Wire Rupture Optimization in Wire Electrical Discharge Machining using Taguchi Approach

Wire electrical discharge machining (WEDM) is one of the most important nontraditional machining process that is well-known for cutting difficult to machine materials. The wire electrode along with machining parameters control the WEDM process. This research work focuses on optimizing WEDM parameters using Taguchi technique to minimize wire rupture. Experiments have been done using the L18 orthogonal array. Each experiment is repeated three times to ensure accurate readings of the wire rupture. The statistical methods of signal to noise ratio (S/N ratio) is applied to study effects of peak current, pulse width, charging time, wire speed, and wire tension on wire rupture. As a results, the peak current, pulse width, and wire tension have the most significant effect on wire rupture followed by charging time and wire speed. The developed analysis can be used in the metal cutting field to identify the optimum machining parameters for less wire rupture

Effects of Different Wire Electrodesand Cooling Methods on Surface RoughnessIn Wire Electro Discharge Machining

One of the most important criteria in assessing machine performance in wire electro discharge machining technology is surface roughness. In this study, the effects of wire electrodes made from different materials and cooling techniques on surface roughness of various workpiece materials were experimentally investigated in wire electro discharge machining. As test materials, AISI D2 tool steel and AISI 304 stainless steel and as wire electrodes, brass, copper and zinc coated brass wires and as cooling method, flushing and submerged techniques were used. Surface roughness results of square shaped machining samples were evaluated depending on different types of electrodes, cooling methods, and workpiece materials. Depending on the type of the electrode, while the lowest surface roughness values were obtained with zinc coated brass wire electrodes, the highest surface roughness values were obtained with uncoated brass wire electrodes. It was found that surface roughness values obtained from AISI D2 material gave better results compared to AISI 304 material. When it was assessed in terms of cooling techniques, the best surface roughness values were obtained while machining with flush cooling.Tel erozyon ile işlemede, makine performansının değerlendirmesinde en önemli kriterlerden biri yüzey pürüzlülüğüdür. Bu çalışmada, tel erozyonla işlemede farklı malzemelerden yapılmış tel elektrotların ve farklı soğutma tekniklerinin farklı iş parçası malzemelerinin yüzey pürüzlülüğüne etkisi deneysel olarak araştırılmıştır. Deney malzemesi olarak AISI D2 takım çeliği ve AISI 304 paslanmaz çelik, tel elektrot olarak pirinç, bakır ve çinko kaplı pirinç teller ve soğutma yöntemi olarak ise püskürtmeli ve daldırılmış yöntem kullanılmıştır. Kare şeklinde işlenen numunelerin farklı tip elektrotlara, soğutma yöntemlerine ve iş parçası malzemesine bağlı olarak yüzey pürüzlülük sonuçları değerlendirilmiştir. Elektrot tipine bağlı olarak en düşük yüzey pürüzlülük değerleri çinko kaplı pirinç tel elektrotlarla elde edilirken en yüksek yüzey pürüzlülük değerleri ise kaplamasız pirinç tel elektrotlarla elde edilmiştir. AISI D2 malzemesinden elde edilen yüzey pürüzlülük değerleri AISI 304 malzemesine göre daha iyi sonuçlara verdiği tespit edilmiştir. Soğutma yöntemine göre değerlendirildiğinde, en iyi yüzey pürüzlülük değerleri püskürtmeli soğutmayla işlemede elde edilmiştir

Design of an electrochemical micromachining machine

Electrochemical micromachining (μECM) is a non-conventional machining process based on the phenomenon of electrolysis. μECM became an attractive area of research due to the fact that this process does not create any defective layer after machining and that there is a growing demand for better surface integrity on different micro applications including microfluidics systems, stress-free drilled holes in automotive and aerospace manufacturing with complex shapes, etc. This work presents the design of a next generation μECM machine for the automotive, aerospace, medical and metrology sectors. It has three axes of motion (X, Y, Z) and a spindle allowing the tool-electrode to rotate during machining. The linear slides for each axis use air bearings with linear DC brushless motors and 2-nm resolution encoders for ultra precise motion. The control system is based on the Power PMAC motion controller from Delta Tau. The electrolyte tank is located at the rear of the machine and allows the electrolyte to be changed quickly. This machine features two process control algorithms: fuzzy logic control and adaptive feed rate. A self-developed pulse generator has been mounted and interfaced with the machine and a wire ECM grinding device has been added. The pulse generator has the possibility to reverse the pulse polarity for on-line tool fabrication.The research reported in this paper is supported by the European Commission within the project “Minimizing Defects in Micro-Manufacturing Applications (MIDEMMA)” (FP7-2011-NMPICT- FoF-285614)

ANFIS modelling of mean gap voltage variation to predict wire breakages during wire EDM of Inconel 718

The study aims to correlate the mean gap voltage variation and wire breakage occurrences during the wire EDM of Inconel 718. A novel approach to predict the wire breakage is introduced by considering the mean gap voltage variation (ΔVm) as an indicator of the instabilities in the spark gap. Such instabilities are regarded as the primary reason for wire breakages and inferior part quality of wire electric discharge machined components. The parameter ΔVm is a process data obtained as the difference between servo voltage and mean gap voltage (Vm). It was found experimentally that if the value of ΔVm crosses a threshold limit, the process interruptions through wire breakages were observed. In order to predict the wire breakage situations, the study models ΔVm using adaptive neuro fuzzy inference system (ANFIS). Based on central composite design (CCD) of response surface methodology (RSM), 31 experiments were conducted and ΔVm is recorded as the response. The input parameters considered were pulse on time, pulse off time, servo voltage and wire feed rate. The ANFIS model was found very accurate in predicting ΔVm, based on which wire breakage alerts can be given. The capability of the model is further confirmed by verification experiments. EDS and microstructural analysis further revealed the effect of ΔVm on wire wear and part quality. Higher value of ΔVm resulted in greater wire wear and inferior part quality. The surface finish and flatness error of machined parts were measured to compare the part quality

