The design and tuning of a three-input fuzzy logic controller for electrical discharge machining (EDM) of diesel injector spray holes are presented. The tuning process is based on the variable type and discretization level to balance the data precision and computational time for servo motion updates in the fuzzy logic controller and is performed to improve the micro-hole EDM drilling time. The type and number of input parameters are studied to select the gap voltage, spark ratio, and change of spark ratio as input parameters for the fuzzy logic controller. A gain scheduling controller is used as the baseline and shows excellent drilling time in drilling a 1.14 mm thick workpiece using a 150 μm diameter wire electrode. The tuned fuzzy logic controller is comparable with the gain scheduling controller in drilling time and demonstrates its advantages on different EDM drilling configurations, including deep-hole and small-diameter micro-hole drilling. Analysis of EDM pulse trains reveals insights for controller design and identifies requirements for further improvement.
Potassium dihydrogen phosphate (KDP) crystal, widely used for important electro-optic parts, is a typical hard-to-machine material because of its soft, brittle, and anisotropic properties. High quality is usually required for machined surfaces on KDP parts. Reported machining methods for KDP crystal include diamond turning, grinding, magnetorheological finishing, and polishing. Each of these methods has its limitations. Therefore, it is desirable to develop new machining methods for KDP crystal. This paper presents an experimental investigation on surface roughness in rotary ultrasonic machining (RUM) of KDP. It was found that the surface roughness obtained when using a tool with a chamfered corner was lower than that obtained using tools with right-angle corners. Other process variables (spindle speed, feedrate, and ultrasonic power) also affected the surface roughness obtained.
In this paper, the effect of silicon powder mixing into the dielectric fluid of EDM on machining characteristics of AISI D2 (a variant of high carbon high chrome) die steel has been studied. Six process parameters, namely peak current, pulse-on time, pulse-off time, concentration of powder, gain, and nozzle flushing have been considered. The process performance is measured in terms of machining rate (MR). The research outcome will identify the important parameters and their effect on MR of AISI D2 in the presence of suspended silicon powder in a kerosene dielectric of EDM. The study indicated that all the selected parameters except nozzle flushing have a significant effect on the mean and variation in MR (S/N ratio). Optimization to maximize MR has also been undertaken using the Taguchi method. The ANOVA analysis indicates that the percentage contribution of peak current and powder concentration toward MR is maximum among all the parameters. The confirmation runs showed that the setting of peak current at a high level (16 A), pulse-on time at a medium level (100 μs), pulse-off time at a low level (15 μs), powder concentration at a high level (4 g/l), and gain at a low level (0.83 mm/s) produced optimum MR from AISI D2 surfaces when machined by silicon powder mixed EDM.
This paper describes the characteristics and the cutting parameters performance of spindle speeds (n, rpm) and feed-rates (f, mm/s) during three interval ranges of machining times (t, minutes) with respect to the surface roughness and burr formation, by using a miniaturized micro-milling machine. Flat end-mill tools that have two-flutes, made of solid carbide with Mega-T coated, with 0.2 mm in diameter were used to cut Aluminum Alloy AA1100. The causal relationship among spindle speeds, feed-rates, and machining times toward the surface roughness was analyzed using a statistical method ANOVA. It is found that the feed-rate (f) and machining time (t) contribute significantly to the surface roughness. Lower feed-rate would produce better surface roughness. However, when machining time is transformed into total cut length, it is known that a higher feed-rate, that consequently giving more productive machining since produce more cut length, would not degrade surface quality and tool life significantly. Burr occurrence on machined work pieces was analyzed using SEM. The average sizes of top burr for each cutting parameter selection were analyzed to find the relation between the cutting parameters and burr formation. In this research, bottom burr was found. It is formed in a longer machining time compare the formation of top burr, entrance burr and exit burr. Burr formation is significantly affected by the tool condition, which is degrading during the machining process. This knowledge of appropriate cutting parameter selection and actual tool condition would be an important consideration when planning a micro-milling process to produce a product with minimum burr.
