Influence of needle pulse shifting on the basis pulse for wire-EDM of hard metals

The needle pulse can be shifted by the modular structure of the process energy source on a basis ignition pulse. In the Paper is presented that one basis pulse in connection with a needle pulse an improved roughness can be achieved. The simulation of the thermal influence of the needle-basis pulse-combination shows the influences of the pre-burning-duration and/or the past-burning-duration on the needle pulse. The result shows that the needle pulse shifts are efficient only in selected time ranges. At REM pictures typical surface textures are shown, which can occur by the needle pulse shift

Improved cemented carbide properties after wire-EDM by pulse shaping”, Journal of materials processing technology

Abstract In many applications the wire-EDM of cemented carbides (WEDM) (WC-(TiC)-Co) is restricted by the basic properties of this family of materials. Therefore, this research was aimed at developing an optimal process energy source that produces improved material properties after WEDM. The studies showed that it is important to use the correct parameter selection for main-cut and post-cut. Deterioration in the material properties by processing with high pulse energies can be corrected only by a limited extent in the post-cut. The primary actuating variable of pulse is the pulse duration, i.e. with pulse duration <500 ns higher current magnitudes can also be used without problems. Through the use of a new process energy source increase of bending strength of average 30% could be achieved. Simulation of the pulse waveforms and how the thermal load of the cut surface can be reduced and the technical conditions can be adapted to a particular application are shown in this paper

Comparison of measured and simulated crater morphology for EDM

Abstract The crater morphology has been investigated in different procedures. An analytical relation between pulse parameters and roughness has been achieved and differences between a single discharge and a sequence of discharges are described. Simulations of thermal-affected zones are identified for a single discharge and a sequence of discharges. The characteristics describing the changed gap conditions of the discharge types in the simulation model are shown. Starting from measured current and voltage curves, the thermal channel base parameters are computed. For single discharges with fixed base localization secure expansion parameters of the discharging channel can be determined if the geometries of measured and simulated thermal-affected regions match. The simulation of moving or jumping bases is considerably more complicated and more time-consuming. The channel movement is determined by more degrees of freedom. These additional degrees of freedom permit multiple solutions and the number of them must be reduced by further limiting conditions

Dysregulation of valvular interstitial cell let-7c, miR-17, miR-20a, and miR-30d in naturally occurring canine myxomatous mitral valve disease

Canine myxomatous mitral valve disease (MMVD) resembles the early stages of myxomatous pathology seen in human non-syndromic mitral valve prolapse, a common valvular heart disease in the adult human population. Canine MMVD is seen in older subjects, suggesting age-related epigenetic dysregulation leading to derangements in valvular cell populations and matrix synthesis or degradation. We hypothesized that valvular interstitial cells (VICs) undergo disease-relevant changes in miRNA expression. In primary VIC lines from diseased and control valves, miRNA expression was profiled using RT-qPCR and next generation sequencing. VICs from diseased valves showed phenotypic changes consistent with myofibroblastic differentiation (vimentinlow+, a-SMAhigh+), increases in senescence markers (p21, SA-b-gal), and decreased cell viability and proliferation potential. RT-qPCR and miRNA sequencing analyses both showed significant (p<0.05) downregulation of let-7c, miR-17, miR-20a, and miR-30d in VICs from diseased valves compared to controls. Decreased let-7c, miR-17, and miR-20a may contribute to myofibroblastic differentiation in addition to cell senescence, and decreased miR-30d may disinhibit cell apoptosis. These data support the hypothesis that epigenetic dysregulation plays an important role in age-related canine MMVD

Near net shape machining by Micro-EDM and Micro-WEDM

Near net shape is a concept that is widely used in the recent years to address the issues of sustainability and resource optimization in the manufacturing sector. Near net shape (NNS) processes are the processes that require least or no post-processing to manufacture a product. Electro-discharge machining (EDM) is a non-conventional machining process that uses spark erosion principle for machining conductivematerial. If the tool in the EDMis a flexible metallic wire, then the process is termed as wire EDM. Further to this, when the discharge energy, tool and wire diameter, and the machined features are in micron domain, the machining technique is termed μEDM or μWEDM. In μEDM/μWEDM, the resultant structure does not require any post-processing to attain the final dimensional accuracy and surface finish; therefore, these processes can be considered as NNS processes. In this chapter, different applications of μEDM and μWEDM have been discussed as NNS process