Analysis of surface integrity for minimum quantity lubricant—MQL in grinding

The quality of machined components is currently of high interest, for the market demands mechanical components of increasingly high performance, not only from the standpoint of functionality but also from that of safety. Components produced through operations involving the removal of material display surface irregularities resulting not only from the action of the tool itself, but also from other factors that contribute to their superficial texture. This texture can exert a decisive influence on the application and performance of the machined component. This article analyzes the behavior of the minimum quantity lubricant (MQL) technique and compares it with the conventional cooling method. To this end, an optimized fluid application method was devised using a specially designed nozzle, by the authors, through which a minimum amount of oil is sprayed in a compressed air flow, thus meeting environmental requirements. This paper, therefore, explores and discusses the concept of the MQL in the grinding process. The performance of the MQL technique in the grinding process was evaluated based on an analysis of the surface integrity (roughness, residual stress, microstructure and microhardness). The results presented here are expected to lead to technological and ecological gains in the grinding process using MQL.     

Experimental evaluation of the lubrication performance of MoS2/CNT nanofluid for minimal quantity lubrication in Ni-based alloy grinding

A nanofluid minimum quantity lubrication with addition of one kind of nanoparticle has several limitations, such as grinding of difficult-to-cutting materials. Hybrid nanoparticles integrate the properties of two or more kinds of nanoparticles, thus having better lubrication and heat transfer performances than single nanoparticle additives. However, the use of hybrid nanoparticles in nanofluid minimum quantity lubrication grinding has not been reported. This study aims to determine whether hybrid nanoparticles have better lubrication performance than pure nanoparticle. A hybrid nanofluid consisting of MoS₂ nanoparticles with good lubrication effect and CNTs with high heat conductivity coefficient is investigated. The effects of the hybrid nanofluid on grinding force, coefficient of friction, and workpiece surface quality for Ni-based alloy grinding are analyzed. Results show that the MoS₂/CNT hybrid nanoparticles achieve better lubrication effect than single nanoparticles. The optimal MoS₂/CNT mixing ratio and nanofluid concentration are 2:1 and 6 wt%, respectively.     

Cutting performance of different coatings during minimum quantity lubrication drilling of aluminum silicon B319 cast alloy

Cutting performance of cemented carbide drills with various coatings was investigated in detail under minimum quantity lubrication (MQL) conditions. An advanced dual-channel Bielomatik MQL system was installed in an Okuma machining center. A specially designed Mapal drill was selected for the studies to eliminate voids between the tool and the MQL tool holder that can interfere with mist delivery. Using this design, a mist flow rate of 25 mL/min was achieved through the drills.Progressive frictional/wear studies were performed. Coated drills were tested in three stages (50, 500, and 7000 holes). During short term drilling tests (50-hole level), cutting performance was comprehensively evaluated for a range of coatings by measuring several in-situ frictional characteristics of the cutting process, such as cutting forces, and related characteristics including, chip type and undersurface morphology. Wear patterns of the cutting tools were indentified as well. Selected coatings were tested further. The best cutting performance based on the 500-hole testing was found with the diamond coating. However, excessive brittleness of the entire coating/substrate system led to premature failure of the drill after 4300 holes. The low-hydrogen DLC coating that also showed promising cutting performance based on the 500-hole test was selected as the next candidate for further testing. Drills with low-hydrogen DLC coating achieved 7200 drilled holes with a flank wear of only 110 μm and moderate intensity of workpiece material pickup. This results in a better surface finish of drilled holes.Based on this study, the Mapal drills with the low-hydrogen DLC coating provided comparable machining performance to that possible with traditional wet machining, but with the environmental and cost advantages possible with MQL.     

An analysis of grinding power and surface roughness in external cylindrical grinding of hardened SCM440 steel using the response surface method

The aim of this study was to analyze effectively the grinding power spent during the process and the surface roughness of the ground workpiece in the external cylindrical grinding of hardened SCM440 steel using the response surface method. A Hall effect sensor was used for measuring the grinding power of the spindle driving motor. The surface roughness was also measured and evaluated according to the change of the grinding conditions. Response surface models were developed to predict the grinding power and the surface roughness using the experimental results. From adding simply material removal rate to the contour plot of these mathematical models, it was seen that useful grinding conditions for industrial application could be easily determined.     

