Surface Integrity Aspects Research Articles

Effect of ultrasonic vibration on fatigue life of Inconel 718 machined by high-speed milling: Physics-enhanced machine learning approach

Ultrasonic assisted high-speed machining (UAHSM) can be served as a thermomechanical surface sever plastic deformation (SSPD), because of the high-frequency impact load exerting to the sample together with thermomechanical loads due to shearing and plowing. Despite existing of few works which studied the impact of ultrasonic vibration on fatigue life assessment of difficult-to-cut material by experimental approach, they couldn’t provide an in-depth analysis to identify the underlying mechanisms of fatigue due time-consuming and costly fatigue life tests. Hence, elucidating the role of ultrasonic vibration in UAHSM on variation of fatigue life needs further studies. In order to do so, in the present work, a hybrid predictive approach based using ANFIS-based machine learning model and micromechanical Navaro-Rios (NR) fatigue crack propagation model has been introduced to directly correlates the UAHSM’s parameters to fatigue life. Here the former correlates feed rate, cutting velocity and vibration amplitude as process inputs, to surface integrity aspects (SIA) viz residual stress, roughness and grain size as output. Then, the modeled SIA are correlated to fatigue life using the former. The introduced hybrid model was then verified through series of UAHSM by examining the fatigue lives of milled Inconel 718 using four-point bending fatigue tests. Upon confirmation of the developed model, a comprehensive study was carried out to find how the process factors impact variation of SIA and subsequently fatigue. It was found from the results of developed models and confirmatory experiments that the role of ultrasonic vibration on improved fatigue life is mainly due to inducing compressive residual stress and more refined microstructure than the roughness.

Mechanistic Model of Fatigue in Ultrasonic Assisted Machining.

Anti-fatigue design in the machining process of aviation material requires advanced processes to enhance the surface integrity and a holistic model which can optimize the process aiming at maximum fatigue life. In the present study, the axial ultrasonic assisted milling process was utilized to machine the Inconel 718 while the process executes the thermomechanical cutting and peening action simultaneously. To optimize the process factors, a hybrid model using a combination of regression analysis and an analytical model was developed to correlate the machining factors, i.e., vibration amplitude, cutting velocity and feed rate to fatigue life. Herein, the former was used to map the process inputs to surface integrity aspects (SIAs), viz. roughness, hardness and residual stress; then, the SIA was mapped to fatigue life through a stress-based approach. The obtained results revealed that there is close agreement between the measured and predicted values of fatigue life where the prediction error is less than two times the dispersion. On the other hand, applying ultrasonic vibration at the highest amplitude together with the maximum feed rate and cutting velocity yield significant improvement in fatigue life, i.e., three times the same condition without ultrasonic vibration in light of the enhancement of compressive residual stress and work hardening of the surface layers.

A framework toward fatigue life modeling of machining process verified in burnishing

In the present work a multiscale model was developed to predict fatigue lives of Inconel 718 after a machining process. The model captures the effects of surface integrity like residual stress, microstructure, hardness and roughness. Within this holistic predictive model, firstly burnishing process factors (viz static force, feed rate, spindle speed and pass number) are correlated to surface integrity aspects. Herein, residual stress is modeled using theory of incremental plasticity; also grain size and hardness were correlated to process factors through dislocation density evolution. In order to model the surface roughness, the Z-map approach considering the work hardening of the surface layers was utilized. The foresaid developed models of surface integrity aspects were utilized to predict the fatigue life using Navaro-Rios crack propagation together with Chen’s crack initiation models. Thus, a novel holistic model correlating machining parameters directly to fatigue life has been developed through this hybrid approach. The developed models of fatigue life and surface integrity aspects were then confirmed by series of burnishing experiments on Inconel 718. Later, the confirmed model was utilized to identify the parametric influence of burnishing process on variation of fatigue life where the results were justified using variation of surface integrity factors. Through this developed model, it was found that burnishing setting of 1000 N static force, 0.05 mm/rev feed rate, 300RPM spindle speed and 2 pass number results in improvement of HCF, MCF and LCF of 242 %, 184 % and 212 % where the obtained results from the developed framework were compatible well with experimental values.

