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,
Analysis of Wire Wear in WEDM
Objective: This paper emphasizes the effect of cutting parameter on the size of crater and wire wear ratio because wire breakage is most common problem in WEDM and wire crater is very much responsible for wire breakage. Methods/statistical Analysis: Many researchers had adopted various methods for the evaluation of the dominating parameters on wire EDM process. In this study Response Surface Methodology (RSM) was used as a statistical analytical tool for the evaluation of the parametric effect on wire creator of wire EDM process. OLYAMPUS BX51M optical microscope was used for the observation of wire creator. For experiment MAXICUT WEDM machine was used and experiment were conducted on INCONEL 625 work piece and zinc coated brass wire of 0.25mm diameter was used. Finding: The experiments were conducted under different cutting parameters, which are open circuit voltage, pulse duration, wire speed and flushing pressure. As a result it was found that crater size increases with increase in pulse duration because increased pulse duration contributes to large energy content of spark discharge further it was also found that the creator size also increases with open circuit voltage and feed wire speed whereas decrease with increase in flushing pressure. Applications/Improvements: This analysis can become the basis for industries where the manufacturing is done by the wire EDM process and wire breakage is the common problem.
Hygroscopic Expansion of some Casting Investments
CREDIT is generally given to Taggart1 for introducing the cast gold inlay to the dental profession. Although he realized that gold shrinks when cooled from molten state to solid state of room temperature, the investment available to him did not supply sufficient compensation. In 1910, Van Horn2 published a paper dealing with a method by which he obtained the compensation by means of wax expansion. The next major research in connection with this problem was the work of Coleman3 at the National Bureau of Standards. He determined the gold shrinkage to be 1.25 per cent and presented a casting technic with compensation values of quantitative nature. The total compensation for the gold shrinkage was obtained by the combination of the setting and thermal expansion of the mold. This procedure is the general practice followed at the present time for compensation. There are some disadvantages to this method. Skinner has indicated the difficulty of obtaining smooth castings and the improper compensation for the casting shrinkage.4 It has been found by Hollenback5 and Scheu6a that castings made at a high temperature are rougher than those made at a low temperature (450° C.), depending upon the great difference in thermal expansion between plaster of Paris and silica, which causes a poor union of the fine particles. This may also result in friability and there may be some warpage due to the differential expansion. A method which provides sufficient compensation at a low mold temperature is the hygroscopic casting technic.b Wilson7 showed that certain plasters expand as much as 0.0044 inch to the inch by taking up moisture from the air. With this information at hand, Scheula, b tested some commercial investment to determine what results the addition of moisture would have. He found6b: (1) All of the casting investments that were tested expanded. (2) The thicker the mix, the greater the expansion. (3) A mix with hot water expanded more than one with cold water. (4) The time at which the mix is placed in the water is of great importance. It was found that if the mix is placed in the water early, it would not expand so much as when placed in a little later. It was also found that if the mix was placed in the water after a certain time, it could not expand to the maximal amount. (5) The temperature of the water in which the mix is placed is important, for two reasons; (a) the temperature of the water controls slightly the expansion of the investment, and (b) water at a temperature of 1000 F. slightly softens the wax pattern so that the fine margins are not marred while expansion is taking place. The mix should remain in the water at least 20 minutes to obtain the full expansion, after which time no further expansion is obtained.