Recast Layer Thickness Research Articles

Surface modification of titanium alloy using hBN powder mixed dielectric through micro-electric discharge machining

In the present study, hard, wear, and corrosion resistance coating is deposited on titanium alloy with hexagonal boron nitride powder (avg. size 70 nm) suspended in deionized water by micro-electro discharge coating process. The influence of input process parameters on surface integrity, wear properties, and corrosion resistance is studied. XRD analysis of coating surface shows the presence of phases such as BN, Al2O3, TiN, TiAlN, TiO, and CuO. Micro-hardness of the coating surface increases by five times as compared to titanium alloy (parent material). At the parameter settings of 60 V, 0.7 duty factor, and 12 g/l, the maximum deposition rate of 5.65 ± 0.1 × 10−4 g/min and recast layer thickness of 13.1 μm is obtained. Pin on disk wear test results reveal the reduction of wear rate of the coated surface to one-fourth of that of the base material. The average coefficient of friction (COF) for the deposited BN surfaces reduces to 0.26 from 0.4 (substrate material). Corrosion resistance of the coated surface is found to be 1.24 μm/year in flowing water conditions and 1.07 μm/year in stagnant water whereas for the parent material it is 5.92 μm/year in flowing water condition and 4.89 μm/year for stagnant water condition.

Analysis and reduction of process energy consumption and thermal deformation in a micro-structure wire electrode electric discharge machining thin-wall component

Abstract In order to reduce process energy consumption and geometric error induced by thermal deformation simultaneously in sustainable wire electrode discharge machining(WEDM) process, this work applies a new micro crack wire electrode to enhance machine characteristic, and describes the reduction mechanism of above two critical factors compared with brass wire when machining thin-wall components. Firstly, a number of experiments are conducted to explore the effects trend of machining parameters on thermal deformation and material removal rate(MRR) by above two wire tools. The results indicate that micro crack wire can achieve a significant decrease by an average of 32.60% in MRR and 42.69% in thermal deformation compared with brass wire. And the best parameters combination for micro crack wire is pulse on time:13 μs、pulse off time:8 μs、wire speed:0.09 m/s、water pressure:1.1 MPa. The analysis of residual stress and discharge points distribution explains the improvement mechanism of micro crack wire by decreasing the magnitude of residual stress (33.14% on average) and non-uniformity of discharge points distribution (36.32% on average). Besides, the results of energy consumption and environmental effect demonstrate that micro crack wire can obviously reduce energy consumption by an average of 22.68% and debris pollution. Eventually, the analysis of surface topography, debris shape, micro structures, recast layer thickness and surface element composition are also performed. It can be concluded that the micro crack wire shows prominent superiority and potential for applications in the sustainable manufacturing field.

Investigation of cutting speed, recast layer and micro-hardness in angular machining using slant type taper fixture by WEDM of Hastelloy X

Wire electric discharge machining (WEDM) is a thermo-electric spark erosion process that can machine any difficult to cut materials. Taper cutting in WEDM is a unique feature that has many problems such as taper angular inaccuracies, wire cut and distribution of dielectric fluid during machining. In the present research work, angular machining is performed for generating a tapered component using a novel slant type taper fixture which overcomes the disadvantages of taper cutting in WEDM. The machining was performed on Hastelloy X at various angles namely 0°, 30° and 60° with different parameters in the machining range. The behaviour of cutting speeds for Taguchi’s L9 set of experiments at 0°, 30° and 60° angle of tilt in machining was reported. The cutting speed is ranging from 0.16 mm/min to 2.49 mm/min during angular machining. From the SEM micrographs, the highest average recast layer thickness for highest cutting speed parameter was 26.4 μm at 0° and for the lowest cutting speed parameter, it was measured 6.4 μm lowest at 60° compared to the remaining angle of cut. The variation of micro-hardness at 0°, 30° and 60° tapered components at the highest cutting speed parameter were measured using Vickers micro-hardness test. The lowest Vickers hardness was found to be 167Hv at 0°. However further it is increased to 173Hv and 180Hv at 30° and 60° angle of cut respectively.

