Optimization of the EDM parameters on machining Ti–6Al–4V with multiple quality characteristics

In this paper, parameter optimization of the electrical discharge machining process to Ti–6Al–4V alloy considering multiple performance characteristics using the Taguchi method and grey relational analysis is reported. Performance characteristics including the electrode wear ratio, material removal rate and surface roughness are chosen to evaluate the machining effects. The process parameters selected in this study are discharge current, open voltage, pulse duration and duty factor. Experiments based on the appropriate orthogonal array are conducted first. The normalised experimental results of the performance characteristics are then introduced to calculate the coefficient and grades according to grey relational analysis. The optimised process parameters simultaneously leading to a lower electrode wear ratio, higher material removal rate and better surface roughness are then verified through a confirmation experiment. The validation experiments show an improved electrode wear ratio of 15%, material removal rate of 12% and surface roughness of 19% when the Taguchi method and grey relational analysis are used.     

Exploring the hybrid metal extrusion and bonding process for butt welding of Al–Mg–Si alloys

The hybrid metal extrusion and bonding (HYB) process is a new solid-state joining technique developed for aluminum alloys. By the use of filler material addition and plastic deformation sound joints can be produced at operating temperatures below 400 °C. The HYB process has the potential to compete with commonplace welding technologies, but its comparative advantages have not yet been fully explored. Here, we present for the first time the results from an exploratory investigation of the mechanical integrity of a 4-mm AA6082-T6 HYB joint, covering both hardness, tensile and Charpy V-notch testing. The joint is found to be free from defects like pores, internal cavities and kissing bonds, yet a soft heat-affected zone (HAZ) is still present. The joint yield strength is 54% of that of the base material, while the corresponding joint efficiency is 66%. The indications are that the HYB process may compete or even outperform conventional welding techniques for aluminum in the future after it has been fully developed and optimized.     

Modeling and analyzing the effects of air-cooled turning on the machinability of Ti–6Al–4V titanium alloy using the cold air gun coolant system

This study provides the mathematical models for modeling and analyzing the effects of air-cooling on the machinability of Ti–6Al–4V titanium alloy in the hard turning process. A cold air gun coolant system was used in the experiments and produced a jet of compressed cold air for cooling the cutting process. The air-cooling process seems to be a good environment friendly option for the hard turning. In this experimental investigation, the cutting speed, feed rate and cutting depth were chosen as the numerical factor; the cooling method was regarded as the categorical factor. An experimental plan of a four-factor (three numerical plus one categorical) D-optimal design based on the response surface methodology (RSM) was employed to carry out the experimental study. The mathematical models based on the RSM were proposed for modeling and analyzing the cutting temperature and surface roughness in the hard turning process under the dry cutting process and air-cooling process. Tool wear and chip formation during the cutting process were also studied. The compressed cooling air in the gas form presents better penetration of the lubricant to the cutting zone than any conventional coolants in the cutting process do. Results show that the air-cooling significantly provides lower cutting temperature, reduces the tool wear, and produces the best machined surface. The machinability performance of hard turning Ti–6Al–4V titanium alloy on the application of air-cooling is better than the application of dry cutting process. This air-cooling cutting process easily produces the wrinkled and breaking chips. Consequently, the air-cooled cutting process offers the attractive alternative of the dry cutting in the hard turning process.     

The effects of nickel and carbon concentrations on the wear resistance of Fe–Ni–C austenitic alloys

The effects of nickel and carbon concentrations on the wear resistance of Fe–xNi–yC (x = 14–20 wt.%, y = 0.6–1.0 wt.%) were investigated with respect to strain energy initiation of the martensitic transformation and hardness. The strain energy needed to initiate the martensitic transformation increased with increasing carbon and nickel concentrations, except in 1.0 wt.% C alloys. The wear resistance of the material decreased with increasing carbon concentration up to 0.9 wt.% C. This effect is most likely due to decrement of the martensite volume fraction with increasing carbon concentration induced by the incremental strain energy required to begin the martensitic transformation. In the case of 1.0 wt.% C, the improved wear resistance may be due to carbide precipitation.     

