature on surface integrity analysis of superalloys by performing a comprehensive investigation to analyze the nature of deformation beneath the machined surface and arrive at the thickness of machining affected zone (MAZ). The residual stress analysis, microhardness measurements and degree of work hardening in the machined sub-surfaces were used as criteria to obtain the optimum machining conditions that give machined surfaces with high integrity. It is observed that the highest cutting speed, the lowest feedrate, and the moderate depth of cut coupled with the use of honed cutting edge can ensure induction of compressive residual stresses in the machined surfaces, which in turn were found to be free of smeared areas and adhered chip particles.     

Dynamic variable depth of cut machining using piezoelectric actuators

This paper describes the design of a piezoelectric actuated cutting tool and implementation of digital servo controls for machining surfaces with dynamically varying depth of cut. Through a flexure hinge, the tool holder could generate 50 μm travel at the tip of the cutting insert. Tool motion errors of less than 0.5 μm were achieved in tracking cyclic waveforms by employing a digital repetitive servo control. When applied to turning aluminum and steel workpieces with variable depth of cut using carbide tools, less than 5 μm machined surface errors were measured.     

Influences of chip serration on micro-topography of machined surface in high-speed cutting

Saw-tooth chip changes from macroscopically continuous ribbon to separated segments with the increase of cutting speed. The aim of this study is to find the correlations between chip morphology and machined surface micro-topography at different chip serration stages encountered in high speed cutting. High strength alloy steel AerMet100 was employed in orthogonal cutting experiments to obtain chips at different serration stages and corresponding machined surfaces. The chips and machined surfaces obtained were then examined with optical microscope (OM), scanning electron microscope (SEM), and white light interferometer (WLI). The result shows that chip serration causes micro-waves on machined surface, which increases machined surface roughness. However, wave amplitudes (surface roughness) at different serration stages are different. The principal factor influencing wave amplitude is the thickness of the sawed segment (tooth) of saw-tooth chip. With cutting parameters in this study, surface roughness contributed by chip serration ranges from 0.39 μm to 1.85 μm. This may bring on serious problems in the case of trying to replace grinding with high-speed cutting in rough machining. Some suggestions have been proposed to control the chip serration-caused surface roughness in high-speed cutting based on the results of the current study.     

718铬镍铁合金热车削比切削能的仿真与实验分析

对热加工镍基合金进行了仿真和实验研究。在大量火焰加热和室温切削条件下,采用氧气和液化石油气加热,用无涂层硬质合金刀片分别以切削速度66、188 m/min,进给速度0.1、0.15 mm/r和恒定的切削深度对718铬镍铁合金进行加工。以测量比切削能、切削力为重点,对室温和加热条件下的加工过程进行了实验分析。采用有限元软件对718铬镍铁合金的热车削过程进行了分析。结果表明：与室温条件相比,在加热温度下切削力和比切削能有所降低,仿真结果与实验结果一致。     

切削条件对已加工表面残留应力的影响

用X射线应力测量仪测量了不同切削条件下铝合金工件表面的残留应力。结果表明,硬质合金刀具薄切削铝合金时,切削速度、进给量、切削深度对已加工表面残留应力的影响具有不同的规律。     

Performance parameters studies in machining of AISI D2 steel with dot-textured,groove-textured & non-textured cutting tool at the flank face

Surface texturing is a method where there is a change in tribological properties due to change in surface characteristics. The present work is a comparison of the performance of dot-textured coated carbide tool with groove-textured and non-textured coated carbide tool in machining AISI D2 steel. Micro dot textures are made on the flank face using micro-electric discharge machining. Considering full factorial design, total 8 experiments are performed with cutting speed, feed and depth of cut as process parameters. For each parameter, two levels are considered. Flank wear and surface roughness are investigated to compare the function of dot-textured coated carbide tool with the groove-textured and non-textured coated carbide tool. In every condition, flank wear is less in machining with both types of textured tool in comparison to the non-textured coated carbide tool. In most of the cases, surface roughness is less for both types of textured tool than the non-textured tool. Comparing dot-textured tool over groove-textured tool, it is observed that dot-textured tool is better than the groove-textured tool in reducing flank wear and surface roughness. Analysis of white layer and micro hardness at the machined surfaces revealed that dot-texturing helps in minimizing the thickness of white layer and micro-hardness property in comparison to groove-textured and non-textured tool. Thus, dot texturing is found to be better in improving machinability than groove-textured and non-textured tool.     