Adaptive neuro-fuzzy inference system based modeling of recast layer thickness during laser trepanning of Inconel-718 sheet

Re-solidification of molten material during the laser trepanning of Inconel-718 is a major hindrance in achieving good quality drill with high precision and accuracy. Re-solidification affects the performance of the drilled hole. Many researchers have tried for the optimization of laser trepan drilling in order to improve the drilled hole quality characteristics. But till now, limited work has been reported in concern with recast layer formation in laser trepan drilling of Inconel-718. This paper experimentally investigated the recast layer formation during laser trepan drilling followed by the prediction of the recast layer formation using the adaptive neuro-fuzzy inference system (ANFIS). Experiments are performed on 1.4-mm-thick Inconel-718 sheet using pulsed Nd: YAG laser. Recast layer thickness has been measured for each experiment followed by the ANFIS-based prediction of recast layer. Moreover, the effect of different input parameters on the recast layer has also been discussed.

Empirical modeling and optimization of process parameters in ultrasonic assisted laser micromachining of Ti–6Al–4V

In the present study an attempt was made to create micro holes in Ti–6Al–4V titanium alloy by laser machining process. In order to enhance the machinability of the in terms of material removal rate (MRR) and recast layer thickness (RLT), ultrasonic vibration has been associated with the process. A comprehensive experimental study has been carried out to understand interaction effect of ultrasonic assisted laser machining parameters viz. ultrasonic vibration amplitude, laser power, pulse frequency and gas pressure on process quality characteristics. Analysis of variances has been carried out to find which factors has greatest effect on performance measures. Finally an optimization approach based on response surface method was carried out to obtain parameter setting regarding maximum MRR and minimum RLT and taper. Results indicated that the vibration amplitude has greatest effect on improving the MRR and RLT. Results revealed that selection of 40 μm vibration amplitude, 980 W laser power, 1200 Hz modulation frequency and 0.25 MPa gas pressure is an optimal parameter setting yields material removal rate of 2 mm3/min and RLT of 439 μm. The desirability for this parameter setting is 78%.

Surface morphology evaluation of hardened HSLA steel using cryogenic-treated brass wire in WEDM process

Surface morphology of a high strength low alloy steel is analyzed on wire electric discharge machining (WEDM) process with a cold-treated (CT) brass wire. Cold treatment process is carried out at − 70 °C for 24 h to refine the microstructure of brass wire for smooth discharge energy during machining process. Fractional factorial design is used to measure the response of recast layer thickness (RLT), wire material infusion (WMI), and micro-hardness (MH) of hardened HSLA steel. CT brass wire, servo voltage (SV), pulse on time (Ton), pulse off time (Toff), wire tension (Tw), and flushing pressure (Fp) of deionized water are selected as input process parameters. Analysis of variance (ANOVA) is performed to test the adequacy and significance of the developed mathematical models. Ton is observed as the most effective input process parameter followed by Toff and CT brass wire. Low-energy parameters with CT brass wire exhibits results with reduced RLT and WMI on machined surface as compared to NCT brass wire. CT brass wire is less wear off with respect to NCT brass wire while machining workpiece at same input process parameters.

High-speed EDM milling with in-gas and outside-liquid electrode flushing techniques

The high-speed EDM milling process using hollow tool electrode with high-speed gas flushing inside electrode and high-speed liquid flushing outside electrode is investigated (gas-liquid high-speed EDM). The liquid in electrode outer is used to compress and cool the gas dielectric, which can add to the capacity of expelling the debris and cooling the machining gap for gas dielectric. The high-speed EDM milling experiments were carried out by using gas, liquid, and gas-liquid combinations as the dielectric. Compared with gas EDM, the MRR of gas-liquid EDM can improve 23% and the WOC can reduce 15% with the same SR. Gas-liquid EDM shows advantages over the liquid EDM in reducing 30% SR, 50% WOC, 82% recast layer thickness, and significantly fewer micro-cracks. The flow field simulation results show that the higher pressure in gas-liquid leads to a higher MRR compared with that in gas.

