Surface Crack Density Research Articles

Electro-discharge machining using copper-coated additively-manufactured AlSi10Mg electrodes

Customized fabrication of electrodes for electro-discharge machining (EDM) is considered as a useful emerging application of metal additive manufacturing technologies for building complex shaped tools in a short period of time. This approach of producing electrodes not only effectively addresses the design flexibility and complexity issues of the tools but also enables the use of various materials so as to ingrain the desired properties in them. The current study explores the production of laser powder bed fusion (LPBF) AlSi10Mg tools for machining of titanium alloy. Moreover, it explicitly assesses the machining performance of additively manufactured electrodes when the tools are subjected to a thin layer of copper coating. Three types of acidic baths are used for electroless coating of tools. The machining performance of the tools in terms of material removal rate, tool wear rate, surface crack density, surface roughness, white layer thickness, and microhardness of the white layer is compared for different electroless copper coating processes. It is observed that the coated tools significantly enhance material removal rate; however, uncoated LPBF tools exhibit superior surface morphology and surface roughness.

Machining performance analysis of wire-EDM for machining of titanium alloy using multi-objective optimization and machine learning approach

This study investigates the multi-objective optimization of process parameters in wire electrical discharge machining (WEDM) using titanium alloy grade 5 and zinc-coated brass microwire. The novelty lies in the comprehensive investigation of the effects of varying pulse on time (Ton), wire tension (WT), and wire feed rate (WF) on output responses, including surface roughness (SR), surface crack density (SCD), corner diameter (CD), and kerf width (KW). The Box-Behnken design, a sophisticated response surface methodology (RSM) technique, is employed to efficiently explore the complex relationships and interdependencies between these input and output parameters. The study's novel approach incorporates machine learning algorithms, including decision tree, light gradient boosting machine (LightGBM) and random forest, to predict the characteristics of the laser-cut components based on the input parameters. The contour plots generated provide valuable insights into the underlying patterns and associations between input and output features, aiding in the understanding of the WEDM process. The results reveal that the optimized values for SR, SCD, CD, and KW are obtained at specific machining conditions: Ton of 10 μs, WF of 3.79 m/min, and WT of 8 gf. Among the machine learning algorithms employed, random forest outperforms the others in predicting KW, SR, SCD and CD, exhibiting significantly lower mean squared error (MSE) and mean absolute error (MAE) values. This study contributes to the field of WEDM by providing a comprehensive analysis, incorporating advanced experimental design techniques and machine learning algorithms, which can aid in process optimization and quality control in manufacturing applications.

Exploring the machined surface characteristics of Haynes 25 superalloy: Cost mitigation and quality enhancement perspective

The current study investigates the surface characteristics and machining cost of electrical discharge machining (EDM) of Haynes 25 superalloy using tools made by additively manufactured CuCr1Zr, pure copper and graphite. Before assessing machinability, the workpiece and tool materials were characterized using Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD) and evaluations of tensile strength, micro-hardness, density and thermal conductivity. The effects of current (I), voltage (V), pulse duration (Ton), duty cycle (τ) and flushing pressure (Fp) is analyzed on surface characteristics viz. surface roughness (SR), surface crack density (SCD), recast layer thickness (RCT), heat-affected zone (HAZ), micro-hardness (MH) and machining cost (MC). Post machining XRD analysis revealed the formation of cobalt oxides like (CoO and Co3O4) affecting the micro-hardness of the machined surface. Alongside, a field emission scanning electron microscopy (FESEM) is carried out which confirms, the deposition of metal carbides and oxides on the EDMed surface. Current and pulse-on-time significantly influenced performance, with optimal EDM parameters identified and validated through confirmative experiments, resulting in a mean error of ∼2.84 %. It is seen that the use of additively manufactured CuCr1Zr tools resulted in improved machined surface characteristics and a more cost-effective approach for producing intricate profiles with minimal surface defects.