Experimental studies on optimization of process parameters and finite element analysis of temperature and stress distribution on joining of Al�CAl and Al�CAl2O3 using ultrasonic welding

This study is carried out to optimize the process parameters like weld time, weld pressure, and amplitude of vibration to maximize the weld strength in Al?CAl welding using Taguchi??s design of experiments methodology. Experiments are conducted using 0.3-mm thick pieces of aluminum, and the temperature generated at the weld interface and the weld strength for all the specimens are measured. Also, a finite element model is developed that is capable of predicting the interface temperature and stress distribution during welding. Further, a preliminary study on the joining of alumina to aluminum is also carried out, and the finite element models of temperature and stress distribution during welding are simulated. Results of experimental work and FEM studies are compared and found to be in good agreement.     

Numerical analysis on the static performance of tilting pad–journal gas bearing in subsystems

For tilting pad–journal bearing, each pad and the journal form a subsystem with its own local parameters reflecting the relative position of the journal and pad. In this paper, tilting pad–journal gas bearing has been studied numerically in perspective of subsystems to prevent pad spragging. The effect of eccentricity, preload and gas compressibility on local parameters have been studied in this fluid–solid coupled problem. Finite element method is adopted to solve the compressible Reynolds equation, and the load between pads configuration is chosen as a specific example.     

Multi-characteristic optimization of wax patterns in the investment casting process using grey–fuzzy logic

The present investigation focuses on optimizing the injection process parameters with multiple performance characteristics in the investment casting process using the orthogonal array with grey–fuzzy logics. A grey–fuzzy reasoning grade obtained from the grey–fuzzy logics analysis is used as a performance index to determine the optimal injection process parameters. The selected injection process parameters are injection temperature, injection time, and injection pressure, while the considered performance characteristics are linear shrinkage and surface finish. The response table, response graph, and analysis of variance are used to find the optimal setting and the influence of injection process parameters on the multiple performance characteristics. The results of confirmation experiments reveal that grey–fuzzy logics can effectively acquire an optimal combination of the process parameters. Hence, quality of wax patterns in the investment casting process can be significantly improved through this approach.     

Effects of electromagnetic stirring and rare earth compounds on the microstructure and mechanical properties of hypereutectic Al–Si alloys

In this paper, the effects of rare earth addition and electromagnetic stirring on the microstructure and the mechanical properties of hypereutectic Al–Si alloys have been reported. Hypereutectic Al–Si alloy was prepared using liquid metallurgy route and modified with the addition of cerium oxide. To control the structure, slurry of hypereutectic Al–Si alloy was subjected to electromagnetic stirring before pouring into the mould. It was observed that the addition of cerium oxide (0.2 wt.%) refined the primary silicon particles and modified the eutectic silicon particles. Further, the electromagnetic stirring of the hypereutectic Al–Si alloy reduced the average size of primary silicon particles, from 152?±?9 to 120?±?6 μm, and the length of β-intermetallic compounds decreased from 314?±?12 to 234?±?10 μm. Similarly, the application of electromagnetic stirring on cerium oxide-modified hypereutectic Al–Si alloy also reduced the average size of primary silicon particles from 98?±?5 to 76?±?4 μm and the average length of β-intermetallic compounds from 225?±?7 to 203?±?5 μm. Mechanical properties namely tensile strength, ductility and hardness of the alloys were improved with electromagnetic stirring and addition of cerium oxide appreciably.     

