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The magnetized sintered NdFeB (MS-NdFeB) permanent magnet material is difficult to machine due to high hardness, brittleness, and magnetic force. In this paper, the electrical discharge machining (EDM) of the MS-NdFeB workpiece is studied to improve the machining process of the MS-NdFeB. In addition to the material removal rate (MRR) and the surface roughness (SR), the change rate of the magnetic flux density (MCR) for the MS-NdFeB is proposed and used as the research index of their machining effect by the EDM process. By orthogonal experiments, using the intuitive analysis method and the analysis of variance (ANOVA) method, study the influences of the peak current, the pulse on time, the pulse off time, and the magnetic field intensity of the processing area (MF) on the MRR, the SR, and the MCR. The scanning electron microscope (SEM) pictures of the machined MS-NdFeB surfaces are obtained based on the experimental design with a one-factor variation. The comparative experiment is performed to reveal the change of the MCR in EDM. The intuitive analysis of the orthogonal experimental result reveals regularities of influences. The ANOVA reveals the significance of influences. The regularities and significance of influences of machining parameters on the machining effects are analyzed assisted by the analysis on these SEM pictures and the comparative experimental results. The optimal combinations of machining parameters for MRR, SR, and MCR are obtained by single-objective optimization. The verification experiments prove the reliability of the single objective optimization results. [ABSTRACT FROM AUTHOR]

Electrical discharge machining (EDM) with three-phase flow dielectric medium uses gas-liquid-powder mixture as the dielectric medium to improve the machining performance of the EDM. The appropriate selection of processing parameters makes for the improvement of machining properties for this EDM process. The material removal rate (MRR), tool wear rate (TWR), and surface roughness (SR) of EDM with three-phase flow dielectric medium are studied experimentally. The influence of process parameters, including peak current, pulse on time, pulse off time, flow rate, and concentration of powder particles, on these performance parameters, including MRR, TWR, and SR, are found out based on the orthogonal design experiment and the signal-to-noise ratio analysis. The reasons for these influences are analyzed. The optimal combination of process parameters to improve each single performance parameter is obtained. Verification tests are carried out. It is verified that the best combination of process parameters for MRR is powder concentration at the middle level, flow rate at the high level, pulse on time at the middle level, pulse off time at the low level, and peak current at the high level; the best for TWR is powder concentration at the low level, flow rate at the low level, pulse on time at the high level, pulse off time at the low level, and peak current at the low level; the best for Ra is powder concentration at the middle level, flow rate at the high level, pulse on time at the low level, pulse off time at the high level, and peak current at the low level, respectively. [ABSTRACT FROM AUTHOR]

316 L steel-based human implants play an important role in the biomedical field. In order to address the problem of immune rejection of 316 L steel-based human implants and further improve the machining efficiency, the surface roughness (SR) and hydrophilicity of 316 L workpieces are improved by electrical discharge machining milling (EDM-milling) instead of die-sinking electrical discharge machining (EDM) and by the incorporation of nano hydroxyapatite (NHAP) powder into the dielectric. The effects of powder concentration of NHAP, reference voltage, peak current, pulse width, and pulse interval on the material removal rate (MRR), electrode wear rate (EWR), SR, and contact angle (CA) of 316 L workpiece processed by powder mixed EDM-milling with NHAP (NHAP-PMEDM-milling) are investigated by single-factor experiment, and comparisons are done with the powder mixed die-sinking electrical discharge machining with NHAP (NHAP-PMEDM). According to the results, the MRR, EWR, SR, and CA of 316 L by NHAP-PMEDM-milling are varied regularly with the variation of experiment parameters. The addition of NHAP powder into deionized water (DW) can reduce the CA of the surface of 316 L steel workpiece to a great extent, with a maximum reduction of 27.9%, while affecting MRR, EWR, and SR very little. In addition, NHAP-PMEDM-milling can increase MRR by 115.5% and reduce EWR, SR, and CA by 43.2%, 13.2%, and 15.9%, respectively, compared with NHAP-PMEDM. [ABSTRACT FROM AUTHOR]