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Analysis and Performance of Slotted Tools in Electrical Discharge Drilling. Ramy Nastasi, Philip Koshy. McMaster University Canada. NANTES. The objective of this research was to enhance productivity in electrical discharge drilling (EDD). mcmachinery.com. - PowerPoint PPT Presentation
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Analysis and Performance of Slotted Tools in Electrical Discharge Drilling
Ramy Nastasi, Philip KoshyMcMaster University
Canada
NANTES
2/20
64th CIRP General AssemblyNantes, August 25, 2014
Analysis and Performance of Slotted Tools in Electrical Discharge DrillingR. Nastasi, P. Koshy
mcm
ach
ine
ry.c
omThe objective of this research was to enhance productivity in electrical discharge drilling (EDD)
The research involved aspects of gap flushing, and computational fluid dynamic analyses of dielectric flow
horizontal EDM3/20
64th CIRP General AssemblyNantes, August 25, 2014
Analysis and Performance of Slotted Tools in Electrical Discharge DrillingR. Nastasi, P. Koshy
Gap flushing is of critical importance in EDM processes in terms of removal rate, geometric accuracy and surface integrity
through-tool flow
jet flushing jump EDM
orbital EDMReuleaux kinematics
4/20
64th CIRP General AssemblyNantes, August 25, 2014
Analysis and Performance of Slotted Tools in Electrical Discharge DrillingR. Nastasi, P. Koshy
Computational fluid dynamics software are being widely used for modelling fluid flow in EDM
Wang & Han (2014)Simulation of debris transport
5/20
64th CIRP General AssemblyNantes, August 25, 2014
Analysis and Performance of Slotted Tools in Electrical Discharge DrillingR. Nastasi, P. Koshy
Cetin et al. (2004)Flow fields in jump EDM
6/20
64th CIRP General AssemblyNantes, August 25, 2014
Analysis and Performance of Slotted Tools in Electrical Discharge DrillingR. Nastasi, P. Koshy
Okada et al. (2009)Flow analysis in wire EDM
7/20
64th CIRP General AssemblyNantes, August 25, 2014
Analysis and Performance of Slotted Tools in Electrical Discharge DrillingR. Nastasi, P. Koshy
In EDD, at low rotational speeds, fluid in the frontal gap flows along concentric flow patterns, which redistributes the debris without ejecting it
frontal gap
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
8/20
64th CIRP General AssemblyNantes, August 25, 2014
Analysis and Performance of Slotted Tools in Electrical Discharge DrillingR. Nastasi, P. Koshy
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
9/20
64th CIRP General AssemblyNantes, August 25, 2014
Analysis and Performance of Slotted Tools in Electrical Discharge DrillingR. Nastasi, P. Koshy
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
10/20
64th CIRP General AssemblyNantes, August 25, 2014
Analysis and Performance of Slotted Tools in Electrical Discharge DrillingR. Nastasi, P. Koshy
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
11/20
64th CIRP General AssemblyNantes, August 25, 2014
Analysis and Performance of Slotted Tools in Electrical Discharge DrillingR. Nastasi, P. Koshy
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
single start | 22° helix angle
machining depth < 1mm 4 slots | 2 x 1.5 mm2
12/20
64th CIRP General AssemblyNantes, August 25, 2014
Analysis and Performance of Slotted Tools in Electrical Discharge DrillingR. Nastasi, P. Koshy
60 rpm tool speed
For the cylindrical tool, at an aspect ratio of ~3, the removal rate is just 30% of that at the surface
The removal rate of the slotted tool is 200% of that of the cylindrical tool
13/20
64th CIRP General AssemblyNantes, August 25, 2014
Analysis and Performance of Slotted Tools in Electrical Discharge DrillingR. Nastasi, P. Koshy
Computed flow fields highlight the distinct difference between the flow patterns of the helical and slotted tools
ingress and egress through distinct channels within slot
slotted
ingress through lateral gap;egress through helical channel
helical
14/20
64th CIRP General AssemblyNantes, August 25, 2014
Analysis and Performance of Slotted Tools in Electrical Discharge DrillingR. Nastasi, P. Koshy
Particle tracking was activated in the numerical model to characterize flushing effectiveness
Flushing was quantified in terms of the steady state flux of particles ejected through the annular gap at the workpiece surface
Particles were dispersed in the frontal gap, and their flow through and out of the lateral gap was tracked
15/20
64th CIRP General AssemblyNantes, August 25, 2014
Analysis and Performance of Slotted Tools in Electrical Discharge DrillingR. Nastasi, P. Koshy
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)
16/20
64th CIRP General AssemblyNantes, August 25, 2014
Analysis and Performance of Slotted Tools in Electrical Discharge DrillingR. Nastasi, P. Koshy
Slot height wields more influence than the slot width
This is important in order to not compromise machining power
Bands of fluid ingress & egress are aligned along the slot height
17/20
64th CIRP General AssemblyNantes, August 25, 2014
Analysis and Performance of Slotted Tools in Electrical Discharge DrillingR. Nastasi, P. Koshy
Tool with a single slot is comparable to the helical tool
More slots enhance tool performance
For identical slot area & width, a tool with a single deep slot performs better than the one with several detached slots
18/20
64th CIRP General AssemblyNantes, August 25, 2014
Analysis and Performance of Slotted Tools in Electrical Discharge DrillingR. Nastasi, P. Koshy
The removal rate of the tool with a single extended slot was verified experimentally to be 300% of that of a cylindrical one
300%
19/20
64th CIRP General AssemblyNantes, August 25, 2014
Analysis and Performance of Slotted Tools in Electrical Discharge DrillingR. Nastasi, P. Koshy
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
20/20
64th CIRP General AssemblyNantes, August 25, 2014
Analysis and Performance of Slotted Tools in Electrical Discharge DrillingR. Nastasi, P. Koshy
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
Thank you for your kind attention!
Natural Sciences & Engineering Research Council of Canada
Canadian Network forResearch & Innovation in
Machining Technology