Pulsed Discharge Time Research Articles

METALLOGRAPHIC EXAMINATION OF SURFACE LAYER AFTER ELECTRICAL DISCHARGE MACHINING

This paper presents analysis of the influence of selected electrical parameters of hollowing on the state of the surface layer after electrical discharge machining (EDM). Namely, paper focuses on the analysis of the EDM cutting process, in terms of the influence of individual parameters on the number of occurrences and sizes of erosion craters on the machined surface. The basic parameters include electrical pulse discharge time, electrical discharge pause time, voltage, current amplitude and servo voltage. The initial values of the mentioned parameters were selected based on technology tables provided by the machine manufacturer and on the basis of own empirical tests. The tests were carried out according to static determined poliselective experimental plan (Hartley plan). Analysis of the machined surface was carried out using a scanning microscope (SEM) and an optical microscope. Quantitative metallographic analysis was used to determine the stereological features of erosion craters occurring on the surface of the machined material. The results were illustrated by means of three-dimensional graphs. The presented studies show a significant effect of electrical parameters of EDM on the quality of the machined surface, i.e. the number of occurrences and diameter of erosion craters. The research presents an approach based on mathematical modelling of electrical discharge machining. This approach can form the basis for developing methods of modeling technological processes and optimizing their parameters.

Research on self-healing characteristics of metallized film capacitor via acoustic and electric combined detection

Metallized film capacitor is widely used in pulse power generators and HVDC power transmission system. The high reliability of capacitor is mainly beneficial from the self-healing process. With the increase of its operation time and discharge time, frequent self-healing leads to loss of capacitance. Therefore, it is important to develop an effective detection method to monitor the self-healing characteristics of MFC. In this paper, a self-healing detection method based on acoustic and electric combination is proposed for MFC with high sheet resistance and the self-healing ultrasonic signal is analyzed. The influence of pulsed discharge times on the characteristic of self-healing is studied through online self-healing detection method. The results show that peak frequency of ultrasonic signal is between 50 kHz and 60 kHz. As the number of pulsed discharge time increases, low voltage self-healing discharges become more frequent and the self-healing frequency has same increasing trend with capacitance loss. When the capacitor is near the end of its life, the self-healing frequency increases sharply and the probability of high-energy self-healing point increases significantly. It's indicated that this detection method has a good application prospect for the monitor of aging state of the capacitor through the change of the self-healing characteristic.

Experimental investigations on wire electro-discharge machining (WEDM) of TiN/Si3N4 Nano-complex ceramics

In this paper, the surface characteristics of TiN/Si3N4 nano-complex ceramics cut with wire electro-discharge machining are studied. The effect of single pulse energy on surface properties is investigated in detail. The microscopic observation of the surface appearance with the scanning electron microscope shows that the longer the pulse discharge time, the greater the pulse discharge current, the greater the single pulse energy, the deeper the surface discharge pit, the larger the size, the surface melting and re-solidification phenomenon is more serious. The micro-observation of the cross-section of the surface processed shows that the surface metamorphic layer includes the melting and re-freezing layer and the white layer, the thickness of surface metamorphic layer is about 1 to 10 μm. The longer the pulse discharge time, the greater the single pulse energy, the greater the thickness of the surface metamorphosis layer. Due to the randomness of the discharge process, the metamorphic layer is not uniform.

Organic compounds removal in soil in a seven-needle-to-net pulsed discharge plasma system

A pulsed discharge plasma (PDP) system (a seven-needle-to-net electrode geometry) was built to degrade pyrene and p-nitrophenol in soil. Pulse discharge time, contents of the pollutants in the soil, the initial pH value of the soil, Kaolin and Cr6+ addition on removal of pollutants was investigated. The obtained results show that 60 min was the better treatment time; removal of organic compounds decreased with the increase of the contents; removal of pyrene was higher at neutral pH condition, while p-nitrophenol has more oxidation in the basic soil; Kaolin and Cr6+ addition has positive effect on the organic compounds degradation.