In the present work, metal-cored arc welding process was used for joining of modified 9Cr-1Mo (P91) steel. Metal-cored arc welding process is characterized by high productivity, slag-free process, defect-free weldments that can be produced with ease, and good weldability. Toughness is essential in welds of P91 steel during hydro-testing of vessels. There is a minimum required toughness of 47 J for welds that has to be met as per the EN1557:1997 specification. In the present study, welds were completed using two kinds of shielding gases, each composition being 80% Argon + 20% CO2, and pure argon respectively. Microstructural characterization and toughness evaluation of welds were done in the as – weld, PWHT at 760 °C – 2 h and PWHT at 760 °C – 5 h conditions. The pure argon shielded welds (‘A2’ and ‘B2’) have higher toughness than 80% argon + 20% CO2 shielded welds (‘A1’ and ‘B1’). Pure argon shielded welds show less microinclusion content with low volume fraction of δ-ferrite (<2%) phase. Themo-calc windows (TCW) was used for the prediction of equilibrium critical transformation points for the composition of the welds studied. With increase in post-weld heat treatment (PWHT) duration from 2 h to 5 h, there was increase in toughness of welds above 47 J. Using metal-cored arc welding process, it was possible to achieve the required toughness of more than 47 J after PWHT at 760 °C – 2 h in P91 steel welds.
The 2205 duplex stainless steel (DSS) is of both good properties austenitic steel and ferritic steel, which applies to the shipbuilding industry usually. In this paper, the OM, XRD and microhardness test methods are used to analyze the variation of submerged arc welded (SAW) joints with and without post weld heat treatment (PWHT). The research results show that the σ phase disappear in the fusion edge zone near heat affect zone (HAZ) and an increase in the welded center zone during the follow-up PWHT, while the amount of γ phase is decreased in the welded center zone with PWHT. A segregation distribution of some second phases is also found in the welded center zone after PWHT. There have two pick values of microhardness arise in the fusion edge zone and the welded center zone separately without PWHT. However, a maximum value of microhardness at the fusion edge zone near HAZ is disappeared and the other is still held at the welded center zone during PWHT. It can be attributed to the changes of second phases, element diffusions and particle segregation during PWHT. A developing mechanism is issued to demonstrate the second phases transferring of the 2205 DSS SAW joints by PWHT.
Effects of switching over from gas tungsten arc welding (GTAW) to pulsed current gas tungsten arc welding (PCGTAW) on the quality of joints produced in Hastelloy C-276 material were investigated. Welding was carried out both by autogenous mode and using ERNiCrMo-3 filler wire. Microstructures of weld joints produced with and without current pulsing were studied using optical and scanning electron microscopy. Microsegregation occurring in GTAW and PCGTAW joints was investigated using energy dispersive X-ray spectroscopy (EDS). Strength and ductility of weld joints produced with and without pulsing were evaluated. The results show that pulsing results in refined microstructure, reduced microsegregation and improved strength of weld joints. Secondary phase(s) noticed in GTA weldments were found to be absent in PCGTA weldments. Autogenous PCGTA weldments were found to be the best in terms of: (i) freedom from microsegregation, (ii) strength and (iii) freedom from unwanted secondary phases.
The needs of stainless steel 304 micro cups have been increasing tremendously due to the trend of miniaturization in medical and electronic devices, etc. For application purpose, it is highly desired to have stainless steel micro cups with high CH/OD (cup height/outer diameter) ratios. Due to the constraints of the limit draw ratio (LDR) of stainless steel 304 sheets in micro deep drawing, forming a micro cup with high CH/OD ratio at room temperature cannot be achieved by using a single stage deep drawing die. A process consisting of one micro deep drawing and two ironing stages was proposed for achieving this goal; three micro dies were designed, fabricated and used for experimental validation. A series of experiments were conducted by using the stainless steel 304 sheets of 200 μm thickness annealed at four different temperatures to understand the influence of size effects on this process for generating knowledge, know-how and technologies to form high quality stainless steel micro cups with large CH/OD ratio. No lubricant was used in this study. It was proven that the proposed process is a robust process as long as the sheets are annealed at the temperature no less than 900 °C for more than 3 min.
This paper presents numerical and experimental investigations on laser melting of SS grade 316L powder on top of AISI 316L substrate using a pulsed Nd:YAG laser. The objectives of the present study are to understand the effect of process parameters such as laser power, scanning speed and beam size on geometry characteristics of the melt zone and ball formation. We formulated a moving heat source problem and obtained transient temperature solutions using commercial finite element solver. The geometry characteristics of the melt zone are evaluated from the temperature solutions and compared with experimental results. The effect of laser parameters on the geometry, morphology and homogeneity of single track realization was methodically analyzed by utilizing characterization tools such as laser particle size analyzer, macro and microscopic inspection, Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). The results presented in this paper are beneficial to realize homogenous layer formation in additive manufacturing processes involving powder melting by laser beam.
