Increase in TON from to s resulted in

Increase in TON from 0.65 to 0.8 μs resulted in the formation of larger craters on the machined surface. This is reason for the increase in Ra with input power and TON. It is recommended to use TON of 0.65μs and IP of 12 A, respectively, for obtaining minimum Ra. The thermal power generates the high temperatures and causes the melting and vaporization of the material. Figs. 3 and 4 demonstrate Ra in function of the parameters of TON and peak current. The data indicates that Ra decreases by decreasing TON and peak current values. The influence of spark voltage on response characteristics is shown in Fig. 5, for TON of 0.85 μs, TON of 32 μsec and peak current of 16 A. The influence of spark voltage on surface roughness (Ra) is illustrated in Fig. 6. The plot exhibits a trend of increase from 1.26 to 2.35 μm. MRR is found to increase with spark voltage up to certain range and then it decreases at higher spark voltage due to widening of discharge gap. Fig. 3 depicts the effect of spark voltage on Ra. The Ra enhances with the raise in TON. With longer period of spark duration, the number of discharges increases, resulting in the wider craters. Hence, the surface finish will be rougher. When spark gap voltage is increased, the discharge gap gets widened, resulting in better surface accuracy due to stable machining. The influence of wire tension is not very significant. The surfaces of machined samples were examined using scanning renin inhibitor microscope (SEM). It is observed from SEM micrographs (Figs. 7 and 8) that the machined surfaces contain spherical modules, craters, pochmarks and microcracks. The TON (0.8 μs) and peak current (18 A) were observed as the most significant parameters affecting the surface properties. The increase in TON resulted in the formation of craters on the surface. These craters were developed due to a succession of sparks. Small portion of the melted material generated by the electric discharge was removed by the dielectric fluid (Fig. 11). The generation of spherical particles was noticed and it was attributed to the surface tension of molten material. Macro-ridges were also observed on the surface due to the protrusion of molten material (Fig. 10). Fig. 4 demonstrates that fewer numbers of craters were formed at peak current (12 A) and TON (0.65 μs). Due to low peak current and TON, the machined surface is bombarded with fewer energy sparks. The crack formation is mainly attributed to the fast heating and cooling of the machined surface by dielectric fluid. The uneven heating and cooling caused the development of stresses, which leads to crack formation (Fig. 9). At a large current, a stronger discharge generates more heat energy. By virtue of the size of workpiece, some amount of heat is absorbed by it. The remaining portion of energy is accumulated at the wire, resulting in higher wear rate. This leads to frequent wire breakages. The wire breakage occurs due to the reduction of tensile strength of the brass wire through thermal softening. It is observed that the third levels of TON, peak current and spark voltage provide a maximum value of MRR. It demonstrates that the first levels of TON, peak current and spark voltage result in the minimum value of surface roughness.
Conclusions The significance of machining variables of WEDM on MRR and Ra of hot-pressed boron carbide has been studied. The effects of machining variables on the mechanism of MRR and surface roughness have been assessed by using scanning electron microscope. The conclusions are as follows:
Introduction Waverider configuration, originally intended for hypersonic cruise vehicle (HCV) has become extremely popular because of DARPA\'s X-41 common aero vehicle (CAV) program [1] and the Boeing X-51 scramjet engine demonstrator waverider program [2]. The waverider configuration has an immense aerodynamic advantage because of highest possible trim lift-to-drag ratio of greater than 3.0 in the hypersonic regime [3] as compared to trim lift-to-drag ratio of greater than 2.0 for wing-body configuration [4,5] and that of slightly greater than one for lifting-body design [6–8]. Common examples of lifting body designs include X-33, X-38 and HL-20 vehicles while shuttle orbiter and X-37B orbital test vehicle (OTV) are the examples of wing-body vehicles. The larger nose radius of lifting-body and the wing-body design have a better volumetric efficiency and also allow the use of conventional nose-mounted terminal sensors such as millimeter wave radar. The lifting-body and wing-body vehicles are subject to maximum heat rate on the fin leading edges. With advancement of the material technology (carbon–carbon materials) capable of bearing a temperature up to 2900 K [9], the utility of wing-body and lifting-body designs for medium and intermediate range military applications cannot be ignored.