Evolution of mechanical properties of boron/manganese 22MnB5 steel under magnetic pulse influences

The boron/manganese 22MnB5 steel can be noted as the widely used material for creation of details, which must withstand high amount of load and impact influences. The complexity and high labor input of restoration of boron steel parts leads to growing interest in the new forming technologies such as magnetic pulse forming. There is the investigation of the evolution of mechanical properties of 22MnB5 steel during the restoration by means of magnetic pulse influence and induction heating. The heating of 22MnB5 blanks to the temperature above 9000C was examined. The forming processes at various temperatures (800, 900 and 9500C) were performed during the experiments. The test measurements allowed to obtain the relationships between the strain and the operation parameters such as induced current, pulse discharge time and the operation temperature. Based on these results the assumption about usage of these parameters for control of deformation process was made. Taking into account the load distribution and the plasticity evolution during the heating process, the computer simulation was performed in order to obtain more clear strain distribution through the processed area. The measurement of hardness and the comparison with the properties evolution during hot stamping processes confirmed the obtained results.

Capacity Fade Analysis of a Battery/Super Capacitor Hybrid and a Battery under Pulse Loads – Full Cell Studies

A detailed analysis of the capacity fade of a battery/supercapacitor hybrid and a battery alone has been carried out at 55 °C by discharging them at three different pulse rates. The applied peak current amplitudes were 5C (7 A), 3C (4.2 A), and 1C (1.4 A), respectively. The results indicated that for hybrids the pulse discharge run time was extended for all pulse discharge rates. The ohmic resistances estimated as a function of the pulse discharge rates were smaller for hybrids when compared with those for batteries. The variation of the ohmic resistance under pulse discharge with cycling, irrespective of the pulse discharge rate was smaller for hybrids than that for the batteries. The batteries and hybrids cycled at the lowest pulse discharge rate (high pulse discharge time) have larger capacity fade when compared with the capacity fade of the batteries and the hybrids discharged using higher discharge rates (low pulse discharge time). Impedance, cyclic voltammogram, and the rate capability studies were carried out on batteries cycled alone and on batteries cycled as part of the hybrid. The battery showed larger increase in the interfacial impedance with cycling when compared with the hybrid system.

The structure of multi-electrode-pair pulse laser and discharge pulse time selection

Applying multi-electrode-pair pulse TEA CO 2 laser to one optical resonance cavity will have several advantages over traditional method, including higher gain, shorter pulse discharge time interval, and in particular, continuous adjustable time interval of multi-pulse laser output can be achieved without high vacuum condition. To improve laser's working stabilization, we proposed new approaches to optimize laser structure design and discharge pulse time interval selection.

Rapid Consolidation by Spark Sintering of Rapidly Solidified 7075 Aluminum Alloy Powder

Compacts of 7075 aluminum have been produced from rapidly solidified powders by optimizing spark sintering parameters, such as pulse discharge time, fixed maximum temperature, holding time at this temperature, and method of cooling to room temperature after the sintering. High-grade compacts can be obtained by a short process (40-50 s) consisting of heating to 773 or 873 K at a heating rate of 9.6 K/s and holding this temperature for 10 s. The rapidly cooled compacts show the same supersaturated state at room temperature as the received as-atomized powder. Compacts quenched in water just after spark sintering at 873 K for 1.2 ks show the same age-hardening behavior as solution-heat treated compacts. Compacts that are quenched in water and aged after sintering at 873 K for 1.2 ks show the same elongation and flow stress as compacts aged after solution heat treatment. Elongation data suggest that compacts produced with longer holding time at a higher temperature and rapid cooling show a large amount of main alloying elements in solid solution and sufficient promotion of sintering.

Bonding Test for Tungsten Plates by Pulse Discharge Sintering Method

Bonding experiment has been performed for tungsten plates with the Pulse Discharge Sintering (PDS) method. The bonded interfaces have been evaluated by observing the optical microstructure and ultrasonic imaging, and the effect of bonding condition on the bending strength of the bonded samples was examined. For the samples bonded without insert material in between the tungsten component plates, evidence of grain growth across the bonded interface was observed, indicating the occurrence of diffusion bonding. Many pores have been found at the interface of the bonded sample when tungsten powder was used as insert material, whereas pores were not observed for the sample bonded with tantalum powder as insert material. The bending strength of the samples bonded with tantalum and tungsten powder as insert materials, and that bonded without insert material has been measured to be about 400, 200 and 100 MPa, respectively. The bonded sample with tantalum has been found to possess a higher bending strength than that of the tungsten component plate. It has been demonstrated that a longer activating pulse discharge time in the PDS process leads to a higher bending strength for both samples bonded with tungsten powder and without insert material.