This paper addresses the weldability of 6 mm thick plates of super-duplex stainless steel by electron beam welding (EBW) process. Microstructure investigations conducted using optical and SE microscopy showed the presence of large ferrite grains with intra- and inter-granular austenite. Ferrite content studies on the weld zone estimated that there is no significant element partitioning between austenite and ferrite phases. Hardness studies portrayed that the weld hardness is found to be greater than the parent metal which is acquainted due to the solid solution strengthening effect. Tensile results corroborated that the joints obtained by EB welding process have better strength than the base metal. A detailed structure–property relationships has also been carried out through point and line mapping EDAX analysis across the weldment to substantiate the discussions.
This paper presents a novel 3D finite element model for the radial forging process with consideration of mandrel. As different with the previous works, the proposed model captures more accurately the features of the radial forging process. The proposed model is validated. With the proposed model, a comprehensive analysis of the deformation for the tube is presented. The contributions of the present work are: (1) a full 3D finite element model which captures more features of the radial forging process than the models in literature, (2) a proof that a full 3D finite element model is needed, (3) a proof of the effectiveness of the spring bar in stabilizing the contact between the hammer die and work-piece, and (4) the spindle speed has little effect on forging load. Finally, this model can be well used for the analysis and comprehensive understanding of the radial forging process and optimization of the process in future.
Equal channel angular pressing (ECAP) is currently being widely investigated because of its potential to produce ultra-fine grained microstructures in metals and alloys. Considerable research has been reported on finite element analysis (FEA) of this process, assuming 2D plane strain condition. The 2D models do not give details of strain distribution in the work-piece. Reports of all the researches are on effect of one-parameter-at-a-time. Combined effect of all geometric parameters is not reported. This paper aims in fulfilling the gap. In the present work 3D FEA of ECAP process was carried out for different combinations of channel angle, inner and outer corner radii. Results in terms of peak pressure, strain and strain inhomogeneity were obtained and analyzed by analysis of mean (ANOM). Main effects and interaction effect of all geometric parameters were quantified by analysis of variance (ANOVA). From the analysis it was found that the peak pressure is largely influenced by channel angle. To obtain desired strain the most important factors are channel angle and outer corner radius. Outer corner radius has the largest influence followed by channel angle on the strain inhomogeneity. There exists an optimum outer corner for which strain inhomogeneity is minimum, which depends on the channel angle. Inner corner alone has no influence on the strain inhomogeneity but its interaction with channel angle has some influence.
Additive manufacturing is an emerging manufacturing technology that enables production of patient specific implants, today primarily out of titanium. For optimal functionality and proper integration between the titanium implant and the body tissues surface properties, such as surface oxide thickness is of particular importance, as it is primarily the surface of the material which interacts with the body. Hence, in this study the surface oxidation behavior of titanium parts manufactured by Electron Beam Melting (EBM®) is investigated using the surface sensitive techniques ToF-SIMS and AES. Oxide thicknesses comparable to those found on conventionally machined surfaces are found by both analysis techniques. However, a build height dependency is discovered for different locations of the EBM® manufactured parts due to the presence of trapped moisture in the machine and temperature gradients in the build.
As part of an aircraft fleet fatigue life improvement program, investigation has been carried out into the effect pitting corrosion has on bare 7075-T651 which had undergone split sleeve cold hole expansion. Constant amplitude sinusoidal loading was applied to fatigue test coupons which had pitting corrosion induced upon them by a modified cyclic immersion process using a 3.5% NaCl solution. A pit depth of 39–58 μm was found to significantly reduce the increased fatigue life gains achieved by carrying out cold hole expansion. At 137.9 MPa fatigue life was reduced from achieving run out of ten million cycles to an average 371 × 103 cycles, while at 165.5 MPa average fatigue life was reduced from 810 × 103 to 65 × 103 cycles. The fracture surfaces were analysed under a scanning electron microscope where each displayed an individual crack initiation site located on the material surface within the zone of residual circumferential stress.
The ball-end milling process is widely used for generating three-dimensional sculptured surfaces with definite curvature. In such cases, variation of surface properties along the machined surface curvatures is not well understood. Therefore, this paper reports the effect of machining parameters on the quality of surface obtained in a single-pass of a ball-end milling cutter with varying chip cross-sectional area. This situation is analogous to generation of free form cavities, pockets, and round fillets on mould surfaces. The machined surfaces show formation of distinct bands as a function of instantaneous machining parameters along the periphery of cutting tool edge, chip compression and instantaneous shear angle. A distinct variation is also observed in the measured values of surface roughness and micro-hardness in these regions. The maximum surface roughness is observed near the tool tip region on the machined surface. The minimum surface roughness is obtained in the stable cutting zone and it increases towards the periphery of the cutter. Similar segmentation was observed on the deformed chips, which could be correlated with the width of bands on the machined surfaces. The sub-surface quality analysis in terms of micro-hardness helped define machining affected zone (MAZ). The parametric effects on the machining induced shear and residual stresses have also been evaluated.
