Micro Machining Technology

downtownbeeΜηχανική

18 Νοε 2013 (πριν από 3 χρόνια και 6 μήνες)

87 εμφανίσεις

Tahsin

Tecelli Öpöz

Micro Machining Technology



Micro EDM



High speed precision grinding



Micro scratching tests


Modelling and simulation of machining processes


Outline


Research environment


Micro EDM


High speed precision grinding


Micro
s
cratching tests


Finite Element Modelling and Simulation


Impact of the research


Publications




2/25

Research environment

Micro Electrical Discharge Machining

Robotic polishing

Precision grinding/diamond turning

Surface metrology


3/25


Micro EDM


Micro electrical discharge machining of micro holes

4/25

Hole shape formation

(Disclosure of technological
features of micro EDM)

2

Micro Tool Manufacturing using WEDG

(Dia.<10 µm)

Etched with nitric acid

Etched with nitric+chromic acid

Surface Damage in Micro
EDMed

Holes

1

3

(a) Discharge energy 12.7 µj

(b) Discharge energy 123 µj

Micro EDM


Discharge pulse form and surface characteristics

5/25

Micro EDM


Micro hole end
-
tip shape formation

C
oncave tip shape

Flat (rough) tip shape

Bullet tip shape

E= 0.78 µJ, OGP=75 V

E= 223 µJ, OGP=75 V

E= 33.4 µJ, OGP=80 V

6/25

Micro EDM


Heat affected layer in Micro
EDMed

holes’ wall

7/25

Micro EDM


Material removal response with machining time

8/25

Micro EDM


Micro hole entrance diameter with machining time

9/25

Precision grinding

High speed applications and
m
icro scratching tests


High speed precision grinding

(20k


160k rpm)

Material removal mechanism stages

at micro scale grinding

Single grit grinding test to reveal
micromechanics concept in grinding



Rubbing



Ploughing



Cutting

1

2

4

Steel wheel
Super glue
A CBN grit from
top view
3

A single grit glued onto the wheel

10/25

Deepest
point
around 450
Cross section profile extracted at 450 using 2
nd
line shown in previous figure
Longitudinal
section profile extracted using 1
st
line
shown in previous figure
(a)
(b)
Micro Scratching tests

Scratch form measurement and profile extraction


Increasing depth of cut
Traverse scratching
Workpiece :
Inconel 718
Grit :
CBN (40/50)
Speed =
3000 rpm (
V
c
= 327.6 m/min)
Work table
speed = 200
mm/min
Scratches with increasing
depth of cut: An example

Talysurf

CCI interferometer measurement

11/25

Micro Scratching tests

Abrasive grit cutting edge shape alteration during scratching:
Single edge and multiple edges scratch formation


Groove section
area
Total Pile
-
up area
Depth of
cut
(a
p
)
Depth of
cut
(a
p
)
Total Pile
-
up area
Groove
section
area
(a) Single scratch
(b) Multiple scratches
Groove section
area
Total Pile
-
up area
Depth of
cut
(a
p
)
Depth of
cut
(a
p
)
Total Pile
-
up area
Groove
section
area
(a) Single scratch
(b) Multiple scratches
12/25

R² = 0.6748
0
0.1
0.2
0.3
0.4
0.5
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Pile
-
up ratio
Depth of cut
(µm
)
Traverse scratching; Workpiece: En24T; Grit: CBN (40/50 mesh); V
c
= 546.6 m/min
R² = 0.3949
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0
0.5
1
1.5
2
2.5
3
3.5
4
Pile
-
up ratio
Depth of cut
(µm
)
Traverse scratching; Workpiece: En24T; Grit: CBN (40/50 ); V
c
= 327.6 m/min
1
2
3
R² = 0.5083
R² = 0.7924
0
0.2
0.4
0.6
0.8
1
0
2
4
6
8
10
Pile
-
up ratio
Depth of cut (um)
single edge scratch
multiple edges scratch
Traverse scratching; Workpiece: En24T; Grit: CBN (40/50 ); V
c
= 327.6 m/min
R² = 0.5354
0
0.5
1
1.5
2
2.5
3
3.5
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
6.5
Pile
-
up ratio
Depth of cut (µm)
Traverse scratching; Workpiece: Inconel 718; Grit: CBN (40/50) ;
Vc
= 327.6 m/min
Micro Scratching tests