Multi-objective optimization in wire-EDM process using grey relational analysis method (GRA) and backpropagation neural network–genetic algorithm (BPNN–GA) methods

PurposeThe purpose of this paper is to investigate prediction and optimization of multiple performance characteristics in the wire electrical discharge machining (wire-EDM) process of SKD 61 (AISI H13) tool steel.Design/methodology/approachThe experimental studies were conducted under varying wire-EDM process parameters, which were arc on time, on time, open voltage, off time and servo voltage. The optimized responses were recast layer thickness (RLT), surface roughness (SR) and surface crack density (SCD). Arc on time was set at two different levels, whereas the other four parameters were set at three different levels. Based on Taguchi method, an L18 mixed-orthogonal array was selected for the experiments. Further, three methods, namely grey relational analysis (GRA), backpropagation neural network (BPNN) and genetic algorithm (GA), were applied separately. GRA was performed to obtain a rough estimation of optimum drilling parameters. The influences of drilling parameters on multiple performance characteristics were determined by using percentage contributions. BPNN architecture was determined to predict the multiple performance characteristics. GA method was then applied to determine the optimum wire-EDM parameters.FindingsThe minimum RLT, SR and SCD could be obtained by setting arc on time, on time, open voltage, off time and servo voltage at 2 ms, 3 ms, 90 volt, 10 ms and 38 volt, respectively. The experimental confirmation results showed that BPNN-based GA optimization method could accurately predict and significantly improve all of the responses.Originality/valueThere were no publications regarding multi-response optimization using a combination of GRA and BPNN-based GA methods during wire-EDM process available.

Modeling and Analysis of Machining Parameters and Responses of Wirecut Electric Discharge Machining of Al2124/SiCp using Response Surface Methodology and Soft Computing Techniques

In this work, Wirecut Electric Discharge Machining (WEDM) of Al 2124/ SiCp metal matrix composite material is studied to evaluate the influence of input parameters on response characteristics namely, kerf, Material Removal Rate (MMR), Surface Roughness (SR), Recast Layer Thickness (RCT), and Surface Crack Density (SCD). Central composite design, a technique from design of experiments is used to conduct 31 experiments. The input parameters selected for estimation of machinability are pulse on time (Ton), pulse off time (Toff), current (IP), and Servo Voltage (SV). Analysis of variance (ANOVA) is carried out to know the effect of influence parameters on responses. The regression models are developed in Response Surface Methodology (RSM)and are used in soft computing techniques as input equations for optimizing the single and multi-response optimization of response parameters. Desirability approach is used in single and multi-objective optimization of response parameters. Single objective optimization is carried out by RSM, the Genetic Algorithm (GA), Particle Swarm Optimization (PSO), and Firefly Algorithms (FA). Confirmation experiments are conducted on the adequacy of the mathematical models developed in RSM and it shows good agreement between experimental and predicted values. The variation of predicted responses from different optimization techniques for single objective optimization is found to be less than 1%. From the results it is also observed that for single objective optimization all evolutionary algorithms are found to be suitable for WEDM.

Wire electrical discharge machining of AZ91 magnesium alloy; investigation of effect of process input parameters on performance characteristics