A combination of tool force monitoring and post weld assessment has been used to determine effective welding parameters for the production of good quality friction stir welds at the highest possible welding speeds. Results indicate that it is possible to achieve good weld quality at speeds up to 355 mm/min by welding with a scroll shoulder and triflute pin at a rotational speed of 450 rpm. Welds produced at this speed achieved a tensile strength of 93.9% of that of the parent material with relatively good ductility (8.5% tensile elongation) and the presence of no internal or surface defects.
The goal of the research was to determine the limits and conditions in which the sheet hydroforming process provides a significant advantage over stamping in deep drawing of AA5754 aluminum sheets. Specifically, the maximum draw depth achievable by stamping, warm stamping (WF), sheet hydroforming (SHF), and sheet thermo-hydroforming (THF) of AA5754 aluminum alloy were quantified through experimental and computational modeling. A limited number of forming experiments were conducted with AA5754 aluminum sheets using a cylindrical punch and counteracting fluid at different temperatures and pressures. Several parameters, such as force–displacement, hydroforming pressure and temperature, and the maximum draw depth prior to wrinkling or tearing were measured during the forming process to make comparisons with simulations. The computational study included the simulation of stamping, WF, SHF and THF of AA5754 aluminum sheet with the LS-Dyna code, and the Barlat 2000-2d yield function with temperature-dependent coefficients. To predict the onset of wrinkling and tearing, the numerically generated, temperature-dependent forming limit diagrams (FLDs) based on the Barlat 2000-2d yield function were used. It was found that compared with stamping, SHF and THF can achieve more than 100% deeper draw depths with AA5754 aluminum sheet. The stamping simulations were used also to calculate the optimum blank size and die corner radii for the limiting draw ratio (LDR). The LDR was found to be very sensitive to the punch and die corner radii used in the experiments, which represent the curvature of character lines in an actual part. The LDR for AA5754 aluminum sheet was found to be 1.33 and 2.21 for sharp and round die corner radii, respectively. Overall, it was concluded that SHF is most ideal for deep drawing of aluminum sheets with sharp radii features. With the additional drawability provided by SHF, the automotive industry would be able to make difficult-to-form aluminum parts that cannot be stamped without product concessions such as increasing the die radii.
A study was carried out to evaluate how the friction stir spot welding process parameters affect the temperature distribution in the welding region, the welding forces and the mechanical properties of the joints. An experimental campaign was performed by means of a CNC machine tool and FSSW lap joints on AA6060-T6 aluminum alloy plates were obtained. Five thermocouples were inserted into the samples to measure the temperatures during the tool plunging. A set of tests was carried out by varying the process parameters, namely rotational speed, axial feed rate, plunging depth and dwell time. Axial welding forces were measured during the execution of the experiments by means of a piezoelectric load cell. The mechanical properties of the joints were assessed by executing shear tests on the specimens. A correlation between process parameters and joints properties was found.
The collected experimental data were also used to set up and to validate a simulative model of the process. The peculiarity of the developed FEM model is a 2D approach used for the simulation of a 3D problem, in order to guarantee a very simple and practical model able to achieve results in a very short time. The 2D FEM model, based on a specific external routine for the calculation of the developed thermal energy due to the friction between tool and workpiece, was set up using the commercial code Deform 2D. An index for the prediction of the joint shear resistance using FEM simulations was finally proposed and validated.
The surface characteristics of a machined product strongly influence its functional performance. During machining, the grain size of the surface is frequently modified, thus the properties of the machined surface are different to that of the original bulk material. These changes must be taken into account when modeling the surface integrity effects resulting from machining. In the present work, grain size changes induced during turning of AA7075-T651 (160 HV) alloy are modeled using the Finite Element (FE) method and a user subroutine is implemented in the FE code to describe the microstructural change and to simulate the dynamic recrystallization, with the consequent formation of new grains. In particular, a procedure utilizing the Zener–Hollomon and Hall–Petch equations is implemented in the user subroutine to predict the evolution of the material grain size and the surface hardness when varying the cutting speeds (180–720 m/min) and tool nose radii (0.4–1.2 mm). All simulations were performed for dry cutting conditions using uncoated carbide tools. The effectiveness of the proposed FE model was demonstrated through its capability to predict grain size evolution and hardness modification from the bulk material to machined surface. The model is validated by comparing the predicted results with those experimentally observed.
