Experimental investigations on effects of tool flank wear on surface integrity during orthogonal dry cutting of Ti-6Al-4V

Machining titanium alloy Ti-6Al-4V is a challenging task since tool flank wear adversely affects surface integrity. Quantitative effects of predetermined tool flank wear values (VB) on the surface integrity were investigated through the orthogonal dry cutting of Ti-6Al-4V. Experimental results indicated that three-dimensional (3D) average surface roughness increased with the VB ranging from 0 to 0.2 mm but decreased at VB = 0.3 mm. Given the effects of rubbing and ironing enhanced, surface material burning and plastic flows emerged on the machined surface at VB = 0.3 mm. Not only the plastic deformation layer became deeper but also the grains were greatly distorted with the increase of tool flank wear. When machined by using the tool at VB = 0.3 mm, the β phase of Ti-6Al-4V decreased near the machined surface layer than that of using the fresh tool. Besides, the depth of work-harden layer increased from 20 to 60 μm with the VB increasing from 0 to 0.3 mm. The softened layer was generated near the machined surface by using the tool at VB = 0.3 mm. In addition, the residual compressive stresses of the machined surface had the trend of decreasing. Experimental results indicated that the VB less than 0.2 mm was the most suitable condition for better surface integrity during orthogonal dry cutting of Ti-6Al-4V. This study aims at providing experimental data for optimizing the processing parameters and improving the surface integrity of Ti-6Al-4V.     

Experimental and numerical research on magnetic pulse forming of DP600 high-strength steel with driver sheet

This study aims to investigate the effect of the three cutting parameters (rotation, feed rate, and number of tool strokes) on the values of roughness (Rk, Rpk, Rvk, Mr1, Mr2, Rp/Rt ratio, and Vo) in flexible honed crankcase cylinder of hermetic compressors. The study was based on a full factorial design 2 × 2 × 3, where the rotation and the feed rate were investigated in two levels and the number of tool strokes in three levels. The cylinders were initially honed using a multi-spindle honing machine, Gehring model. A set of three honing tools was used each with two strokes, the first for roughing (120 mesh), the second for semi-finishing (270 mesh), and the third for finishing (600 mesh). For conventional honing (CH), the depth of the cut and the feed rate were kept constant. The flexible honing process was carried out after conventional honing (C+FH) in a CNC milling machine using a Silicon Carbide flex hone tool 800 mesh and 24.2 mm nominal diameter considering 12 different cutting conditions. An electromechanical surface roughness tester was used to carry out roughness measurements. The measurement uncertainty was assessed following the recommendations of the GUM-JCGM 101. The analysis of variance (ANOVA) technique was applied, and it was observed that the number of the tool strokes was the factor that contributed the most to the improvement of the surface finish of the cylinders.     

Determination of a coupling equation for milling parameters based on optimal cutting temperature

Nanofluid minimum quantity lubrication (NMQL) is one of the main modes of sustainable manufacturing. It is an environment-friendly, energy-saving, and highly efficient lubrication method. With the use of nanoparticles, the tribological properties of debris–tool and workpiece–tool interfaces will change. However, spectrum analyses of force and power spectral density (PSD) of surface microstructures are limited. In the present work, the milling force, friction coefficient, specific energy, surface roughness, and surface microstructure of debris were evaluated in milling of 45 steel for different lubrication conditions, namely, dry, flood, minimum quantity lubrication, and Al₂O₃ NMQL. Results demonstrated that compared with other lubrication conditions, NMQL achieves minimum milling force peak (F_x?=?270 N, F_y?=?160 N, F_z?=?50 N), friction coefficient (μ?= 1.039), specific energy (U?= 65.5 J/mm³), and surface roughness value (R_a?=?2.254 μm, RS_m?=?0.0562 mm). Furthermore, a spectrum analysis of the milling force and PSD of the surface microstructure was conducted for validation. The spectral analysis of milling force revealed that NMQL obtained the lowest milling force and amplitude in the middle-frequency region, thereby indicating the minimum abrasion loss of the tool. Meanwhile, the PSD analysis indicated that NMQL had the lowest proportional coefficient in the low-frequency region (0.4766) and the highest proportional coefficient in the high-frequency region (0.0569). These results revealed that the workpiece surface gained by Al₂O₃ NMQL obtained higher wave fineness than other working conditions. By combining with the lowest R_a, NMQL contributes the best workpiece surface quality. Therefore, machining experiments using NMQL showed the best lubrication performance.     