Evaluation of the performance of CBN tools when turning Ti–6Al–4V alloy with high pressure coolant supplies

Cubic Nitride Boron (CBN) tools are generally used for machining harder alloys such as hardened high Cr steels, titanium and nickel alloys. The tools are expected to withstand the heat and pressure developed when machining at higher cutting conditions because of their high hardness and melting point. This paper evaluates the performance of different CBN tool grades in finish turning Ti–6Al–4V (IMI 318) alloy at high cutting conditions, up to 250 m min⁻¹, with various coolant supplies. Tool wear, failure modes, cutting and feed forces and surface roughness of machined surfaces were monitored and used to access the performance of the cutting tools. Comparative trials were carried out with uncoated carbide tools when machining at a speed of 150 m min⁻¹. Test results show that the performance of CBN tools, in terms of tool life, at the cutting conditions investigated is poor relative to uncoated carbide tools, as expected and often, reported due probably to rapid notching and excessive chipping of the cutting edge associated with a relatively high diffusion wear rate that tends to weaken the bond strength of the tool substrate. An increase in the CBN content of the cutting tool also led to a reduction in tool life when machining at the cutting conditions investigated.     

切削速度对切屑形态和加工表面微观形貌的影响

为了研究钛合金车削过程中切削速度和切屑形态特征对已加工表面微观形貌的影响。采用硬质合金涂层刀具车削钛合金TC4,研究了切削速度对切屑形态特征、已加工表面粗糙度和轮廓最大高度的影响规律,分析了切屑底部毛边形貌、已加工表面形貌与表面粗糙度三者之间的关系。结果表明:在切削速度40~120m/min时,切屑底边出现锯齿形毛边,且随切削速度增大锯齿越明显。切屑底部锯齿毛边的形成是造成已加工表面波峰损伤形成的主要原因。影响已加工表面粗糙度的微观形貌特征包括硬质颗粒、粘结现象和波峰损伤。因此,为了获得高质量的加工表面,加工参数选择时必须规避硬质颗粒和严重的粘结现象,并控制切屑底部毛边形态特征。     

Fabrication of deep micro-holes in reaction-bonded SiC by ultrasonic cavitation assisted micro-EDM

Ultrasonic vibration was applied to dielectric fluid by a probe-type vibrator to assist micro electrical discharge machining of deep micro-holes in ceramic materials. Changes of machined hole depth, hole geometry, surface topography, machining stability and tool material deposition under various machining conditions were investigated. Results show that ultrasonic vibration not only induces stirring effect, but also causes cloud cavitation effect which is helpful for removing debris and preventing tool material deposition on machined surface. The machining characteristics are strongly affected by the vibration amplitude, and the best machining performance is obtained when carbon nanofibers are added into the vibrated dielectric fluid. As test pieces, micro-holes having 10 μm level diameters and high aspect ratios (>20) were successfully fabricated on reaction-bonded silicon carbide in a few minutes. The hybrid EDM process combining ultrasonic cavitation and carbon nanofiber addition is demonstrated to be useful for fabricating microstructures on hard brittle ceramic materials.     

Machining characteristics and fracture morphologies in a copper-beryllium (Cu-2Be) alloy

The technology of materials removal is improved greatly by the introduction of advanced cutting tools like cubic boron nitride, ceramics, polycrystalline diamond and the more recent whisker-reinforced materials. In this paper, the influence of cutting temperature on machinability, mechanical properties, microstructure, and fracture morphology of Cu-2Be alloy using a polycrystalline diamond cutter is investigated. The information on machining, microstructure, and fracture morphology of Cu-2Be alloy are very useful to understand their fabrication characteristics and the basic mechanisms of its deformation and fracture. The machinability (in terms of surface finish) of Cu-2Be alloy is evaluated as a function of cutting temperature, resulting from wet and dry cutting. Machining is carried out on a Hardinge Cobra 42 CNC machine (Hardinge Inc., Elmira, NY), and the machining parameters used—cutting speed, depth of cut, and feed rate—are kept constant during both wet and dry cutting. The machined surface finish on Cu-2Be alloy is measured using a surface finish analyzer (Surftest 401, series 178) technique. The machined specimens are examined for their strength and hardness properties using a standard Universal Testing Machine and Rockwell hardness tester, respectively. Wet cutting (using coolants) produced a smooth surface finish when compared with dry cutting of the Cu-2Be alloy. The machined specimens are examined for their microstructural features using a Nikon optical microscope. The specimens are etched using a suitable etchant solution for revealing such microstructure constituents as grain size, phase proportions, and the possible overheated areas (especially in dry cutting). The fractured surfaces from the tensile and impact toughness tests are investigated for their fracture morphologies (dry and wet cutting) using a microprocessor-controlled scanning electron microscope (Jeol Model JSM 5910 LV). A detailed analysis is also made to understand and interpret the basic fracture mechanisms responsible for crack initiation and crack propagation. The Cu-2Be alloy showed relatively higher mechanical properties in wet cutting in comparison to dry cutting operations. Fracture studies demonstrated intergranular and ductile fractures as dominant modes of fracture mechanisms in Cu-2Be alloy.     

