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Fig. 6. A graph of the average white layer thickness (AWLT) against Sa From the experimental results, graphs of average thickness of the white layer against Sa, 55,, Sas, and Vyc have been plotted (Figs. 6-9). The empirical regression analysis of the average thickness of the white layer against these four 3D surface texture parameters is given in Table 2. The R? values for the two amplitude parameters (Sa and $5,) and Vyc are relatively good (70 and 80%). But when observing the graphs for these three surface texture parameters, some scattering Fig. 8. A graph of the average white layer thickness (AWLT) against Sys.

Figure 6 A graph of the average white layer thickness (AWLT) against Sa From the experimental results, graphs of average thickness of the white layer against Sa, 55,, Sas, and Vyc have been plotted (Figs. 6-9). The empirical regression analysis of the average thickness of the white layer against these four 3D surface texture parameters is given in Table 2. The R? values for the two amplitude parameters (Sa and $5,) and Vyc are relatively good (70 and 80%). But when observing the graphs for these three surface texture parameters, some scattering Fig. 8. A graph of the average white layer thickness (AWLT) against Sys.

Related Figures (17)

Fig. 1. a Micrograph of the white layer due to the EDM process (200x); (b) SEM picture (at 370x) of an EDM surface showing globules and microc- racks.
Fig. 1. a Micrograph of the white layer due to the EDM process (200x); (b) SEM picture (at 370x) of an EDM surface showing globules and microc- racks.
of the 3D surface texture parameters for the different exper imental spark erosion conditions are shown in Appendix A. The graphs of the product of current (/) and the pulse on- time (1) agains t Sa, S52, Sds, and the average thickness of tl white layer are shown in Figs. 2-5. The product of curre and pulse on-time has been used because it represents tl varying part o age is normally constant). From Figs. 2 and 3 it can be seen that the two amplitude surface texture parameters (Sq and f the pulse energy parameter (since the vo S5z) increase al magnitude of ( long a parabolic curve with an increase in tl I x t). The increase is more significant in tl he nt he t ne ne initial range [(/ x t) <0.005]. The magnitude of Sgs (mm~)
of the 3D surface texture parameters for the different exper imental spark erosion conditions are shown in Appendix A. The graphs of the product of current (/) and the pulse on- time (1) agains t Sa, S52, Sds, and the average thickness of tl white layer are shown in Figs. 2-5. The product of curre and pulse on-time has been used because it represents tl varying part o age is normally constant). From Figs. 2 and 3 it can be seen that the two amplitude surface texture parameters (Sq and f the pulse energy parameter (since the vo S5z) increase al magnitude of ( long a parabolic curve with an increase in tl I x t). The increase is more significant in tl he nt he t ne ne initial range [(/ x t) <0.005]. The magnitude of Sgs (mm~)
Empirical regression equation for 3D surface texture parameters in EDM process
Empirical regression equation for 3D surface texture parameters in EDM process
A graph of the average white layer thickness against I*t Fig. 5. Variation of the average white layer thickness with J x t. Note: [=peak pulse current (A), t=pulse on-time (s).
A graph of the average white layer thickness against I*t Fig. 5. Variation of the average white layer thickness with J x t. Note: [=peak pulse current (A), t=pulse on-time (s).
Fig. 7. A graph of the average white layer thickness (AWLT) against S5,.
Fig. 7. A graph of the average white layer thickness (AWLT) against S5,.
Empirical regression equation of average white layer thickness (AWLT against 3D surface texture parameters
Empirical regression equation of average white layer thickness (AWLT against 3D surface texture parameters
Fig. 10. EDM35c (27.85 A and 60 us). It is known that during an EDM discharge the plasma channel grows in size, and that the final size depends on the magnitude of the pulse duration and pulse current. In this study the 3D axonometric plots (Figs. 10-15) have revealed substantial increase in the crater size upon both increase in the pulse current and the pulse duration. Though it has been experimentally proven that the depth of the craters is more dependent on the current than the pulse duration, the degree
Fig. 10. EDM35c (27.85 A and 60 us). It is known that during an EDM discharge the plasma channel grows in size, and that the final size depends on the magnitude of the pulse duration and pulse current. In this study the 3D axonometric plots (Figs. 10-15) have revealed substantial increase in the crater size upon both increase in the pulse current and the pulse duration. Though it has been experimentally proven that the depth of the craters is more dependent on the current than the pulse duration, the degree