Effect of the process parameters on the three-dimensional shape of molten pool during full-penetration laser welding process

Slow tool servo (STS) turning is superior in machining precision and in complicated surface. However, STS turning is a complex process in which many variables can affect the desired results. This paper focuses on surface roughness prediction in lenses STS turning. An exponential model, based on the five main cutting parameters including tool nose radius, feed rate, depth of cut, C-axis speed, and discretization angle, for surface roughness prediction of lenses is developed by means of orthogonal experiment regression analysis. Meanwhile, a prediction model of surface roughness based on least squares support vector machines (LS-SVM) with radial basis function is constructed. Orthogonal experiment swatches are studied, and chaotic particle swarm optimization and leave-one-out cross-validation are applied to determine the model parameters. The comparison of LS-SVM model and exponential model is also carried out. Predictive LS-SVM model is found to be capable of better predictions for surface roughness and has absolute fraction of variance R² of 0.99887, the mean absolute percent error e_M of 8.96 %, and the root mean square error e_R of 10.68 %. The experimental results and prediction of LS-SVM model show that effects of tool nose radius and feed rate are more significant than that of depth of cut on surface roughness of lenses turning.     

Effect of Oxygen on the Self-formation of Carbonaceous Tribo-layer with Carbon Nitride Coatings under a Nitrogen Atmosphere

The ball-on-disk friction and wear tests of CN _X coatings (CN _X /CN _X ) were conducted under a nitrogen atmosphere with controlled relative humidity (RH) (3.4–40.0%RH) and oxygen concentration (100–21 × 10⁴ ppm) in this study. We found that the specific wear rate of CN _X coating on ball (W _b), which could give stable and low friction coefficient (<0.05), was below 3.0 × 10^?8 mm³/Nm. Average friction coefficients (µ _a) and W _b of CN _X /CN _X increased (µ _a: 0.02–0.33, W _b: 1.6 × 10^?8–2.4 × 10^?7 mm³/Nm) with increasing oxygen concentration (230–211,000 ppm) as well as RH (4.7–21.1%RH) under a nitrogen atmosphere. However, the W _b remained low value below 2.3 × 10^?8 mm³/Nm regardless of oxygen concentration (100–207,000 ppm) of a nitrogen atmosphere (3.4–3.9%RH) when CN _X -coated balls were slid against a hydrogenated CN _X (CN _X :H) coatings (CN _X /CN _X :H). Besides, the CN _X /CN _X :H achieved low and stable friction coefficient below 0.05 under a nitrogen atmosphere (10,000 ppmO₂) regardless of increasing RH up to 20%RH. Raman analysis indicated that the structure of carbon on the top surface of CN _X coating was changed from as-deposited CN _X coating in the case of low friction coefficient (<0.05). Furthermore, TOF-SIMS analysis provided the evidence that the carbon derived from CN _X -coated disk was considered to diffuse into the ball surface, and it mixed with the carbon derived from CN _X -coated ball on the wear scar, which formed the chemically bonded carbon tribo-layer. Low friction coefficient (<0.05) with CN _X coatings under a nitrogen atmosphere was achieved due to self-formation of the carbon tribo-layer.     

Soft computing models and intelligent optimization system in electro-discharge machining of SiC/Al composites

In this paper, a multi-variable regression model, a back propagation neural network (BPNN) and a radial basis neural network (RBNN) have been utilized to correlate the cutting parameters and the performance while electro-discharge machining (EDM) of SiC/Al composites. The four cutting parameters are peak current (I_p), pulse-on time (T_on), pulse-off time (T_off), and servo voltage (S_v); the performance measures are material remove rate (MRR) and surface roughness (Ra). By testing a large number of BPNN architectures, 4-5-1 and 4-7-1 have been found to be the optimal one for MRR and Ra, respectively; and it can predict them with 10.61 % overall mean prediction error. As for RBNN architectures, it can predict them with 12.77 % overall mean prediction error. The multivariable regression model yields an overall mean prediction error of 13.93 %. All of these three models have been used to study the effect of input parameters on the material remove rate and surface roughness, and finally to optimize them with genetic algorithm (GA) and desirability function. Then, an intelligent optimization system with graphical user interface (GUI) has been built based on these multi-optimization techniques, in which users can obtain the optimized cutting parameters under the desired surface roughness (Ra).     