Pile
-
up ratio variation with depth of cut at different grit cutting
edges


13/25

(a) Lateral cross sectional view of a scratch
(b) Longitudinal cross sectional view of a scratch
Workpiece: En24T steel
Grit: CBN (40/50)
S=3000 rpm (
V
c
= 327.6 m/min)
Hardness= 289.2 HV at 1 kg load
0
5
10
15
20
25
30
35
0
100
200
300
400
500
600
700
800
900
Pile
-
up ratio
Dimensional length along scratch direction (µm
)
0
0.5
1
1.5
2
2.5
200
300
400
500
600
Pile
-
up ratio
Scratching direction
Traverse scratching; S=3000 rpm (
V
c
= 327.6 m/min);
Workpiece: En24T steel; Grit: CBN (40/50)
Micro Scratching tests

Material removal along scratch length: Pile
-
up ratio


14/25

-
10
0
10
20
30
40
50
60
70
0
1
2
3
4
Chip removal strength (µm
2
)
Depth of cut (µm)
scratch first part (grit entrance side)
-
40
-
30
-
20
-
10
0
10
20
30
40
50
60
0
1
2
3
4
scratch second part (grit exit side)
Traverse scratching; S=3000 rpm (
V
c
= 327.6 m/min);
Workpiece: En24T steel; Grit: CBN (40/50)
Micro Scratching tests

Material removal along scratch length: Chip removal strength


15/25

Traverse scratching; Workpiece: En24T; Grit: CBN (40/50);
Signal recorded with Labview software
S=3000 rpm
GA=236 µm
2
Depth of cut= 4.55 µm
S=500 rpm
GA=154µm
2
Depth of cut=3.59 µm
R² = 0.4748
R² = 0.332
R² = 0.6721
R² = 0.6896
0
1
2
3
4
5
6
7
8
9
2
2.5
3
3.5
4
4.5
5
5.5
6
Cutting forces (N)
Depth of cut (µm)
Fn, Vc=54.6 m/min
Ft, Vc=54.6 m/min
Fn, Vc=327.6 m/min
Ft, Vc=327.6 m/min
Traverse scratching; Workpiece: En24T; Grit: CBN (40/50 );
Signal recorded with Labview software
S=3000 rpm
GA=236 µm
2
Depth of cut= 4.55 µm
S=500 rpm
GA=154µm
2
Depth of cut=3.59 µm
R² = 0.9674
R² = 0.9289
R² = 0.7598
R² = 0.7477
0
1
2
3
4
5
6
7
8
9
0
50
100
150
200
250
300
350
400
Cutting forces (N)
Groove area (
µm
2
)
Fn, Vc=54.6 m/min
Ft, Vc=54.6 m/min
Fn, Vc=327.6 m/min
Ft, Vc=327.6 m/min
Traverse scratching; Workpiece: En24T; Grit: CBN (40/50 );
Signal recorded with Labview software
S=3000 rpm
GA=236 µm
2
Depth of cut= 4.55 µm
S=500 rpm
GA=154µm
2
Depth of cut=3.59 µm
R² = 0.9674
R² = 0.9289
R² = 0.7598
R² = 0.7477
0
1
2
3
4
5
6
7
8
9
0
50
100
150
200
250
300
350
400
Cutting forces (N)
Groove area (
µm
2
)
Fn, Vc=54.6 m/min
Ft, Vc=54.6 m/min
Fn, Vc=327.6 m/min
Ft, Vc=327.6 m/min
0
0.5
1
1.5
2
2.5
3
3.5
4
0
50
100
150
200
250
300
350
400
Fn/Ft
Groove area (
µm
2
)
Vc=54.6 m/min
Vc=327.6 m/min
Traverse scratching; Workpiece: En24T; Grit: CBN (40/50)
Signal recorded
with Labview software
Traverse scratching; Workpiece: En24T; Grit: CBN (40/50)
Signal recorded with Labview software
0
2
4
6
8
10
12
14
16
18
20
0
1
2
3
4
5
6
Specific energy
(J/mm
3
)
Depth of cut (µm)
Vc=54.6 m/min
Vc=327.6 m/min
Micro Scratching tests

Cutting forces, force ratio, and specific energy


16/25

6.614
6.615
6.616
6.617
6.618
x 10
6
-0.015
-0.01
-0.005
0
0.005
0.01
0.015
Time (Micro seconds)
Raw AE signal (V)


6.694
6.696
6.698
6.7
x 10
6
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
Time (Micro seconds)
Raw AE signal (V)


1
st
signal
rubbing
4
th
signal
cutting & ploughing
7.29
7.291
7.292
7.293
7.294
7.295
x 10
6
-0.015
-0.01
-0.005
0
0.005
0.01
0.015
Time (Micro seconds)
Raw AE signal (V)


