In this study, the optimization of recast layer thickness and surface roughness (SR) simultaneously in a Wire-EDM process by using Taguchi method with fuzzy logic has been applied. The Wire-EDM process parameters (arc on time, on time, open voltage, off time and servo voltage) were optimized with considerations of multiple performance characteristics, i.e., recast layer thickness and SR. Based on the Taguchi method, an L18 mixed-orthogonal array table was chosen for the experiments. Fuzzy reasoning of the multiple performance characteristics has been developed based on fuzzy logic, which then converted into a fuzzy reasoning grade or FRG. As a result, the optimization of complicated multiple performance characteristics was transformed into the optimization of single response performance index. Experimental results have shown that machining performance characteristics of Wire-EDM process can be improved effectively through the combination of Taguchi method and fuzzy logic.
Purpose The purpose of this paper is to investigate prediction and optimization of multiple performance characteristics in the wire electrical discharge machining (wire-EDM) process of SKD 61 (AISI H13) tool steel. Design/methodology/approach The experimental studies were conducted under varying wire-EDM process parameters, which were arc on time, on time, open voltage, off time and servo voltage. The optimized responses were recast layer thickness (RLT), surface roughness (SR) and surface crack density (SCD). Arc on time was set at two different levels, whereas the other four parameters were set at three different levels. Based on Taguchi method, an L18 mixed-orthogonal array was selected for the experiments. Further, three methods, namely grey relational analysis (GRA), backpropagation neural network (BPNN) and genetic algorithm (GA), were applied separately. GRA was performed to obtain a rough estimation of optimum drilling parameters. The influences of drilling parameters on multiple performance characteristics were determined by using percentage contributions. BPNN architecture was determined to predict the multiple performance characteristics. GA method was then applied to determine the optimum wire-EDM parameters. Findings The minimum RLT, SR and SCD could be obtained by setting arc on time, on time, open voltage, off time and servo voltage at 2 ms, 3 ms, 90 volt, 10 ms and 38 volt, respectively. The experimental confirmation results showed that BPNN-based GA optimization method could accurately predict and significantly improve all of the responses. Originality/value There were no publications regarding multi-response optimization using a combination of GRA and BPNN-based GA methods during wire-EDM process available.
In-situ (on-site) metallography has been proven as a method to assess metallurgical condition of material without damaging the material (Non Destructive Testing). However in this case, in-situ metallography must be completed together with several analysis to prevent metallography misinterpretation. This paper also provides an overview of inspection technique continuity, together with result from in-situ (on-site) and laboratory analysis.Water wall tube in-situ metallography was conducted during periodic inspection of a 200 MW Steam Power Plant Boiler. It was found another phase beside ferrite and pearlite. The phase is in horizontal direction and suspected as micro crack, delta ferrite or retained austenite.The further investigation was carried out by performing laboratory analysis including: metallography, scanning electron microscopy (SEM) equipped with EDX (Energy-dispersive X-ray spectroscopy) and hardness test.Result of the investigation showed that the phase was oxide as a corrosion product derived from tube surface and hot gas reaction during combustion. The oxide is identical as dry corrosion oxide, without liquid electrolyte. The oxide was only found on fireside tube surface. It also can be described that the fireside tube was over exposed to high temperature as shown the change lamellar pearlite to globular spheroidized pearlite.
Abstract.This research aimed to analyze the viability of the minimum quantity of lubricant (MQL) technique towards normal force, tangential force, surface roughness and chip formation in surface grinding of SKD 11 tool steel. The three surface grinding parameters were varied including the type of cooling method (MQL and dry), table speed, and depth of cut. Based on statistical analysis, depth of cut is the most influential factor which affects the four responses in both dry and MQL grinding. MQL could reduce normal force and tangential force considerably, but produce higher surface roughness. In MQL grinding, the chips removal took place mostly by shearing and fracturing.
Purpose The purpose of this paper is to analyze the failure of the left waterwall tube of a boiler furnace in the steam power plant which led to cracks and rupture. Macro visual observation showed the rupture like a fish mouth with slag adhering at the outer surface of the tube. Magnetite as a protective layer was peeled off. Changes in the thickness were analyzed through dimensional measurement. In this research, an analysis to find the cause and determine the fracture mechanism is presented. Design/methodology/approach A physical analysis was performed through visual observation of changes in the thickness. Micro visual testing with a metallography test provided the data required to measure the change of grain size. The mechanical analysis used Von Mises criteria and API 530 standard and provided the pressure limits data. Findings The thickness of the tube decreased at the peak curvature of the tube. The smallest thickness at the peak curvature of the tube was 0.108 inches. The working pressure was 40.74 percent from permit limits with Von Mises calculations. The percentage of pressure calculated by the API standard was 48.42 percent from permit limits. Larger crystal grains occurred only in the nearby area of the oxide layer and at the end of the crack tip. It indicated that part of the inner surface had a relatively high temperature and plastic deformation occurred because of the pressure from inside the tube. Combining all these factors ruptured the tube at this location because the cross-section could not hold up the pressure. Originality/value The analysis of this discussion focuses on the combined effect of those factors causing the ability to decrease stress being received. It restricts the tube from holding up the stress and furthermore it will generate fractures.
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