Comparative performance evaluation and economic assessment between traditional and vibration assisted EDM during machining of Inconel 718

Nickel based superalloy, Inconel 718 offers extensive applications in aerospace and gas turbine industries because of its outstanding properties, enabling high performance in various critical components. Despite the wide application of electric discharge machining (EDM) for difficult-to-cut conductive materials, the process becomes less productive due to unstable arcing and inadequate debris flushing during machining, leading to reduced operational efficiency. This research focuses on comparative performance evaluation and economic assessment between conventional-EDM and vibration assisted EDM (VA-EDM) while machining Inconel 718 with copper electrode. The workpiece was excited to vibrate with low frequency by employing unbalanced mass attached in a rotary motor with the aim of enhancing EDM performance. Material removal rate MRR, surface integrity (surface crack density SCD, surface roughness Ra, white (recast) layer thickness WLT) and tool wear rate TWR are analyzed to determine machining performance in comprehensive analysis. The results of the performance comparison show that vibration assisted is superior to the conventional-EDM process concerning enhanced material removal rate, and surface morphology with minimum surface crack density, tool wear rate and white layer thickness. The mean value ratios for Ra EDM/ Ra VA-EDM, TWR EDM/ TWR VA-EDM, WLT EDM/ WLT VA-EDM, and SCD EDM/ SCD VA-EDM are 1.35, 1.52, 1.21, and 1.74, respectively. Additionally, the surface integrity was enhanced using vibration-assisted EDM because it (a) increases the plasma flushing efficiency and the gap pressure gradient; (b) raises the energy of electrically charged plasma particles; (c) increases the effective flow of dielectric in the gap; (d) minimizes the number of ineffective pulses (short-circuiting and arching) on the surface; and (e) improves the dielectric flushing conditions in sparking gap. According to the findings, the overall machining expenditure per part under VA-EDM in Indian rupees (INR) 534 is lowered by 8% than expenditure under conventional-EDM (INR 576.60). The outcomes of this research have the potential to benefit numerous industries that deal with difficult-to-cut materials.

DIC to evaluate a model composite system cracking due to CTE mismatch

Coefficient of thermal expansion (CTE) mismatch in composites under temperature variation can lead to the system cracking. In this study, Digital Image Correlation (DIC) was used to investigate this phenomenon in a model composite system (MCS) composed of a single cylindrical inclusion into a ceramic mortar matrix. Temperature variation experiments assisted by DIC were conducted to evaluate the CTE mismatch of the MCS and to observe its cracking. An analytical model was used to fit the experimental radial displacement field of the MCS, which allowed the computation of the inelastic maximum principal strain field, highlighting the radial crack pattern. The crack initiation and propagation were evaluated via damaged elements in the interface region and the computation of the average Mean Crack Opening Displacement and Surface Crack Density for crack regions. This methodology is appliable for a single inclusion MCS, with improvement perspectives for application in multiple inclusions MCS.

Experimental investigations into surface crack density and micro hole dimensions during ultrashort pulse laser ablation

Experimental investigations into surface crack density and micro hole dimensions during ultrashort pulse laser ablation

Study on Dynamic Crack Expansion and Size Effect of Back–Filling Concrete under Uniaxial Compression

With the continuous expansion of the application range of gob–side entry retaining technology, the depth, height, and advancing speed of coal seams also increase, which brings great problems to the stability control of surrounding rock structures of gob–side entry retaining. As one of the main bearing structures of the surrounding rock, the stability of the roadway–side support body is a key factor for the success of gob–side entry retaining. In order to study the deformation characteristics and instability mechanism of roadway-side support body, based on the roadway–side support materials of gob-side entry retaining, the dynamic expansion test of back–filling concrete cracks under uniaxial compression was carried out. The YOLOv5 algorithm was applied to establish the fine identification and quantitative characterization method of macroscopic cracks of the samples, and the dynamic expansion rule of roadway-side support body cracks and its dimensional effect were revealed by combining the fractal theory. The results show that the F1 value and average precision mean of the intelligent dynamic crack identification model reached 75% and 71%, respectively, the GIoU loss value tends to fit around 0.038, and the model reached the overall optimal solution. During the uniaxial compression process, micro cracks on the surface of the back–filling concrete first initiated at the end, and after reaching the yield stress, the macroscopic cracks developed significantly. Moreover, several secondary cracks expanded, pooled, and connected from the middle of the specimen to the two ends, inducing the overall instability of the specimen. The surface crack expansion rate, density, and fractal dimension all show stage change characteristics with the increase in stress, and the main crack expansion rate has obvious precursor characteristics. With the increase in the size, the decrease in crack density after back–filling concrete failures gradually decreases from 93.19% to 4.08%, the surface crack network develops from complex to simple, and the failure mode transits from tensile failure to shear failure. The above research results provide a basic experimental basis for design optimization and instability prediction of a roadway–side support body for engineering-scale applications.