Magnesium alloys have wide application in aerospace and automotive industries due to their high strength to weight ratio and desired mechanical properties. In this present research, the effects of three input parameters of the wire electrical discharge machining (WEDM) process, including pulse on time, pulse current, and servo feed rate were studied on the performance characteristics namely; material removal rate, kerf width, and surface roughness during machining of AZ91 magnesium alloy. This research is the first comprehensive study of the electrical discharge machining of magnesium alloys and aims to analyses the machinability and behavior of materials with low melting point and high thermal conductivity during WEDM. For this purpose, 15 experiments were designed by the design of experiments technique. Using response surface methodology, mathematical models were developed and the contribution percentage of each variable input parameter on output parameters was found. Analysis of variance results revealed that pulse on time and pulse current have the most effect on process output parameters, respectively, while the effect of the servo feed rate was insignificant. The experimental results showed that the material removal rate and the kerf width during the WEDM of magnesium is considerably higher than hard materials and it can be reached to about 180 mm3 min−1 while kerf width and surface roughness are about 0.450 and 4.683 μm, respectively. Despite the high cutting rate, the surface roughness is appropriate and comparable to hard materials, indicating high machinability of magnesium alloys by WEDM. To study the surface topography and microstructural changes, atomic force microscope, scanning electron microscope and EDX analysis have been used. SEM micrographs show that the number of microcracks, indicating the surface damage, is low in the machined surface which shows WEDM capability in producing non-damaged work surfaces. The maximum recast layer thickness is about 6.91 μm and minimum is 3.09 μm.

EDM performance of Inconel 718 superalloy: application of multi-walled carbon nanotube (MWCNT) added dielectric media

Electro-discharge machining (EDM) is very promising non-traditional machining route to cut ‘difficult-to-machine’ materials like Inconel 718 superalloy. However, low material removal efficiency and inferior surface integrity restricts EDM application on Inconel 718. In order to improve EDM performance, multi-walled carbon nanotube (MWCNT) dispersed into kerosene is explored as dielectric media. Experiments are conducted by varying peak discharge current with a fixed concentration of MWCNT (0.5 g/l) added to kerosene. EDM performance is assessed in purview of material removal efficiency, tool wear rate, and surface integrity (morphology and topography) of the EDMed specimen. Apart from morphological study, surface topography including surface roughness, crack density, recast layer thickness, metallographic alteration, residual stress, and micro-indentation hardness of the machined specimen are studied in detail. It is concluded that as compared to conventional EDM, use of MWCNT-mixed dielectric media (0.5 g/l) significantly improves machining performance.

Experimental analysis of WEDM machined surface of Inconel 825 using single objective PSO

The present research focuses on the analysis of surface topography of Inconel 825 superalloy, machined with Wire Electrical Discharge Machining. Surface texture analysis includes cracks, craters, pockmarks, heat affected zone and recast layer thickness. Particle swarm optimization used response surface methodology (RSM) to find the optimum combination of WEDM characteristics viz. pulse on time, pulse off time, gap voltage, peak current, wire tension and wire feed. Surface crack density (SCD) and recast layer thickness (RCLt) are the output responses. The results manifest that pulse on time, peak current and gap voltage are the most influential parameters for surface topography. At optimum combination of process parameters, the value obtained for SCD is 0.000423 μm/μm2 and RCLt is 8.044 μm. Under optimized conditions, surface topography of the machined specimen is improved that makes it suitable for implementation in industry.

Study of material characteristics in laser trepan drilling of ZTA

Zirconia Toughened Alumina (ZTA) ceramic is used to make distinct components of aerospace, military and biomedical industries which require suitable machining method free of mechanical forces. Recent researchers reveal that Laser Beam Machining has diverse potential to overcome machining difficulty of structural ceramics. But to enhance the durability and performance of these components, study of material properties became essential after laser machining because this process involves intense heat or thermal energy. Present study investigates the material characteristics of laser trepanned ZTA plate with the aim to explore the effects of process parameters on recast layer thickness, microcrack width and microhardness. The outcome of study may be helpful in setting the processing regime for laser trepanning of ZTA ceramic which may furnish the products with minimum recast layer thickness and microcrack width along with minimum change in microhardness. The experimental results show that lower pulse width or trepanning speed, and higher air pressure reduce the recast layer thickness and microcrack width.

