Research on surface integrity of grinding Inconel718

Inconel718 is widely used in the aerospace industry; the finished surface quality has significant effect on service performance of component. The surface integrity in grinding Inconel718 respectively by using a vitrified bond single alumina (SA) wheel and a resin cubic boron nitride (CBN) wheel were investigated. First, effects of different grinding parameters on grinding temperature and grinding force and grinding chips feature by using a SA and a CBN wheel respectively were investigated. Then, the surface roughness and topography by using a SA and a CBN wheel through single factor experiment were compared, and in the grinding parameters range of the present study, the better surface can be obtained by a SA wheel. Finally, surface integrity by using a SA wheel and the different grinding depth was studied and analyzed by the grinding temperature and the grinding force. It was possible to conclude that better surface can be achieved by using a SA, and taking a _p?=?0.005 mm, v _w?=?16 m/min, v _s?=?25 m/s for grinding Inconel718. In this grinding case, the surface roughness was Ra0.112 μm, the surface residual stress was +700Mpa, and the surface hardness was 440 HV; the depth of residual stress layer was 40～60 μm, the depth of softened layer was 30～40 μm and the depth of plastic deformation layer was 10～15 μm.     

Study on the mechanism and the suppression method of wrinkling in side wall using hydroforming of the fairing

Ultrasonic assisted grinding (UAG) is an outstanding technology suitable to machine advanced ceramics. During UAG, the effect of ultrasonic vibration on grinding process is mainly determined by matching performance between grinding and vibration parameters in theory. However, this problem is still lack of deep study. With an objective to study the matching performance deeply, conventional grinding (CG) and UAG tests were conducted. The effects of grinding parameters on grinding force, ground surface profile wave, and ground surface roughness between UAG and CG were studied. The results showed that the grinding force, ground surface profile wave height, and ground surface roughness during UAG were reduced in varying degrees compared to CG. Additionally, the reduction percentage that means the effect of ultrasonic vibration on grinding process decreased significantly with increasing grinding speed while affected slightly by increasing of feedrate and grinding depth. To deeply analyze this variety law of the ultrasonic vibration effect during UAG, a matching performance equation referred to grinding wheel diameter, grinding, and vibration parameters is proposed. When the grinding speed increases from 1.26 to 31.5 m/s for feedrate of 100 mm/min and grinding depth of 5 μm, reduction percentage in grinding force for UAG compared to CG (K _F) decreases from about 20 to 4 % and in ground surface roughness (K _R) decreases from 35 to 4 %. With regard to the average difference height (Δh) between the UAG and CG profile waves, it decreases from 2.77 μm almost to zero.     

Grindability of high-temperature alloy with ceramic alumina wheels

The grindability of high-temperature alloy by using ceramic alumina wheels is studied on the basis of extensive analysis of the grinding force, grinding temperature, surface roughness and topography of ground surfaces, residual stress, hardness distribution of surface layer, and morphology of the surface layer from a metallographic point of view. The grinding burn mechanism of high-temperature alloy is unveiled and the feasible grinding parameters to avoid burning are analyzed. Some conclusions are obtained as follows. Increasing the grinding depth or the wheel velocity makes grinding temperature and residual tensile stress of the surface rise, which deteriorates the surface topography. Appropriate liner velocity of the wheel is 18–22 m/s and the depth of grinding should not exceed 0.02 mm in grinding GH2132 alloy with ceramic alumina wheels to assure the surface quality. When a _p increases enough to cause grinding burn, the strengthening effect of particles γ′ in γ base decrease and the micro-hardness of the surface is obviously lower than that of the base material, which deteriorates the mechanical properties and heat resistance of GH2132 alloy. Results provide a theoretical and experimental basis for technical optimization in the grinding of high-temperature alloy with high efficiency and high quality.     