EXPERIMENTAL INVESTIGATION AND PARAMETRIC OPTIMIZATION OF ELECTRO DISCHARGE MACHINING FOR TI-5553 ALLOY USING GREY RELATION ANALYSIS COUPLED WITH TAGUCHI METHOD

In this paper, the machinability aspects of Ti-5553 have been experimentally investigated during Electro-Discharge Machining using three different geometrical shapes of copper electrodes i.e. cylindrical, triangular, and square. TIMETAL (Ti-5553) is a titanium-based alloy extensively used for special aerospace and marine applications due to its high strength and higher hardenability. By changing each of the aforementioned process parameters at three distinct levels, experiments based on the [Formula: see text] orthogonal array (OA) design of the experiment (DOE) were carried out. The machining performance has been carried out by utilizing different input parameters i.e. current, pulse off time ([Formula: see text]), flushing pressure ([Formula: see text]), tool shape ([Formula: see text]), and voltage (V) to examine machining performance characteristics like material removal rate (MRR), tool wear rate (TWR), surface roughness (Ra), white layer thickness (WLT), and surface crack density (SCD). Surface integrity in contents of surface morphology and surface topography is discussed herein. In this MRR, TWR, and Ra have been optimized by using a methodology (combining Grey relational analysis method and Taguchi’s philosophy) and found the optimal parameters that will have more MRR and less TWR, Ra. Later SCD and WLT were investigated by employing the optimal setting (A3, B2, C2, D2, E1, F3) and arbitrary setting (A3, B2, C1, D3, E3, F2) and concluded that SCD and WLT are less by utilizing optimal settings for machining as compared to arbitrary settings. Among all three different geometrical shapes of copper electrodes, the cylindrical tool has been found to be the best suitable tool for machine Ti-5553.

Evolution of tensile strength and cracking in granite containing prefabricated holes under high temperature and loading rate

For present applications in deep significant rock engineering, including underground repositories of high-level nuclear waste, an exhaustive comprehension of the impacts of high temperature and loading rate effects on the mechanical characteristics of granite emerges as an imperative necessity. Based on the Brazilian splitting test, Brazilian disc specimens with prefabricated holes were meticulously employed to guarantee the occurrence of radial compression failure. Combining microscopic experiments such as scanning electron microscopy and X-ray diffraction, the indirect tensile strength and damage mechanism of granite from the Yueyang area under the action of different temperatures and loading rates were thoroughly investigated. Furthermore, a nonlinear fitting equation between the two factors and tensile strength is suggested. At the same time, a simplified surface crack density based on pixel processing was defined. This allowed for a comparative assessment of how variations in temperature and loading rates induce varying degrees of macroscopic crack development and damage to the specimens. The findings suggest a direct proportionality between the tensile strength of granite and the loading rate, while an inverse proportionality is observed concerning temperature above 400 °C. However, a transient "gain effect" phenomenon manifests at temperatures below 400 °C. However, the impact of temperature on tensile strength is significantly greater than that of the loading rate, exhibiting a difference of approximately 8.7 times. Furthermore, the temperature is more prone to lead to the occurrence of secondary tensile cracks in specimens. The results of this research provide valuable guidance for ensuring the security of deep major rock engineering during construction.

