Statistical Modeling and Optimization of Process Parameters in Electro-Discharge Machining of Cobalt-Bonded Tungsten Carbide Composite (WC/6%Co)

AbstractIn this paper, attempts have been made to model and optimize process parameters in Electro-Discharge Machining (EDM) of tungsten carbide-cobalt composite (Iso grade: K10) using cylindrical copper tool electrodes in planing machining mode based on statistical techniques. Four independent input parameters, viz., discharge current (A: Amp), pulse-on time (B: μs), duty cycle (C: %), and gap voltage (D: Volt) were selected to assess the EDM process performance in terms of material removal rate (MRR: mm3/min), tool wear rate (TWR: mm3/min), and average surface roughness (Ra: μm). Response surface methodology (RSM), employing a rotatable central composite design scheme, has been used to plan and analyze the experiments. For each process response, a suitable second order regression equation was obtained applying analysis of variance (ANOVA) and student t-test procedure to check modeling goodness of fit and select proper forms of influentially significant process variables (main, two-way interaction, and pure quadratic terms) within 90% of confidence interval (p-value≤0.1) It has been mainly revealed that all the responses are affected by the rate and extent of discharge energy but in a controversial manner. The MRR increases by selecting both higher discharge current and duty cycle which means providing greater amounts of discharge energy inside gap region. The TWR can be diminished applying longer pulse on-times with lower current intensities while smoother work surfaces are attainable with small pulse durations while allotting relatively higher levels to discharge currents to assure more effective discharges as well as better plasma flushing efficiency. Having established the process response models, a multi-objective optimization technique based on the use of desirability function (DF) concept has been applied to the response regression equations to simultaneously find a set of optimal input parameters yielding the highest accessible MRR along with the lowest possible TWR and Ra within the process inputs domain. The obtained predicted optimal results were also verified experimentally and the values of confirmation errors were computed, all found to be satisfactory, being less than 10%. The outcomes of present research prove the feasibility and effectiveness of adopted approach as it can provide a useful platform to model and multi-criteria optimize MRR, Ra, and TWR during EDMing WC/6%Co material

Effect of selenium supplementation on lipid profile, Anemia, and inflammation indices in Hemodialysis Patients

Objective: Trace elements deficiency is common among end-stage renal disease (ESRD) patients due to excessive loss during dialysis and the lower intake secondary to loss of appetite. Selenium (Se) is a trace element that plays an important role in the radical scavenging system and helps the body defend against oxidative stress. This study aims to evaluate the effects of Se supplementation on lipid profile, anemia, and inflammation indices in ESRD patients. Methods: Fifty-nine hemodialysis patients enrolled and were randomly divided into two groups. Two hundred microgram Se capsules once daily for the case group and matching placebo for the control group were administered for three months. Demographic data were collected at the study beginning. Uric acid (UA), anemia and inflammation indices, and lipid profiles were recorded at the beginning and the end of the study. Findings: UA and UA-to-HDL (high-density lipoprotein) ratio decreased significantly in the case group (P < 0.001). The changes in lipid profile were not significant among both groups. Hemoglobin slightly increased in the case group, however, it decreased significantly in the control group (P = 0.031). High-sensitivity C-reactive protein (hs-CRP) decreased in the case group and increased in the control group, however, none of these changes were significant. Conclusion: According to the results of this study, selenium supplementation in ESRD patients could reduce some risk factors related to their mortality, such as the ratio of uric acid to HDL. However, the changes related to lipid profile, hemoglobin level and hs-CRP biomarker were not significant