Recast Layer Formation Research Articles

Theoretical investigation of multipulse femtosecond laser processing on silicon carbide: ablation, shielding effect, and recast formation

In this study, we propose a transient multi-physics coupling model for ultrafast laser ablation based on the material point method (MPM). By employing the continuum assumption for material, heat transfer equation and particle phase change, as well as spatial discretization of the model, we achieve simulations of various coupled physical phenomena such as material temperature, phase change, stress, and recast layer formation. In terms of time, we simulate laser processing processes with up to 1000 pulses. The model is validated by comparing with experimental results on ablation morphology, recast layer formation from melted particles, and surface oxidation. The proposed model accurately captures the multi-physics aspects of ultrafast laser ablation processes in SiC ceramics. The experimental validation confirms the model’s reliability and offers valuable insights into the underlying physical phenomena.

Influence of laser texturing on the properties of fusion joints between aluminum alloys and carbon fiber reinforced thermoplastic composites

Laser texturing is an effective method to enhance the fusion joining of aluminum alloy (Al) to carbon fiber reinforced thermoplastics composite (CFRTP). The enhancement effect is related to the morphology and spacing of the microstructures on Al surface. However, because of the correlation between the morphology and the spacing of the microstructures, excessive dense microstructures change the morphology, leading to a reduction in the enhancement effect, while sparse microstructures are also difficult to significantly enhance the joint. To this end, this paper proposes an improved laser texturing process to enhance fusion joints, through the investigation of the recast layer formation process during laser texturing on the Al surface, which comprehensively reveals the synergistic effects of microstructural morphology and spacing on joint properties. The results indicated that the increase of the number of laser processes and the microstructure spacing increased the height of the recast layer, with the difference that the microstructure spacing had less effect after increasing to a certain value. With the increase of microstructure spacing, the morphology of the microstructure on the Al surface transformed from the serrated microstructure to the double-scale microstructure, and finally to the independent microstructure, affected by the recast layer on sides of the microstructure. Once the dual-scale microstructures were formed on the Al surface, the shear strength of the Al/CFRTP fusion joint was the highest with a value of 25.05 MPa. The findings could provide a basis for laser texturing pretreatment for fusion joining.

Performance evaluation in die-sinking EDM of polygonal micro cavities over EN-24 alloy steel using cylindrical electrode and polygon cycle approach

The integration of advanced Electrical Discharge Machining (EDM) technology, incorporating short and electronically pulsed discharges with precise circular electrode movements, has enabled the production of intricate 3D microstructures and cavities. This paper aims to investigate the machining performance of polygonal cavities—triangular, square, pentagon, and hexagon—fabricated on steel samples using a 400 µm cylindrical copper electrode within the polygon cycle approach of EDM. Experimental investigations were conducted to assess shape error, tool wear rate, recast layer formation, and elemental characterization. Various discharge patterns and side discharges were examined to understand their effects on spark gap uniformity, tool deflection, and discharge stability. The results revealed non-uniform spark gaps, tool deflection, and corner rounding due to varying discharge patterns and side discharges. Tool wear rate was found to be directly related to polygon complexity, with higher-order polygons leading to increased wear due to extended machining durations and heat accumulation. The maximum tool wear of 7.69 × 104 µm3/s occurred in case of hexagonal cavities while in case of triangular cavities, the tool wear rate was minimum having value of 5.77 × 104 µm3/s. Scanning Electron Microscopy (SEM) examinations showed the presence of recast layers and micro-cracks, particularly in cavities with higher shape complexities. Energy Dispersive X-ray Spectroscopy (EDS) analysis identified copper deposition, local material evaporation, and foreign element accumulation on the cavity surfaces. This study provides insights into the machining performance of polygonal cavities in EDM processes. The findings underscore the influence of discharge patterns, polygon complexity, and material interactions on tool wear, surface quality, and microstructure integrity. Understanding these factors can inform optimization strategies for EDM processes, leading to enhanced precision and efficiency in microstructure fabrication.