Simulation and experimental study for enhancing surface integrity of micro-slots processed on Nimonic-263 super alloy via electrochemical machining

ABSTRACT The potential of micro electrochemical slotting is significant due to its adaptability and usefulness across diverse manufacturing applications. This technique holds potential, particularly for handling advanced engineering materials like superalloys, with a focus on applications requiring high strength, i.e., micro-cutting for gas-turbine parts, biomedical applications, etc. With this view, this article has been attempted to explore the influence of various considered machining factors, namely as; applied potential difference, tool feed rate (TFR), pulse supply, and modes of tool insulation on the performance measures, i.e. material removal rate (MRR) and surface roughness (Ra) while attempting micro-slotting in Nimonic-263 superalloy work samples. The entire experimentation was conducted on the in-house fabricated 3-axis micro-electrochemical setup designed for performing various complex machining operations at a miniature scale. Furthermore, this study has also been focused toward investigating the impact of varying the electrical conductivity by employing different tool materials (i.e. copper and SS304) on the process characteristics measured. The observed effects of the tool electrode’s conductivity have also been expressed and supported by performing the simulation for electric field distribution using COMSOL Multiphysics software. The experimental results have revealed that the process input variables remarkably influence MRR and Ra, mainly applied voltage and TFR. The best values of MRR and Ra attained with SS304 and copper tool electrodes were 1.521 mg/min and 0.721 mg/min, and 0.038 µm and 0.029 µm, correspondingly. The microstructure analysis has further been conducted on machined micro-slotted work samples that provided detailed insights into various surface integrity aspects, which are essential for microdevice applications.

A bottom-up multi-physics model correlating burnishing factors to fatigue life

Burnishing is type of contact based non-metal removal finishing processes that is used to enhance the service performance of hard material like Ti-6Al-4V through modification of roughness, exerting work hardened surface layer and inducing compressive residual stress. However, the design of process aiming at anti-fatigue machining is a big challenge, since on one hand the experimental trial and errors of fatigue tests are time consuming and costly, on the other hand there is lack of predictive models that directly correlate the process factors to lifetime. Therefore, to study the fatigue behavior of burnished samples, a holistic predictive framework is required. The present study takes lead to solve the problem by developing a model which correlates the surface integrity and fatigue life of the materials processed. Here firstly the roughness, microhardness and residual stress of the burnished samples are modeled and correlated to process factors through multiphysics of burnishing. Then they were correlated to fatigue life by using stress-based approach that includes surface geometrical, mechanical and metallurgical aspects. The accuracy of developed models were compared with the series of experiments which were carried out on as-turned Ti-6Al-4V. The results revealed that the developed analytical model can predict the lifetime of the burnished samples with acceptable accuracy where the average prediction error for 16 data sets is 13.6 % within the range of 6.3 % to 22 %. The verified model was then utilized to identify the mechanism of lifetime variation and to understand how the process factors determines the fatigue life. It was obtained that the static force as a parameter contributed to loading has greatest impact on variation of fatigue life by adjusting all the surface integrity aspects i.e. roughness, microhardness and residual stress. It was also found that the main impact of feed rate on fatigue life is attributed to its influence surface roughness at high static force.