–50 ℃冷风条件下抛光硬质合金刀片加工TC4钛合金的表面粗糙度分析

目的提高硬质合金刀片加工TC4钛合金的表面质量。方法利用化学机械抛光技术对传统磨削的硬质合金刀片分别进行粗抛、半精抛和精抛处理,运用正交试验法,在常温干切和–50℃冷风条件下,分别采用传统磨削的硬质合金刀片(磨削刀片)与化学机械抛光的硬质合金刀片(抛光刀片)进行切削TC4钛合金正交试验,利用方差分析法分析切削参数对已加工表面粗糙度Ra的影响。运用多元线性回归方法建立磨削刀片、抛光刀片在常温干切和–50℃冷风条件下切削TC4钛合金已加工表面粗糙度Ra的经验预测模型。结果硬质合金刀片前刀面通过粗抛、半精抛和精抛后,刀片前刀面的表面粗糙度Ra为19 nm。当切削参数相同时,磨削刀片在–50℃冷风条件下切削TC4钛合金的已加工表面粗糙度,比常温干切条件下平均降低了35.9%;抛光刀片在–50℃冷风条件下切削TC4钛合金的已加工表面粗糙度,比常温干切条件下平均降低了43.5%。在常温干切条件下,抛光刀片比磨削刀片切削TC4钛合金的已加工表面粗糙度平均降低了19.2%;在–50℃冷风条件下,抛光刀片比磨削刀片切削TC4钛合金的已加工表面粗糙度平均降低了28.7%。抛光刀片在–50℃冷风条件下切削TC4钛合金的已加工表面粗糙度Ra,比磨削刀片在常温干切条件下切削TC4钛合金的已加工表面粗糙度Ra平均降低了54.4%。结论采用对硬质合金刀片表面进行化学机械抛光技术和以–50℃冷风为切削介质的组合工艺,可有效降低TC4钛合金已加工表面粗糙度。     

聚晶立方氮化硼刀具刃口放电加工工艺研究

通过调整电火花加工的主要放电参数（脉冲宽度和加工电流）,对聚晶立方氮化硼（PCBN）4~进行放电加工,进而对样刀刃口表面进行x射线衍射分析,并在扫描电子显微镜下观察其表层结构及能谱分析。通过对加工后样刀表面变质层主要成分及产生原因的分析,总结了脉冲宽度和加工电流对样刀表面变质层厚度、刃口表面粗糙度影响的关系曲线,为制定精密快速放电加工PCBN刀具的工艺提供了重要依据。     

Cutting process of glass with inclined ball end mill

Cutting processes with ball end mills are discussed for machining microgrooves on glasses. A surface is finished in undeformed chip thickness less than 1 μm at the beginning and at the end of the cut during the cutter rotation. The milling process is applied to glass machining. A crack-free surface can be finished in a large axial depth of cut more than 10 μm. Because glass undergoes almost no elastic deformation, roughness on a cutting edge in glass machining has a larger influence on surface finish than that of metal machining. The rotational axis of the tool is inclined to improve the surface finish. The cutting processes are modeled to show the effect of the tool inclination on the machined surface with considering the edge roughness. The tool inclination compensates for deterioration of the surface finish induced by the edge roughness in the presented model. The improvement of the surface finish is verified in the cutting experiments with the tool inclination. The orthogonal grooves 15–20 μm deep and 150–175 μm wide, then, are machined with the crack-free surfaces to prove efficiency and surface quality in the milling process.