An investigation on wear mechanism of resin-bonded diamond wheel in Elliptical Ultrasonic Assisted Grinding (EUAG) of monocrystal sapphire

An investigation is carried out to analyze and quantify the wear mechanisms of resin-bonded diamond wheel in Elliptical Ultrasonic Assisted Grinding (EUAG) of monocrystal sapphire. The EUAG is a new grinding method proposed by the present authors in which an elliptical ultrasonic vibration is imposed on the workpiece by using an elliptical ultrasonic vibrator. In this paper, a series of grinding experiments under the presence/absence of ultrasonic vibration assistance are performed. The grinding forces and work-surface roughness are measured, and the wheel surface is examined too. The experimental results indicate that during grinding, the steady process region performed in EUAG is longer than that in Conventional Grinding (CG) by 20%, meaning that the grinding wheel has a longer sharp cutting period in EUAG. It is validated that the main wear mechanisms in EUAG is micro-fracture and cleavage of abrasive grains, which has a positive effect on the better grinding performance, such as lower grinding forces, force ratio F_n/F_t, wheel loading, and smoother work-surface. This study demonstrates that the improved grinding performance of diamond wheel can be realized by using EUAG method.     

Energy aspects and workpiece surface characteristics in ultrasonic-assisted cylindrical grinding of alumina–zirconia ceramics

Ultrasonic assisted grinding is a novel method for improving the grinding process of difficult-to-cut materials. In the present research a novel setup has been designed and manufactured for utilizing ultrasonic vibrations in external cylindrical grinding. The designed ultrasonic head vibrates a rotating workpiece in axial direction. An alumina–zirconia ceramic (AZ90) has been selected as the workpiece material. Energy aspects and workpiece surface characteristics of ultrasonic assisted cylindrical grinding (UACG) and conventional cylindrical grinding (CG) processes have been analytically modeled and corresponding grinding experiments have been performed. The combined kinematics of the cylindrical plunge grinding process and axial ultrasonic vibrations provide a unique surface treatment conditions, which leads to reduced peak heights and increased valley depths of the surface topography. The main axial vibration mode provides the overlap of the adjacent cutting traces and consequently smoothens the surface topography in cylindrical plunge grinding. It has been analytically and experimentally shown that, applying ultrasonic vibrations, grinding energy can be reduced up to more than 35% depending on the process parameters. The surface characteristics of the ground workpieces have been investigated in terms of four surface roughness parameters and the roundness error.     

Effects of cooling air temperature on cryogenic machining of Ti-6Al-4V alloy

This paper presents experimental investigations on influence of different coolant strategies such as dry, wet, minimum quantity lubrication (MQL) and MQL with cooling air on performance in milling of the Ti-6Al-4V alloy with uncoated cemented carbide inserts. Cutting force, tool wear, surface roughness and chip morphology are experimentally studied to compare the effects of different cooling air temperatures. The results showed that minimum quantity lubrication (MQL) with cooling air significantly reduces cutting force, tool wear and surface roughness. Unfortunately, MQL (without cooling air) condition cannot produce evident effect on cutting performance, and flaking wear on the flank surface of the insert has been found under this condition. Four different cooling air temperatures are used to investigate the effects of cooling air temperature on the machinability characteristics of Ti-6Al-4V alloy. Based on the experimental results, MQL with cooling air of −15 °C provides more favourable effects compared to other cooling air temperatures (0 °C, −30 °C,−45 °C). Short chips are produced under MQL with cooling air conditions due to the high velocity of cooling air enhances the chip brittleness for easy chip breaking, and the effective penetration of lubricant to the chip-tool interface results in lower friction. However, due to the dramatic increase in chip hardness at lower temperature, MQL with cooling air environments cannot promote chip curl to some extent.     