Research on the modeling of burr formation process in micro-ball end milling operation on Ti–6Al–4V

Burrs generated along the finished edges and surfaces in micro-milling operation have significant impact on the surface quality and operational performance of the finished parts and microstructures. In order to obtain a better recognition of burr generation process, 3-dimensional micro-ball end milling operation FEM models on Ti–6Al–4V have been established. As a result, a newfound type of burr lying on the slot base has been detected. According to their generating locations, burrs discovered in the simulation are classified into four types: entrance burr, exit burr, top burr, and slot base burr. Their formation processes, especially the generation procedure of slot base burr, are carefully investigated and analyzed. Furthermore, the correlation between cutting parameters and top burr sizes in micro-ball end milling is investigated. At last, effective validation experiments for the proposed model are conducted and good agreements are achieved in the morphologies of burrs between the experiments and simulations. It can be concluded that the adoption of a small ratio of axial depth of cut to the mill radius has a significant effect in the reduction of top burr generation in micro-ball end milling operation.     

Effect of hybrid electrochemical smoothing–roller burnishing process parameters on roundness error and micro-hardness

In this paper, a novel finishing process, which integrates the merits of electrochemical smoothing (ECS) and roller burnishing (RB) for minimizing the roundness error and increasing surface micro-hardness of cylindrical parts, is proposed. Through simple equipment attachments, electrochemical smoothing–roller burnishing (ECS–RB) can follow the turning process on the same machine. To explore the optimum combinations of the ECS–RB process parameters in an efficient and quantitative manner, the experiments were designed on the basis of the response surface methodology technique. The effect of ECS–RB parameters, namely, burnishing force, applied voltage, inter-electrode gap, and workpiece rotational speed on the roundness error and surface micro-hardness was studied. From the multi-objective optimization, the optimal combination of parameter settings are burnishing force of 350 N, applied voltage of 8.2 V, inter-electrode gap of 2.75 mm, and rotational speed of 970 rpm for achieving the required lower roundness error and higher surface micro-hardness. Surface micro-hardness considerably increases about 31.5% compared to the initial surface micro-hardness, and about 2.32 μm roundness error can be achieved using the optimum combination of process parameters. Therefore, the combination of ECS and RB is a feasible process by which it potentially reduces roundness error and surface micro-hardness of axis-symmetric parts improving their reliability and wear resistance.     

Influence of turning parameters on the machinability of homogenized Al–Cu/TiB2 in situ metal matrix composites

The increasing demand for high-strength and lightweight materials in automobile, defense, and aerospace applications necessitates the development of new composite materials and their machinability studies with wide spectrum. In this aspect, an attempt has been made to investigate the machinability characteristics of homogenized Al–Cu/TiB₂ in situ metal matrix composites. The effect of parameters, such as cutting speed, feed, and depth of cut, on performance measures, such as cutting force and surface roughness, were investigated during turning operations. As a secondary objective, the built-up edge (BUE) and chip formation are also examined. Experimental results show that better surface finish is obtained at higher cutting speed and low feed. BUE formation is observed only at low cutting speed. The chip breakability is improved due to the presence of reinforcement.     

The influence of Cu addition on precipitation in Fe–Cr–Ni–Al–(Cu) model alloys

Precipitation in Fe–Cr–Ni–Al–(Cu) model alloys was investigated after ageing for 0.25, 3, 10 and 100 h at 798 K. Characterization of nanoscale precipitates was performed using three-dimensional atom probe microscopy and transmission electron microscopy. The precipitates are found to be enriched in Ni and Al (Cu) and depleted in Fe and Cr. After 0.25 h of ageing the number density of precipitates is ∼8×10²⁴ m⁻³, their volume fraction is about 15.5% and they are near-spherical with an average diameter of about 2–3 nm. During further ageing the precipitates in the both alloys grow, but the coarsening behaviour is different for both alloys. The precipitates of the Cu-free alloy grow much faster compared with the Cu-containing alloy and their density decreases. Precipitates in Cu-free alloy change to plate shaped even after 10 h of ageing, whereas those of Cu-containing alloy remain spherical up to 10 h of ageing. The influence of Cu addition on precipitation in these model alloys is discussed with respect to the different coarsening mechanisms.     

