Suppression of notch wear of a whisker reinforced ceramic tool in air-jet-assisted high-speed machining of Inconel 718

This paper describes the notch and flank wear specific to a SiC whisker reinforced alumina tool in air jet assisted (AJA) turning of nickel-base superalloy Inconel 718 at high cutting speeds. An AJA machining experiment has revealed that the air jet applied to the tool tip in addition to coolant dramatically reduces the depth-of-cut notch wear. As a result, the width of flank wear, but not the size of notch wear, determined the life of a ceramic tool in AJA machining of Inconel 718. This is a reason for the large extension and small variation of the tool life when high speed AJA machining is adopted. The maximum tool life length reached 2160 m at a cutting speed of 660 m/min under the given cutting conditions. Finally, the mechanisms of the notch and flank wear of a SiC whisker reinforced alumina tool in AJA machining are discussed from the viewpoints of tribochemical reactions and tool wear anisotropy.     

高速雕铣硬质红木的微织构刀具的磨损行为研究

针对硬质红木的高速雕铣加工性差、刀具磨损严重及生产效率低的缺点,利用光纤激光对其硬质合金刀具表面设计不同形状和大小的微织构,通过高速雕铣机测试及生产线现场加工试验,并借助光学显微镜、扫描电镜和Kistler测力仪等,分析硬质红木在高速铣削过程中表面微织构铣刀前后刀面的磨损形态、铣削力与刀具磨损的关系。试验结果表明:前后刀面都有磨损且主要类型为磨粒磨损、粘结剂磨损和氧化磨损;铣削力与表面微织构的刀具磨损不是纯粹的正相关关系,刀具最大应力点不断变化,有利于降低磨损;在织构的形状方面,相对于网格织构,同样间隔大小和深度的圆形织构和平行织构的刀具减磨效果更好;圆形凹坑织构比圆形凸起织构的减磨效果好;直径为30μm,间距80μm×80μm的圆形凹坑的减磨效果较好。     

Development of a novel cubic boron nitride cutting tool with a textured flank face for high-speed machining of Inconel 718

Nickel-based superalloys such as Inconel 718 offer several advantages, including high-temperature strength and high corrosion resistance; this has led to a rapid increase in the demand for such materials, particularly in the aircraft industry. In contrast, these alloys are known to be among the most difficult-to-cut materials because of their mechanical and chemical properties, and tools used for this purpose have extremely short lifetimes. Recently, cubic boron nitride (CBN), which is the second hardest of all known materials, has received significant attention as a material for cutting tools and has already established itself in many fields of application. However, the performance of CBN tools is still insufficient for practical use, especially in the high-speed machining of Inconel 718. To overcome this problem, we first conducted orthogonal cutting experiments on Inconel 718 and performed cross-sectional observations of the CBN cutting tool in order to identify its wear mechanisms in continuous cutting operations under high-speed machining conditions (300 m/min). As a result, it was found that fatal tool failure occurs through crater and flank wear because of diffusion led by high cutting temperatures and subsequent chip adhesion to the tool flank face, accompanied by cutting edge chipping. Based on these results, a CBN cutting tool with a textured flank face was newly developed to improve the cutting tool life. Experimental: results showed that micro grooves generated on the flank face significantly suppressed the cutting edge chipping and remarkably extended the lifetime of the CBN tool during high-speed machining of Inconel 718.     

变密度微织构球头铣刀切削性能多目标优化

为深入研究微织构排列形式对微织构理刀具的抗磨减摩机理的影响,分别从理论、仿真及试验等方面对最优的微织构排布形式进行研究。首先,建立微织构在刀具前刀面的数学模型及仿真模型。其次,通过试验验证仿真结果的准确性。仿真及试验研究均发现,变密度微织构球头铣刀的铣削性能优于均匀分布密度的微织构球头铣刀。最后,运用模糊评价法优选最优的铣削性能的微织构球头铣刀,优化结果表明,两排织构间距先为200 μm,再为150 μm,最后为175 μm的微织构球头铣刀的铣削性能最好。该项研究使刀具具有良好的抗磨减磨性,提高加工效率及被加工工件的表面质量。     