Failure detection and control for wire EDM process using multiple sensors

Unstable machining conditions during wire EDM process can lead to process failures, which affects the efficiency and sustainability of process. The study aims to develop a sensor-based failure prediction and process control system. The monitoring system consisting of high sampling rate differential and current probes extracts voltage and current signals during spark machining. Relevant discharge characteristics like pulse proportions, pulse frequency, and discharge energy are extracted from the pulse train data. The proposed process control algorithm works in three stages: failure prediction, failure severity assessment, and process control. Failure conditions considered are wire breakage and spark absence, which are predicted based on the extracted discharge characteristics. Severity of failure is judged based on the spark discharge energy. The proposed process control algorithm retunes the process parameters by adjusting pulse on time, pulse off time, and servo voltage, based on the type of failure and its severity. The methodology is successful in preventing the potential failure situation by restoring the machining stability. The capability of the model is demonstrated by conducting confirmation experiments. Microstructural comparison of machined surfaces and worn wire surfaces also confirms the effectiveness of the proposed strategy to ensure failure free machining with better surface integrity

Investigations on Machining Aspects of Inconel 718 During Wire Electro-Discharge Machining (WEDM): Experimental and Numerical Analysis

Wire electro- discharge machining (WEDM) is known as unique cutting in manufacturing industries, especially in the good tolerance with intricate shape geometry in die industry. In this study the workpiece has been chosen as Inconel 718. Inconel 718 super alloy is widely used in aerospace industries. This nickel based super alloy has excellent resistance to high temperature, mechanical and chemical degradations with toughness and work hardening characteristics materials. Due to these properties, the machinability studies of this material have been carried-out in this study. The machining of Inconel 718 using variation of wire electrode material (brass wire electrode and zinc coated brass wire) with diameter equal to 0.20mm has been carried out. The objective of this study is mainly to investigate the various WEDM process parameters and performance of wire electrodes materials on Inconel 718 with various types of cutting. The optimal process parameter setting for each of wire electrode material has been obtained for multi-objective response. The kerf width, Material Removal Rate (MRR) and surface finish, corner error, corner deviation and angular error are the responses which are function of process variables viz. pulse-on time, discharge current, wire speed, flushing pressure and taper angle. The non-linear regression analysis has been developed for relationship between the process parameter and process characteristics. The optimal parameters setting have been carried out using multi-objective nature-inspired meta-heuristic optimization algorithm such as Whale Optimization Algorithm (WOA) and Gray Wolf Optimizer (GWO). Lastly numerical model analysis has been carried out to determine MRR and residual stress using ANSYS software and MRR model validated with the experimental results. The overlapping approach has been adopted for solving the multi-spark problem and validate with the experimental results

Development of an electrochemical micromachining (μECM) machine

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University London.Electrochemical machining (ECM) and especially electrochemical micromachining (μECM) became an attractive area of research due to the fact that this process does not create any defective layer after machining and that there is a growing demand for better surface integrity on different micro applications such as microfluidics systems and stressfree drilled holes in the automotive and aerospace sectors. Electrochemical machining is considered as a non-conventional machining process based on the phenomenon of electrolysis. This process requires maintaining a small gap - the interelectrode gap (IEG) - between the anode (workpiece) and the cathode (tool-electrode) in order to achieve acceptable machining results (i.e. accuracy, high aspect ratio with appropriate material removal rate and efficiency). This work presents the design of a next generation μECM machine for the automotive, aerospace, medical and metrology sectors. It has 3 axes of motion (X, Y and Z) and a spindle allowing the tool-electrode to rotate during machining. The linear slides for each axis use air bearings with linear DC brushless motors and 2nmresolution encoders for ultra-precise motion. The control system is based on the Power PMAC motion controller from Delta Tau. The electrolyte tank is located at the rear of the machine and allows the electrolyte to be changed quickly. A pulse power supply unit (PSU) and a special control algorithm have been implemented. The pulse power supply provides not only ultra-short pulses (50ns), but also plus and minus biases as well as a polarity switching functionality. It fulfils the requirements of tool preparation with reversed ECM on the machine. Moreover, the PSU is equipped with an ultrafast over current protection which prevents the tool-electrode from being damaged in case of short-circuits. Two different process control algorithms were made: one is fuzzy logic based and the other is adapting the feed rate according to the position and time at which short-circuits were detected. The developed machine is capable of drilling micro holes in hard-to-machine materials but also machine micro-styli and micro-needles for the metrology (micro CMM) and medical sectors. This work also presents drilling trials performed with the machine with an orbiting tool. Machining experiments were also carried out using electrolytes made of a combination of HCl and NaNO aqueous solutions. The developed machine was used to fabricate micro tools out of 170μm WC-Co alloy shafts via micro electrochemical turning and drill deep holes via μECM in disks made of 18NiCr6 alloy. Results suggest that this process can be used for industrial applications for hard-to-machine materials. The author also suggests that the developed machine can be used to manufacture micro-probes and micro-tools for metrology and micro-manufacturing purposes.Brunel University European Commissio