Performance analysis of powder-assisted micro-drilling operation using micro-EDM

Miniaturization is governed by the precise and accurate micro-machining operations of various applications. Micro-EDM has emerged as a feasible method for attaining microscale high-precision drilling. The present paper aims to conduct an experimental investigation for drilling micro-holes on copper using the Alumina (Al2O3) powder mixed Micro-EDM technique. Process parameters, including voltage, feed rate, and powder concentration, are varied in experimentation to evaluate their impact on response measures like MRR, TWR, taper angle, and aspect ratio. ANOVA determines the individual contribution of process parameters on each response measure. Voltage is the primary factor influencing MRR (93.5%), TWR (58.24%), and aspect ratio (67.3%), whereas the interaction effect of voltage with powder concentration primarily affects the taper angle (32.36%). Furthermore, the GRA method has optimized the multiple parameters for different responses. The optimum combination of parameters was obtained at a voltage of 125 V, powder concentration of 0.8 g/L, and tool travel speed of 9 µm/s at which better responses are received. The results obtained from FESEM analyses indicate that utilizing alumina (Al2O3) Nano-powder in the dielectric fluid leads to improved effectiveness and reduces the formation of micro-cracks, and micro-voids. Furthermore, the formation of recast layer is reduced by 36.49% as compared to without powder mixed EDM oil during micro-drilling operations.

Experimental investigation on the surface quality of WEDM machined 20MnCr5 steel for gear application

This experimental study investigates the Wire-cut Electrical Discharge Machining (WEDM) of 20MnCr5 steel, a low alloy steel grade material which is intended for the production of gears, shafts and other parts which need high surface hardness and wear resistance. WEDM is a crucial manufacturing process for producing gears, shafts, spindles, and various mechanical components. The investigation focuses on three key performance parameters: profile error, material removal rate (MRR), and surface roughness (SR), employing five WEDM parameters—wire feed (Wf), wire tension (Wt), servo voltage (SV), discharge arc-off time (Toff), and arc-on time (Ton) - by employing the Taguchi L27 orthogonal array. The study reveals that, in comparison to arc-on time and servo voltage, wire feed rate and tension have a lesser impact. Higher arc-on time and servo voltage result in increased profile error, while reduced wire tension values elevate surface roughness. Recast layer formation has been explored under different WEDM input parameters, revealing its dependence on arc-on time, voltage, wire tension, and feed rate. Higher voltage leads to uneven surfaces with larger globules and deep craters, contributing to a thicker recast layer at higher arc-on time and servo voltage.

Hole formation mechanisms in double-sided laser drilling of Ti6Al4V-C/SiC stacked materials

This is the first investigation on the potential of doubled-sided laser drilling for hole making in Ti6Al4V-C/SiC, a hard-to-machine stacked structure that holds critical significance in high-temperature structural applications. While previous literature reported laser drilling-induced microstructural change in Ti6Al4V and C/SiC single sheets respectively, a comprehensive understanding of the melt pool formation process and its influence on hole morphology/quality is still lacking. The complexity increases when Ti6Al4V is coupled with C/SiC in a stacked structure, highlighting a significant yet understudied knowledge gap in understanding the intricate material interactions at the interface. Here we present a multifaceted study combining novel computational fluid dynamics (CFD) modeling approach with ablation mechanism investigation through advanced microstructure analysis. A hybrid CFD modeling strategy integrating volume of fluid method and level set method has been developed to successfully simulate the evolution of hole shape, recast layer formation, and melt pool flow behaviour in Ti6Al4V-C/SiC. This model provides comprehensive insights into molten pool dynamics under various laser drilling conditions, fostering a fundamental understanding of the mechanism that drives recast layer formation and influencing surface quality. To validate our modeling outcomes, extensive experimental investigations were undertaken across a range of laser drilling conditions. Whenever possible, samples were analysed using advanced materials characterization techniques, including scanning electron microscopy, energy dispersive spectroscopy, and electron backscatter diffraction, to elucidate the microstructural evolution within the recast layer and the formation of the heat-affected zone. Whenever possible, the results were also compared with single side drilled Ti6Al4V-C/SiC stacks, Ti6Al4V or C/SiC single sheets (i.e., the benchmark references). Our experimental findings align well with the modeling results, systematically illustrating that doubled-sided laser drilling of the stacked structure outperforms the conventional single-sided laser drilling in terms of hole morphology, surface roughness, and reduced recast layer formation. Despite these promising results, the proposed technology is currently limited to laboratory scales and lacks capacity in manufacturing certain parts with complex geometry. Future outlook has therefore been proposed with potential solution to address these challenges and enable real world applications in future.