Wear mechanism of coated tools in the turning of ductile cast iron having wide range of tensile strength

In this study different specimens of ductile cast iron with tensile strength ranking from 400 MPa to 675 MPa were turned with K15 carbide, TiN coated and TiAlN coated tool in order to investigate wear mechanism and performance. Cutting forces and cutting temperature were similar for both coated tools, however flank wear and BUE were the lowest on the TiAlN coated tool, for this reason the TiAlN coated tool is suitable in the machining of ductile cast iron. The proposed tool wear mechanism is based on like-intermittent cutting caused by the pass from hard matrix to the soft graphite occasioning wear by adhesion. The analysis of the flank wear on coated tools is proposed by means of the wear curves in logarithmic scale instead of the usual linear scale. In this way, the change in wear rate is easily observed. This phenomenon was related with the wear out of the coating layer. The partial loss of the coating layer on cutting edge was confirmed by the EDS mapping images and SEM photographs.     

Tool wear analysis and improvement of cutting conditions using the high-pressure water-jet assistance when machining the Ti17 titanium alloy

This paper presents experimental results concerning the machinability of the titanium alloy Ti17 with and without high-pressure water jet assistance (HPWJA) using uncoated WC/Co tools. For this purpose, the influence of the cutting speed and the water jet pressure on the evolution of tool wear and cutting forces have been investigated. The cutting speed has been varied between 50 m/min and 100 m/min and the water jet pressure has been varied from 50 bar to 250 bar. The optimum water jet pressure has been determined, leading to an increase in tool life of approximately 9 times. Compared to conventional lubrication, an increase of about 30% in productivity can be obtained.     

3D characterisation of tool wear whilst diamond turning silicon

Nanometrically smooth infrared silicon optics can be manufactured by the diamond turning process. Due to its relatively low density, silicon is an ideal optical material for weight sensitive infrared (IR) applications. However, rapid diamond tool edge degradation and the effect on the achieved surface have prevented significant exploitation. With the aim of developing a process model to optimise the diamond turning of silicon optics, a series of experimental trials were devised using two ultra-precision diamond turning machines. Single crystal silicon specimens (1 1 1) were repeatedly machined using diamond tools of the same specification until the onset of surface brittle fracture. Two cutting fluids were tested. The cutting forces were monitored and the wear morphology of the tool edge was studied by scanning electron microscopy (SEM).The most significant result showed the performance of one particular tool was consistently superior when compared with other diamond tools of the same specification. This remarkable tool performance resulted in doubling the cutting distance exhibited by the other diamond tools. Another significant result was associated with coolant type. In all cases, tool life was prolonged by as much as 300% by using a specific fluid type.Further testing led to the development of a novel method for assessing the progression of diamond tool wear. In this technique, the diamond tools gradual recession profile is measured by performing a series of plunging cuts. Tool shape changes used in conjunction with flank wear SEM measurements enable the calculation of the volumetric tool wear rate.     

Experimental evaluation on micro-texture parameters of carbide ball-nosed end mill in machining of titanium alloy

Parametric optimisation of micro-texture is important to improve the performance of cutting tool in metal cutting. In this study, the simulation models of micro-textured surface of cemented carbide are established by using ABAQUS platform, and fictitious stress distribution is analysed to select the optimum micro-texture structure. Then, many friction tests were carried out to compare the several different micro-textures. Based on the experimental data, the parametric optimisation model of micro-texture on cemented carbide surface is established, and its significant analysis is carried out. Moreover, the optimised parameters are applied to the ball-nose end mill in the machining of titanium alloy. The results show that the micro-texture can absorb stress and change the status of stress distribution on the surface. Among the micro-texture structures, the performance of micro-pit is the best one, i.e. surface stress micro-pit-texture is distributed uniformly, and the stress concentration micro-pit-texture is low, when the micro-pit-texture’s diameter is 46.6 μm, its depth is 27 μm, and its distance is 123 μm. The ball-nosed end mill with the optimised parameters has a stronger wear resistance than a normal tool.     

