The master’s thesis deals with the topic of electrical discharge machining. The first part of the thesis contains a study of the die-sinking EDM. The die-sinking EDM of the silicon carbide ceramic is realized in the experimental part of the thesis. The result of this work was to explore the influence of the EDM sinking parameters, specifically pulse current, open-voltage and pulse on-time, on the machined surface. Furthermore, the analysis of the tool electrode was made. This analysis was focused on the wear in the corners, which has key influence on accuracy of the machining. The machining time was also examined.

In der vorliegenden Arbeit werden die elektrischen und nicht-elektrischen Einstellparameter der Bohrerosion untersucht. Ein neuer Ansatz zur geregelten Zwangsspülung wird vorgestellt und die Mechanismen diskutiert, die zu veränderten Prozessrandbedingungen führen. Abhängig von der Entladeenergie kann eine optimale Durchflussmenge ermittelt werden, die eine direkte Abtragwirkung zur Folge hat, wodurch der Abtragmechanismus in der Funkenerosion erweitert werden muss. Längliche Einzelentladungskrater bestätigen eine erhöhte Mobilität des Entladekanals während einer Entladung infolge der starken Spülung. Wasserbasiertes Dielektrikum führt bei einer kathodischen Elektrodenpolung zu einem verschleißreduzierenden Elektrolyseeffekt, der die Energieumsetzung an der Elektrode direkt beeinflusst. Die Übertragbarkeit der Ergebnisse von Einzelentladungen auf den Folgeprozess kann durch die hier vorgestellte problemangepasste Spüleinrichtung nachgewiesen werden.

Bearing currents are not all the same. Under certain circumstances and special use cases classic bearing insulations are not sufficient anymore to prevent bearing currents due to the operation of frequency converters. Additional corrective measures have to be implemented to reduce the source of bearing currents the common mode current. The usage of nanocrystalline tape wound cores shows high effectiveness. As part of a big field study with more than 50 large drive trains in the primary industry, the damaging mechanics of bearing currents are examined under real conditions. Of exceptional high interest is the influence of disturbances which can hardly be simulated in the laboratory. Additional to the shielded motor cable parallel installed functional potential equalization cables applied multiple times have almost no effect in regard to reducing the bearing current. With an optimal installed functional potential equalization system more than 95 percent of the common mode current can flow back through the motor cable shield to the converter. The disturbance impact in the field can influence the voltage over the bearing that breakthroughs are favored but also reduced.

Ti-6Al-4V has a wide range of applications such as in the automotive and aerospace industries. Nevertheless, titanium alloys are very difficult to machine by conventional methods. Micro-EDM is a non-conventional machining method that uses the thermal effect of precisely controlled sparks. Manufacturers are looking for the methods and optimal settings to increase the productivity of micro-EDM in terms of lessening machining time and tool wear. Moreover, surface integrity of the machined area is crucial for some products such as biomedical implants. The objective of this study was to investigate the effects of the micro-EDM process parameters on response variables, in order to understand the behavior of each parameter as well as to determine their optimal values. Although, there is a substantial amount of literature studying different aspects of micro-EDM, most of them were designed based on the one-factor-at-a-time experiments instead of studying all factors, simultaneously. This research was conducted through a series of experiments using a full factorial design. An analysis of variance was employed to analyze the findings and to determine the effect and significance of each process parameters on the response variables. The process parameters included voltage, capacitance, electrode rotational speed, and electrode coating. Voltage and capacitance were studied separately as well as in combination in terms of the discharge energy. Response variables consisted of machining time, tool wear, crater size, microhardness, and element characterization. The surface morphology and element characterization were studied through the application of SEM and EDS analysis. The findings indicated that voltage had a decreasing effect on machining time, while it increased the crater size. Capacitance decreased machining time and tool wear. It had an increasing effect on the surface hardness. The effects of the TN-coating and electrode rotational speed were not statistically significant. Voltage and capacitance were the only parameters affecting element characterization. The affected elements included Ti, Al, C, and W. The optimal process parameters for two sets of response variables were determined using Minitab 17.

Capacitive sensors are frequently applied to curved target surfaces for precision displacement measurements. In most cases, these sensors have not been recalibrated to take the curvature of the target into consideration. This recalibration becomes more critical as the target surface becomes smaller in comparison to the sensor. Calibration data are presented for a variety of capacitance probe sizes with widely varying geometries. One target surface particularly difficult to characterize is the inner surface of small holes, less than one millimeter in diameter. Although contact probes can successfully measure the inner surface of a hole, these probes are often fragile and require additional sensors to determine when contact occurs. Probes may adhere to the wall of the hole, and only a small number of data points are collected. Direct capacitance measurement of small holes requires a completely new capacitance probe geometry and method of operation. A curved, elongated surface minimizes the gap between the sensor surface and the inner surface of the hole. Reduction in the size of the sensing area is weighed against electronics limitations. The performance of a particular probe geometry is studied using computer simulations to determine the optimal probe design. Multiple, overlapping passes are deconvolved to reveal finer features on the surface of the hole. A prototype sub-millimeter capacitance probe is machined from tungsten carbide, with four additional material layers added using ebeam deposition. Several techniques are studied to remove these layers and create a sensing area along one side of the probe. Both mechanical processes and photolithography are employed.