Unravelling the analysis of electrical discharge machining process parameters, microstructural morphology, surface integrity, recast layer formation, and material properties: A comparative study of aluminum, brass, and Inconel 617 materials

Inadequate research regarding how material characteristics affect vital yield parameters in EDM, particularly for aluminium, brass, and Inconel 617. An limited study has examined how EDM process parameters like peak current (Ip), gap voltage, and pulse on time (Ton) affect recast layer thickness, tool wear rate, surface roughness, crack density, globule formation, material removal rate, and crater formation. The interaction between thermal conductivity, microcracks, and recast layers in EDM is uncertain. Material characteristics' implications on XRD patterns and globule formation during EDM machining were not extensively investigated. EDM process parameters and their impacts on response variables such tool wear rate (TWR), material removal rate (MRR), surface roughness, and globule formation for diverse materials have received minimal analysis. In addition, non-ferrous workpiece materials are integral to the electrical discharge machining process. This study delves into how the physical properties of materials influence key yield parameters, including tool wear rate, surface roughness, crack density, globules, material removal rate, and crater formation. The investigation covers Inconel 617, brass, and aluminum, revealing peak current (Ip) as the most influential factor for highly thermally conductive materials when compared to gap voltage and pulse on time (Ton). Notably, Inconel 617 exhibits longer cracks, while aluminum displays smaller ones, and deeper cracks are found on the surface of aluminum, contrasting with the broader craters observed on Inconel 617. Recast layer thickness varies, ranging from 8.3 μm for brass to 13.8 μm for aluminum. The study validates response values extensively against experimental data and highlights brass's superior surface finish. It further uncovers that plasma-generated craters are predominantly semispherical, with the plasma's diameter expanding faster than the crater's size. Sub-surface re-solidification emerges as a source of stress and micro-cracks, which diminish material's fatigue strength. Notably, aluminum exhibits a greater number of elegant microcracks on the machined surface, while brass and Inconel 617 have fewer. Recast layer thickness measurements indicate approximately 13.8 μm for aluminum, 8.3 μm for brass, and 9 μm for Inconel 617. Additionally, the thermal erosion process enhances the microhardness of the machining zone's subsurface due to the formation of oxides and carbides and the re-solidification of particles. Different material characteristics are revealed through X-ray diffraction (XRD) patterns, while globules, small and spherical, weakly adhere to the machining zone's subsurface. In particular, aluminum machined surfaces feature fewer globules, while brass surfaces exhibit a higher quantity, attributed to their varying thermal conductivity.

Effects of WEDM and AWJ cutting methods on induction motor efficiency and total magnetic losses: Experimental design and response surface methodology

In this study, the effect of cutting electrical steel laminations using abrasive water jet (AWJ) and wire electrical discharge machining (WEDM) techniques on 5.5 kW induction motor efficiency (MEfficiency) and total magnetic losses (TLosses) was investigated. After the stator and rotor packages were formed, winding, varnishing and mechanical assembly processes were carried out and the motors were prepared for MEfficiency and TLosses tests according to the IEC 60034-2-1-1A standard. Tests were performed using different frequencies (f) and motor loading rates (MLoad). While burr formation was observed with the effect of plastic deformation on the cutting edge of electrical steels with AWJ, recast layer formation was observed with the effect of heat in WEDM. MEfficiency decreased while TLosses increased due to increasing f and MLoad in both cutting methods. Maximum MEfficiency and minimum TLosses values were measured in WEDM, it was determined that optimum results using Response Surface Methodology (RSM) were measured at f of 50 Hz and MLoad of 100% values in both cutting methods. The statistical effects of f and MLoad on MEfficiency and TLosses were revealed with ANOVA (Analysis of variance). In addition, mathematical models were developed for the prediction of MEfficiency and TLosses.

