Micro Machining Technology

Report
Micro Machining Technology
• Micro EDM
• High speed precision grinding
• Micro scratching tests
•Modelling and simulation of machining processes
Tahsin Tecelli Öpöz
2/25
Outline
• Research environment
• Micro EDM
• High speed precision grinding
• Micro scratching tests
• Finite Element Modelling and Simulation
• Impact of the research
• Publications
3/25
Research environment
Micro Electrical Discharge Machining
Robotic polishing
Precision grinding/diamond turning
Surface metrology
4/25
Micro EDM
Micro electrical discharge machining of micro holes
1
Micro Tool Manufacturing using WEDG
(Dia.<10 µm)
3
Surface Damage in Micro EDMed Holes
Etched with nitric acid
Etched with nitric+chromic acid
Hole shape formation
2
(Disclosure of technological
features of micro EDM)
Micro EDM
Discharge pulse form and surface characteristics
(a) Discharge energy 12.7 µj
(b) Discharge energy 123 µj
5/25
6/25
Micro EDM
Micro hole end-tip shape formation
Concave tip shape
E= 0.78 µJ, OGP=75 V
Flat (rough) tip shape
E= 223 µJ, OGP=75 V
Bullet tip shape
E= 33.4 µJ, OGP=80 V
Micro EDM
7/25
Heat affected layer in Micro EDMed holes’ wall
Micro EDM
8/25
Material removal response with machining time
Micro EDM
9/25
Micro hole entrance diameter with machining time
10/25
Precision grinding
High speed applications and micro scratching tests
1
High speed precision grinding
(20k – 160k rpm)
2
Single grit grinding test to reveal
micromechanics concept in grinding
 Rubbing
 Ploughing
 Cutting
Super glue
Steel wheel
3
A CBN grit from
top view
4
A single grit glued onto the wheel
Material removal mechanism stages
at micro scale grinding
11/25
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 (Vc = 327.6 m/min)
Work table speed = 200 mm/min
Scratches with increasing
depth of cut: An example
Talysurf CCI interferometer measurement
Longitudinal section profile extracted using 1st line
shown in previous figure
Deepest
point
around 450
(a)
(b)
Cross section profile extracted at 450 using 2nd
line shown in previous figure
12/25
Micro Scratching tests
Abrasive grit cutting edge shape alteration during scratching:
Single edge and multiple edges scratch formation
Groove
section area
Depth of cut
(ap)
Total Pile-up area
(a) Single scratch
(a) Single scratch
Depth of cut
(ap)
Groove
section area
Groove section
area
(b) Multiple scratches
Depth of cut
(ap)
Total Pile-up area
Total Pile-up area
13/25
Micro Scratching tests
Pile-up ratio variation with depth of cut at different grit cutting
edges
0.5
0.8
0.7
R² = 0.6748
1
0.6
Pile-up ratio
Pile-up ratio
0.4
0.3
0.2
3
0.5
0.4
2
0.3
0.2
0.1
0.1
0
0
0.5
1
1.5
2
2.5
3
3.5
Depth of cut (µm)
4
4.5
5
R² = 0.3949
0
5.5
0
Traverse scratching; Workpiece: En24T; Grit: CBN (40/50 mesh); Vc= 546.6 m/min
1
1.5
2
2.5
Depth of cut (µm)
3
3.5
4
Traverse scratching; Workpiece: En24T; Grit: CBN (40/50 ); V c= 327.6 m/min
3.5
1
single edge scratch
3
multiple edges scratch
0.8
2.5
0.6
Pile-up ratio
Pile-up ratio
0.5
R² = 0.7924
0.4
2
1.5
1
R² = 0.5083
0.2
R² = 0.5354
0.5
0
0
0
2
4
6
Depth of cut (um)
8
Traverse scratching; Workpiece: En24T; Grit: CBN (40/50 ); V c= 327.6 m/min
10
0
0.5
1
1.5
2
2.5 3 3.5 4