Last signal
rubbing
(a)
(b)
(c)
No visible scratch
V
isible scratch
No visible scratch
Depth of cut: 2 µm
Sa: ~ 90 nm for all surfaces
AE characteristic of material deformation

Micro Scratching tests

Acoustic Emission (raw signal) during scratching


17/26


(a) γ=

22º




(b) γ=





(c) γ =
-

30º



(d) γ =
-

45º



Modelling and Simulation

FEM simulation of cutting

(
Abaqus
/Explicit, ALE adaptive meshing, JC flow stress and Damage model,


Fracture energy based damage evolution)

18/25

1
st

pass

2
nd

pass

3
rd

pass

Max. Depth (a
p
)
Workpiece surface
Grit
(simulation
start point)
Grit
(end of simulation)
Step
-
3
100 µm
100 µm
100 µm
Clearance
Step
-
1
Step
-
5
X
Y
Material accumulation
(front pile
-
up) ahead of the grit
Plastic + Elastic deformation at the
grit
-
workpiece contact location
Residual plastic deformation
(a)
(b)
Total number of elements is 184085
Element size in grit= ~4 µm
Element size in the contact area of the workpiece is lower than 1 µm
Computational time is approximately 48 hours
Modelling and Simulation

FEM simulation of scratching

19/25

Grit tool path

3D FEM model

Stress and deformation during scratching

3D view during scratching

Multi
-
pass grit simulation with 10 µm apart

(a
) Frictionless µ=0
(b) Friction coefficient µ=0.1
(c) Friction coefficient µ=0.3
(d) Friction coefficient µ=0.5
(a
) Frictionless µ=0
(b) Friction coefficient µ=0.1
(c) Friction coefficient µ=0.3
(d) Friction coefficient µ=0.5
Modelling and Simulation

FEM simulation of scratching

20/25

Material deformation with friction: Longitudinal section

Material deformation with friction: Lateral cross section

Cross section at the end of step
-
2

Cross section at the end of step
-
3

0
50
100
150
200
250
300
0
0.5
1
1.5
2
2.5
3
3.5
4
Aproximate horizontal distance along grit trajectory (micrometer)
Pile-up ratio


Frictionless, max.depth=0.5 micron
Friction=0.2, max.depth=0.5 micron
Frictionless, max.depth=1 micron
Friction=0.2, max.depth=1 micron
Frictionless, max.depth=2 micron
Friction=0.2, max.depth=2 micron
Frictionless, max.depth=5 micron
Friction=0.2, max.depth=5 micron
50
55
60
65
70
75
80
85
0.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
0.7
0.75


step
-
3
step
-
5
step
-
1
step
-
2
step
-
4
300 200 100 0
0
5
10
15
20
25
30
35
0
100
200
300
400
500
600
700
800
900
Pile
-
up ratio
Dimensional length along scratch direction (µm
)
0
0.5
1
1.5
2
2.5
200
300
400
500
600
Pile
-
up ratio
Scratching direction
Traverse scratching; S=3000 rpm (
V
c
= 327.6 m/min);
Workpiece: En24T steel; Grit: CBN (40/50)
FEM scratch simulation

Experimental scratch test

Similar trend obtained
along the scratch length

Modelling and Simulation

FEM simulation of scratching

21/25

-
0.7
-
0.6
-
0.5
-
0.4
-
0.3
-
0.2
-
0.1
0
0
50
100
150
200
250
300
Forces (N)
Horizontal distance along grit trajectory (micrometer)
Fx, Speed= 3 m/min
Fy, speed= 3 m/min
Fx, speed= 6 m/min
Fy, speed= 6 m/min
Fx, speed= 12 m/min
Fy, speed= 12 m/min
Fx, speed= 300 m/min
Fy, speed= 300 m/min
Modelling and Simulation

FEM simulation of scratching

22/25

Cutting forces along scratch length at different
cutting speeds

Impact of the research

Plastic gear for watches

Micro holes on turbine blades

(http://www.sarix.com)

Nozzle for diesel injectors

Applications of
Micro EDM

Micro EDM;


Emerging technology for micro mould manufacturing

(medical devices, surgical equipments, biomedical implants etc.)



Contacted by Rolls
-
Royce Plc. to be consulted on blind micro
holes and micro slots Micro
EDMing

(used in sound reflector)

Grinding;


Optimization of machining process


Designing grinding wheel


Prediction of machining quality


Optics, medical, aerospace, mould industry


23/25

Publications

19 publications including peer reviewed journals and conferences

24/25



Thank You...

25/25