Analysis and Performance of Slotted Tools in Electrical Discharge Drilling

1. Analysis and Performance of Slotted Tools in Electrical Discharge Drilling Ramy Nastasi, Philip Koshy McMaster UniversityCanada NANTES

2. The objective of this research was to enhance productivity in electrical discharge drilling (EDD) mcmachinery.com • The research involved aspects of gap flushing, and computational fluid dynamic analyses of dielectric flow Analysis and Performance of Slotted Tools in Electrical Discharge Drilling R. Nastasi, P. Koshy 64th CIRP General Assembly Nantes, August 25, 2014

3. Gap flushing is of critical importance in EDM processes in terms of removal rate, geometric accuracy and surface integrity orbital EDM through-tool flow Reuleaux kinematics horizontal EDM jet flushing jump EDM Analysis and Performance of Slotted Tools in Electrical Discharge Drilling R. Nastasi, P. Koshy 64th CIRP General Assembly Nantes, August 25, 2014

4. Computational fluid dynamics software are being widely used for modelling fluid flow in EDM Wang & Han (2014) Simulation of debris transport Analysis and Performance of Slotted Tools in Electrical Discharge Drilling R. Nastasi, P. Koshy 64th CIRP General Assembly Nantes, August 25, 2014

5. Cetin et al. (2004) Flow fields in jump EDM Analysis and Performance of Slotted Tools in Electrical Discharge Drilling R. Nastasi, P. Koshy 64th CIRP General Assembly Nantes, August 25, 2014

6. Okada et al. (2009) Flow analysis in wire EDM Analysis and Performance of Slotted Tools in Electrical Discharge Drilling R. Nastasi, P. Koshy 64th CIRP General Assembly Nantes, August 25, 2014

7. frontal gap • In EDD, at low rotational speeds, fluid in the frontal gap flows along concentric flow patterns, which redistributes the debris without ejecting it • With increasing speed, the emergence of centrifugal forces drives a radial fluid outflow, but the close proximity of the lateral workpiece wall tends to recirculate the fluid Analysis and Performance of Slotted Tools in Electrical Discharge Drilling R. Nastasi, P. Koshy 64th CIRP General Assembly Nantes, August 25, 2014

8. This work examined the efficacy of introducing geometric features into cylindrical rotating tools to enhance flushing in the drilling of blind macro holes • In particular, the emphasis was on the design, analysis and testing of slotted tools Analysis and Performance of Slotted Tools in Electrical Discharge Drilling R. Nastasi, P. Koshy 64th CIRP General Assembly Nantes, August 25, 2014

9. Computational fluid dynamics was used as a tool to generate corresponding flow fields • This enabled insights into experimental observations, and the assessment as well as optimization of the geometric features Analysis and Performance of Slotted Tools in Electrical Discharge Drilling R. Nastasi, P. Koshy 64th CIRP General Assembly Nantes, August 25, 2014

10. Meshing of the fluid domain proved to be challenging due to the gap being small relative to tool diameter and machining depth Ironically this is much the same issue that renders flushing difficult Frontal and lateral gaps of 200 µm were assumed Typical computational cycle times were < 20 minutes on a desktop computer Analysis and Performance of Slotted Tools in Electrical Discharge Drilling R. Nastasi, P. Koshy 64th CIRP General Assembly Nantes, August 25, 2014

11. machining depth < 1mm 4 slots | 2 x 1.5 mm2 single start | 22° helix angle φ15.8 mm • Over the entire speed range tested, the slotted tool outperformed the cylindrical and helical tools • At small depths flushing is not quite an issue Analysis and Performance of Slotted Tools in Electrical Discharge Drilling R. Nastasi, P. Koshy 64th CIRP General Assembly Nantes, August 25, 2014

12. 60 rpm tool speed • The removal rate of the slotted tool is 200% of that of the cylindrical tool • For the cylindrical tool, at an aspect ratio of ~3, the removal rate is just 30% of that at the surface Analysis and Performance of Slotted Tools in Electrical Discharge Drilling R. Nastasi, P. Koshy 64th CIRP General Assembly Nantes, August 25, 2014

13. Computed flow fields highlight the distinct difference between the flow patterns of the helical and slotted tools helical ingress and egress through distinct channels within slot ingress through lateral gap; egress through helical channel slotted Analysis and Performance of Slotted Tools in Electrical Discharge Drilling R. Nastasi, P. Koshy 64th CIRP General Assembly Nantes, August 25, 2014

14. Particle tracking was activated in the numerical model to characterize flushing effectiveness • Particles were dispersed in the frontal gap, and their flow through and out of the lateral gap was tracked • Flushing was quantified in terms of the steady state flux of particles ejected through the annular gap at the workpiece surface Analysis and Performance of Slotted Tools in Electrical Discharge Drilling R. Nastasi, P. Koshy 64th CIRP General Assembly Nantes, August 25, 2014

15. Good linear correlation validates the numerical model • Open data points that deviate the most from the linear trend correspond to combinations of extreme machining depths and tool speeds computed tool performance relative to arbitrary datum removal rates were experimentally measured over machining depths of 1-50 mm and tool speeds of 60-240 rpm (cylindrical electrodes) Analysis and Performance of Slotted Tools in Electrical Discharge Drilling R. Nastasi, P. Koshy 64th CIRP General Assembly Nantes, August 25, 2014

16. Bands of fluid ingress & egress are aligned along the slot height • Slot height wields more influence than the slot width • This is important in order to not compromise machining power Analysis and Performance of Slotted Tools in Electrical Discharge Drilling R. Nastasi, P. Koshy 64th CIRP General Assembly Nantes, August 25, 2014

17. For identical slot area & width, a tool with a single deep slot performs better than the one with several detached slots • More slots enhance tool performance • Tool with a single slot is comparable to the helical tool Analysis and Performance of Slotted Tools in Electrical Discharge Drilling R. Nastasi, P. Koshy 64th CIRP General Assembly Nantes, August 25, 2014

18. The removal rate of the tool with a single extended slot was verified experimentally to be 300% of that of a cylindrical one 300% Analysis and Performance of Slotted Tools in Electrical Discharge Drilling R. Nastasi, P. Koshy 64th CIRP General Assembly Nantes, August 25, 2014

19. Computed pressure distribution indicates the single extended slot to correspond to a higher pressure gradient This combined with the larger radial sweep all but eliminates recirculation near the tool center Analysis and Performance of Slotted Tools in Electrical Discharge Drilling R. Nastasi, P. Koshy 64th CIRP General Assembly Nantes, August 25, 2014

20. Conclusions • Helical and radial slot features in cylindrical tools enhance flushing and removal rates in electrical discharge drilling • Numerical flow modeling was developed to gain qualitative insights into flushing performance, and as a quantitative tool for the design, assessment and optimization of tool geometric features • A tool with a single slot approaching the tool center related to the most effective flushing, and yielded a 300% increase in removal rate relative to that of a conventional rotating cylindrical tool, at a hole aspect ratio of just 3 • An enhancement of such magnitude was attained at just a 6% decrease in tool section area, which does not compromise the machining power that scales with the tool frontal area Analysis and Performance of Slotted Tools in Electrical Discharge Drilling R. Nastasi, P. Koshy 64th CIRP General Assembly Nantes, August 25, 2014

21. Canadian Network for Research & Innovation in Machining Technology Thank you for your kind attention! Natural Sciences & Engineering Research Council of Canada