The material removal within different machining process can be performed in distinct modalities. One of the modality is based on the erosion phenomena. In this paper, theoretical model of abrasive jet machining based on erosion phenomenon is discussed. The material is removed from the surface due to erosion. In abrasive jet machining process, the output parameter is achieved by controlling various input parameters. This paper discusses the effects of various input parameters in abrasive jet machining (AJM) on the material removal rate (as the output parameter). The results presented in the paper are obtained from a theoretical study carried out with the help of mathematical model and computational technique. Theoretical investigation indicates that magnetic field, electric field and inhomogeneity in DC electric field have significant effect on metal removal by abrasive jet machining process.
Abrasive slurry jet micro-machining (ASJM) uses a relatively low pressure jet of abrasive slurry to machine features such as holes and channels. This study investigated the effect of alumina particle kinetic energy and jet impact angle on the roughness and erosion rate of channels machined in borosilicate glass using ASJM. A computational fluid dynamics model was used to calculate the local particle impact velocities and angles, and thus the kinetic energies of particles striking the surface. Consistent with earlier work on air-driven abrasive jets, the roughness and erosion rate of the channels machined at perpendicular incidence depended only on the kinetic energy of particles above the apparent cracking threshold of the glass target. Slurry jets of higher kinetic energy produced rougher channels and higher erosion rates since the impacting particles caused larger lateral cracks to form, and thus removed larger chips. The measured erosion rate at various impact angles, and the observed damage due to individual alumina particle impacts, indicated that the dominant mode of material removal was brittle erosion. Two similar analytical brittle-erosion models derived for air-driven abrasive jet micromachining (AJM), were found to predict reasonably well the roughness and the erosion rate of ASJM channels, despite the large differences in the fluid media, flow patterns, and particle trajectories in AJM and ASJM. A key requirement was that the average particle kinetic energy was calculated using the CFD model. With only minor modifications, the models predicted the channel erosion rate and centreline roughness with average errors of 12% and 17%, respectively. In addition, a numerical simulation, previously developed to predict the erosion in AJM of brittle materials, was used to predict the centreline average roughness, shape parameters and depth of ASJM channels for various machining conditions.
Present paper demonstrates the application of double disc magnetic abrasive finishing (DDMAF) process, on planar paramagnetic workpieces (copper alloy and stainless steel) of different mechanical properties like flow stress, hardness, shear modulus, etc. The copper alloy and stainless steel work pieces have been finished using DDMAF process. The experiments were performed based on a response surface methodology. The results obtained after finishing have been analyzed to determine the effect of different process parameters like working gap, rotational speed, percentage weight of abrasive, abrasive mesh size and feed rate for individual work material and to study various interaction effects that may significantly affect the finishing performance of the process. The outcomes of the analysis so obtained for the two different work materials have been critically compared to understand the effect of the considered process parameters based on mechanical properties. The scanning electron microscopy was also conducted on the work piece surface to understand the possible mechanism of material removal and the surface morphology produced.
A mathematical model was developed to estimate the weight percent of diamond abrasive particles incorporated in nickel binder matrix during abrasive microtool fabrication by pulse-plating process. The proposed model is based on the hypothesis that, embedment of an inert micro abrasive diamond particle on the substrate will only occur when a few nickel ions from the adsorbed ionic cloud are chemically reduced at the cathode by hydrogen ions present in the diffusion layer. Experimental verification of the model developed was performed by pulse electroplating of diamond abrasive particles on tungsten micro tool shank using an in-house built experimental setup. The predictive model developed was found to estimate diamond abrasive content in nickel binder matrix within 1–7 wt% of experimental results for different pulse-plating conditions.
Magnetic abrasive finishing (MAF) is a process in which the work surface is finished by removing the material in the form of micro chips by magnetic abrasive particles (MAPs) in the presence of magnetic field in the finishing zone. During the MAF process, the frictional heat is generated at the workpiece surface due to the rubbing action of magnetic abrasive particles with the work surface. The order of temperature rise is important to study, as finishing mechanism and surface integrity of work materials depend upon it. The measurement of temperature distribution during MAF operation at the interface of work piece and flexible magnetic abrasive brush (FMAB) interface is difficult. In the present analysis, finite element based ANSYS software has been used to model and simulate magnetic field distribution, magnetic pressure and temperature distribution at work-brush interface during the process. In this work the maximum magnetic flux density has been simulated of the order of 0.223 T at 0.91 A of current in electromagnet coil. Magnetic pressure on MAPs due to magnetic field of electromagnetic coil has been calculated to evaluate the frictional heat flux generated at the work-brush interface. Transient thermal analysis of workpiece domain has been performed to predict the temperature rise due to frictional heat flux. The predicted temperature on work-brush interface was found in the range of 34–51 °C. The developed simulation results based on FEA have been validated with experimental findings.