STUDY OF MATERIAL REMOVAL RATE OF DIFFERENT TOOL MATERIALS DURING EDM OF H 11 STEEL AT REVERSE POLARITY
Electric Discharge Machining (EDM) is a non-traditional machining process that involved a momentary spark discharges through the fluid due to the potential difference between the electrode and the workpiece. In EDM, improper choose of the electrode material may cause poor machining rate (or) performance. This is due to material removal rate characteristics. Less material removal rate (MRR) needs more time for machining process and become waste which is not good for production. Hence in this study, the effect of input parameters of EDM process ie. electrode type, peak current, gap voltage, and duty cycle on material removal rate of H11 steel are experimentally investigated. A L18 Taguchi’s standard orthogonal array is used for experimental design. Conventional Copper (Cu) and powder metallurgy (PM) copper tungsten (CuW) are used as tool materials. It was found that conventional copper tool electrode gives maximum MRR and best parametric setting for maximum MRR was found at, Cu (99% Cu) tool electrode, 9 ampere current, 50 volts gap voltage and 0.92 duty cycle. ie. A1B2C2D3.
A multi-objective optimization using a combined approach of principal component analysis and TOPSIS during electric discharge machining of H-11 die steel using P/M processed Cu-Cr-Ni metal matrix composite
The present experimental investigation deals with the electric discharge machining of H-11 die steel using metal matrix composite (MMC) as tool electrode. The MMC was prepared using powder metallurgy (P/M) route at a sintering temperature of 800°C. A comparative study has been made using conventional Cu and powder metallurgy (P/M) processed Cu-Cr-Ni MMC as tool electrode. The effect of input parameters like peak current (I<sub>p</sub>), pulse-on-time (T<sub>on</sub>), duty cycle (DC) and gap voltage (V<sub>g</sub>) on response variables like material removal rate (MRR), tool wear rate (TWR), surface roughness (SR) and diametral overcut (DOC) have been analyzed. Multi-objective optimization has been done using a hybrid method of principal component analysis (PCA) and technique for order preference by similarity to ideal solution (TOPSIS) to obtain the optimal set of parameters for copper and Cu-Cr-Ni tool. The optimum parameter setting for copper tool was found to be at I<sub>p</sub>=3A, T<sub>on</sub>=200<sub>μs</sub>, DC=9, V<sub>g</sub>=50V and for Cu-Cr-Ni tool was found to be at I<sub>p</sub>=6A, T<sub>on</sub>=150μs, DC=9, Vg=30V.
The Vascular Theory of Migraine‐Resuscitated or More Moribund?
Your decision to publish an important paper on cerebral blood flow (CBF) in migraine1 as the first in Headache for 1989 is to be applauded. But does it clarify or cloud the issue? After 20 years of CBF studies in migraine the results show 1) a reduction of at least 25 30% in classical migraine1, 2) an average increase of 31% in common and classical migraine2, 3) or no change in common migraine3. Now we learn that the measurements need modifying by 40% to allow for scattering of radiation the Compton scatter effect which has led to "an unbalanced interpretation of the data"1 So the results are as contradictory as they can be, the measurements require adjustment, and the interpretation is therefore doubly doubtful. From the clinical point of view the neurological aura, the enlarging scotoma, the scintillations, the migration of the paraesthesiae up the arm or visual disturbances across the visual field, have not been seen in cerebrovascular disease.4 The headache is throbbing in only 47% of 750 patients questioned during a migraine5; but even when the pain is pulsatlie, it throbs for only a portion of the time at the maximum of the headache (Blau unpublished observations). The evidence for a neurological aetiology has been examined6: the most potent argument against a vascular cause is that the common triggers stress, light and hunger go direct to the nervous system, not via blood vessels. No one denies that vascular changes occur in migraine but are they primary or secondary to a neurological disturbance? Sokoloff7 concluded that the stimulated rat and monkey cortex showed increased glucose uptake, and that the increased local blood flow occurred "in response (my italics) to changes in local functional activity". The evidence, therefore, points to an underlying neurological basis with secondary vascular responses. The vascular theory may need resuscitation but who is going to give it the kiss of life?