Edge burr development when using a cemented carbide micro-drill: Formation and control mechanisms

To explore the mechanism of formation and methods of control of edge burr in the grinding and forming of cemented carbide micro-drill, the morphology, material composition, and the edge structure of the generated area of the edge burrs are studied. Through indentation and scratch experiments, the critical grinding depth (h_c) of grinding machining is calculated to be 0.793–1.052 μm. The grinding experiments have verified the effects of the actual grinding depth h₀ of different single abrasive particles on the edge burr and the effectiveness of the method of controlling the burr by increasing the cutting angle of the abrasive particles. The experimental results show that edge burrs are mainly concentrated on the cutting edge close to the outer cylinder of the micro-drill. When the actual grinding depth h₀ of a single abrasive particle is less than the critical grinding depth h_c, workpiece material is mainly subjected to plastic deformation removal, the length L of the edge burr along the edge direction is 10–20 μm, the width W of the burr perpendicular to the edge direction is 1–3 μm. The formation of edge burrs is mainly related to the actual grinding depth and the abrasive grain cutting angle γ of abrasive grains. With the increase of h₀, the length L of the edge burr decreases, and the width W thereto first increases, then decreases. Increasing the cutting angle of abrasive particles can control the edge burr. By changing the grinding direction of the grinding wheel, the cutting angle of the abrasive particles can be changed from an acute angle to an obtuse angle, thereby eliminating the edge burr without affecting the performance of micro-drilling.     

18CrNiMo7-6钢高速外圆磨削的残余应力

为探究高速外圆磨削工艺对18CrNiMo7-6钢残余应力层分布的影响,使用陶瓷结合剂CBN砂轮进行高速磨削试验,对砂轮线速度vs、工件线速度vw、砂轮径向进给速度vfr和砂轮粒度等工艺参数进行了单因素试验分析;设计制作了圆柱工件外圆面辅助剖层夹具,采用X射线衍射仪对工件应力分布进行检测。研究结果表明：高速磨削工艺为工件表面引入残余压应力,工件表面残余压应力随vs的提高小幅增大,vw和vfr对工件表面残余应力的影响规律不明显;X、Y方向的残余应力分布趋势基本一致,但Y方向的应力略大;vfr对残余应力分布影响较大,应力影响层深达到100～150 μm,应力分布中出现残余拉应力;vs对残余应力分布的影响小于vfr的影响,60 m/s时的残余应力呈“塔”形分布;vw没有明显影响规律;230/270粒度的砂轮对残余应力分布影响较大,应力影响层深为80～100 μm,120/140、W20粒度的砂轮影响较为接近;辅助剖层夹具有效提高了圆柱工件残余应力的检测精度和效率,检测效率提高一倍以上。     

Precision grinding of bearing steel based on active control of oxide layer state with electrolytic interval dressing

The oxide layer state directly relates to machining quality in electrolytic in-process dressing (ELID) grinding. In this paper, intermittent grinding control strategy was used to monitor and control the state of the oxide layer in interval ELID (ELID II) grinding. Some experiments were implemented based on active control of the oxide layer state. The influence of dressing current, wheel speeds, and grit size on surface roughness and waviness has been discussed in detail with ELID II grinding for bearing steel. The experimental results illustrate that the ELID II method can realize a stable grinding process based on active control of the oxide layer state. The surface roughness (Ra) and waviness (Wa) increase with increase of the dressing current. When the dressing current is constant, Ra and Wa reduce as wheel speed increases and decrease as grain size of wheel decreases. The experimental results also show that sufficient abrasive protrusion can be ensured in ELID II grinding, especially for grinding with a W2.5 super-abrasive wheel which may produce a very smooth surface quality, Ra 0.0166 μm and Wa 0.018 μm.     