原位成型微织构自润滑陶瓷材料的制备及其性能研究

表面织构具有改善表面润滑状态和减摩抗磨的作用,在工程领域的应用也越来越广。现有的微织构加工方法很多,但成本较高,且加工周期长。本试验提出了原位成型的加工方法,以石墨为微织构凸模,设计、加工了沟槽型微织构,经热压烧结工艺将微织构置入到陶瓷粉体中,原位成型表面微织构陶瓷材料。对所得材料进行力学性能测试和摩擦磨损试验,用扫描电镜(SEM)观察裂纹、断面形貌以及磨损表面。结果表明:沟槽型织构材料的断裂韧性和抗弯强度分别为7.4MPa·m~(1/2)和504.8MPa,比无织构材料分别提高了约0.4%和12.3%;沟槽型织构试样摩擦系数较为平稳,且与无织构试样相比,最大摩擦系数和最小摩擦系数分别减少了约33.3%和18.2%;沟槽型织构试样的磨损形式主要是磨粒磨损,无织构试样的磨损形式主要是粘结磨损。     

Cutting performance of nano-crystalline diamond (NCD) coating in micro-milling of Ti6Al4V alloy

Hard coatings are an important factor affecting the cutting performance of tools. In particular, they directly affect tool life, cutting forces, surface quality and burr formation in the micro-milling process. In this study, the performance of nano-crystalline diamond (NCD) coated tools was evaluated by comparing it with TiN-coated, AlCrN-coated and uncoated carbide tools in micro-milling of Ti₆Al₄V alloy. A series of micro-milling tests was carried out to determine the effects of coating type and machining conditions on tool wear, cutting force, surface roughness and burr size. Flat end-mill tools with two flutes and a diameter of 0.5 mm were used in the micro-milling process. The minimum chip thickness depending on both the cutting force and the surface roughness were determined. The results showed that the minimum chip thickness is about 0.3 times that of the cutter corner radius for Ti₆Al₄V alloy and changes very little with coating type. It was observed from wear tests that the dominant wear mechanism was abrasion. Maximum wear occurred on NCD-coated and uncoated tools. In addition, maximum burr size was obtained in the cutting process with the uncoated tool.     

Hard turning using HiPIMS-coated carbide tools: Wear behavior under dry and minimum quantity lubrication (MQL)

In the present work, experimental investigations carried out to assess the applicability of HiPIMS (High Power Impulse Magnetron Sputtering)-coated carbide tools to hard turning (55 HRC) and to address the widely debated topic about the use of coolants in hard turning are presented. Tool wear progressions and hence, tool life, different tool wear forms and wear mechanisms observed for tools coated with HiPIMS coating technique, namely, nanocomposite AlTiN, nanocomposite multi-layer TiAlN/TiSiN and nanocrystalline AlTiCrN are presented along with the images captured by digital and electron microscope. Characterization results of all the coated tools in terms of their average coating thickness (measured using Calotest and Fractographs), adhesion strength of the coating(s) (determined using Scratch test), composition and microhardness (using EDAX and Vickers microhardness test, respectively) are presented. Experimental observations indicate higher tool life with nanocrystalline AlTiCrN coated carbide tools which shows encouraging potential of these tools to hard turning. Improvement in tool life of almost 20–25% has been observed under minimum quantity lubrication (MQL) due to better cooling and lubricating effects. However, this effect was more prominent at higher cutting speed of 150 m/min.     