So, if the value of the diameter of the EDM craters is inversely proportional to the magnitude of the Sg, param- eter, then a higher Sgs value would lead to a smaller av- erage diameter, while a small Sy, value would indicate a larger average crater diameter. Thus the empirical relation- ship of Sas with the EDM process factors would show that the average diameter of the crater is highly dependent on both pulse on-time and current, but current seemed to have a slightly higher effect. This would thus imply that the size of the plasma channel is governed to a higher extent by the Fig. 13. EDM19b (6.6A and120 us). Fig. 15. EDM29c (27.85A and120 us). ~ Rebelo et al. [17] reported the following empirical equation for the EDM crater diameter of high strength copper- beryllium alloys:
So, if the value of the diameter of the EDM craters is inversely proportional to the magnitude of the Sg, param- eter, then a higher Sgs value would lead to a smaller av- erage diameter, while a small Sy, value would indicate a larger average crater diameter. Thus the empirical relation- ship of Sas with the EDM process factors would show that the average diameter of the crater is highly dependent on both pulse on-time and current, but current seemed to have a slightly higher effect. This would thus imply that the size of the plasma channel is governed to a higher extent by the Fig. 13. EDM19b (6.6A and120 us). Fig. 15. EDM29c (27.85A and120 us). ~ Rebelo et al. [17] reported the following empirical equation for the EDM crater diameter of high strength copper- beryllium alloys:
Fig. 12. EDM1a (27.85A and 750 us). of importance of the process factors in affecting the diameter of the crater is not very clear.
Fig. 12. EDM1a (27.85A and 750 us). of importance of the process factors in affecting the diameter of the crater is not very clear.
Fig. 14. EDM30b (16.67A and120 us). Fig. 11. EDM38b (27.85 A and 250 us).
Fig. 14. EDM30b (16.67A and120 us). Fig. 11. EDM38b (27.85 A and 250 us).
Fig. 17. Liquid and solid metal phases with contact angle. It is also assumed that at the surface, the area of molten metal is completely ejected, i.e., crater diameter is equal to the diameter of molten area.
Fig. 17. Liquid and solid metal phases with contact angle. It is also assumed that at the surface, the area of molten metal is completely ejected, i.e., crater diameter is equal to the diameter of molten area.
It has been established that the pulse on-time has a direct effect on the size of the plasma channel. It is also assumed that the resulting crater diameter is directly proportional to the final size of the plasma channel. The final diameter over which the plasma is impacting (towards the end of the pulse on-time) and the related depth of penetration of the plasma heat are believed to influence the magnitude of the surface tension between the liquid and solid part of the metal. The resistive force due to surface tension at the interface between the two phases is believed to play a major role in the ejec- tion mechanism. Thus the magnitude of the surface tension will have a significant influence over the material removal efficiency. Consequently, it will also affect the ratio of $5, to AWLT. sion, which enables the extent of contact between these two phases to be determined. If the contact angle tends towards zero (Fig. 16), then a complete wetting of the solid by the liquid phase is achieved. Wetting means that the contact an- gle @ between a liquid and a solid is close to zero, and that spreading of the liquid occurs. Non-wetting is often defined by 6>90°.
It has been established that the pulse on-time has a direct effect on the size of the plasma channel. It is also assumed that the resulting crater diameter is directly proportional to the final size of the plasma channel. The final diameter over which the plasma is impacting (towards the end of the pulse on-time) and the related depth of penetration of the plasma heat are believed to influence the magnitude of the surface tension between the liquid and solid part of the metal. The resistive force due to surface tension at the interface between the two phases is believed to play a major role in the ejec- tion mechanism. Thus the magnitude of the surface tension will have a significant influence over the material removal efficiency. Consequently, it will also affect the ratio of $5, to AWLT. sion, which enables the extent of contact between these two phases to be determined. If the contact angle tends towards zero (Fig. 16), then a complete wetting of the solid by the liquid phase is achieved. Wetting means that the contact an- gle @ between a liquid and a solid is close to zero, and that spreading of the liquid occurs. Non-wetting is often defined by 6>90°.
Calculation of the contact angle between solid and liquid phases during an EDM spark
Calculation of the contact angle between solid and liquid phases during an EDM spark
Average thickness of white layer and 3D surface texture results
Average thickness of white layer and 3D surface texture results
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EngineeringTechnologyPrecision EngineeringSurface Texture
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