A Wear Investigation of Repeatedly Used Wire in Wire Cut Electrical Discharge Machine
Wire electro-discharge machining (WEDM) is a fully extended and competitive machining process widely used for hard and difficult to machine materials. In the present research, experimental investigation have been conducted to find out the wire wear rate at different machining parameter Such as peak current, pulse on time, pulse off time, based on full factorial design of experiment. Molybdenum wire of 0.18 mm and EN-8 material were used as tool and work piece material for the experiment, ANOVA analysis were done to find out the effect of peak current, pulse on time, pulse off time on wire wear and found that the increasing in peak current slowly increase the wire wear but increasing in pulse on time increase the wire wear rapidly and pulse off time not much affects the wire wear. Keywords— WEDM, WWR, ANOVA, Full factorial,
Optimization of Material Removal Rate of WEDM Process on Mild Steel Using Molybdenum Wire
For any manufacturing process and, particularly, in process related to WEDM the correct selection of process parameters is one of the most important aspects to be taken into consideration. WEDM is capable of machining geometrically complex shapes or hard material components, such as composites, carbides, heat treated tool steels, super alloys, ceramics and heat resistant steels etc. These hard material components are widely used in die and mold making industries, aerospace, aeronautics and nuclear industries.
This study discusses the influence of process parameters like current, Pulse on time, Pulse off Time and Voltage on the performance parameters such as material removal rate. The experiment has been conducted on Mild Steel work piece using brass wire, because Mild Steel has various industrial applications in manufacturing of frame of motorcycles, dies, automobile chassis, base of boilers and cook wares etc. The experimental layout is based on Taguchi L16 orthogonal array. Further, the analysis of variance [ANOVA] is used to analyze the results obtained from Taguchi method. The analysis of results obtained for material removal rate indicate that current and pulse on time has the highest impact on material removal rate. As the current and pulse on time increases, the material removal rate also increases. Pulse off time and voltage has no significant effect on material removal rate.
Cytoplsmic uridine phosphorylase of rat liver. Characterization and kinetics.
Abstract Uridine phosphorylase (uridine:orthophosphate ribosyltransferase, EC 2.4.2.3) of rat liver cytoplasm has been purified 1900-fold. Initial velocity patterns of the phosphorolysis of uridine or deoxyuridine and of the synthesis of uridine indicated a sequential mechanism. Product inhibition patterns with uracil or ribose 1-phosphate as inhibitors were consistent with an "ordered Bi Bi" reaction in which inorganic phosphate is the first substrate to bind to the enzyme and ribose 1-phosphate the last product to leave the enzyme. The most highly purified enzyme fractions still retained uridine-, deoxyuridine-, and thymidine-cleaving activities in the ratio of 10:7:1 at pH 7.4. The fractions separated into a major and a minor band of protein on electrophoresis in phosphate buffer. Aging of the enzyme with loss of activity resulted in an increase in the proportion of the minor band. The pH optimum of the enzyme for uridine cleavage was 8.2, for deoxyuridine cleavage, 6.5, and for uridine synthesis, 8.5. Uridine or deoxyuridine synthesis was inhibited 50% in the presence of 1 mm uracil. The enzyme did not catalyze the direct transfer of ribose from uridine to uracil in the absence of phosphate. Uridine protected the enzyme to a greater degree than phosphate against inhibition by o-iodosobenzoate. Thus, at least one sulfhydryl group and possibly three are present at or near the active site. Uridine cleavage, uridine synthesis, and deoxyuridine cleavage were inhibited by deoxyglucosylthymine. The phosphorolysis of deoxyuridine and thymidine by thymidine phosphorylase, also purified from rat liver cytoplasm, was not inhibited by deoxyglucosylthymine. The molecular weights of both uridine and thymidine phosphorylases were estimated to be 110,000.