Comparative performance investigation and sustainability assessment in electrical discharge machining of SS316 using different dielectrics

In electrical discharge machining, the material removal phenomenon is heavily influenced by the breakdown strength of the dielectric fluid and the inter-electrode gap monitoring. This innovative research addresses a comparative performance evaluation and sustainability assessment between biodegradable palm oil and conventional EDM oil during machining of stainless steel (SS-316) using copper electrode. The cutting performance is investigated by comprehensive result analysis of various machinability aspects including material removal rate, surface integrity, tool wear rate, radial overcut of machined components. According to the findings, machining with palm oil dielectric outperformed the usual EDM oil with regards to improved material removal, surface morphology and finish, increased machined surface hardness with minimum surface crack density and hole overcut. Pyrolysis of conventional EDM dielectric oil leads to deposition of thin film carbon on bottom surface of the copper electrode which prevents the quick tool wear due to its higher breakdown voltage. The total machining cost expenditure per component under palm oil (INR383) is reduced by 11% than expenditure in traditional EDM oil (INR426). Compared to EDM oil, machining under biodegradable palm oil as dielectric fluid is better socio-economical viable and environmental conscious to enhance sustainability.

Correlation between machining-induced surface alterations and stress corrosion cracking susceptibility of au stenitic stainless steels

Correlation between machined surface alterations and stress corrosion cracking (SCC) susceptibility of austenitic stainless steels is investigated. The machining-induced residual stress, roughness, micro-hardness and dislocation density were characterized and the surface/subsurface cracks were examined after SCC tests in boiling magnesium chloride solution. The results showed SCC crack initiation and early propagation were highly related to the machining-induced alterations. By establishing a quantitative relationship between the surface characteristics and surface crack density, the comprehensive impact of the residual stress, surface roughness as well as the dislocation density on SCC susceptibility is revealed. The predicted crack density is in good agreement with the measured data. As a result, the SCC susceptibility of the machined surface is described by the surface integrity properties.

Investigation on Surface Roughness and MRR in WEDM of Titanium Grade 7 (Ti-0.15Pd) Alloy using Statistical Techniques

Wire Electric Discharge Machining (WEDM) of Titanium grade alloys with coated electrodes has several advantages over the traditional machining process such as increased productivity, reduction of processing cost, and improved material properties. The main objective is to create a relationship between WEDM parameters such as Pulse-on (TON), Pulse-off (TOFF), and Indicated Power (IP) with surface roughness (Ra) and Material Removal Rate (MRR). In the present work, the performance of zinc-coated brass electrodes for WEDM of Titanium Grade-7 alloy was assessed and optimized with statistical technique. ANOVA analysis is used to analysis of the MRR and Ra and validated with regression. The ANOVA analysis results indicated that TON is the highest statistically significant and followed by TOFF and IP on MRR and surface roughness. The optimum combination of higher IP(6 A) and TON time(60 μs) and lower TOFF time (12 μs) is lucrative for a higher MRR of 8.5682 mm3/min and lower surface roughness of 1.66 μm. The SEM images showed homogeneous solidification, columnar grain structure, recast layer surface, and minor surface crack density were noticed at higher cutting conditions. The predicted model and confirmation test results were close to each other with minimum error (<5%), so the model is adequate.

鉄筋腐食に伴うコンクリート内部に進展するひび割れが表面ひび割れ性状に与える影響

Concrete structure is usually inspected by appearance at the periodical inspection. However, highly skilled engineers are necessary for this preliminary and qualitative inspection. Considering decrease in expert and increase in deteriorated concrete structures, more quantified inspection method is needed to evaluate the performance more accurately and easily. Previous researches have presented the relationship between corrosion mass loss of reinforcing steel bar in concrete and surface crack width. These studies were often conducted by using reinforced concrete specimen which includes single longitudinal rebar. On the other hand, on-site structures include not only longitudinal rebar also transverse rebar which is located with larger cover thickness. For this reason, the accelerated corrosion test using the specimens and inspection at an on-site corroded structure were conducted to evaluate the effect of the transverse rebar and its corrosion on the behavior of surface crack. As a result, it was revealed that internally propagated crack would have a large influence on the surface crack and the index of the surface crack density could bring more accurate evaluation of the corrosion mass loss of rebar than only the crack width.