Manufacturing and mechanical characterization of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/β-TCP/TiO<Subscript>2</Subscript> biocomposite as a potential bone substitute

This paper focuses on the mechanical characterization of a bioceramic based on commercial alumina (Al₂O₃) mixed with synthesized tricalcium phosphate (β-TCP) and commercial titania powder (TiO₂). The effect of β-TCP and TiO₂ addition on the mechanical performance was investigated. After a sintering process at 1600 °C for 1 h, various mechanical properties of the samples have been studied, such as compressive strength, flexural strength, tensile strength, elastic modulus, and fracture toughness. The measurements of the elastic modulus (E) and the tensile strength (σ _t ) were conducted using the modified Brazilian test while the compressive strength (σ _c ) was determined through a compression test. Also, semi-circular bending (SCB) specimens were used to evaluate the flexural strength (σ _f ) and the opening mode fracture toughness (K _IC). From the main results, it was found that the best mechanical performance is obtained with the addition of 10 wt.% TCP and 5 wt.% TiO₂. Alumina/10 wt.% tricalcium phosphate/5 wt.% titania composites displayed the highest values of mechanical properties and a good combination of compressive strength (σ _c ?≈?352 MPa), flexural strength (σ _f ?≈?98 MPa), tensile strength (σ _t ?≈?86.65 MPa), and fracture toughness (K _IC?≈?13 MPa m^1/2).     

Lubricity of High Water Content Aqueous Gels

Aqueous gels such as biopolymer gels, mucus, and high water content hydrogels are often qualitatively described as lubricious. In hydrogels, mesh size, ξ, has been found to be a controlling parameter in friction coefficient. In the tribology of aqueous gels, we suggest that the Weissenberg number (Wi) is a useful parameter to define different regimes, and following the original formulations in rheology, Wi is given by the polymer relaxation time (ηξ³/k_BT) multiplied by the shear rate due to fluid shear through a single mesh (V/ξ): Wi?=?ηVξ²/k_BT. At sliding speeds below a Weissenberg number of approximately 0.1, Wi?<?0.1, the friction coefficient is velocity-independent and scales with mesh size to the ??1 power, µ ∝ ξ^?1. De Gennes’ scaling concepts for elastic modulus, E, give a dependence on polymer mesh size to the ??3 power, E ∝ ξ^?3, and following Hertzian contact analysis, the contact area is found to depend on the mesh size squared, A ∝ ξ². Combining these concepts, the shear stress, τ, and therefore the lubricity of aqueous gels, is predicted to be highly dependent on the mesh size, τ ∝ ξ^?3. Studies aimed at elucidating the fundamental mechanism of lubricity in biopolymer gels, mucus, and hydrogels have wrestled with comparisons across mesh size, which can be extremely difficult to accurately quantify. Using scaling concepts relating polymer mesh size to water content reveals that shear stress decreases rapidly with increasing water content, and plots of shear stress as a function of swollen water content are suggested as a useful method to compare aqueous gels of unknown mesh size. As a lower bound, these data are compared against estimates of fluid shear stress for free and bound water flowing through a mesh size estimated by the water content of the gels. The results indicate that the strong dependence on lubricity is likely due to a synergistic combination of a low viscosity solvent (water) coupled to a system that has a decreasing friction coefficient, modulus, and the resulting contact pressure with increasing water content. Although the permeability, K, of aqueous gels increases dramatically with water content (and mesh size), K ? ξ²/η, the stronger decrease of the elastic modulus and subsequent decrease in contact pressure due to an increase in the contact length, predicts that the draining time under contact, t, actually increases strongly with increasing water content and mesh size, t ∝ ξ². Consistent with the finding of extremely high water content aqueous gels on the surfaces of biological tissues, these high water content gels are predicted to be optimal for lubrication as they are both highly lubricious and robust at resisting draining and sustaining hydration.     

Optimized bending angle distribution function of contour plate roll forming

Regarding the roll forming of contour plates, traditional roll forming techniques often result in peak longitudinal strain during the forming process, which causes defects such as longitudinal bowing and springback. The bending angle, sheet thickness, and the number of forming passes are all important process parameters that cause the aforementioned problems. This study proposes quantifying the projection track regarding the edge of the profile section in the horizontal plane that follows a cubic curve and uses the curve function to reasonably distribute the bending angle to study the maximum forming strain and the average strain for all passes of the sheet between the forming passes. Simultaneously, the influence law of the sheet thickness and number of forming passes was studied. Based on theoretical simulation and experimental verification, the optimal bending angle distribution function is A1: y?=?x³?+?x²?+?x. When the thickness of the sheet is 1.5 mm, both the maximum forming strain between the passes during roll forming and the average strain of all passes are the smallest, which are 3.91 and 0.609%, respectively. Moreover, with the increase in the number of passes, the longitudinal bowing and springback decrease to varying degrees.     