硬质合金刀具高速车铣和铣削TC4钛合金磨损试验对比

采用H13A未涂层硬质合金刀具对TC4钛合金进行高速正交车铣和铣削试验,并从刀具磨损破损形态、磨损机理及其寿命等方面进行对比分析。研究表明:高速正交车铣和铣削钛合金时,前、后刀面主要以粘结磨损为主,车铣加工时在切削刃口易形成积屑瘤及连续切屑,但对刀具材料粘结较轻;高速铣削时,对刀具材料粘接较重,在前刀面刃口附近形成凹坑及崩刃;后刀面最大磨损的位置不相同。试验对比了相同切削条件时刀具使用寿命,结果表明采用正交车铣加工可以获得更长的刀具使用寿命。     

The effect of oil mist supply on cutting point temperature and tool wear in driven rotary cutting

We examined cutting point temperature and tool wear in driven rotary cutting. Cutting tests under dry and minimum-quantity-lubrication (MQL) conditions of stainless steel (SUS304) were carried out. Cutting point temperature was measured using a tool-work-thermocouple method at various cutting speeds. Cutting point temperature tends to increase with increased cutting speed. In driven rotary cutting, cutting point temperature was lower than that of non-rotation cutting. At high-speed cutting of 500 m/min, cutting point temperature was over 1200 °C in the non-rotation tool, but 1000 °C with driven rotary cutting. In addition, when driven rotary cutting was used with MQL, cutting point temperature was decreased to 900 °C. The magnitude of tool wear corresponded almost precisely to cutting point temperature. Severe adhesion on the rake face was observed and resulted in progressive wear on the rake face in rotary cutting at a cutting speed of 100 m/min. The appropriate cutting speed range passively shifts higher from the viewpoint of cutting temperature with rotary cutting.     

Crater and flank wear resistance of cutting tools having micro textured surfaces

We have proposed cutting tools with various textured surfaces to increase cutting tool life. Our previous studies have developed cutting tools having periodical stripe-grooved surfaces on their rake face formed using femtosecond laser technology, which displayed high crater wear resistance in cutting of steel materials. In this study, the mechanism for suppressing the crater wear on the tool surface and the relationship between texture dimensions and wear resistance were investigated to provide a guideline for developing tools with textured surfaces. Furthermore, we newly introduced the textured surfaces into a flank face of cutting tools to improve flank wear resistance. Face milling experiments on steel materials exhibited that the newly developed tool having the textured flank face significantly reduced the flank wear. Moreover, the influences of texture dimensions and cutting conditions on the flank wear resistance were also discussed.     

Minimal quantity lubrication in turning: Effect on tool wear

Industries and researchers are trying to reduce the use of coolant lubricant fluids in metal cutting to obtain safety, environmental and economical benefits. The aim of this research is to determine if the minimal quantity lubrication (MQL) technique in turning gives some advantages in terms of tool wear reduction. This paper reports the results obtained from turning tests and SEM analysis of tools, at two feed rates and two cutting lengths, using MQL on the rake and flank of the tool. The results obtained show that when MQL is applied to the tool rake, tool life is generally no different from dry conditions, but MQL applied to the tool flank can increase tool life.     

微织构(W,Mo)C基刀具和YG8刀具对钛合金干切削性能的影响

刀具切削钛合金时存在切削温度高、单位面积上切削力大等问题,微织构刀具可以有效减小摩擦力,减小切削力。通过正交实验法设计微织构参数,研究微织构参数对Al 2O 3/La 2O 3/(W,Mo)C无黏结相硬质合金刀具以及YG8刀具切削钛合金实验的切削性能影响。实验结果表明,合适参数的沟槽型微织构能有效降低Al 2O 3/La 2O 3/(W,Mo)C无黏结相硬质合金刀具和YG8刀具切削TC4钛合金的切削力,相同沟槽参数下,无黏结相硬质合金刀具的切削力明显低于YG8刀具的切削力;合适参数的沟槽型微织构能有效降低刀具刀屑界面的摩擦系数,相同沟槽参数下,无黏结相硬质合金刀具的摩擦系数大都低于YG8刀具的摩擦系数;沟槽深度10μm、沟槽间距100μm以及沟槽宽度30μm的沟槽参数下,切削钛合金时,无黏结相硬质合金刀具前刀面无明显磨损,后刀面只有边界磨损,YG8刀具发生崩刃,前刀面出现切屑的滞留。     