Exploring the intricacies of machine learning-based optimization of electric discharge machining on squeeze cast TiB2/AA6061 composites: Insights from morphological, and microstructural aspects in the surface structure analysis of recast layer formation and worn-out analysis

Aluminium (Al) Alloy-6061/TiB2 was developed with Squeeze casting while varying composite quantities with titanium diboride (TiB2). The metallographic structure of the composite was investigated using EDS and scanning electron microscopy (SEM). The machining of developed composite is challenging with the conventional methods due to higher tool wear and surface roughness (Ra). This study analyses the output responses, and machinability of TiB2 of 15% volume reinforced AA6061 composites using Electrical Discharge Machining (EDM). The EDM operation variables such as current, pulse on time, and voltage gap were utilized to examine material removal rate (MRR), tool wear rate (TWR) and Ra employing Box–Behnken design of experiments. The MRR, TWR and Ra data acquired from various experiments were optimized considering single and multiple objectives by a hybrid approach. Machine learning (ML) was applied to predict responses using linear regression (LR), decision tree (DT) and random forest (RF). The samples' recast layer was examined using SEM, and the thickness of the recast layer was also documented. The Al6061 alloy's SEM micrographs reveal deep equiaxed dimples on its fracture surface, indicating a high level of plastic deformation before failure. TiB2 is evenly distributed as darker particles in the Al-matrix alloy with no directional-orientation. The Al6061-15 wt% TiB2 composites' fracture surfaces display deep dimples, ductile-fracture for Al6061 alloy due to higher plastic deformation, and cleavage facets in some areas. The aluminum alloy's wear pattern depicts long, extensive ploughing grooves with short cracks parallel to the sliding direction at the grooves' bottom. SEM micrographs in recast-layer formation have reported that molten metal ligaments break into droplets during flushing, exposing fresh surfaces. The aluminum alloy's groove width is larger compared to the composites. Thus, it can be observed that the wear tracks on the base Al6061 alloy are larger and deeper in comparison to the Al- 15 wt% TiB2 surface composites due to the presence of hard TiB2 particles. Also, the recast layer may be advantageous due to its wear-resistant properties. TiB2 has importance in an industry where components slide with each other it is used in disc brakes in automobiles. Compared to industry standards, single-objective optimization considerably enhanced the outcomes: MRR increased by 10.61%, TWR enriched by 25.91%, and Ra increased by 17.60%. According to an ANOVA, peak current contributed 87.88%, 98.18%, and 95.80% respectively to MRR, TWR, and Ra. It is requisite to investigate multi-objective optimization for EDM of Al6061-15 wt% TiB2 composites' owing to the diverse optimal factor combinations for responses. Ra was slightly increased by 1.14% due to simultaneous optimization utilizing hybrid techniques with Equal and Entropy weights, which diminished TWR by 11.74% and increased MRR by 11.66%. ML, particularly DT, improves machining performance by assisting productivity, durability, and cost-efficiency under changeable circumstances and raising forthcoming study possibilities.

MICRO-GROOVING OF ALUMINUM-BASED COMPOSITES USING Nd:YAG LASER MACHINING

This paper describes the pulsed Nd:YAG laser machining characteristics on 6351 aluminum reinforced with silicon carbide (SiC) and boron carbide (B4C) particles. The composites are prepared using stir casting route by varying the weight percentage of B4C (0, 5, and 10 wt.%). During experimentation, the traverse speed (5, 15, and 30 mm/s) and the laser pulse frequency (5, 9, and 15 kHz) are considered to evaluate the groove width. The results reveal that the lower pulse frequency produced poor groove surface quality. Higher thermal energy dissipation at lower traverse speed may also result in the formation of recast layer and heat-affected zone. This is evident from the microscopic image and the EDS analysis. Thus, the optimum condition (composite with 10 wt.% B4C machined at 30 mm/s and 15 kHz) to achieve minimum grove width with improved surface morphology is identified by desirability analysis. Additionally, the regression model is developed to predict future values ([Formula: see text] at 91.86% and [Formula: see text] (adj) at 87.55%). Finally, the probability plot confirms the effectiveness of the proposed model at 95% confidence level.

Revealing the Formation of Recast Layer around the Film Cooling Hole in Superalloys Fabricated Using Electrical Discharge Machining

A film cooling hole is an efficient and reliable cooling method, which is widely used in aeroengine turbine blades to effectively improve the thrust–weight ratio of the engine. Electrical discharge machining is the most common manufacturing process for film cooling holes. Due to the rapid quenching after high-temperature melting, a certain thickness of the recast layer will be formed in the vicinity of the hole wall. The microstructure of the recast layer is considered to be an important factor affecting the performance of single-crystal blades. Generally, the recast layer has been thought of as one of the main reasons for the failure of turbine blades. Accordingly, the formation of the recast layer is an important and interesting issue to be revealed. In this work, the recast layer formed using electrical discharge machining on a single-crystal superalloy is studied with TEM. It is found that the recast layer is in the state of supersaturated solution with a single-crystal structure epitaxially grown from the matrix, and many dislocations were observed therein.

