Performance of electrical discharge textured cutting tools P. Koshy, J. Tovey McMaster University Canada

Performance of electrical discharge textured cutting tools

P. Koshy, J. ToveyMcMaster University

Canada

2/18

Performance of electrical discharge textured cutting toolsP. Koshy, J. Tovey

61st CIRP General AssemblyBudapest, August 24, 2011

Lubrication in cutting

Infiltration of lubricant is controlled by capillary action and chip velocity-induced shear flow

Retention of the lubricant in the interface is as critical as its ingress

Lubrication may be enhanced through texturing the tool rake face surface

sticking

sliding

tool

chip

tool

chiptool

chip

lubricant

3/18



Femtosecond laser texturing

Enomoto & Sugihara (2010)

Texture is to be preferably oriented normal to the chip flow direction

Kawasegi et al (2009)

micro nano

4/18



Electrochemical texturing

anode (workpiece)

metal layer(cathode)

insulation layer

Zhu et al (2009)

dimpled texture

5/18



Electrical discharge texturing

Surfaces generated in electrical discharge machining (EDM) are isotropic and entail a positive skewness, which predisposes them towards effectively entraining lubricant

surface height

frequency

+ve skew

6/18



Objective of this work

To prove the concept of ED-textured cutting tools

Identify the envelope of EDM and cutting parameters in which such textures are effective

areal texture machinedwith a block electrode

cutting edge

linear texture machinedwith shim stock tooling

rake face

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Experimental - EDM



copper electrodes with positive polarity

oil based dielectric

average gap voltage 100 V; duty factor 50%

Pulse current <72 A; pulse on-time <133 µs

Pulse current and on-time were varied to alter the geometry of the characteristic crater

8/18

Experimental - Cutting

continuous & intermittent orthogonal cutting

AISI T-15 High Speed Steel ground inserts

SPG 432 geometry with 0° rake angle

annealed 1045 steel & 6061 Al workpieces

cutting speed 2−75 m/min; feed 0.025−0.1 mm

cutting width 3 mm; oil lubricant



toolchip

Fc

Ff

friction angle

In comparison to surface roughness and tool life, machining force is a better indicator of lubrication effectiveness, in terms of repeatability and resolution

De Chiffre & Belluco (2000)

9/18



Texture parameters

Texture depth was limited to prevent the tool from functioning as a restricted rake tool

relief on the rake face to restrict tool chip contact

restricted rake tool

de

Distance de is to be optimized with respect to the uncut chip thicknessMaximum force reduction referred to the texture with a roughness of 12 µm Ra, generated at a current of 39 A and an on-time of 42 µs

Texturing time is ~10 seconds

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Effectiveness of ED-texture

0 30 60 90 120 150 18016

20

24

28

32

Time (s)

ground tool

Fri

ctio

n a

ng

le (

°)

lubricant application

0 30 60 90 120 150 18016

20

24

28

32

Fri

ctio

n a

ng

le (

°)

Time (s)

textured tool

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Force reduction in continuous cutting

0

1.5

3.0

4.5

6.0

Fe

ed fo

rce

(x1

02 N

)

non-

text

ured

text

ured

0

2

4

6

8

10

12

Cu

ttin

g fo

rce

(x1

02 N

)

text

ured

non-

text

ured

Texturing decreases the forces and the variability, with the effect more pronounced in the feed direction

12/18



Force reduction in intermittent cutting

0 1 2 3 4 5

0

1

2

3

4

5

6

Fe

ed fo

rce

(x1

02 N

)

Time (s)0 1 2 3 4 5

0

2

4

6

8

10

12

Cu

ttin

g fo

rce

(x1

02 N

)Time (s)

textured

non-textured

Feed force reduction is higher in intermittent cutting as the lubricant is directly replenished on the tool rake face during the non-cutting interval

13/18



Effect of cutting parameters on force reduction

0 5 10 15 20 25

0

10

20

30

40

50

Cutting speed (m/min)

continuous

intermittent

Cutting speed (m/min)

50 µm

0 15 30 45 60 75 90

0

5

10

15

20

25

30%

re

duc

tion

in fe

ed

forc

e

25 µm feed

Texturing is more effective at the low end of typical cutting speeds, at fine feeds and in intermittent cutting

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Force reduction in cutting of aluminum

0 5 10 15 20 25

0.0

0.5

1.0

1.5

2.0

2.5

Fe

ed fo

rce

(x1

02 N

)

Time (s)0 5 10 15 20 25

0

1

2

3

4

5

Cu

ttin

g fo

rce

(x1

02 N

)

Time (s)

non-texturedtextured

Forces and the associated variability were significantly lower as the lubricant used was specifically formulated for cutting aluminum

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Effect of texture location

0 3 6 9 12 15 18

18

20

22

24

26

Fri

ctio

n a

ng

le (

°)

(de/h)

h = 25 µm100 µm 50 µm

toolchip

h

Force reduction is maximized when (de/h) is ~2−3

As the tool chip contact length is typically 4−6 times the feed h, this implies that texturing needs to correspond to just the sliding region

de

16/18



Comparison of linear and areal textures

linearTextured area was varied by altering the pitch in the linear texture

0 20 40 60 80 1000

5

10

15

20

25

30

% r

ed

uctio

n in

forc

e

% area textured

feed force

cutting force

areal

Results confirm that the areal texture is to be preferred over a linear one

17/18



Role of texture parameters on force reduction

Force reduction showed no systematic trends with respect to either the Ra roughness or the pulse parameters

1.5 2.0 2.5 3.0 3.5 4.0

0

5

10

15

20

25

30

35

KurtosisSkewness0.0 0.2 0.4 0.6

0

5

10

15

20

25

30

35%

re

duc

tion

in fo

rce feed force

cutting force

Force reduction exhibited defined maxima with respect to skewness and kurtosis of the texture

18/18

Electrical discharge texturing has been demonstrated to bring about a significant (15−40%) reduction in machining force through enhanced lubrication at the tool-chip interface

The skewness and kurtosis of the texture are good indicators of the extent of force reduction

The concept is attractive for application in broaches, taps, gear cutting tools and possibly forming tools

Mechanical imprinting of said texture during the compaction phase of tool inserts (as opposed to EDM of inserts) may be explored

Conclusions



Thank you for your kind attention!

Canadian Network of Centers of Excellence

Natural Sciences & Engineering Research Council of Canada

Documents

Performance of electrical discharge textured cutting tools P. Koshy, J. Tovey McMaster University Canada