The entry part introduce into the problematic of rework processes by molding injection tools for thermoplastic. Aim is necessity of change current rework process usage by electro discharge machining (EDM) technology.The theoretical part of the thesis describes the physical essence of EDM technology, the system of production of cutting electrodes and related issues. The practical part of work compare the process of production of copper and graphite electrodes with focus on production time and costs. The production parameters of the EDM process were analyzed and the wear of copper and graphite electrodes during the production process was compared. Main result of the thesis is an evaluation of the research activity, interpretation of the results of this activity and a proposal of measures to shorten the production time of the cutting electrodes and the time of the EDM machining by these electrodes.

Student affect can play a profoundly important role in students' post-school lives. Understanding students' affective states within online learning environments in particular has become an important matter of research, as digital tutoring systems have the potential to intervene at the moment that students are struggling and becoming frustrated, bored or disengaged. However, despite the importance of assessing students' affective states, there is no clear consensus about what emotions are most important to assess, nor how these emotions can be best measured. This dissertation investigates students’ self-reports of their emotions and causal attributions of those emotions collected while they are solving math problems within a mathematics tutoring system. These self-reports are collected in two conditions: through limited choice Likert response and through open response text boxes. The conditions are combined with students’ cognitive attributions to describe epistemic (neither purely affective nor purely cognitive) emotions in order to explain the relationship between observable student behaviors in the MathSpring.org tutoring system and student affect. These factors include beliefs, expectations, motivations, and perceptions of ability and control. A special emphasis of this dissertation is on analyzing the role of causal attributions for the events and appraisals of the learning environment, as possible causes of student behaviors, performance, and affect.

This paper aims to create a hard modification layer of WC/Co/Fe on the surface of SKD11 work steel by using a new closed-type method of surface electrical discharge coating with the self-made tool electrode and CNC electrical discharge machine. The tool electrode is the composition of a semi-sintered powder compacted electrode and a cooper rod. The sintered powder compacted electrode making process is first to mix the WC/Co and Fe powders uniformly at 8:1, 4:1, 2:1 and 1:1 in weight ratio. Continually, it will form the cylinder of 8mm in diameter and 18mm in length approximately by compacting in different pressure (50~200 MPa) and sintering temperature (300~900 ¢J). The EDM condition is 1~12A discharge current, 25~500£gs pulse time, and 50% duty factor. The electrical discharge machining is proceeding in kerosene with tool electrode as cathode and workpiece as anode. The result is as following. It can be concluded that the best condition to fabricate the sintered powder compacted electrode is 1:1 in weight ratio between WC/Co and Fe powders; with 200Mpa compacting pressure and sintering temperature at 900¢J, which results in lowest electrical resistivity. Under such condition, the area covered ratio can reach 100% at best EDM condition, which is pulse time £non = 50 £gs, rest time £noff = 50 £gs, 8A in current and 1.5 min in machining time. The surface hardness of workpiece increases with machining time. The surface hardness dramatically increases to Hv1500 as machining time over 1.5 min. The hardness of modification layer equals to the WC/Co particle itself which brings to the best wear ability. Moreover, the hardness of under surface in between 48 £gm is much higher than it of the SKD11 work steel. The hardness in between 30 £gm can reach up to Hv1200 in particular. The hardness of surface modification layer increases linearly with machining time. However, the limit of surface modification layer is about 30 £gm, and the needed time is below 5 min.

The ACME collaboration has completed a measurement setting a new upper limit on the size of the electron's permanent electric dipole moment (EDM). The existence of the EDM is well motivated by theories extending the standard model of particle physics, with predicted sizes very close to the current experimental limit. The new limit was set by measuring spin precession within the metastable H state of the polar molecule thorium monoxide (ThO). A particular focus here is on the automated data acquisition system developed to search for a precession phase odd under internal and external reversal of the electric field. Automated switching of many different experimental controls allowed a rapid diagnosis of major systematics, including the dominant systematic caused by non-reversing electric fields and laser polarization gradients. Polarimetry measurements made it possible to quantify and minimize the polarization gradients in our state preparation and probe lasers. Three separate measurements were used to determine the electric field that did not reverse when we tried to switch the field direction. The new bound of |de|< 8.7 &times; 10^-29 e cm is over an order of magnitude smaller than previous limits, and strongly limits T-violating physics at TeV energy scales. / Physics

The observation of a permanent electric dipole moment (EDM) in a non-degenerate system would indicate the violation of discrete symmetries of Time reversal (T) or combined application of Charge (C) and Parity (P) symmetry violation through the CPT theorem. The diamagnetic 225Ra atom with nuclear spin I=1/2 is a favorable candidate for an EDM search. Experimental sensitivity to its EDM is enhanced due to its high atomic mass and the increased Schiff moment of its octupole deformed nucleus. An experimental setup is developed where laser cooled neutral radium atoms are collected in a magneto-optical trap (MOT). The collected atoms are transported 1 meter with a far off-resonant optical dipole trap (ODT) and then the atoms are transferred to a second standing-wave ODT in an experimental chamber. The atoms are then optically polarized and allowed to Larmor precess in parallel and antiparallel electric and magnetic fields. The difference between the Larmor precession frequency for parallel and antiparallel fields is experimentally determined to measure the EDM. This thesis is about the first measurement of the EDM of the 225Ra atom where an upper limit of |d(225Ra)|<5.0*10-22 e cm (95\% confidence) is reached.