Surface integrity of NiTi-SMA during WEDM: effect of spark parameters

ABSTRACT The current study looks at surface integrity measures for example surface crack density, surface roughness, recast layer thickness, and foreign elements content in wire electric discharge machining (WEDM) of the Ni55.95Ti44.05 shape memory alloy (SMA) with purposefully varied spark parameters (spark frequency, spark energy density, and spark gap voltage). Surface roughness has a similar tend to surface crack density, which increases with an increase in spark energy density and decreases with an increase in spark gap voltage and spark frequency. As the spark energy density declines and the spark gap voltage and spark frequency rise, foreign elements content and recast layer thickness decrease. Scanning electron microscope (SEM) and optical profilometer observations of the surface topography of SMA following WEDM show the presence of lumps, voids, pockmarks, discharge craters, microcracks, and a layer of melted material that has resolidified. Energy dispersive spectroscopy (EDS) studies show that foreign elements are deposited on machined surfaces from wire electrode and dielectric fluid.

Experimental investigation into the evolution of microstructure and nanomechanical characterization of electric discharge deposited surface layers on Ti64

In the current study, Ti64′s surface has been transformed by electric discharge machining, and its microstructure, surface crack density, layer composition, and nanomechanical properties are examined, as well as the effects of peak current and pulse on time. The studies were carried out using a two-factor, three-level full factorial design. On the deposited layer, OM, XRD, EDS, SEM, and nanoindentation tests were performed. According to the variation in the process parameters, it was discovered that the deposited layer is not uniform and has a thickness range of 45–182 μm. Additionally, it has a dual microstructure that is both equiaxed and dendritic. Carbon deposition (up to 70% by weight), andcarbide formationwere all found to increase with parameter values. It is discovered that the layer's hardness is twice (718HV) as compared tothe basematerial. Additionally, a minor modification in reduced modulus has been noted. SCD and crack width were discovered to be rising as parameter level rose.

Influence of Maghemite (γ-Fe2O3) Nano-Powder Mixed Micro-EDM on the Surface Integrity Characteristics of Co-Cr-Mo

Surface integrity in electric discharge machining (EDM) has always been a major concern in the manufacturing industry. Although EDM with powder suspended dielectric has shown good potential in enhancing material removal rate and improving surface finish, the influence of the same on overall surface integrity is not very clear. The current work utilized (γ-Fe2O3) nano-powder and evaluated its role in combination with concentration and machining parameters, on surface roughness (Ra, Rmax), surface crack and thickness of recast layer, during powder-mixed micro-EDM (PMµEDM) of Co-Cr-Mo. SPM data are obtained through the database and its morphologies and meteorology are studied using the gwyddion software. Results showed that significant reduction in surface roughness, crack density and recast layer thickness is possible with the PMµEDM process.

Evaluation of Bronze Electrode in Electrical Discharge Coating Process for Copper Coating.

One of the widely used non-traditional machines for machining of hard materials into complex shapes and different sizes is the electrical discharge machine (EDM). Recently, the EDM has been used for deposition by controlling the input parameters (current and duty cycle). This work was carried out to evaluate the readily available bronze (88% Cu + 12% Sn) electrode for deposition of copper material on titanium alloy. Experiments were conducted according to Taguchi experimental design considering the input parameters of current, Ton, Toff and preheating temperature of substrates. Titanium alloy was further hardened by preheating at temperatures of 100 °C, 300 °C and 500 °C and quenching in brine, castor oil and vegetable oil in order to avoid workpiece erosion. After this treatment, hardness, grain area, grain diameter and number of grains were characterized to compare with pretreated substrates. Then, the treated substrates were taken for copper deposition with the EDM. Output parameters such as material deposition rate (MDR), electrode wear rate (EWR), coating thickness (CT), elemental composition and surface crack density (SCD) were found. Material characterization was carried out using a scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDX) and optical microscopy. Output parameters were optimized with technique for order of preference by similarity to ideal solution (TOPSIS) to find optimum parameters. A sixth experiment with parameter values of Ton of 440 µs, Toff of 200 µs, preheating temperature of 300 °C and quenching medium of castor oil was optimum with MDR of 0.00506 g/m, EWR of 0.00462 g/m, CT of 40.2 µm and SCD 19.4 × 107 µm2.