High‐Quality Femtosecond Laser Surface Micro/Nano‐Structuring Assisted by A Thin Frost Layer

AbstractFemtosecond laser ablation has been demonstrated to be a versatile tool to produce micro/nanoscale features with high precision and accuracy. However, the use of high laser fluence to increase the ablation efficiency usually results in unwanted effects, such as redeposition of debris, formation of recast layer, and heat‐affected zone in or around the ablation craters. Here this limitation is circumvented by exploiting a thin frost layer with a thickness of tens of microns, which can be directly formed by the condensation of water vapor from the air onto the exposed surface whose temperature is below the freezing point. When the femtosecond laser beam is focused onto the target surface covered with a thin frost layer, only the local frost layer around the laser‐irradiated spot melts into water, helping to boost ablation efficiency, suppress the recast layer, and reduce the heat‐affect zone, while the remaining frost layer can prevent ablation debris from adhering to the target surface. By this frost‐assisted strategy, high‐quality surface micro/nano‐structures are successfully achieved on both plane and curved surfaces at high laser fluences, and the mechanism behind the formation of high‐spatial‐frequency (HSF) laser‐induced periodic surface structures (LIPSSs) on silicon is discussed.

Investigations on a hybrid chemo-magnetorheological finishing process for freeform surface quality enhancement

Surface roughness improvement of the freeform surfaces is essential for the enhanced functionality of the components, including implants, turbine blades, microchannels, etc. The exclusion of human involvement during the finishing of freeform surfaces prevents hazardous exposure to particulate and provides uniform surface quality. Different surface finishing techniques, including vibratory finishing, Abrasive Flow Finishing (AFF), Electron Beam (EB) Irradiation, Electrolytic in-process Dressing (ELID) grinding, etc., have been developed to automate the finishing operation. However, some limitations are associated with the preexisting techniques, e.g., the process controllability of AFF and vibratory finishing, recast layer formation during EB irradiation, and low productivity of ELID grinding. Hence, a novel method for surface improvement, namely, Hybrid Chemo-Magnetorheological Finishing (HC-MRF), is proposed in the present study to reduce the surface roughness (Ra) (~up to a few nanometer) without affecting the surface topography of the workpiece. HC-MRF simultaneously utilizes the synergic action between Magnetorheological Finishing (MRF) and chemical etching to reduce surface finishing time and escalate process efficiency. Herein, the carrier medium of the Magnetorheological (MR) fluid is replaced by a reagent to facilitate the chemical etching process, and its synchronized action with mechanical abrasion reduces surface irregularities. Furthermore, the design of the developed apparatus to enable the HC-MRF process, where permanent magnets are used to produce the desired external magnetic field, is also discoursed. A case study on the surface roughness enhancement through the HC-MRF on the WC-Co (tungsten carbide in a cobalt-rich matrix) is investigated using Response Surface Methodology (RSM). Herein, Murakami's reagent is used as the carrier medium in the MR fluid, and a reduction in surface roughness (Ra) from an initial value of 312.87 nm to a final value of 34.50 nm is noticed. Moreover, the inclusion of Murakami's reagent enhances the process efficiency. The change in surface roughness with and without Murakami's reagent in the MR fluid is 88.97 % and 43.12 %, respectively, for a constant finishing time.

Effect of pulse duration and vibration tumbling on re-cast layer thickness and surface roughness of super alloy undergoing EDM