Surface integrity analysis of Nitinol-60 shape memory alloy in WEDM

ABSTRACTNitinol-60, which belongs to the group of Nickel-Titanium based Shape Memory Alloys, offers remarkable properties like high wear resistance, high strength, shape memory, and super-elasticity; thereby making it convenient for use in aircraft and biomedical applications. However, these properties make Nitinol a ‘difficult-to-machine’ material during the traditional machining processes. Hence an experiment based study on Wire Electrical Discharge Machining of Nitinol-60 has been executed based on the parametric effects. This study attempts to provide the quantitative details of the machined surfaces in terms of maximum peak to valley height, the average peak to valley height, recast layer thickness, and surface crack density. In addition, Response Surface Methodological models of these surface parameters along with the cutting rate have been developed. Monte Carlo simulation of the generated regression equations is carried out to study the behavior of the models using randomly generated data. The results show that the developed models are in agreement with the experimental data; which further indicates that the optimal parameters are suitable for mass production.

Assessing the Influence of Surfactant and B4C Powder Mixed in Dielectric Fluid on EDM of Titanium Alloy

The aim of the present investigation is to optimize process parameters by mixing various additives in dielectric fluid on EDM of Ti-6Al-4V alloy using Taguchi technique. Span20 surfactant and B4C powder are considered as additives. Span20 surfactant mixed in dielectric fluid degrades the agglomeration of tar debris and powder particles. It also improves the discharge gap and breakdown strength. Five input process parameters were selected, viz. discharge current (Ip), pulse on time (Ton), pulse off time (Toff), B4C powder concentration (B4C Con.) and surfactant concentration (Surf Con.) and varied to explore their performances on Material Removal Rate (MRR), Surface Roughness (SR) and Recast Layer Thickness (RLT). In this study, Taguchi L27 Orthogonal Array (OA) was adopted for planning and designing the experiments. It was observed from the experimental results that the additives in dielectric fluid significantly improved MRR, reduced SR and RLT. Analysis of Variance (ANOVA) test has identified that Ip, Ton and Surf con., are important process parameters affecting MRR and SR; Ip, Ton, Surf con., and B4C con., were highly relevant process parameters influencing RLT. An empirical expression for MRR, SR and RLT was developed by using statistical software. Additionally, surface modification was studied at optimized EDM conditions by using Scanning Electron Microscope (SEM) micrographs.

Effect of Machining on Workpiece Surface Characteristics in Electric Discharge Drilling (EDD)

In electric discharge drilling (EDD), rapid local heating and cooling of the workpiece surface by means of electric discharges results in surface layers (recast, heat affected and base material). In this study, the main workpiece surface texture measures, namely the recast layer thickness (RLT) and average surface roughness (Ra) characteristics were investigated for varying machining parameters (discharge current and pulse on time). The conducted experiments revealed the strong dependence of surface characteristics on machining parameters.

Characterization, adhesion strength and in-vitro cytotoxicity investigation of hydroxyapatite coating synthesized on Zr-based BMG by electro discharge process

In this study, biocompatible hydroxyapatite (HA) coatings by HA mixed electro discharge coating (HA-EDC) process was synthesized on the Zr-based bulk metallic glass (BMG) surface. The aim is to promote the cells proliferation by synthesizing a strongly adhered oxide and carbide coating on the Zr-based BMG and blocking the release of Ni and Be in the BMG alloy. Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), X-ray Photoelectron Spectroscopy (XPS) and X-ray Diffraction (XRD) were employed to characterize the surface morphology, elemental compositions and the phases present in the electro-discharge coated Zr-based BMG. SEM analysis presented the formation of various micro and nano-sized craters, porosities and cracks on the coated and uncoated BMG surface. The EDX and XPS results depicted the migration of HA elements (Ca, P, O and K) to the workpiece surface, which replaced the Ni and Be in the Zr-based BMG alloy. The SEM cross-section revealed the formation of the nanoporous coating of about 27.2 μm thick and a reduced recast layer thickness. The XRD characterization identified the phases like CaZrO3, ZrO2, Ca5(PO4)3OH, ZrC and TiC formed on the coated BMG surface. A strongly adhered HA coating with adhesive failure of about 132 N load was achieved during the scratch test. A cytotoxicity study using an in-vitro 3-(4,5 dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) Assay revealed a significant rise in cells viability on the coated Zr-based BMG specimen.