Interaction of electric current with burnishing parameters in surface integrity assessment of additively manufactured Inconel 718

One of main problem associated with surface sever plastic deformation (SSPD) techniques like low plasticity burnishing (LPB) of metallic materials is limitation of surface integrity improvement at further loads (i.e. static force or pass number). It is due to interlocking of dislocation motion that limits further plastic deformation. As a plausible solution, in the present work, electric current assisted burnishing (ECAB) is introduced to use the concept of electroplasticity in surface integrity (roughness, hardness and residual stress) enhancement of Inconel 718 by additive manufacturing. Nevertheless, there are some researches which use this method to enhance performance of SSPD, the interaction effect of electrical parameter like current density with other parameters haven’t been studied well. Thus, to make the process optimized in terms of surface integrity aspects, parametric study of ECAB process with focus on interaction of current density with other LPB parameters merits further investigations. Thus, in the present work, an experimental study was carried out to identify the interaction effect of current density (as main parameter of ECAB) with other burnishing parameters (spindle speed, feed rate, current density, pass number and static force) on surface integrity aspects. Analysis of variances was further carried out to identify the contribution of each parameter on performance measures. Then, the interaction plots based on polynomial regression were developed, analyzed and discussed based on the physic of plastic deformation and some microscopic analysis like surface topography, scanning electron microscopy and X-ray diffraction analysis. It was found from the results that electric current density has the greatest effect on surface integrity aspect with contribution of 60 % on surface roughness, 68.5 % on hardness and 30 % on surface compressive residual stress. On the other hand it was found that this parameter has high interaction with process factors while applying different current density changes the optimum burnishing setting for each performance measures. Application of LPB at optimum parameter setting causes improvement of surface roughness of as-built material about 54 %; further improvement of 70 % and 85 % in roughness values were also achieved when the electric current with densities of 5A/mm2 and 10A/mm2, respectively were applied to burnishing process at optimum setting. It was also found that application of optimum LPB as well as optimum ECAB with densities of 5A/mm2 and 10A/mm2, results in improving the surface hardness about 17.5 %, 42 % and 68 %, respectively. In addition, under foresaid post-processing sequence, the surface compressive residual stress enhanced from 121 MPa (tensile type) for as-built material to −208 MPa, −345 MPa and −488 MPa (compressive type). Finally, the most optimum solution results in minimum surface roughness as well as maximum hardness and residual stress were identified by desirability approach function as 300RPM spindle speed, 0.08 mm/rev feed rate, 10A/mm2 current density, 3 pass number and 300 N force. To show the application of this optimization in a real life problem, fatigue resistance of optimum samples for high cycle and low cycle testing were obtained and compared with as-built material. It was found that following this post-treatment, the life cycle of samples improves from 160 % to 270 %, respectively that affirms practical application and manufacturing efficiency of proposed approach.

Influence of martensitic transformation on the surface integrity aspects during sustainable turning of NiTi-SMA

With the development of the equipment manufacturing industry towards the direction of intelligence, the demand for the use of intelligent materials is increasing, and high-performance shape memory alloy (SMA) products are getting more and more attention. However, the current machining quality of shape memory alloy products can not meet the existing quality requirements. The mechanism of surface integrity of NiTi SMA needs to be revealed. The influence of martensitic transformation on microstructure, roughness, hardness, and superelasticity was explored. The occurrence of martensitic transformation is determined by controlling the cutting speed (lower and higher cutting speeds) and machining conditions (dry and liquid nitrogen conditions). The superelasticity was expressed quantitatively by the remnant depth ratio. The occurrence of martensitic transformation promoted the formation of the affected layer and work hardening. Meanwhile, it is an important reason for the increase in roughness and the decrease in superelasticity.

Characteristics and improvement of the double-pass electro-chemical discharge machining

Glass and ceramics have broad applications in modern industries; however, unique properties such as brittleness, and low machinability limit their fabrication processes. This way, electro-chemical discharge machining (ECDM) is a new method that can shape hard, brittle, and non-conductive materials. ECDM improvement is the subject of recent investigations through the application of chemical and physical phenomena. Current research studies the accuracy and surface integrity (cracks and HAZ) aspects of the double-pass ECDM process (DP) which is a new and straightforward method. During the double-pass process, two sequential passes are employed to shape the final geometry. In addition, the variable voltage technique is studied to achieve higher machining efficiency in DP. Results showed that in the diameter difference of 100 µm, the double-pass process reduced overcut by up to 21% compared to the typical ECDM process. Also, the size and number of cracks and the extent of HAZ were significantly decreased. Finally, in the diameter difference larger than 300 μm (the constant voltage of 32 V), the enhancement modification (variable voltage) reduced the overcut by more than 80%. At the same time, depth results remained close (less than 5% difference) to the simple ECDM process.