Parametric optimization of CNC turning process for hybrid metal matrix composite

Machining of hybrid metal matrix composite is difficult as the particulates are abrasive in nature and they behave like a cutting edge during machining resulting in quick tool wear and induces vibration. An attempt was made in this experimental study to evaluate the machining characteristics of hybrid metal matrix composite, and a mathematical model was developed to predict the responses, namely surface finish, intensity of vibration and work-tool interface temperature for known cutting condition while machining was performed in computer numerical control lathe. Design of experiments approach was used to conduct the trials; response surface methodology was employed to formulate a mathematical model. The experimental study inferred that the vibration in V _x, V _y, and V _z were 41.59, 45.17, and 26.45 m/s², respectively, and surface finish R _a, R _q, and R _z were 1.76, 3.01, and 11.94 μm, respectively, with work-tool interface temperature ‘T’ of 51.74 °C for optimal machining parameters, say, cutting speed at 175 m/min, depth of cut at 0.25 mm and feed rate at 0.1 mm/rev during machining. Experimental results were in close conformity with response surface method overlay plot for responses.     

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.     

Impact of aspect ratio and surface heating on pollutant transport in street canyons

This paper investigated the impacts of surface heating on pollutant transport and Air Exchange Rate (AER) in street canyons of different aspect ratios (building heightH to street widthW) using computational fluid dynamic (CFD) technique. Street canyons ofH/W varied from 0.1 to 2 were employed in the study. These street-canyon aspect ratios covered a range of basic flow regimes including skimming flow (H/W=1 and 2), wake interference flow (H/W=0.5), and isolated roughness flow (H/W=0.1). Different façade/surface heating imposed different influence on the flow field and pollutant transport in street canyons of differentH/W. The AER induced by vertical velocity fluctuationAER _w, and mean vertical velocityAER _w . AER of street canyon with differentH/W and different surface heating exhibited their unique characteristics.     

Sustainability analyses of cutting edge radius on specific cutting energy and surface finish in side milling processes

The aim of this work is to determine the influence of cutting edge radius on the specific cutting energy and surface finish in a mechanical machining process. This was achieved by assessing the direct electrical energy demand during side milling of aluminium AW6082-T6 alloy and AISI 1018 steel in a dry cutting environment using three different cutting tool inserts. The specific energy coefficient was evaluated as an index of the sustainable milling process. The surface finish of the machined parts was also investigated after machining. It was observed that machining with the 48.50-μm cutting edge radius insert resulted in lower specific cutting energy requirements when compared with the 68.50 and 98.72-μm cutting edge radii inserts, respectively. However, as the ratio of the undeformed chip thickness to cutting edge radius is less than 1, the surface roughness increases. The surface roughness values gradually decrease as the ratio of undeformed chip thickness to cutting edge radius (h/r _e) tends to be 1 and at minimum surface roughness values when the ratio of h/r _e equalled to 1. However, the surface roughness values increased as h/r _e becomes higher than 1. This machining strategy further elucidates the black box and trade-offs of ploughing and rubbing characteristics of micro machining and optimization strategy for minimum energy and sustainable manufacture.     

Improvement of AA5052 sheet properties by electromagnetic twin-roll casting

Although servo scanning 3D micro electro discharge machining (SS-3D MEDM) can achieve a high discharge ratio, the processing efficiency is still lower than expected because the discharge area at micro-electrode tip is much smaller than the area to machine. In particular, for 3D micro cavities, the processing efficiency and the machining accuracy inherently contradict each other. In this paper, an on-machine process of rough-and-finishing SS-3D MEDM is proposed with consideration that most cavity material cannot affect the dimensional accuracy. In the rough machining process, technological measures such as high discharge energy and large-diameter tool electrodes are applied to maximize processing efficiency. In the finishing machining process, a small amount of material is removed for dimensional accuracy, smooth surface, and clear edges-and-corners by changing multi-factors of machining parameters. The research is concentrated on two key techniques: rough-and-finishing border strategy and micro tool-electrode precision measurement for the process transformation from rough to finishing. Moreover, an online measurement method is proposed by the point electric contact between a micro electrode and a standard thin-rod, and the measurement accuracy was up to ±1 µm in our experimental system. Machining experiments of 3D micro cavities < 800 µm verified the proposed methods and the processes including 3D model design, rough-machining, micro-electrode measurement and fabrication, and finishing machining. The experimental results were successfully achieved as follows: the dimensional accuracy < 5 µm, surface roughness Sa0.38 µm, and the processing efficiency being improved to 2.4 times.     