Study and optimization of recast layer thickness and surface quality in laser trepan drilling of ZTA

Zirconia-toughened alumina (ZTA) has promising characteristics to be used for combustion chambers, pump, heat exchanger, armor, bearings, cutting tool inserts, aerospace, and nuclear parts. But it has limited applications due to its adverse machining characteristics. Laser machining has been proven to machine difficult-to-cut-materials with certain limitations. Being thermal energy–based advanced machining process, laser machining develops extreme thermal stresses and causes melting/vaporization. Therefore, ceramic samples are preheated at high temperature before applying laser machining. Control of laser machining quality without preheating of ZTA samples is a difficult task. The present paper investigates the laser trepan drilling (laser hole cutting) of 6.0-mm thick ZTA without preheating with the aim to optimize recast layer thickness, microcrack width on hole surface, and surface roughness. The optimal solution is determined by using a genetic algorithm. The results show an average improvement of approximately 15% in the above characteristics, considered simultaneously. The surface microcrack widths have been reduced much below than earlier claimed in laser processing of ceramics by other researchers. Mathematical relationship between input and output parameters has been developed and validated. The effect of process parameters on quality characteristics has also been discussed, scientifically.

Effect of water-based ultrasonic vibration on the quality of laser trepanned microholes in nickel super-alloy workpieces

Effusion cooling holes are commonly drilled in nickel super-alloy aero-engine components using electro-discharge machining (EDM) or pulsed laser drilling. While drilling quality of EDM is high, its machining efficiency is normally relatively low, in addition to its high tooling cost. The drilling efficiency of a millisecond pulsed laser is much higher, while a recast layer often forms on the hole wall. In this paper, an ultrasonic-assisted laser trepanning technology is reported for trepanning blind and through holes in nickel super-alloy samples. The influence of ultrasonic vibrations on hole geometry, morphology, microstructure, recast layer thickness and mechanical performance was investigated through comparing holes trepanned with and without ultrasonic assistance. It was found that ultrasonic vibrations contributed to laser trepanning process mainly by means of grain refinement strengthening, hard phase precipitation and dispersion strengthening, and led to recast layer reduction and negative taper for the through hole trepanned. The percentage of the measured recast layer reduction induced by ultrasonic vibrations approximately ranged from 15.73% to 31.82%. Besides, a maximum percentage of around 19.43% was achieved for micro hardness improvement induced by ultrasonic vibrations. However, the width of laser trepanned heat affected zone (HAZ) was increased by around 36.00% due to ultrasonic vibration assistance. In addition, the HAZ grains near the recast layer was refined via increasing the trepanning speed, decreasing pulse width. Compared with the base metal, the impact toughness was increased by using ultrasonic-enhanced laser trepanning mainly due to grain refinement strengthening.

Research on Electrolyte Jet Assisted Laser Micromachining Technology

For the traditional laser processing method, processing defects such as recasting layer, microcrack and high concentration of heat affected zone are inevitably generated, which reduces the surface quality and service life of the microstructure. In this paper, the electrolyte jet assisted laser micromachining technology is proposed. This technology applies the laser beam and the corrosive electrolyte jet beam coaxially to the workpiece. At the same time as the laser acts, the corrosive electrolyte jet continuously scour, cool and slightly corrode the processing area. The effect can reduce the thickness of the recast layer, reduce the number of microcracks, and eliminate the high concentration of the heat affected zone. In this paper, the causes of recasting layer in laser processing are analyzed firstly. The material removal mechanism involved in the laser jet assisted laser micromachining and the mechanism of laser coupled electrolyte jet beam are studied. The flow field in the laser jet assisted laser drilling process is established. And the mathematical model of the temperature field; the effects of laser pulse energy, laser repetition frequency, electrolyte concentration and electrolyte jet velocity on the thickness of material recast layer were studied, and the basic processing technology of electrolyte jet assisted laser micromachining was preliminarily mastered, laying the foundation for further research on electrolyte jet assisted laser micromachining technology.