Depth of cut (µm)
4.5
5
5.5
6
6.5
Traverse scratching; Workpiece: Inconel 718; Grit: CBN (40/50) ; Vc= 327.6 m/min
14/25
Micro Scratching tests
Material removal along scratch length: Pile-up ratio
35
30
2.5
2
Pile-up ratio
Pile-up ratio
25
20
1.5
1
0.5
15
0
200
300
400
500
600
10
(a) Lateral cross sectional view of a scratch
Scratching direction
5
0
0
Workpiece: En24T steel
Grit: CBN (40/50)
S=3000 rpm (Vc= 327.6 m/min)
Hardness= 289.2 HV at 1 kg load
(b) Longitudinal cross sectional view of a scratch
100
200
300
400
500
600
Dimensional length along scratch direction (µm)
700
800
Traverse scratching; S=3000 rpm (Vc= 327.6 m/min); Workpiece: En24T steel; Grit: CBN (40/50)
900
15/25
Micro Scratching tests
Material removal along scratch length: Chip removal strength
Chip removal strength (µm2)
70
scratch first part (grit entrance side)
scratch second part (grit exit side)
60
60
50
50
40
40
30
30
20
20
10
10
0
0
0
1
2
3
4 4
3
2
1
-10
0
-10
Depth of cut (µm)
-20
-30
-40
Traverse scratching; S=3000 rpm (Vc= 327.6 m/min); Workpiece: En24T steel; Grit: CBN (40/50)
16/25
Micro Scratching tests
Cutting forces, force ratio, and specific energy
Fn, Vc=54.6 m/min
9
Ft, Vc=54.6 m/min
8
Fn, Vc=327.6 m/min
Cutting forces (N)
R² = 0.4748
5
R² = 0.6721
4
3
6
5
4
7
R² = 0.332
R² = 0.6896
1
2
2.5
3
R² = 0.9674
3.5
4
4.5
Depth of cut (µm)
5
5.5
R² = 0.7598
S=3000 rpm
R² = 0.7598
S=3000
rpmµm2
GA=236
GA=236 µm2
Depth of cut= 4.55 µm
Depth of cut= 4.55 µm
R² = R²
0.9289
= 0.9289
2
R²R²==0.7477
0.7477
1
0
0 50
0
6
Ft, Vc=327.6 m/min
5
0
2
Fn, Vc=327.6 m/min
Ft,
Vc=327.6 m/min
R² = 0.9674
6
1
0
S=500
rpm
Depth
of cut=3.59 µm
GA=154µm2
Depth of cut=3.59 µm
Vc=54.6 m/min
Fn,Ft,Vc=327.6
m/min
S=3000 rpm
4
GA=236 µm2
Depth of3cut= 4.55 3
µm
2
S=500 rpm
GA=154µm2
Fn,Vc=54.6
Vc=54.6 m/min
m/min
Ft,
8
7
Ft, Vc=327.6 m/min
6
50 100 100 150 150 200200 250
250
2
Groove area (µm
2 )
300
300
350
350
400
400
Groove area (µm )
Traverse scratching; Workpiece: En24T; Grit: CBN (40/50 );
Traverse scratching;
En24T;
Grit:
CBN (40/50 );
SignalWorkpiece:
recorded with
Labview
software
Traverse scratching; Workpiece: En24T; Grit: CBN (40/50);
Signal recorded with Labview software
Signal recorded with Labview software
4
20
3.5
Vc=54.6 m/min
18
Vc=54.6 m/min
Vc=327.6 m/min
16
Vc=327.6 m/min
Specific energy
(J/mm3)
3
2.5
Fn/Ft
Cutting forces (N)
7
Fn, Vc=54.6 m/min
S=500 rpm
9
8 2
GA=154µm
Depth of cut=3.59 µm
Cutting forces (N)
9
2
1.5
1
14
12
10
8
6
4
0.5
2
0
0
0
50
100
150
200
250
Groove area (µm2)
300
Traverse scratching; Workpiece: En24T; Grit: CBN (40/50)
Signal recorded with Labview software
350
400
0
1
2
3
Depth of cut (µm)
4
5
Traverse scratching; Workpiece: En24T; Grit: CBN (40/50)
Signal recorded with Labview software
6
17/26
Micro Scratching tests
Acoustic Emission (raw signal) during scratching
AE characteristic of material deformation
No visible scratch
Visible scratch
No visible scratch
Depth of cut: 2 µm
Sa: ~ 90 nm for all surfaces
0.015
0.5
0.015
0.4
0.01
0.01
0.3
0
-0.005
0.005
Raw AE signal (V)
0.2
Raw AE signal (V)
Raw AE signal (V)
0.005
0.1
0
-0.1
0
-0.005
-0.2
-0.01
-0.01
-0.3
-0.015
6.614
6.615
6.616
6.617
Time (Micro seconds)
(a)
1st signal
rubbing
6.618