Performance assessment of different cooling conditions in improving the machining and tribological characteristics of additively manufactured AlSi10Mg alloy

Owing to the poor surface characteristics, the AM parts require additional processing, such as machining, polishing, etc. Hence, the present work highlighted the new observations of tool wear and surface integrity aspects in the milling of Laser powder bed fusion produced AlSi10mg alloy under different cooling conditions such as dry, flood, minimum quantity lubrication (MQL) and cryogenic cooling conditions. It was determined that adhesion wear is the primary failure mode observed under milling of AM AlSi10Mg alloy. Flank wear was reduced by 59–63%, 42–45%, and 24–26% under dry, flood, and CO2 conditions, respectively over MQL, which in turn has the effect on surface quality. In addition, it has been noticed that the microstructure has a great effect on the quality of the machined parts and the cryogenic cooling outperformed the MQL cutting method.

Relationship between energy consumption and surface integrity aspects in electrical discharge machining of hot work die steel

The present work deals with the relationship between energy consumption and surface integrity aspects in electrical discharge machining (EDM) of hot work die steel. Initially, the non-conventional machining experiments were performed with 1.2344 hot work die steel material and the surface integrity aspects such as surface topography, power spectral density analysis, surface roughness etc. were measured with high end instruments. Then, the energy consumption data during machining was analyzed with Labview software. Finally, the relationship between two technological contributors were established and the results were compared with different process parameters. The results demonstrated that there is a direct relationship between the energy and surface integrity aspects while performing EDM experiments. The lowest Sa and Sz values were reached for the highest tested pulse voltage values (U = 200 V) and were respectively lower by 34% and 44% than ones reached during EDM with the lowest pulse voltage U = 80 V.

A critical review on tool wear mechanism and surface integrity aspects of SiCp/Al MMCs during turning: prospects and challenges

A critical review on tool wear mechanism and surface integrity aspects of SiCp/Al MMCs during turning: prospects and challenges

Surface finishing of an additively manufactured part using electrochemical jet machining

The development and expansion activities of additive manufacturing (AM) are at their peak as complex parts with intricate features can be easily manufactured by various AM processes. However, obtaining a good surface finish for the AM parts has remained a challenging task. The surface defects and irregularities over intricate parts pose challenges during machining with conventional processes. Therefore, a simple, cost-effective, non-contact surface finishing approach is required to post-process the external and internal surfaces of AM metallic parts. This article reports the surface finishing of the SS316L part made by laser powder bed fusion (L-PBF) using a toolless electrochemical jet machining (ECJM), and investigations were performed to evaluate the different aspects of surface integrity. The experimental results revealed that surface irregularities and defects highlighted on the as-deposited samples were eliminated after ECJM.Moreover, after post-processing, the overlaid layer of oxides and carbides over the as-deposited sample surfaces was also removed. The maximum peak and valley height of the as-deposited surface were 30.1 µm and 41.6 µm, respectively. These heights have been reduced to 13.3 µm and 9.9 µm, respectively, while the arithmetical average roughness value 'Ra' has been reduced from 7.8 µm to 3 µm. The improvement in the mean value of 'Rz' and 'Ra' after post-processing was found to be 72%, and 61%, respectively. Therefore, the study concluded that the unique characteristic of the toolless electrochemical machining process is suitable for finishing the AM part.