Grindability of high-temperature alloy with ceramic alumina wheels

The grindability of high-temperature alloy by using ceramic alumina wheels is studied on the basis of extensive analysis of the grinding force, grinding temperature, surface roughness and topography of ground surfaces, residual stress, hardness distribution of surface layer, and morphology of the surface layer from a metallographic point of view. The grinding burn mechanism of high-temperature alloy is unveiled and the feasible grinding parameters to avoid burning are analyzed. Some conclusions are obtained as follows. Increasing the grinding depth or the wheel velocity makes grinding temperature and residual tensile stress of the surface rise, which deteriorates the surface topography. Appropriate liner velocity of the wheel is 18–22 m/s and the depth of grinding should not exceed 0.02 mm in grinding GH2132 alloy with ceramic alumina wheels to assure the surface quality. When a_p increases enough to cause grinding burn, the strengthening effect of particles ?′ in ? base decrease and the micro-hardness of the surface is obviously lower than that of the base material, which deteriorates the mechanical properties and heat resistance of GH2132 alloy. Results provide a theoretical and experimental basis for technical optimization in the grinding of high-temperature alloy with high efficiency and high quality.     

On the grindability of low-carbon steel under dry, cryogenic and neat oil environments with monolayer brazed cBN and alumina wheels

Grinding of low-carbon steel often exhibits severe wheel loading due to the formation of long chips and high adhering tendency of the work material with the grits. Conventional composite-type alumina wheels are commercially utilised for grinding low-carbon steel. However, the actual nature of grit wear cannot be truly understood in a composite wheel. The truing and dressing conditions also have some influences on the wear mechanism. Therefore, in order to explore the wear pattern on a single layer of grits, monolayer brazed cBN, white and grey Al₂O₃ wheels were used in the present study. The grindability of AISI 1020 steel was evaluated under dry, liquid nitrogen and neat oil environments. The surface profile of the workpiece after being ground in each environmental condition was traced with a surface profilometer to reveal the mechanism of grit wear. The post-grinding conditions of the wheels were observed using scanning electron microscopy. The cBN wheel was found to outperform the alumina wheels in terms of grinding forces and grit wear. The wear of the cBN wheel was remarkably arrested with the application of neat oil. On the other hand, large-scale adhesion and breakage of grits in white alumina wheel were observed under cryogenic environment. In fact, the beneficial role of liquid nitrogen could not be realised in reducing grinding forces and grit wear with all the three types of wheel. A lubricating agent like neat oil appeared to be more suitable than cryogenic cooling when grinding low-carbon steel.     

Design and validation of a grinding wheel optical scanner system to repeatedly measure and characterize wheel surface topography

This paper describes the design and validation of an upgraded grinding wheel scanner system that controls the position of a Nanovea CHR-150 Axial Chromatism sensor along the x- and y-directions of the wheel surface to measure and characterize wheel surface topography. The scanner features a novel homing system that enables the wheel to be removed from the scanner, used on a grinding machine and then re-mounted and re-homed so that the same location on the wheel surface can be repeatedly measured and monitored. The average standard deviation for homing was 27.6 μm and 19.3 μm in the x- and y-directions, respectively, which is more than adequate for typical area scans of 25 mm². After homing, the scanner was able to repeatedly measure features that were similar in size to an abrasive grain (∼200 μm diameter) with an average error of 9.3 μm and 5.9 μm in the x- and y-directions, respectively. The resulting topography measurements were compared with Scanning Electron Microscope images to demonstrate the accuracy of the scanner. A custom particle filter was developed to process the resulting data and a novel analysis technique involving the rate of change of measured area was proposed as a method for establishing the reference wheel surface from which desired wheel topography results can be reported such as the number of cutting edges, cutting edge width and cutting edge area as a function of radial depth.     

