International Journal of Machine Tools and Manufacture
Improvement of surface finish on SKD steel using electro-discharge machining with aluminum and surfactant added dielectric
Introduction
The superior performance of electrical discharge machining (EDM) than traditional machining technology has already been proved in applying toward the materials with high strength, high hardness or more complicated shapes. Since the mechanism of EDM is done by melting the unwanted parts of workpiece by high temperature spark, many defects such as cracks, porosity, residual stress, improper recast layer are easily found on the workpiece surface due to the rapid high temperature melting and cooling process during EDM. Thus, a comprehensive study to improve the surface roughness of EDMed workpiece is the crucial topics. Many researchers have noticed this inevitable effect in EDM applications and have also proposed many prescriptions to fulfill the various criteria of industrial demanding. For instance, Mohri et al. [1], [2], [3], [4] demonstrated that by adding powder into dielectric via EDM process, a mirror-like surface could be achieved. Luo et al. [5] suggested that either the low peak current or the short pulse duration for EDM could gain a better surface roughness in machining process. Narumiya et al. [6] improved the surface roughness of workpiece by optimizing various combinations of powder added into dielectric. Saito et al. [7], [8] added conductive powders into dielectric to gain a better surface roughness on a large surface area of workpiece in EDM process. Yan et al. [9] mixed nonconductive Al2O3 powder with dielectric to create a phoresis effect by interrupting the unwanted stacking of electrical discharge profile. Chow et al. [10] added powders into kerosene for machining micro-slit of Titanium alloy to investigate the bridging effect and discharging energy dispersion mechanism. Ming et al. [11], [12] studied the influence on adding various powders including aluminum, silicon, nickel, and chromium. It is suggested that hardness, wear resistance, and corrosion resistance of the machined surface could be significantly improved.
Accordingly, dielectric with Si or Al powder can improve the surface roughness effectively during EDM process by electrical discharge dispersion effects. With the additional of surfactant in the dielectric, the added aluminum powders would aggregate and thus degraded its performance [13], [14]. However, the effect of surfactant to the dispersion of aluminum powder in the dielectric has never been studied. Nor has any suitable machining parameter for EDM with both surfactant and aluminum powder in dielectric been investigated. In this work, the influence of surfactant on the surface roughness of the working piece was discussed. Optimal machining parameters for EDM were also proposed.
Section snippets
Experimental layout and arrangement
Experiments were conducted on an EDM machine attached with a dielectric cycling system. Aluminum powder was mixed with surfactant in a certain proportion and added into kerosene, which was cycled to maintain a uniform distribution of the added powder. The essential machining parameters for EDM were listed in Table 1 and the experimental layout was shown else where [12].
A Taguchi L18 orthogonal array was employed to explore the relationship between surfactant and machining performance. The
Taguchi's optimization
In Taguchi method, two types of quality of the characteristic property, the large-the-better and the smaller-the-better were utilized to assess the effect of working parameters on properties [15]. In this study, the quality of surface roughness is the smaller-the-better. Thus, a higher S/N ratio implies a better surface roughness and surface quality. Fig. 1 shows the S/N ratio response graphs after calculating the experimental data of EDM surface roughness (SR). Table 5 shows the optimal
Conclusion
This work discussed the improvement of the machined surface of EDM by adding aluminum powder and surfactant into dielectric. Conclusions are summarized as follows.
- 1.
Owing to the electrostatic force, the pure aluminum powder added into the dielectric may agglomerate together to degrade the expected effect. Surfactant moleculars act as steric barrier to separate the agglomerated aluminum powder and disperse them within dielectric. The surface roughness of workpiece in EDM process is thus improved.
- 2.
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