Investigation on Surface Integrity in Hard Turning of AISI 4140 Steel with SPPP-AlTiSiN Coated Carbide Insert under Nano-MQL

The machined surface integrity in the turning of hardened steels is adversely influenced by heat generation and friction which requires pacification of the temperature by the effective cooling-lubrication approach and cutting tool performance. The present research analyzes the surface integrity of hardened AISI 4140 steel during turning with recently developed scalable pulsed power plasma SPPP-AlTiSiN coated carbide tool under nanofluid-assisted minimum quantity lubrication (MQL). Zinc oxide nanoparticles and environmentally friendly radiator coolant are mixed to prepare the nano cutting fluid. This analysis addresses the various aspects of surface integrity concerning surface morphology, machined surface hardness, residual stress and white layer development, and machined surface finish under varying cutting parameters (depth of cut, speed, feed, nose radius). Response surface methodology (RSM) is suggested to predict and to optimize the surface roughness in hard turning. Thereafter, the predictive modelling and optimization results are implemented for economic analysis. According to the findings of the experiments, with a contribution of 58.18%, the feed rate possesses a high impact on the surface finish, followed by the nose radius (12.32%) and speed (0.85%). Consequently, the machined surface quality improved with the increase of the nose radius because of the minimum tool wear and due to the increase of the effective length of the cutting edge. At optimum cutting conditions, the tool life of SPPP-AlTiSiN coated carbide insert is noted as 46 minutes under nanofluid-MQL and consequently, it estimated the overall machining cost per component as Rs.23.12 in Indian currency.

Parameter optimization and surface integrity aspects in MWCNT-based nano-PMEDM process of Inconel 718

This study examines the effects of Inconel 718's Nano PMEDM process parameters on Material Removal Rate (MRR), Tool Wear Rate (TWR), Surface Roughness (SR), and the integrity of surface and subsurface layers. It also examines the concentration of MWCNT nanoparticles in distilled water as a dielectric medium. Peak Current, Pulse on Time, and Powder Concentration were input variables in 20 experimental runs utilizing the Central Composite Design (CCD) of Design of Expert (DOE). To create and evaluate empirical models for MRR, TWR, and SR, response surface methodology (RSM) and ANOVA were used. According to the results of the improved RSM, the best responses for MRR, TWR, and SR are 0.012 g/min, 0.001 g/min, and 5.098 µm, respectively. These were accomplished by cutting parameters of 1.5 g/L for powder concentration, 307.967 s for pulse on time, and 19.925 Amps for peak current. GA optimization produced slightly different optimal values for MRR, TWR, and SR: 0.012 g/min, 0.003 g/min, and 5.229 µm, respectively. 20.178 Amps for Peak Current, 398.753 seconds for Pulse on Time, and 3.66 g/L for Powder Concentration were the suggested ideal cutting conditions for GA optimization. In the validation tests, both the GA-predicted outcomes and RSM-optimized values closely matched the experimental results.

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.

Grinding of composite materials

Grinding plays an important role in ensuring the final machining quality in the manufacturing process of composite parts. Problems such as grinding damage, grinding wheel wear and loading undermine the grinding efficiency and quality. This review presents relevant research progress in the field of composites grinding in recent years from the aspects of material removal mechanisms, surface integrity, and advanced grinding technologies. It further discusses the common problems of composites grinding and summarizes grinding process strategies to suppress damage. It can provide an in-depth understanding of the fundamental mechanisms involved in composites grinding and solutions to the composites grinding problems.

Multi Regression Model for Cutting Force During Dry Turning of Duplex Stainless Steels Using Definitive Screening Design