Fatigue analysis of electro discharge machined Nitinol 60

Nitinol 60 (NiTi60) is a shape memory alloy (SMA) where the atomic percentage of nickel is slightly higher than titanium. It advantages the material to have higher hardness and better sensitivity to phase transformation. One of the machining techniques that is preferred to cut hard material is electrical discharge machining (EDM). This study aims to examine the fatigue characteristics of a NiTi60 alloy that has undergone electro-discharge machining and examine the impact of machining parameters on microstructural changes. In this investigation first, the influence of EDM process parameters such as pulse current, voltage, pulse on time, and pulse off time on surface integrity aspects was investigated. Second, the impact of these process variables on fatigue strength was examined. The surface integrity parameters of EDM-machined specimens, such as microcracks, surface crack density (SCD), white layer thickness (WLT), and residual stress formation have been examined by various characterization techniques. The obtained results show that pulse current and voltage are dominating factors affecting SCD. The thickness of the white layer seems to be increased with the rise in the pulse current and pulse on time, and tensile kinds of residual stresses are present in the WLT region, whose magnitude is dependent on process parameters. The fatigue tests were performed using a servo hydraulic testing machine at a frequency of 20[Formula: see text]Hz for 106 number of cycles. The fatigue crack initiation, propagation, and effects of process parameters have been examined. It has been found that an increase in pulse current and voltage leads to the generation of microvoids in the WLT region and thereby causes fatigue cracks to take birth. Later on, a correlation between WLT and SCD was observed by implementing an artificial neural network (ANN) model. The accuracy of ANN model prediction is reported to be high, where WLT and SCD have a 0.98 observed correlation coefficient.

Influence of Process Parameters on Surface Crack Density in Electrical Discharge Machining of Ni35Ti35Zr15Cu10Sn5 high-temperature high entropy shape memory alloy by Response Surface Methodology Approach

Influence of Process Parameters on Surface Crack Density in Electrical Discharge Machining of Ni35Ti35Zr15Cu10Sn5 high-temperature high entropy shape memory alloy by Response Surface Methodology Approach

SURFACE TOPOGRAPHY AND OPTIMAL MACHINING CHARACTERISTICS INVESTIGATION FOR ADVANCED ENGINEERING MATERIAL INCONEL 825 ALLOY EXPLORING STATISTICAL TGRA ACCOMPANIED WITH T-TOPSIS METHODOLOGY

The electrical discharge machining (EDM) is an extremely effective manufacturing process to create deep and three-dimensional complex cavities. In EDM, machining occurs due to the generation of thermoelectric energy between the work piece and an electrode. EDM widely engaged for cutting superalloy material that are having high strength to wear ratio, corrosion resistance, etc. In this work, Inconel 825 material, which is nickel–chromium based superalloy, is opted due to its outstanding mechanical and thermal properties. We considered various important EDM input parameters, i.e. spark gap (Sg), gap voltage (Vg), pulse on time ([Formula: see text]), pulse off time ([Formula: see text]), peak current ([Formula: see text]), servo feed (Sf), depth of cut (Dc) and difficulty index (Di) with Taguchi L[Formula: see text] orthogonal array for optimizing output responses, i.e. tool wear rate (TWR), material removal rate (MRR) and surface crack density (SCD) in multi-objective optimization (MOO) realm. Undertaking repeated experimental runs are very expensive, tedious, time consuming and economically unjustified. Hence, we have robustly introduced a novel integrated computational Taguchi based grey relational analysis (TGRA) accompanied with Taguchi based technique for order of preference by similarity to ideal solution (T-TOPSIS) to optimize the EDM process. This research represents that the pulse on time is the chief significant factor and the [Formula: see text] value is found as 0.002 for both TGRA and T-TOPSIS. Experimentally, it has been confirmed that the optimum settings yielding an improvement of 0.01627 and 0.28071 in TGRA and T-TOPSIS score, respectively. The comparative analysis for the methodologies is fruitfully discussed and the results clearly present the effective parametric combinations to be implicated for optimizing MOO framework. Investigation of surface topography is fruitfully presented and the effects of the pulse on time, gap voltage and pulse off time on heat affected layers, machining debris and surface cracks were also discussed. Validation tests were carried out and show closer relationship with the experimental results.