A comparison between conventional speed grinding and super-high speed grinding of (TiCp + TiBw) / Ti–6Al–4V composites using vitrified CBN wheel

Comparative grinding experiments of (TiC_p?+?TiB_w)?/?Ti–6Al–4V composites were conducted using vitrified CBN wheel at the conventional wheel speed of 20 m/s and the super-high wheel speed of 120 m/s, respectively. The grinding behavior, i.e., grinding force and force ratio, grinding temperature, specific grinding energy, and ground surface morphology were analyzed. The results obtained indicate that the normal and tangential grinding forces at the super-high wheel speed are smaller than that at the conventional wheel speed. However, the force ratio, the specific grinding energy, and the grinding temperature show a contradictory trend compared to the grinding force between the conventional speed grinding and the super-high speed grinding. The main defects of the ground surface of (TiC_p?+?TiB_w)?/?Ti–6Al–4V composites are voids, micro-cracks, fracture or crushed, pulled-out, and smearing.     

Strength and residual stress of Mg-PSZ after grinding

The influence of grinding with two grinding wheels, differing mainly in diamond-grain size, on the properties of Mg-PSZ was examined. The residual stress, the amount of monoclinic zirconia and the strength of the material were determined. From these measurements depth profiles were obtained for the phase content and the residual stress. The fracture surfaces were examined optically to estimate the critical flaw size. Material ground with “coarse” diamond grains was significantly weaker than that ground with “fine” diamond grains. “Coarse” diamond grains in the grinding wheel resulted in more residual stress and a thicker layer of transformed zirconia than when “fine” grains were in the wheel. This apparent discrepancy is explained with a model based on the occurrence of localized spots of tensile stress beneath the residual stress layer near grain boundaries. These spots are assumed to be larger in number and to contain higher tensile stresses after grinding with “coarse” grains.     

Subsurface crystal lattice deformation machined by ultraprecision grinding of soft-brittle CdZnTe crystals

Cd_0.96Zn_0.04Te (111) single crystals were ultraprecisely ground by #1500, #3000, and #5000 diamond grinding wheels, and the corresponding surface roughness Ra is 49.132, 18.746, and 5.762 nm. High-resolution field emission scanning electron microscope and transmission electron microscope were employed to investigate the surface and subsurface damage. After ultraprecision grinding by three kinds of diamond wheels, the subsurface can achieve ultra-low damage layer with thickness of 1–2 nm made of amorphous state material and lattice distortion layer. For the #1500 precision grinding, the subsurface damage is mainly multi-nanocrystal with diameter in the range of 5–20 nm. While for the #3000 precision grinding, the subsurface damage is made of amorphous state material containing nanocrystals with diameter mainly in the range of 2–5 nm, and the bending deformation is mainly conducted through dislocation pleat formation. For #5000 ultraprecision grinding, the subsurface damage is mainly amorphous state material, and nanocrystals with diameter in the range of 2–5 nm enrich adjacent to the ground surface. Moreover, the size of nanocrystal ground by #5000 diamond grinding wheel is mainly 2 nm. Fracture mechanism ground by #5000 diamond grinding wheel firstly turns onto thin amorphous state film, then fracture.     

Experiment research on grind-hardening of AISI5140 steel based on thermal compensation

The grind-hardening process utilizes the heat generated to induce martensitic phase transformation. However, the maximum achievable harden layer depth is limited due to high grinding forces, and the tensile residual stress appears on the ground surface in the grind-hardening process. This paper proposes a new grind-hardening technology using thermal compensation. The workpiece of AISI5140 steel is preheated by electric resistance heating, and ground under the condition of the workpiece temperature 25°C, 120°C, 180°C and 240°C. The grinding force, harden layer depth and surface quality including residual stress on ground surface, surface roughness and micro-hardness are investigated. The experimental results show that a deep harden layer with a fine grain martensite can be obtained with the thermal compensation. The ground workpiece surface produces a certain compressive residual stress, and the residual compressive stress value increases with preheating temperature. As the preheating temperature increases, grinding force slightly decreases, while there is slightly increment of surface roughness. Compared with the conventional grind-hardening process, both the harden layer depth and residual stress distribution are significantly improved.

