In order to improve the machining efficiency and the surface quality of EDM/ECM, adding a small amount of sodium nitrate into deionized water as the working medium, a novel simultaneous machining approach of EDM and ECM (SEDCM) was developed. In this work, a comparative study was conducted on the SEDCM performance of TC4 alloy using different electrode materials viz. brass, copper and copper-tungsten alloy. In addition, the effects of process parameters, such as peak current, pulse on time and gap voltage on material removal rate (MRR), tool wear rate (TWR), surface roughness (Ra), and surface micromorphology were investigated. The results show that brass electrode provides the smallest MRR, the highest TWR and the worst surface quality. The copper electrode has the smallest average diameter of a single discharge craters and the best surface finish. The MRR and TWR of copper-tungsten electrode are similar to those of copper electrode. As peak current increases, TWR increases and Ra deteriorates for all the electrodes, as well MRR increases and then decreases for copper and copper-tungsten electrodes. Increase in pulse on time and gap voltage, MRR and TWR increases and then decreases gradually. At higher pulse on time and gap voltage, Ra becomes greater for three type electrodes.
In order to improve the corrosion resistance of brass treated by plasma electrolytic oxidation (PEO), Na2WO4 additive was introduced into a mixed electrolyte of sodium silicate and sodium hydroxide, and a composite oxide coating was formed on the surface of H62 brass. The effect of Na2WO4 concentration from 0 to 3 g/L in silicate-based electrolyte on the properties of PEO coatings was investigated by SEM, EDS, XRD and electrochemical workstation. The results show that the element of W in the form of metal oxides can be successfully incorporated into PEO coatings. The addition of Na2WO4 can significantly improve the corrosion resistance of PEO coatings, and the best corrosion resistance is obtained when the addition amount is 1.0 g/L.
In view of the di cult machining characteristics of titanium alloys and the limitations of EDM/ECM serial machining, a study of parallel machining of EDM and ECM with the aid of abrasive particles was carried out using a low conductivity NaNO 3 salt solution as the working medium. Firstly, the in uences of the electrical conductivity of working medium, abrasive material and abrasive particle size on material removal rate, electrode loss rate, surface roughness and surface microstructure were analyzed. Then, the material removal rate, electrode loss rate and surface roughness were taken as evaluation indexes, and the multi-process objectives were transformed into a single evaluation index by orthogonal test and grey correlation analysis. The optimal combination of the main process parameters including peak current, pulse width, abrasive particle concentration and gap voltage was obtained, and the experimental veri cation was carried out. The results show that under the same electrical parameters and machining conditions, the comprehensive machining effect is better when the conductivity of working medium is 300 µS/cm. Compared with Cu and Al abrasives, although SiC abrasives have the lowest material removal rate, the electrode loss rate and surface roughness are the smallest; according to the analysis of multi-objective grey correlation degree, the optimal combination of process parameters for EDM and ECM parallel machining assisted by SiC abrasive particles with particle size of 50 µm is as follows: peak current 1.5 A, pulse width 15 µs, abrasive concentration 5 g/L and gap voltage 40 V. Compared with other parameter combinations, the electrode loss rate, surface roughness and surface morphology are improved obviously under this parameter combination.
IntroductionPrevious studies have highlighted the experiences of caregivers for patients with chronic heart failure (CHF), specifically focusing on their negative experiences. There are few systematic reviews on the topic to synthesise the positive experiences of family caregivers for patients with CHF. This study will examine how experiences such as developing new skills, strengthening their relationships (between caregivers and recipients) and receiving appreciation from the care recipient assist to improve caregivers’ perception of their circumstances.Methods and analysisThis review will be conducted in accordance with the Joanna Briggs Institute (JBI) methodology for qualitative systematic reviews. Qualitative and mixed methods studies related to the positive experiences of family caregivers for patients with CHF, reported in English or Chinese and published from inception in the following databases will be included: PubMed, MEDLINE, Embase, Cochrane Library, Web of Science, PsycINFO, CINAHL, Wan Fang Data, China National Knowledge Infrastructure, Chongqing VIP, Chinese Biomedical Literature Database, Open Grey and Deep Blue Library databases. The standard JBI Critical Appraisal Checklist for Qualitative Research will be used by two independent reviewers to appraise the quality of the included studies, and the standardised JBI Qualitative Data Extraction Tool for Qualitative Research will be applied to extract data. The final synthesised findings will be graded according to the ConQual approach for establishing confidence in the output of qualitative research synthesis.Ethics and disseminationEthical approval is not required as no primary data are being collected. The results will be made available through a peer-reviewed publication.PROSPERO registration numberCRD42021282159.
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