Many geometrically complex functional parts of turbo-pumps of Liquid Oxygen (LOX)-Hydrocarbon based rocket engines (Semi-Cryogenic Engines) which are difficult to be realized through conventional machining processes, are realized through Electric Discharge Machining (EDM). Every EDM process, deposits a re-cast layer on the spark eroded surface due to melting and subsequent quenching of the eroded surface. Studies show that structure and hardness of the re cast layer, differs from the parent material. Energy Dispersive Spectroscopic (EDS) analysis reveal that the chemical composition of the re-cast layer matches very closely to that of the parent metal itself. Re-cast layer has inherent micro cracks due to both thermal and tensile stresses during cooling. Even though re-cast layer is a superficial phenomenon, cracks once initiated on the re-cast layer, penetrate deep down to the parent metal as well, under fatigue loads causing fractures. In order to reduce the micro cracks on such spark eroded surfaces, thickness of the re-cast layer is to be reduced to the extent possible by fine tuning the EDM parameters. Failure analysis carried out on the fractured turbine blades of a LOX-Hydrocarbon based engine, realized through 4-axis EDM, which failed during the functional tests, indicated the propagation of such micro cracks from spark eroded surface into parent material causing fatigue fracture at turbine blade tips. Amongst the significant parameters governing the formation of re-cast layer in the EDM process, the effect of pulse duration is studied for its effect on re-cast layer thickness and surface roughness on super Nickel alloy turbine blades. Additionally, a vibration tumbling process is introduced and its effect on re-cast layer thickness and surface roughness is demonstrated. Turbine blades realized from the fine-tuned pulse duration, followed by vibration tumbling, show great improvements in surface finish, reduction of micro cracks, surface porosities and thickness of recast layer. This turbine successfully passes through the functional tests without any fractures.

An electrochemical discharge drilling method utilising a compound flow field of different fluids

To fabricate small holes in a nickel-based single crystal superalloy without formation of recast layer and stray corrosion, electrochemical discharge drilling utilising a compound flow field of different fluids (DF-ECDD), is investigated in this study. DF-ECDD is a compound machining method that electrical discharge machining (EDM) and electrochemical machining (ECM) can occur simultaneously in the process. In this method, the internal flushing of a low-concentration salt solution and external flushing of a deionized water occur simultaneously. By means of the internal flushing, EDM and ECM occur synchronously in the process. Owing to the external flushing, the conductivity of the solution on the surface of the workpiece is significantly reduced, thus reducing the stray electric field distribution. In this study, the influence of the conductivity of the external flushing liquid in the DF-ECDD process was analysed. The simulation results showed that when deionized water with a conductivity of 2 μS/cm was used as the external flushing liquid, the stray current on the workpiece surface was almost completely eliminated. Furthermore, the expression is theoretically derived for the relationship between the radii of the stray corrosion areas and the conductivity of solution domain. The experiments verified that the radii of the stray corrosion areas decrease with the decreasing of external flushing liquid conductivity. Finally, the stray corrosion could also be almost eliminated with the DF-ECDD process, and the machined holes were free of recast layer.

Recast Layer Formation during Wire Electrical Discharge Machining of Titanium (Ti-Al6-V4) Alloy

Recast Layer Formation during Wire Electrical Discharge Machining of Titanium (Ti-Al6-V4) Alloy

Study on the evolution process of recast layer for fast EDM drilling based on observation experiment and a novel thermal-fluid coupling model

The existence of a recast layer of film cooling holes on turbine blades imposes a crucial problem that affects the quality of fast electrical discharge machining (EDM) drilling. This paper focuses on an evolution process from molten material generation to recast layer formation. Single pulse discharge observation experiments with a high speed camera and a self-built observation platform were carried out to observe the formation and movement of the molten material. A novel thermal-fluid coupling model is proposed to combine fast EDM drilling methods with special materials and geometric properties of film cooling hole machining. A heat transfer module, a turbulent flow computational fluid dynamics module, a phase change module and a level set method are combined in this model. The complete process of generation, flow and solidification of molten materials is investigated by simulation with a single pulse discharging. The simulation results agree well with the experimental observation results. A thermal-mechanical coupling analysis of a molten material evolution process is carried out based on the temperature, velocity and pressure fields from the thermal-fluid model. Simulation results show that the molten material is generated at 1 μs after the starting of a discharge, and solidifies within 20 μs after the ending of the discharge. Under the influence of a high-speed flushing fluid, molten materials will not splash into a gap channel along the radial directions. Most of the molten material enters the gap channel along the workpiece surface with a velocity of over 25 m s−1. The moving direction of the molten material is consistent with that of a flushing fluid. The thickness of a recast layer gradually increases from bottom to top in the fast EDM drilling.