     

Evaluating the effect of coolant pressure and flow rate on tool wear and tool life in the steel turning operation

High-pressure coolant (HPC) delivery is an emerging technology that delivers a high-pressure fluid to the tool and workpiece in machining processes. High fluid pressure allows for better penetration of the fluid into the cutting zone, enhancing the cooling effect, and decreasing tool wear through lubrication of the contact areas. The main objective of this work is to understand how tool wear mechanisms are influenced by fluid pressure under different cutting speeds in the finish turning of AISI 1045 steel using coated carbide tools. The main finding was that the use of a lower cutting speed (v _c ?=?490 m/min) in dry cutting resulted in tool life close to that obtained with cutting fluid, but when the cutting speed was increased (v _c ?=?570 m/min), the high-pressure coolant was effective in prolonging the life of the cutting tool. It was also concluded that, regardless of the cutting speed and cooling/lubrication system, the wear mechanisms were the same, namely abrasion and attrition.     

基于新型金刚石砂轮的Al2O3陶瓷磨削性能

利用粉末注射成形和真空钎焊技术制备了一种新型金刚石砂轮,制备的新型金刚石砂轮具有金刚石把持力大、金刚石微刃有序排布等特点。进行了基于新型金刚石砂轮的Al2O3陶瓷磨削性能研究。实验结果表明：相对于普通树脂结合剂金刚石砂轮,新型金刚石砂轮磨削Al2O3陶瓷的加工表面形貌完整性较好,宏观裂纹和表面损伤相对较少;表面粗糙度较小,当进给速度为40mm/s、磨削深度为40μm时,加工表面粗糙度Ra在0.68μm左右;在相同实验条件下,新型金刚石砂轮的磨削力减小了12%~17%,磨削温度降低了80~120℃。     

Thermal influence on surface layer of carbon fiber reinforced plastic (CFRP) in grinding

In this study, we investigated thermal influence on surface layer of CFRP in grinding with heat conduction analysis using grinding temperature at wheel contact area on dry and wet condition. Moreover, the thermal affected layer was analyzed through an experiment to examine the temperature of glass transition and thermal decomposition of the matrix resin that composes the CFRP used in this study. The influence of thermal effect on grinding of CFRP was verified based on observation of ground surface finish after grinding using SEM and the measurement of surface roughness. From the measurement result of DSC (Differential Scanning Calorimetry),TG-DTA (Thermogravimetry-Differential Thermal Analysis), It was found that the thermal affected layer of CFRP includes a layer in which the matrix resin is changed in quality by exceeding the glass transition temperature and a layer in which the matrix resin is thermally decomposed by exceeding the thermal decomposition temperature. In addition, it was found that the surface roughness was significantly reduced if the thermal affected layer with thermal decomposition was generated. In each grinding atmosphere, it tended to increase of grinding temperature at wheel contact area with increasing in the setting depth of cut. In the case of dry grinding, grinding temperature at wheel contact area increased up to t thermal decomposition temperature of the matrix resin. However, in the case of the wet grinding, grinding temperature at wheel contact area did not increase until thermally decomposition temperature. From the result of simulation about thermal affected layer, influence of grinding heat increased with increasing in the setting depth of cut. Ultimately, the thermal affected layer with thermal decomposition was generated in dry grinding. Moreover, from the results of SEM observation, it was confirmed that the surface finish properties deteriorated significantly due to thermal decomposition of the matrix resin in the case of Δ = 400 μm in the setting depth of cut at fiber angle θ = 0°. On the other hand, it was confirmed that the micro damage of carbon fiber was occurred in wet grinding at each setting depth of cut.     