x 10
6
-0.4
6.694
6.696
6.698
Time (Micro seconds)
(b) 4th signal
cutting & ploughing
6.7
x 10
6
-0.015
7.29
7.291
7.292
7.293
7.294
Time (Micro seconds)
(c) Last signal
rubbing
7.295
x 10
6
Modelling and Simulation
FEM simulation of cutting
(Abaqus/Explicit, ALE adaptive meshing, JC flow stress and Damage model,
Fracture energy based damage evolution)
(a) γ= 22º
(b) γ= 0º
(c) γ = - 30º
(d) γ = - 45º
18/25
Modelling and Simulation
FEM simulation of scratching
Grit tool path
Grit
(end of simulation)
Step-5
Grit
(simulation
start point)
Step-1
Workpiece surface
Clearance
3D view during scratching
Max. Depth (ap)
Y
Step-3
100 µm
100 µm
100 µm
X
3D FEM model
Multi-pass grit simulation with 10 µm apart
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
Stress and deformation during scratching
Material accumulation
(front pile-up) ahead of the grit
1st pass
Residual plastic deformation
(a)
Plastic + Elastic deformation at the
grit-workpiece contact location
2nd pass
3rd pass
19/25
Modelling and Simulation
20/25
FEM simulation of scratching
Material deformation with friction: Longitudinal section
Cross section at the end of step-2
(a) Frictionless µ=0
(b) Friction coefficient µ=0.1
(c) Friction coefficient µ=0.3
(d) Friction coefficient µ=0.5
Material deformation with friction: Lateral cross section
Cross section at the end of step-3
(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
21/25
FEM simulation of scratching
FEM scratch simulation
4
Frictionless, max.depth=0.5 micron
3.5
Friction=0.2, max.depth=0.5 micron
0.75
2.5
2
Frictionless, max.depth=1 micron
0.7
0.65
Friction=0.2, max.depth=1 micron
0.6
Frictionless, max.depth=2 micron
0.55
Friction=0.2, max.depth=2 micron
0.5
Frictionless, max.depth=5 micron
Similar trend obtained
along the scratch length
0.45
Friction=0.2, max.depth=5 micron
0.4
0.35
1.5
0.3
50
55
60
65
70
75
80
85
1
300
step-5
200 100
step-4
0
0
0
step-1
step-2
step-3
50
100
150
200
250
Aproximate horizontal distance along grit trajectory (micrometer)
Experimental scratch test
300
35
30
2.5
2
25
Pile-up ratio
0.5
Pile-up ratio
Pile-up ratio
3
20
1.5
1
0.5
15
0
200
300
400
500
600
10
Scratching direction
5
0
0
100
200
300
400
500
600
Dimensional length along scratch direction (µm)
700
800
900
Modelling and Simulation
FEM simulation of scratching
Cutting forces along scratch length at different
cutting speeds
Horizontal distance along grit trajectory (micrometer)
0
0
50
100
150
200
250
300
-0.1
Forces (N)
-0.2
-0.3
-0.4
Fx, Speed= 3 m/min
Fy, speed= 3 m/min
-0.5
Fx, speed= 6 m/min
Fy, speed= 6 m/min
Fx, speed= 12 m/min
-0.6
Fy, speed= 12 m/min
Fx, speed= 300 m/min
Fy, speed= 300 m/min
-0.7
22/25
23/25
Impact of the research
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)
Applications of
Micro EDM
Nozzle for diesel injectors
Grinding;
• Optimization of machining process
• Designing grinding wheel
• Prediction of machining quality
• Optics, medical, aerospace, mould industry
Plastic gear for watches
Micro holes on turbine blades
(http://www.sarix.com)
Publications
19 publications including peer reviewed journals and conferences
24/25
25/25
Thank You...

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