Machining of titanium alloy grade V (Ti6Al4V) is very difficult by conventional metal cutting process due to low thermal conductivity, ability to retain strength at elevated temperature, tendency to ...work harden. This may result in high heat at the cutting zone and the generation of thermal stresses. Therefore, in the present research die-sinking electrical discharge machining is used to machine Ti6Al4v alloy. A non-dominated sorting genetic algorithm (NSGA II) coupled with rotary central composite design (RCCD) based on response surface methodology (RSM) is employed to optimize machining parameters in die-sinking electrical discharge (EDM) machining of Ti6Al4V. A quadratic mathematical model has been developed for material removal rate (MRR) and surface roughness (Ra) in terms of peak current (I), pulse on time (Ton) and pulse off time (Toff) as independent input parameters. Die-sinking EDM experiments are planned using RCCD based on response surface methodology. Results revealed that peak current is the most influencing EDM parameter on both MRR and Ra with PC of 35.86% and 57.10% respectively. MRR continuously increases with peak current. MRR firstly decreases and then increases with an increase in Ton. Ra continuously increases with peak current and starts decreasing after a coded value of 1.5. The Optimization result obtained by NSGA II is validated through confirmation experiments which are in good agreement with the experimental value with an absolute error of 6% and 4.8% in MRR and Ra respectively.
A numerical simulation under plane-strain assumption of residual stresses and damage on titanium alloy Ti6Al4V in die-sinking electrical discharge machining (EDM) process is presented using ...Johnson–Cook (J–C) model and dynamic explicit temperature-displacement algorithm. A special attention is given to model the damaged thermo-mechanical behavior of EDMed Ti6Al4V alloy while considering the ductile damage evolution via a fully uncoupled damage formulation. A rigorous selection method including analytical and finite-element (FE) computations of tensile fracture behavior with thermal effect is proposed for suitable selection of J–C model parameters for the grade of Ti6Al4V alloy under investigation. The relationships between the machining parameters and both the heat flux density and the available sparking radius are considered for defining sparking analysis input. For a selected set of machining settings, the residual stresses and surface damage profiles were retrieved at the end of a cooling analysis. It has been concluded that J–C constitutive model can be used to describe material damaged thermo-plastic behavior under die-sinking EDM process conditions and thereby forecast temperature distribution, crater cavity shape, thermally induced residual stresses, white layer thickness and EDM thermal cracks formation. Unusually, an approach including damage criterion was proposed for assessment of both the geometry of crater cavity and the thickness of white layer and compared to based-on temperature criterion classical approach. Thus, numerical simulation of damage in die-sinking EDM offers a new insight into the mechanism of surface damage creation and helps to find out such phenomenon very precociously, which is otherwise difficult to access by experiment, such as surface crack formation due to damage mechanism as triggered in sparking phase and which was re-established in cooling. The numerical model yields reliable results for residual stresses profiles when compared with titanium alloy Ti6Al4V experimental results available in literature in the same machining conditions.
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•The performance characteristics laws in EDM of Ti-6Al-4 V were established.•Performance characteristics are affected by EDM settings and tool electrode material.•Melting isotherm bounding the crater ...was calculated based on removal efficiency.•TiC carbides formation must be considered to improve EDM model reliability.•The laws established are relevant for predicting the surface integrity of EDMed Ti-6Al-4 V.
The generation of performance characteristics laws may improve the reliability of EDM models, thus limiting experimentation and the resulting ecological effects and waste. In the present research, a finite element (FE) computational approach combined with experiment and regression analysis is employed to identify the laws relating power density and removal efficiency to the process settings in EDM of Ti-6Al-4 V alloy with various tool electrode materials. The experimental results for material removal rate (MRR), tool wear rate (TWR) and white layer thickness (WTL) are used as input data for the identification procedure. It was found that the performance characteristics are strongly affected by the machining parameters and tool-anode material. The power fraction going to the cathode varies between 7 and 30 % depending on the machining conditions and tool electrode materials studied. When employing a graphite electrode as opposed to copper or aluminum electrodes, the removal efficiency is maximized, at 51 %. Thus, the highest and lowest values of performance characteristics are obtained under the same processing conditions, irrespective of the tool material. The performance characteristics laws of the cathode are generated through a regression analysis. The established laws were validated by comparing the erosion ratio from the numerical simulation with the experiment. Qualitatively, the results of such a confrontation are deemed satisfactory. The established laws may be helpful in modeling the EDM process to predict the EDMed Ti-6Al-4 V surface integrity in the biomedical and aerospace sectors.
The high cost of manufacturing microplate implants is a primary issue. This is because the production of microplate implants uses the micro-milling and wire-EDM process. Production costs can be ...reduced using one machining process, and die-sinking EDM is an alternative in the manufacturing of microplate implants. This paper investigates the capability of EDM die-sinking in manufacturing microplate implants. This paper also studies the reaction of electrode materials and pulse currents to the microplate’s dimensional accuracy, surface roughness and hardness. The process of EDM die-sinking uses electrodes of graphite and copper with pulse current variance of 6, 9, and 13 A. The experiment results indicate that the process of EDM die-sinking success in manufacturing microplates on commercially pure titanium sheets. Decreasing the pulse current can improve dimensional accuracy, smoothen surface roughness and minimize the hardness decrease of the microplate. These results are better using the copper electrode compare with the graphite electrode. The best quality of the microplate is at 93.3% dimensional accuracy, 5.28 µm surface roughness, and a 12% decrease in hardness. The best quality microplates was achieved by using copper electrodes with a 6 A pulse current.
