Electro Erosion Edge Honing

N. Z. Yussefian, P. KoshyMcMaster University, Canada

S. Buchholz, F. Klocke RWTH Aachen University, Germany

Electro-erosion edge honing of cutting tools

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Electro-erosion edge honing of cutting toolsN.Z. Yussefian, P. Koshy, S. Buchholz, F. Klocke

60th CIRP General AssemblyPisa, August 25, 2010

Edge preparation of cutting tools

toolchip

work

Influences chip formationAffects surface integrityPrecludes catastrophic tool failureEnhances tool life & coatabilityEnsures consistent tool performance

~ µm

chamferhone

X

X

nose radius

edge radius measured in X-X plane

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An increase in edge radius from 8 µm to 35 µmDelay in the onset of coating fractureFour-fold improvement in tool life

Bouzakis et al (2002)

Influence of edge radius on carbide inserts

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Edge honing enhanced the life of ground tools by ~400%Existence of an optimal cutting edge radius

Enhancement in high speed steel tool life

Rech et al (2005)

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As high as ~50% variability in edge radius (Schimmel et al, 2000)Variability between edges as well as along the same edgeManufacturers hence generally specify edge hones in a rangeSomewhat limited when processing polycrystalline diamond tools

Edge honing processes

micro blasting

ww

w.c

omco

inc.

com

brush honing

ww

w.o

sbor

n.co

m

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Possibility of honing cutting edges by sink EDM

tool wear in EDM

rounded edges

Edge rounding in EDM

honesharphoning

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Honing of tools by sinking them into an appropriate counterfaceThe high level of precision in EDM could address the variability issueTools could be processed irrespective of material hardness

The relatively low material removal rate of sink EDM is

of little consequence

Conservative EDM parameters may be employed with a view to

preserving the integrity of the surface

counterface

tool

Electro-erosion edge honing

The volume of material removal associated with hone generation is

very minimal

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Kinematic configurations

symmetric hone

tool

counterface

feed

increasing radiusalong the edge

rotation about X axis

X

Y

Z

asymmetric hone

rotation of tool about Z axis

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Experimental

average voltage 80 V

peak current 1.8 A

polarity tool (−)

pulse on-time 0.6 µs

duty factor 50%

machining time 80 s

AISI T-15 High Speed Steel

Aluminum counterface

Finish ground SNEA 320 inserts

10 mm edge length; 90° wedge angle

Dielectric oil; no external flushing

Proof of concept & shape evolutionAssessment of tool performance & edge geometry

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Measurement of edge radius

confocal microscope

NURBS model

100 150 200 250 300 350 400-50

0

50

100

150

X [m]

Y [

m]

Knot PointsEdge Cross SectionFitted Circle

circular regression on profile data

point cloud data

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cutting edge

counterface

Effect of counterface material on edge geometry

Aluminum counterfaceHoned edgeWear ratio = 0.5

Copper counterfaceChamfered edgeWear ratio = 7.5

cutting edge

counterface

cutting edge

counterface

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Geometric simulation of electro-erosion honing

sparking across closest gap

material removal from electrodes as

per wear ratio

electrode feed to restore gap width

wear ratio = 0.10.5

2.07.515 µm

Fig. 3. Simulated effect of wear ratio on edge geometry.

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Comparison of simulation with experiment

wear ratio = 0.10.5

2.07.515 µm

Fig. 3. Simulated effect of wear ratio on edge geometry.

cutting edge

counterface

wear ratio = 0.5

cutting edge

counterface

wear ratio = 7.5

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tool

counterface

Mechanism of edge generation

“high” wear ratio

“low” wear ratio

chamfer

hone

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Concept of a threshold wear ratio

tool

counterface

s

rβfeed

β

For β = 90°, rβ = 40 µm & s = 15 µm, threshold wear ratio = 0.4

cutting edge

counterface

wear ratio = 7.5 A wear ratio much higher than the threshold results in the generation of a chamferA wear ratio much lower than the threshold results in extensive in-feed of the tool into the counterface

wear ratio = (Vt /Vc)

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cemented carbide

200 µm

high speed steel

ground EE-honed

Electro-erosion honed surfaces

extensive in-feed of cutting edge into counterface (wear ratio ~ 0.01)

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Time evolution of edge geometry

Fig. 5. Profilometer traces of HSS edges showing their evolution.

-60 -40 -20 0 20 40 60-70

-60

-50

-40

-30 B D F H J N10 µm

-60 -40 -20 0 20 40 60-70

-60

-50

-40

-30 B D F H J N

-60 -40 -20 0 20 40 60-70

-60

-50

-40

-30 B D F H J N

unprepared edge

30 s (rβ = 22 µm)

60 s (32.6 µm)

120 s (40.3 µm)

circle fit (40.3 µm)

30 s (rβ = 22 µm) 60 s (rβ = 33 µm)

120 s (rβ = 40 µm)ground edge

a a b b

Greater rate of recessionon b-b compared to a-a

tool

workb b

aa

Concept of relative duty (Crookall & Fereday, 1973)

fit circle Absolute radial deviation from fit circle is ~5% of edge radius

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Variable speed tool life test (Armarego & Brown, 1969)

Comparison of tool life

Significant increase in tool life due to:Electro-erosion edge honing offsetting the negative influence of grinding-induced micro-chippingReduction in the maximum tool temperature on account of enhanced heat transfer associated with larger contact area

20 25 30 35 40 45 501

10

100

To

ol li

fe (m

in)

Cutting speed (m/min)

EE-honed edge

ground edge

Annealed AISI 1045; dry cutting0.15 mm feed; 0.5 mm depth of cut300 µm max. flank wear tool life criterion

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Variability in edge geometry

140 measurements over an edge length of 10 mm (edge 1 above) indicated a mean of 32.1 µm and standard deviation of 1.6 µm, which refers to a variability of ~15%This is a significant improvement over conventional processes wherein the corresponding variability could be on the order of 50% about the mean radius

1 2 3 4 5 625

30

35

40

45

Edg

e ra

dius

(µm

)

Edge number

Boxes and whiskers refer to 25/75 and 1/99 percentiles, respectively

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The application of electrical spark discharges for edge honing has been demonstratedThe counterface material plays a critical role in the geometry of the generated edgeEdge hones generated by electro-erosion honing significantly improved the life of ground toolsElectro-erosion honing corresponds to robust edge geometry generation as compared to conventional processes

Conclusions

Thank you for yourkind attention!



Canadian Network of Centers of Excellence

C4 Consortium of Ontario

Technology

Electro Erosion Edge Honing