On the mechanics of the grinding process – Part I. Stochastic nature of the grinding process

Grinding of metals is a complex material removal operation involving cutting, ploughing, and rubbing depending on the extent of interaction between the abrasive grains and the workmaterial under the conditions of grinding. It is also a stochastic process in that a large number of abrasive grains of unknown geometry, whose geometry varies with time, participate in the process and remove material from the workpiece. Also, the number of grains passing through the grinding zone per unit time is extremely large. To address such a complex problem, it is necessary to analyze the mechanics of the grinding process using probability statistics, which is the subject of this investigation. Such an analysis is applicable to both form and finish grinding (FFG), such as surface grinding and stock removal grinding (SRG), such as cut-off operation. In this investigation, various parameters of the process including the number of abrasive grains in actual contact, the number of actual cutting grains per unit area for a given depth of wheel indentation, the minimum diameter of the contacting and cutting grains, and the volume of the chip removed per unit time were determined analytically and compared with the experimental results reported in the literature. Such an analysis enables the use of actual number of contacting and cutting grains in the grinding wheel for thermal and wheel wear analyses. It can also enable comparison of analytical work with the experimental results and contribute towards a better understanding of the grinding process. The analysis is applied to some typical cases of fine grinding and cut-off operations reported in the literature. It is found that out of a large number of grains on the surface of the wheel passing over the workpiece per second (˜million or more per second), only a very small fraction of the grains merely rub or plough into the workmaterial (3.8% for FFG and 18% for SRG) and even a smaller fraction (0.14% for FFG and 1.8% for SRG) of that participate in actual cutting, thus validating Hahn’s rubbing grain hypothesis.     

Finishing characteristics of brittle materials by ELID-lap grinding using metal-resin bonded wheels

ELID-lap grinding is a method of constant pressure grinding which utilizes an electrically conductive wheel and the electrolytic in-process dressing (ELID) method. This method has the advantage of using micro grain-wheels above #10 000 and also, through simple modification, can be used on existing lap machines. To find the characteristics of metal-resin bonded wheels developed for ELID-lap grinding, experiments on the grinding of brittle materials were performed using wheels with a variety of grain diameters. The wheels used in the experiments were #8000, #120 000 and #3 000 000 metal-resin bonded diamond wheels (#8000 MRB-D, #120 000 MRB-D and #3 000 000 MRB-D wheels). The workpieces were silicon and glass. The results of the experiments showed that stable grinding can be achieved with the #8000 to #3 000 000 MRB-D wheels. With the #3 000 000 MRB-D wheel, very smooth surface finishes were obtained for both silicon (PV 2.8 nm) and glass (PV 2.5 nm). Atomic Force Microscope (AFM) and Scanning Electron Microscope (SEM) observations indicated these surfaces to be very smooth in the order of several nanometers, obtained by mechanical removal using an ultrafine wheel.     

Laser surface alloying of Gr22 ferritic steel with Ni(Al): Effect of processing parameters on the microstructure and high temperature performance

The aim of this work is modify the surface composition of a Gr22 ferritic steel component with Ni(Al) using a high-power diode laser (HPDL). Two different combinations of parameters were used to obtain a superficial alloy modification macroscopically homogenous, with low porosity and low presence of cracks. From a microscopically point of view the surface presents a band structure due to the rapid cooling process. Isothermal oxidation tests at 640 °C were performed to evaluate the performance of the solution at high temperature. The introduction of Ni(Al) with this technique has allowed to reduce the degradation of the components, without modifying the ferritic structure of the steel.     

