Performance Evaluation of SiC Powder Mixed Electrical Discharge Machining: A Case of Wire Cut Mode with Re-Circulating Molybdenum Wire

Review of the available literature on powder mixed electrical discharge machining (PMEDM) indicates, that most of the research has been done for “die sinking machining mode” whereas the “wire cut machining mode” has not received due attention despite being an important process variant. This work employs Silicon Carbide (SiC) powder mixed dielectric fluid for machining of AISI D2 in “wire cut” mode with re-circulating molybdenum wire (an economic and chemically stable proposition as tool). The effect of five process parameters (powder concentration, peak current, pulse on time, nozzle flushing pressure and stand-off distance) have been evaluated on surface roughness, kerf width, material removal rate and wire wear ratio using Taguchi’s approach. It is found that for surface roughness, higher current and low to moderate concentration levels (2 to 4g/l) deteriorate surface quality; higher values of pressure and stand-off distance are also seen to adversely affect it. For material removal rate, pulse on time as well as its interactions with powder concentration and current, are statistically significant. A higher pulse on with smaller and moderate powder concentrations (2g/l and 4g/l) reduces MRR. For wire wear ratio, current is the sole significant factor (PCR of ~ 65%). SEM analysis of the machined workpiece for the maximum MRR condition quantifies recast layer as ~ 19microns. An indirect comparison with the reported values for non-powdered EDM process indicates that for the similar wire (molybdenum), the use of SiC powder maintains the surface roughness and kerf values, for a much harder D2 material used in this work.

The Effects of Different Slurry Concentrations and Wire Speeds for Swinging and Non-Swinging Wire-Saw Machining

Slurry concentration and wire speed affect the yield and machining quality of ceramics (Al2O3) that are produced using wire-saw machining (WSM). This study determines the effect of slurry concentration and wire speed on the material removal rate (MRR), the machined surface roughness (SR), the kerf width, the wire wear and the flatness for swinging and non-swinging WSM. The experiments show that swinging WSM results in a higher machining efficiency than non-swinging WSM. WSM with swinging also achieves a peak MRR at a medium slurry concentration (25 wt%) and a higher wire speed (5.6 m/s) using the cutting conditions for the experimental region. However, slurry concentration and wire speed have no significant effect on the machined SR, the kerf width, the wire wear or the flatness for WSM with swinging mode.

Experimental model on the wire wear for WEDM of hard to machine materials

In this study, the wear of wire electrodes was investigated experimentally in wire electrical discharge machining. Naked brass wire, 0.25mm diameter, zinc oxide coated brass wire and brass CuZn20 coated with brass CuZn50 wire were applied in the conducted research. The wire wear ratio of WEDM of titanium alloy Ti6Al4V and cemented carbide B40 was described. As important WEDM parameters, the following variables were chosen: discharge time ton, average working voltage U. The following properties of machined materials, such as: melting point Tt, electrical conductivity σ, thermal conductivity K, thermal expansion coefficient k, density ρ, heat capacity cp, were also selected to develop the semi – empirical model of the wear of wire electrodes. The variation of the wire wear with cutting different materials by applying three different wire electrodes and process parameters was modelled semi – empirically by employing dimensional analysis.

Microstructural analysis and multi response optimization of WEDM of Inconel 825 using RSM based desirability approach

Increasing demand of aerospace industry for more heat resistant and tough material have open up the possibility of the use of Inconel 825 for making of combustor casing and turbine blades. Because of its robust nature, Inconel 825 is a difficult-to-cut material with conventional methods. Wire-cut electrical discharge machining (WEDM), a non traditional method uses thermoelectric erosion principle to produce intricate shape and profiles of such difficult-to-cut material. In this study, various operating parameters of WEDM are optimized using desirability approach and microstructural behavior at optimum combinations was studied. Input parameters viz. pulse-on time, pulse-off time, peak current, spark gap voltage, wire tension, wire feed and performance has been measured in term of material removal rate, surface roughness and wire wear ratio. It has been observed that at 110 machine unit pulse-on time (Ton), 35 machine unit pulse-off time (Toff), 46 volt gap voltage (SV), 120 ampere peak current (IP), 11 machine unit wire tension (WT) and 5 m/min wire feed (WF), the values obtained for material removal rate (MRR), surface roughness (SR) and wire wear ratio (WWR) were 27.691mm2/min, 2.721 μmand 0.117 respectively. Scanning electron microscopy, energy dispersive spectrograph and X-ray diffraction analysis has also been carried out to study the surface characterization. Comparatively less numbers of cracks, pockmarks, craters, and pulled out material were found on work specimen surface and wire electrode surface under standardized conditions, thus maintaining the surface integrity of the machined surface.

Wear Characteristics of Self-Damping Conductors for Large Crossing

The Aeolian vibration wear test of the self-damping conductors for large crossing was carried on a fretting fatigue wear test-bed. This test has been finished in three different vibration times under 25% ultimate tensile strength (UTS). The morphology observations and dimension measurement of aluminum wire wear scar has been analyzed by means of scanning electron microscope (SEM) and DMR multifunctional microscope. By observing the surface morphology and composition of the conductors, the influence law on the wire wear has been analyzed, and the analysis results reveal the contact wear mechanism, which is basically in accord with the working wires. The result shows the worn spots of the transmission line is an elliptic shape. The test result has important guiding meaning in further study on wear characteristics of self-damping conductors for large crossing under aeolian vibration.

Improved Overhead Contact System Operation With Inclined Pendulum Suspension

Overhead Contact Systems for electric transit vehicles utilize catenary or single contact wire suspended from cantilevers, bracket arms or span wires. For single contact wire, inclined pendulum suspension provides optimal performance for pantograph or trolley pole current collectors, though it is under-utilized in the United States. Typical suspension for single contact wire consists of direct suspension hangers or stitch suspension with steady arms where stagger is achieved by pulling off the contact wire with the hanger (direct suspension) or steady arms (stitch suspension). This results in the full weight of the contact wire in the span length being supported by the stitch or line insulator. This rigid point of attachment results in a heavy, stiff suspension leading to current collector bouncing, arcing and premature contact wire wear as the upward movement of the wire is restricted and a hard spot is created. It also results in excessive sag at elevated temperatures and contributes to an increased angle at the support span approach. Inclined pendulums can be utilized in constant tension systems or variable tensioned systems where they impart a semi-constant tensioning into the line and keep the wire tension relatively stable over a particular temperature range. The expansion/contraction of the contact wire is taken up in the inclination of the pendulums where they rise or fall so that the tension and sag in the contact wire remains relatively consistent. In addition, they provide less resistance to uplift of the current collectors at the suspension point so that rising of the contact wire occurs as the collector approaches and passes under it. The vertical angle of the contact wire approaching the span support is kept to minimum levels and collector performance during hot weather conditions tends to remain trouble free. Further, the energy wave set up in the wire from the moving collector is not grossly reflected at the suspension point as with direct suspension thus allowing the collector to pass through smoothly without bounce or loss of continuous contact. This paper describes the benefits of inclined pendulums in constant and variable tensioned systems such as creating a semi-constant tensioning effect, preventing current collector bounce and premature contact wire wear at the supports by reducing the uplift resistance on current collectors. It also provides the least visual obtrusiveness of all the suspension systems. In addition, this paper will present the associated costs of the inclined pendulum suspensions.