High-precision and high-efficiency machining of scroll compressor components

Fixed and orbiting scrolls of scroll compressor components have spiral grooves known as scroll wraps. High-precision contour milling using end mills is the best method to produce these scrolls. The aim of our present work is to recognize the mechanism of tool wear on end mills in bottom face machining and to reduce tool wear in highly efficient milling. This paper describes an effective coolant supply system to the cutting point and an appropriate tool geometry developed in the study. The following conclusions can be drawn: (1) By supplying coolant to the cutting edge through the center hole of the tool at a cutting speed of 230 m/min, the wear rate of the flank wear can be reduced to approximately 1/50 of the wear observed in conventional coolant supply. (2) The optimal back clearance angle is 5° for abrasive resistance in the turning operation. (3) By applying 5° to the back clearance angle, the wear rate of the corner edge can be reduced to 1/6 of that observed when the back clearance angle was 15°.     

Detection of chipping in ceramic cutting inserts from workpiece profile during turning using fast Fourier transform (FFT) and continuous wavelet transform (CWT)

Ceramic cutting tool inserts are prone to premature failure by chipping instead of gradual wear due to their low impact toughness. Thus, in-process detection of failure of ceramic tools is important to prevent workpiece surface deterioration. The objective of this study is to develop a method of detection of the onset of chipping in ceramic cutting tool inserts during dry finish turning from the workpiece profile signature. The profile of the workpiece surface opposite the cutting side was captured using an 18-MP DSLR camera at a shutter speed of 0.25 ms during the turning of AISI01 oil-hardening tool steel. The edge profile was extracted to sub-pixel accuracy from the 2-D image of the workpiece surface using the invariant moment method. The effect of chipping in the ceramic insert on the surface profile signature of the workpiece was investigated using the fast Fourier transform (FFT) and continuous wavelet transform (CWT). The results show that the stochastic behavior of the cutting process after tool chipping manifest as sharp increase in the amplitude of spatial frequencies below the fundamental feed frequency. The proposed sub-window FFT method is effective in resolving the time resolution by detecting tool chipping at cutting time duration of around 17.13 s. Compared to the sub-window FFT method the CWT method is able to detect the exact onset of chipping in the cutting tool insert.     

Evaluation of Minimal of Lubricant in End Milling

When considering machinability parameters, the use of coolant is indispensable in metal cutting operations. However, stricter environmental regulations are making the use of an ample amount of conventional coolant impossible because of its negative impact on the environment. Consequently, the use of minimal quantities of lubricant (MQL) can be regarded as an alternative solution in which the functionality of cooling and lubrication can be achieved by a tiny amount of cutting oil. In this study, flood coolant (42 l min _1) was used compared to the MQL amount of 8.5 ml h_1 and the comparative effectiveness was investigated in terms of cutting force, tool wear, surface roughness, and chip shape. Unlike the catastrophic tool failure in flood cooling, the use of MQL resulted in the cutting edge remaining intact, in spite of a higher flank width. The findings of this study show that MQL may be considered to be an economical and environmentally compatible lubrication technique.     

Optimization of surface roughness and flank wear using the Taguchi method in milling of Hadfield steel with PVD and CVD coated inserts

In this paper, the Taguchi method and regression analysis have been applied to evaluate the machinability of Hadfield steel with PVD TiAlN- and CVD TiCN/Al₂O₃-coated carbide inserts under dry milling conditions. Several experiments were conducted using the L₁₈ (2 × 3 × 3) full-factorial design with a mixed orthogonal array on a CNC vertical machining center. Analysis of variance (ANOVA) was used to determine the effects of the machining parameters on surface roughness and flank wear. The cutting tool, cutting speed and feed rate were selected as machining parameters. The analysis results revealed that the feed rate was the dominant factor affecting surface roughness and cutting speed was the dominant factor affecting flank wear. Linear and quadratic regression analyses were applied to predict the outcomes of the experiment. The predicted values and measured values were very close to each other. Confirmation test results showed that the Taguchi method was very successful in the optimization of machining parameters for minimum surface roughness and flank wear in the milling the Hadfield steel.