Influence of the microstructure of Al–Si alloy on the surface-layer quality in microarc oxidation

The properties of the hardened surface layers formed by microarc oxidation on Al–Si alloy billet are investigated. The microhardness, thickness, and porosity of the surfaces formed depend on the alloy structure.     

Temperature effects on the tensile strength of brazed Fe-Cr-Al alloy (Fecralloy®) with Ni-based filler metal and corresponding image processing based analysis

Journal of Mechanical Science and Technology - Brazing bonding of iron-chromium-aluminum alloy (Fecralloy) with nickel based filler metal (MBF20) were performed at different maximum temperatures,...     

Influence of microstructure and texture on the corrosion and tribocorrosion behavior of Ti–6Al–4V

In this paper, the corrosion and tribocorrosion behaviors of Ti–6Al–4V alloy having different phase composition, texture and microstructure was investigated. Potentiodynamic polarization and electrochemical impedance spectroscopy measurements were performed to evaluate the corrosion behavior. Sliding wear tests under anodic and cathodic polarization conditions were made to assess the tribocorrosion properties. SEM, OM, and XRD were used to characterize the microstructure, texture, and morphology of the samples. The corrosion resistance was found to depend on to the microstructure, as well as the texture of the surface. A bi-modal microstructure and prismatic texture showed the best corrosion behavior. However, when corrosion was coupled to sliding wear (tribocorrosion), the hardness was found to be the controlling factor.     

Influence of the electromagnetic gap in gas–magnetic bearings on the output characteristics of high-speed rotor systems

The electromagnetic gap in gas–magnetic bearings has a considerable influence on the output load and rigidity characteristics of high-speed rotor systems, as shown by experiments and simulation.     

Experimental analysis of coating layer behavior of Al–Si-coated boron steel in a hot bending process for IT applications

The utilization of high-strength steel for automotive structural parts has increased since the oil crisis in the 1970s owing to its high strength and potential for weight reduction. Because of the limited formability of high-strength steels, automotive components are increasingly produced through hot press forming. In some instances, high-strength steel sheets are coated with an Al–Si layer in order to prevent scaling of components during hot press forming, and this can increase their reliability with a view to the dimensional accuracy and stress distribution when they are in service. In this contribution, the coating degradation mechanisms of Al–Si-coated boron steel after the hot bending process are reported. The issues related to coating degradation during hot press forming are critically reviewed at different positions on a part that was subject to hot bending. In addition, the hardness and friction coefficient were tested by a nano-indenter at various positions. The relationship between the experimental parameters and coating layer properties is also reported. It is concluded that the bending deformation affected the coating layer behavior the most.     

Experimental investigation and optimization of EDM process parameters for machining of aluminum boron carbide (Al–B4C) composite

This study investigates the effect of electric discharge machining (EDM) process parameters [current, pulse-on time (T_on), pulse-off time (T_off) and electrode material] on material removal rate (MRR), electrode wear rate (EWR) and surface roughness (SR) during machining of aluminum boron carbide (Al–B₄C) composite. This article also summarizes a brief literature review related to aluminum metal matrix composites (Al-MMCs) based on different process and response parameters, work and tool material along with their sizes, dielectric fluid and different optimization techniques used. The MMC used in the present work is stir casted using 5% (wt) B₄C particles of 50 micron size in Al 6061 metal matrix. Taguchi technique is used for the design of experiments (L₉-orthogonal array), while the experimental results are analyzed using analysis of variance (ANOVA). Response table for average value of MRR, EWR and SR shows that current is the most significant factor for MRR and SR, while electrode material is most important for EWR. ANOVA also confirms similar results. It is also observed that the optimum level of process parameters for maximum MRR is A₃B₁C₃D₃, for minimum EWR is A₁B₂C₃D₁, and for SR is A₁B₃C₃D₃.