Die sinking EDM processes are widely employed in advanced aerospace applications where part quality and machining time are main concerns. The aim of this research work is to develop an advanced EDM ...process monitoring procedure in the perspective of Zero Defect Manufacturing based on the identification of correlations between die sinking EDM process parameters and improper process conditions that could increase machining time and cause unacceptable part quality. To this purpose, the Real Time Acquisition (RTAQ) module installed on a AgieCharmilles FORM P 600 sinker spark erosion machine tool is utilized to monitor and acquire online data related to 8 selected process parameters with 32 ms sampling interval. An anomaly detection methodology is then applied to timely identify improper process conditions based on relevant features extracted from the EDM process parameters.
Die sinking EDM processes require continuous monitoring due to the typically severe application requirements, especially in advanced aerospace parts machining, where part quality and machining time ...are main concerns. As the process conditions cannot be recognized based on the behaviour of a single monitored value, it is necessary to consider a number of relevant sensor signals together. The aim of this research work is to recognize the machining conditions which lead to an improper process performance, e.g. by increasing machining time and causing unacceptable part quality, and to highlight the most relevant sensorial features. Using the Real Time Acquisition (RTAQ) module installed on an AgieCharmilles FORM P 600 sinker spark erosion machine, eight process parameters are acquired. Hierarchical cluster analysis is then applied to identify different groups of improper process conditions based on relevant features extracted from the EDM process parameters.
Titanium alloy has a high specific resistance, excellent machining performance is non-corrosive, and the capability to withstand greater temperatures while maintaining outstanding mechanical ...properties. This alloy is, therefore, the right choice for aerospace, maritime, biomedical, and industrial applications. But machinability of titanium alloy is challenging as a result of its poor thermal conductivity, highly chemically reactive, and low elastic modulus hence it is treated as a difficult-to-cut material. Fast tool wear is observed during the machining of titanium alloy in conventional machining methods. Therefore, unconventional processing methods are used for the treatment of titanium alloy. Electric discharge machining (EDM) is one of these unconventional machining processes which are used for cutting with high precision, having a high degree of machinability, and getting a better surface finish. It is considered the best choice for machining titanium alloy. In the EDM process, different techniques are used to understand the effects of process parameters such as polarity, peak current, electrode type, pulse on time, and gap voltage on material removal rate, tool wear rate, surface roughness, and wear ratio. This paper critically investigates different types of EDM processes, experimental setups used for machining of titanium alloy, the effect of different tool electrodes and dielectric media on machining parameters, machined surface characteristics, and metal removal rate and tool wear rate.
Bulk metallic glass composites (BMGCs) have good combination of mechanical properties when compared with monolithic bulk metallic glasses (BMGs) and conventional crystalline alloys. However, with ...high strength, high hardness and metastable atomic structures, BMGCs are classified as difficult-to-cut materials, and how to process BMGCs is important before their engineering applications. In this work, die-sinking electrical discharge machining (EDM) of BMGCs was conducted, and compared with conventional industrial pure Zr (Zr702), under both rough and refined conditions. The EDM performance, including material removal rate (MRR), surface roughness, surface morphology, element variation, and crystallization, was investigated. The findings have shown that the peak current contributed most to the variation of MRR and surface roughness of BMGCs, followed by pulse-on time. BMGC workpiece material was more easily removed by sparking than Zr702 due to the relatively lower melting point and smaller thermal conductivity. During sparking, the melted BMGC workpiece material tends to have smaller viscosity and larger explosive forces, resulting in larger craters, corrugated ridges, and resultant higher surface roughness. Nevertheless, good surface quality with low surface roughness comparable to conventional Zr702 was also obtained for BMGCs under refined conditions. After EDM, the composite microstructure of BMGCs changed to amorphous matrix and ZrC/TiC carbides for ZrCu-based and TiCu-based BMGCs, respectively. The mechanisms for the change of atomic structures in BMGCs during die-sinking EDM were discussed, and the findings have shown that the carbonization effect can be reduced or even eliminated by optimizing the processing parameters. Finally, strategies for achieving better die-sinking EDM performance of BMGCs were proposed.
The present research focuses on optimizing the process parameters of die-sinking electric discharge machining on tool steel. The basic objective of this research is to investigate the influence of ...two categorical factors including dielectric type and electrode polarity, and two numeric factors including discharge current, and Spark/Discharge Gap on material removal rate (MRR) and surface roughness (
R
a
) for machining of AISI D2 steel. Box-Bhenken design based on response surface methodology (RSM) was applied for experimental design. For estimation and evaluation, the effects of the process parameters on response variables, RSM has been integrated with grey relational analysis (GRA). Ranking of factors has been done with respect to the grey relational grade. (ANOVA) was further performed for determining the significance of grey relational grade. ANOVA results reveal that that polarity having 50% of percentage contribution was the most significant factor affecting the performance measures followed by the spark gap, discharge current, and dielectric type. The grey relational grades were further optimized through desirability function and the optimal condition for input parameters was obtained. The optimum levels were discharge current at 15 A, dielectric type of kerosene oil, spark gap at 6 mm, and polarity of positive has been determined. The confirmatory tests were run for verifying and validating the results and improvement in productivity (MRR) up to 17.23 mm
3
/min and quality (
R
a
) up to 3.86 μm at an optimum have been observed.
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