Considering the current trend in environmentally friendly machining or dry machining, it is observed that it’s adverse effect on various surface integrity aspects is usually not covered adequately in the literature. This adverse effect leads to untimely in-service failure of components subjected to fatigue loads. This research work has advocated the use of dry machining with consideration on minimizing its adverse effects by selecting appropriate machining parameters for Duplex Stainless Steel (DSS). These materials pose various challenges during secondary processing operations, like machining, due to lower values of thermal conductivity, higher values of tensile strength, toughness, work hardenability & tendency for built-up edge formation. In such applications, higher values of cutting forces are generated, and efforts are required to minimize them in order to reduce the carbon footprint. A multiple regression model for cutting force, during turning of DSS was generated as part of the study, based on experiments conducted using Definitive Screening Design (DSD). Four process parameters, viz. cutting speed, tool feeding rate, depth per pass and radius of curvature of tool nose were varied at three different values independently and their effect on main cutting force was observed. The multiple regression model generated using the stepwise procedure has coefficient of determination (R2) of 99.7 %. Cutting depth followed by rate of feeding and radius of curvature of tool nose were found to be influential parameters in the model. Minimization of force by desirability optimization method was further carried out. This resulted in minimum value of force as 128.6 N. For this, cutting speed of 120 m/min, feed rate of 0.1 mm/rev, depth per pass of 0.5 mm and tool nose curvature radius of 1.6 mm should be selected. The composite desirability score for these optimum settings was 98.79 %.

Selected Aspects of Surface Integrity of Inconel 625 Alloy after Dry-EDM in Carbon Dioxide

The dry-EDM process is environmentally neutral and enables to obtain good machining accuracy and relatively good surface quality. On the other hand, the application of dry-EDM is limited due to problems with the effective dissipation of heat from the machining zone and instability of material removal. The machining of Inconel 625 alloy was carried out in the carbon dioxide as a dielectric supplied to the machining gap through the channel in the working electrode, in the milling kinematics. In one of the investigated variants, the workpiece was submerged additionally in the deionized water during machining. The main aim of this research was to determine an influence of EDM milling in carbon dioxide with and without external workpiece cooling on the workpiece technological surface integrity ie. roughness, morphology and microhardness. The pulse time, current amplitude and gas pressure were selected as investigated parameters. Obtained results indicate significant differences in surface layer properties for both investigated machining variants.

Effect of wire material and discharge energy on productivity and surface integrity of WEDM-processed Inconel 718

ABSTRACT The current work aims to study the influence of discharge energy and debris accumulation on wire break failure and surface integrity aspects like surface roughness, subsurface hardness, and geometrical errors during the wire EDM of Inconel 718. The responses considered for analysing the geometrical accuracies are flatness error, roundness error and cylindricity error. Four different wire electrodes were considered for the study based on the wire strength and coatings, namely hard zinc coated brass, half-hard zinc coated brass, hard uncoated brass, and half-hard uncoated brass wire electrodes. The geometric accuracy of the machined parts is closely related to the choice of wire electrode. High-tensile strength hard wires were observed to machine the surfaces with maximum accuracy. Also, the zinc coated wires were observed to cut faster compared to the uncoated wire electrodes. The study revealed that there exists a strong influence of discharge energy on the surface integrity of wire electric discharge machined surface. The zinc and copper elemental contamination was minimal for uncoated wire electrodes at lowest discharge energy mode. Wire wear phenomena was analysed for both coated and uncoated wires. Discharge energy had a significant impact on the electrode wear of coated and uncoated wire electrode.

Investigation of surface quality, microstructure, deformation mechanism, and fatigue performance of additively manufactured 304L stainless steel using grinding

Ground 304L stainless steel (SS) made by laser powder bed fusion (LPBF) process was comprehensively investigated from the aspects of surface integrity, residual stress, microstructure, and mechanical properties. The experimental results indicated that grinding substantially improved the surface quality characteristics and significantly increased the fatigue life by more than two times. The removal of LoF (Lack of fusion) defects and keyholes near the as-built surface plays a critical role in improving fatigue performance due to the enhancement of fatigue crack initiation resistance. In addition, the ground subsurface cracks and newly formed lath-like grains were discovered in ground LPBF 304L SS, and their formation mechanisms were discussed with the aid of electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). This work brings new insights into the underlying principles of improving the mechanical properties of LPBF metallic materials through high-efficiency grinding.