Study of trajectory and experiment on steel polishing with elastic polishing wheel device

Since the curvature of free-form surfaces are variable, it is difficult to guarantee the quality of the surface polished with traditional polishing technology. The chief aim of this paper is to investigate the features of an original elastic polishing wheel device. The polishing trajectory of the elastic polishing wheel was simulated to study the relationship between the uniformity of a kind of polishing trajectory and the ratio of rotational speed “i” which is the ratio of the velocity of the rotation and the revolution. Orthogonal experiment was carried out to explore the effect of various factors (rotational ratio, press amount h, speed of rotation, and granularity of abrasive grains) on surface roughness polished. The writer has come to the conclusion that i has an influence on the uniformity of polishing trajectory. The polishing coefficient of variation “CV” of i?=?10.645751 is 32% lower than i?=?10. Increasing the number of digits after the decimal point of i, the polishing track performs more uniform and densely. The experimental tests show that the influence of rotational ratio, press amount h, speed of rotation, and granularity of abrasive grains on surface roughness polished decreases progressively.     

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.     

Big data analysis of a mini three-axis CNC machine tool based on the tuning operation of controller parameters

The characteristic responses of a mini three-axis computer numerical control (CNC) machine tool based on the controller tuning operation were investigated for big data estimation. The major tuning parameters included the position control gains K _p, the position feed-forward control gains K _f, the speed control gains K _v, and the gain ratios K _g of the position and speed control values in manufacturing industries. K _p gains of 10, 30, 50, 80, 100, 200, 300, and 400 rad/s, K _f gains of 0, 30, 50, 60, 80, and 100 %, K _v gains of 30, 50, 70, 100, 300, 900, 2000, and 3000 rad/s, and K _g ratios of (1:1), (3:1), (5:1), and (7:1) were analyzed for smart productivity. The results show that the settling times at different K _p values were almost constant when the K _p gain was over 200 rad/s. The maximum overshoots, when the feed-forward gain is over 60 %, almost increased with increasing feed-forward gains. However, the overshoot of the three-axis CNC machine tool decreased as the K _v gain increased until the K _v gain reached 70 rad/s. The settling times at a constant K _g ratio decreased with an increase in the K _p and K _v gains. The characteristic responses of the tuning operations were enabled with connectivity to a cloud network to share the big data, to support decision making, and to adjust operations in real time.     

Integrated ANN-LWPA for cutting parameter optimization in WEDM

In this paper, we present a new approach to determinate cutting parameters in wire electrical discharge machining (WEDM), integrated artificial neuron network (ANN), and wolf pack algorithm based on the strategy of the leader (LWPA). The cutting parameters considered in this paper are pulse-on, current, water pressure, and cutting feed rate. Models of the effects of the four parameters on machining time (T_p), machining cost (C_p), and surface roughness (Ra) are mathematically constructed. An ANN-LWPA integration system with multiple fitness functions is proposed to solve the modelling problem. By using the proposed approach, this study demonstrates that T_p, C_p, and Ra can be estimated at 164.1852 min, 239.5442 RMB, and 1.0223 μm in single objective optimization, respectively. For example, as for Ra, integrated ANN-LWPA has optimized the Ra value by the reduction of 0.1337 μm (11.6 %), 0.3377 μm (24.8 %), and 0.105 μm (10.3 %) compared to experimental data, regression model, and ANN model, respectively. Consequently, the ANN-LWPA integration system boasts some advantages over decreasing the value of fitness functions by comparison with the experimental regression model, ANN model, and conventional LWPA result. Moreover, the proposed integration system can be also utilized to obtain multiple solutions by uniform design-based exploration. Therefore, in order to solve complex machining optimization problems, an intelligent process scheme could be integrated into the numeric control system of WEDM.     

Adatom concentration distribution on an extrawide Si(111) terrace during sublimation

The formation of an adsorption layer on the Si(111) surface during sublimation at temperatures of 1000–1100 °C and subsequent quenching at T = 750 °C is studied by methods of in situ ultrahigh-vacuum reflection electron microscopy and ex situ atomic force microscopy. The adatom concentration distribution on an extrawide (~60 μm) atomically flat terrace is determined for the first time, and the diffusion length x_s = 31±2 μm at T = 1000 °C is obtained. The analysis of the temperature dependence of the equilibrium concentration of adatoms near a monatomic step allows pioneering measurements of the energy necessary for adatom detachment from the step and attachment to the terrace E _ad ≈ 0.68 eV. Based on these results, the energy parameters for some atomic processes on the Si(111) surface are estimated.