Edm surface finish and machining accuracy

It deals with the surface finish and machining accuracy in EDM process. In this slide you will come to know surface characteristics of EDM process.

1. EDM- Surface Finish and Machining Accuracy Submitted by:- Md Naiyer Kalam Khan Fac. No.- 17 MEIM 036 En. No.- GG 9523

2. Contents What is EDM? Surface Integrity Surface Roughness Surface Finish Surface Finish with Forced Circulation Machining Accuracies

3. What is EDM? Electric Discharge Machining (EDM) is an electro-thermal non-traditional machining process, where electrical energy is used to generate electrical spark and material removal mainly occurs due to thermal energy of the spark. EDM is mainly used to machine which is difficult-to-machine and high strength temperature resistant alloys. EDM can be used to machine difficult geometries in small batches. Work material to be machined by EDM has to be electrically conductive.

4. Surface Integrity Surface consists of a multitude of overlapping craters that are formed by the action of microsecond-duration spark discharges. Crater size depends on physical and mechanical properties of the material composition of the machining medium discharge energy and duration Surface roughness increases linearly with an increase in MRR. MRR in practice does increase with increase in working voltage, current, pulse on time and decreases with increase in pulse off time. Kuneida and Furuoya (1991) claimed that the introduction of oxygen into discharge gap provides extra power by the reaction of oxygen.

5. Surface Roughness EDM is achieved through the formation of craters due to the sparks. Larger the crater size result in rough surface. The crater depth( h c ) can be approximately expressed in terms of the energy released per spark(E) h c ≈K1E 0.33

6. Surface Finish As with conventional metal cutting, surface roughness is inversely proportional to cutting power and speed. In other words, the key to achieving better EDM finish quality is to cut slower . The surface unevenness, when machining steel under normal conditions are approximately related as H rms ≈ 1.11 Q 0.384 The dependence of surface finish on the pulse energy E and the comparison of surface finish with that obtained by the conventional processes are indicated in fig in the next slide.

7. Surface Finish with Forced Circulation The forced circulation of the dielectric has been found to generally improve the surface finish. It is clear that the forced circulation leads to a significant improvement in the surface finish.

8. Machining Accuracies The inaccuracies introduced during the EDM operation are mainly the following: Taper of the hole machined Overcut due to sparks at the side faces of the electrodes Errors due to the gradual change in the electrode shape and size

9. Taper A taper results because the upper portion of the hole walls is subjected to a more number of sparks than the bottom portion. The taper is found to depend on the square of the tool diameter(in case of round tools). It can be controlled by an appropriate alteration of the electrical parameters.

10. Overcut An overcut is that dimension by which the hole in the workpiece exceeds the electrode size. The magnitude of the overcut is dependent on the spark length and to some extent on the crater dimensions.

11. References Manufacturing Science by Amitabha Ghosh and Asok Kumar Mallik http://nptel.ac.in/courses/112105127/pdf/LM-39.pdf https://www.micropulsewest.com/our-blog/surface-finish-achievable-with-edm/

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