Influence of optimization techniques and nano surface coating materials on microstructure of iron-nickel-chromium alloy using wire EDM process

Abstract This research proposes developing the new hybrid optimization techniques for getting optimized wire EDM machining parameters and analysing the performance and microstructure of hybrid treatment alloy 20 material (high-velocity oxygen fuel spraying and plasma nitriding on iron-nickel-chromium alloy) after machining in wire EDM. The devising optimization is carried out using back-propagation neural networks (BPNN) integrated with fuzzy logic techniques. Taguchi L27 method uses optimized parameters in 3 factors and 3 level methods to BPNN wire EDM processing parameters. Those processing parameter errors are controlled by applying fuzzy logic system in hybrid optimization techniques. The hybrid optimization provides best results (±5% error) while comparing other techniques. This proposal was started with research review of defined factors and BPNN parameters level for hidden layer number, learning algorithm, neurons numbers, and so on. The analysis of variance (ANOVA), analysis of means (ANOM) and signal to noise (S/N) ratio have been used to identify Taguchi results. The BPNN techniques have been employed significantly to tackle hidden layer's uncertain parameter structures. The fuzzy logic controllers in general have been designed engaging the relations between system performance and factor through error method calculation. The microstructure analysis showed that the no evidence was found of recast layer formation on hybrid treated material after machining in wire EDM due to compressive stress and compound layer on material surface.

Multi-objective optimization of process variables for MWCNT-added electro-discharge machining of 316L steel

Fabrication of 316L steel with the desired surface integrity and thin modified recast layer for manufacturing various devices is very challenging using the traditional techniques and requires post-processing. Nevertheless, electro-discharge machining (EDM) is an evolving candidate among the non-traditional processes offering concurrent machining and surface alteration for the instrument manufacturing industry. To explore its full potential, this research work provides a thorough investigation of process variables on the machining performances and surface features primarily required for processing 316L steel in the industry. In this study, nano multi-walled carbon nanotubes (MWCNT) are utilized to improve the machining and surface responses. In addition to this, the parametric optimization is conducted through a Taguchi-based design which assists to obtain the highest material removal rate (MRR) of 42.25 mg/min corresponding to a 10-A peak current, 16-μs pulse-on time, 1-g/l MWCNT amount, and 45% duty cycle while the lowest surface roughness (SR) and recast layer thickness (RLT) of 1.58 μm and 5.243 μm respectively are attained at a 5-A peak current, 8-μs pulse-on time, 0.7-g/l MWCNT amount, and 45% duty cycle. Analysis of variance (ANOVA) reports peak current being the most momentous parameter complied by the MWCNT amount, pulse-on time, and duty cycle for MRR, SR, and RLT. The best 21 solution sets predicted through the multi-objective optimization tool called non-dominated sorting genetic algorithm-II (NSGA-II) obeying the set objective functions are proposed which are obtained from the Pareto optimal frontiers. Accuracy levels of the predicted solution sets are verified by the confirmatory experiments showing the estimated errors of less than 10%. SEM analyses confirm excellent surface integrity with a comparatively thin recast layer formation.

Numerical Simulation on Pulsed Laser Ablation of the Single-Crystal Superalloy Considering Material Moving Front and Effect of Comprehensive Heat Dissipation.

In the present research, an iterative numerical model is proposed to investigate the nanosecond pulsed laser ablation (PLA) mechanism of the DD6 single-crystal superalloy. In the numerical model, two subroutines are introduced to trace the moving boundary and update the thermal load. The iteration between the main governing equation and the two subroutines enables the PLA numerical simulation to consider material moving front and effect of comprehensive heat dissipation including thermal convection and radiation. The basic experimental results exhibit a good agreement with simulation results which indicates the good accuracy of the simulation model. Therefore, the PLA mechanism of the DD6 single-crystal superalloy is studied base on the improved iterative model, which indicates the evolution of temperature field, ablation zone morphology, formation of recast layer and heat-affected zone are closely related with time. The temperature of the laser spot center increases sharply at the first stage, reaching a maximum value of 5252 K, and then decreases gradually. The thermal dissipation postpones the ablation rate but promotes the formation of a recast layer and heat-affected zone. Due to the evaporation and thermal dissipation, the depth of the molten layer exhibits two rapid increasing stages. The comprehensive analysis of the PLA processing by the improved simulation model helps the understanding of the intrinsic mechanism, which would contribute to the further optimizing parameters of PLA fabrication of the DD6 single-crystal superalloy.