TC4钛合金板材激光冲击强化动态应力波传播特性的数值模拟与实验

对广泛应用于飞行器构件上的TC4(Ti-6Al-4V)钛合金,当受到激光冲击强化后的内部动态应力波传播特性建立模型,并进行数值模拟和实验验证。结果表明,实验测试与仿真结果比较接近,证明该文数值模拟的合理性,为后续实验研究提供了理论依据。     

An investigation on the elastic modulus and density of vacuum casted aluminum alloy 2024 containing lithium additions

The elastic modulus and density of (2024+LiX) alloys are investigated. To the alloy of 2024, the weight percentages of lithium added are 2,3, and 4. Melting is carried out in an induction furnace under argon gas protection; casting is done under vacuum. To obtain the maximum strength and hardness, the specimens are solution heat treated under 495 C and quenched in water at room temperature. Then, they are aged naturally and artificially. For the purposes of comparing, some of the specimens are melted under argon gas, but casting is done without vacuum. All the specimens are subjected to tension tests. As a result of this work, the alloys of aluminum that are difficult to manufacture by the known methods are manufactured safely by the vacuum casting method. For 1% of lithium added to the alloy, an increase of 6% in the elastic modulus and 3% decrease in the density are obtained. The specific elastic modulus, E/ρ, ratio increases by about 10% for each 1% addition of lithium.     

The effects of hydrogen on the deformation and fracture of β-titanium

The hydrogen-induced ductile–brittle transition in the BCC β-titanium alloy, Timetal® 21S, occurs abruptly at a critical hydrogen concentration that decreased with decreasing tensile test temperature. Mechanical property tests showed that solute hydrogen reduced the yield strength of ductile specimens and decreased the fracture stress of brittle specimens. To identify the operative mechanism a series of experiments were performed to test the applicability of the stress-induced hydride mechanism, the hydrogen-enhanced plasticity mechanism, and the decohesion mechanism of hydrogen embrittlement. The experiments showed that no hydrides were associated with the fracture process, indicating that the stress-induced hydride mechanism was not responsible for the observed sharp ductile–brittle transition. In situ straining experiments in a controlled environment transmission electron microscope showed that hydrogen enhanced the mobility of dislocations in both uncharged and hydrogen charged alloys, showing that the hydrogen-enhanced localized plasticity mechanism cannot account for the observed behavior. The experimental results are, however, fully consistent with the decohesion mechanism of hydrogen embrittlement.     

Effect of increasing tellurium content on the electronic and optical properties of cadmium selenide telluride alloys CdSe1−xTex: An ab initio study

An all electron full potential linearized augmented plane wave method, within a framework of GGA (EV-GGA) approach, has been used for an ab initio theoretical study of the effect of increasing tellurium content on the band structure, density of states, and the spectral features of the linear and nonlinear optical susceptibilities of the cadmium-selenide-telluride ternary alloys CdSe_1−xTe_x (x = 0.0, 0.25, 0.5, 0.75 and 1.0). Our calculations show that increasing Te content leads to a decrease in the energy band gap. We find that the band gaps are 0.95 (1.76), 0.89 (1.65), 0.83 (1.56), 0.79 (1.44) and 0.76 (1.31) eV for x = 0.0, 0.25, 0.5, 0.75 and 1.0 in the cubic structure. As these alloys are known to have a wurtzite structure for x less than 0.25, the energy gaps are 0.8 (1.6) eV and 0.7 (1.55) eV for the wurtzite structure (x = 0.0, 0.25) for the GGA (EV-GGA) exchange correlation potentials. This reduction in the energy gaps enhances the functionality of the CdSe_1−xTe_x alloys, at least for these concentrations, leading to an increase in the effective second-order susceptibility coefficients from 16.75 pm/V (CdSe) to 18.85 pm/V (CdSe_0.75Te_0.25), 27.23 pm/V (CdSe_0.5Te_0.5), 32.25 pm/V (CdSe_0.25Te_0.75), and 37.70 pm/V (CdTe) for the cubic structure and from 12.65 pm/V (CdSe) to 21.11 pm/V (CdSe_0.75Te_0.25) in the wurtzite structure. We find a nonlinear relationship between the absorption/emission energies and composition, and a significant enhancement of the electronic properties as a function of tellurium concentration. This variation will help in designing better second-order susceptibility materials by manipulating of the electronic structures of these materials with different compositions to achieve more delocalized atomic bonds.