Modeling of grinding wheel topography based on a joint method of 3D microscopic observation and embedded grindable thermocouple technique

The grinding wheel generally has a complicated topography for the irregularity of abrasive grits, which always has an important influence on the final quality of the grinding workpiece. In this paper, a joint method of microscopic observation and grindable thermocouple technique was adopted to model the wheel topography. The grinding wheel topography was first modeled through microscopic observation by an in-position 3D microscope KH-7700 installed on the grinding machine. Based on the measurement of grit sizes, shapes, and distributions through the 3D microscope, a wheel surface model was established and a static grit number model based on Rayleigh distribution was proposed. Moreover, a numerical model was given to validate the proposed Rayleigh distribution model of an active grit number. In order to investigate the real abrasive grit number in a grinding process, an embedded grindable thermocouple was used to detect the dynamic variation of temperature signals, which will reflect the variation of in-process wheel topography under different process parameters, machine status, and even the grit-workpiece interaction status. Through the experimental analysis, it can be concluded that the increase of depth of cut a_p could help to greatly increase the active grit number to the grinding process, while the increase of workpiece speed V_w and decrease of wheel speed V_s could lead to a subtle increase of the grit number. Moreover, the active grit number is about one fourth to one third of the static grits. The contact arc length between the wheel (CBN) and the workpiece (Ti-6Al-4V) was calculated by the contact time from the workpiece surface temperature data, and it was found that the actual contact arc length was about 1.5~2 times of the geometric size.     

Performance and wear mechanisms of whisker-reinforced alumina, coated and uncoated PCBN tools when high-speed turning aged Inconel 718

Inconel 718, an efficient superalloy for energy and aerospace applications, is currently machined with cemented carbide tools at low speed (v _c?≈?60 m/min) due to its unfavorable mechanical and thermal properties. The article presents results of a study of superalloy machinability with whisker-reinforced alumina, uncoated and coated polycrystalline cubic boron nitride (PCBN) tools. Turning of age-hardened Inconel 718 (45 HRC) was done under high-speed machining conditions (v _c?=?250…350 m/min). Aspects of tool life, tool wear, and generated surface quality were studied. Application of uncoated PCBN tools resulted in surface quality and force level superior to other tool materials. Considerable sideflow of workpiece material was found to affect surface quality, especially for coated PCBN and ceramic tools. It was found that protective function of the coating, which increases the tool life up to 20 %, is limited only to low cutting speed range. EDX and AFM analyses suggested dominance of chemical and abrasive wear mechanisms. EDX mapping of worn tools pointed absence of diffusional wear for PCBN tools and intensive degradation of whisker reinforcement in ceramic tools due to diffusion of Ni, Fe, and Cr.     

A model for wafer rotational nanogrinding of soft-brittle CdZnTe wafers

Nanogrinding was conducted on soft-brittle cadmium zinc telluride (CdZnTe or CZT) wafers using a ceramic bond ultrafine diamond wheel. Surface roughness R _a and PV achieved by nanogrinding are 1.5 and 12.2 nm, respectively. The highest feed rate was 83.3 nm/r, which is lower than 89 nm that is the critical value of brittle-ductile transition for CZT. As a result, ductile grinding was obtained. A novel model for wafer rotational grinding of undeformed chip thickness was proposed, based on the kinematics and geometric characteristics between wheel and workpiece. The undeformed chip thickness simulated was used to elucidate the fundamental mechanism for nanogrinding conditions, and it is in good agreement with the results found experimentally.     

A study on the surface grinding of 2D C/SiC composites

This paper aims at studying the machinability of 2D C/SiC composite with 0°/90° woven carbon fibers using a resin bond diamond grinding wheel. The effects of grinding parameters on the grinding force, force ratio, specific grinding energy, surface topography, surface roughness, and grinding chips were investigated. And the grinding mechanism of the 2D C/SiC composite was discussed by analyzing the chip components and material removal characteristics. The results indicate that the grinding force and surface roughness increase with the increase of feeding speed and depth of cut, while decrease with the increase of wheel speed. The force ratio F _n /F _t and the specific grinding energy of 2D C/SiC composite were lower than those of conventional ceramics under the defined experimental conditions. Additionally, the grinding chips were composed of carbon powder, carbon fiber fragments, and SiC matrix debris. It can be deduced that the dominant removal mechanism of the 2D C/SiC composite was brittle fracture mode during grinding process.