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Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002
COMPOSITE TECHNOLOGIES FOR INTELLIGENT INDUSTRIAL
LASER PROCESSING
prof. VINCENZO PIURIDepartment of Information Technologies, University of Milanvia Bramante 65, 26013 Crema (CR), Italy
prof. VINCENZO PIURIDepartment of Information Technologies, University of Milanvia Bramante 65, 26013 Crema (CR), Italy
EU Project SLAPSSelf-Tuning and User-Independent Laser Material Processing Units
Philips Centre for Industrial Technology
Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002
Information SourcesPartners in IMS/Brite-Euram Project
SLAPS• Philips-CFT• Laser Zentrum
Hannover• Odense Steel Shipyard
LTD.• Jurca Opto-elektronik• Fiat-CRF
• Trumpf • Lasag AG• Politecnico di Milano• Ecole Politechnique
Federale de Lausanne - IOA
• University of Vienna
Contributions to the Tutorial: Prof. Cesare Alippi, Politecnico di Milano, ItalyDr. Toon Bloom, Philips CFT, The Netherlands
Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002
Laser ProcessingApplying energy to a work piece
in the form of (high intensity) light beam
• Laser seam welding
• Laser cutting
• Laser spot welding
• Laser drilling
• Laser cladding
• Laser marking
• Laser adjustment
• …...
Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002
Carbon Dioxide LaserTypical gas laser construction
Discharge power supply
Outputbeam
Gas mixture
Brewster windows
Cavity end mirrors
Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002
Nd:YAG Laser
Flash lamp
Nd:YAG rod
Water cooling circuit
Lamp driver
Laser beam outFolding mirror
Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002
Solid State Laser Diode
n-type AlGaAs n-type AlGaAsp-type AlGaAs p-type AlGaAsGaAs GaAs
Three layer structure in equilibrium Three layer structure with forward current
EF
EV
EC
-eV-eV
-
++
-EC
EFN
EFP
EV
h
Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002
Solid State Laser Diode
• Low output power
• Laser diode arrays for processing
• Low beam quality
• Good control qualities
• High efficiency
P-GaAsP-GaALAsGaAlAs (active layer)N-GaAlASN-GaAs
HEATSINK
Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002
Beam Delivery
Cavity
Beam manipulation over multiple (5) axis
Beam expandingand collimating
Translating and rotating mirrors
Focussing mirror
Work piece
Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002
Beam Delivery
Cavity Collimatorlens
Work piece
Processmonitoring
Scanningmirrors
Glass fibre delivery
Fibre
F1
F2
Spot size = Fibre core diameter x F1F2
Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002
Absorption, Reflection, Transmission
• Kirchhoff: Absorption +reflection+transmission = 1• Extinction of the penetrating light wave
• Penetration depth:fc
c
k oo
o
1
2
1
I(z)
Io
x
xo
kx
ox eIeII
24
)(
1/e
Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002
Absorption and Heat Diffusion = F(T)
D a
Temperature
Copper
D a
Temperature
Aluminium
D a
Temperature
Stainless steel
Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002
Process Phases
• 1: Heating: Absorption, heat diffusion• 2: Phase transition of top material, change
of properties• 3: Vaporisation, recoil pressure pushes
liquid metal aside• 4: Liquid level reaches bottom and is blown out
Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002
Laser Cutting
Laserbeam
Movement
Laserbeam
Top view laser cutting Cross section laser cutting
• Medium to high power CW lasers (CO2)• Process gas, reactive (O2. extra reaction energy)
or not (N2), to blow out molten material• Wave guide kind of energy transfer through
the cutting slit
Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002
Spark Pattern During Laser CuttingLaserbeam
Laserbeam
Good qualitycutting
Bad qualitycutting
Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002
Process Monitoring
Focussing mirror
AV
2- Impedance measurement
Reactive:Nozzle - work piece distance
Resistive:Plasma detection
1- Optical emission from processing area * Photo diode * spectrometer
Processgas
CCD3- Spreading of sparks
workpiece
Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002
Laser Seam Welding
Part A
Part B
Part A
Part B
But-joint Lap joint
Part A
Part B
T-joint
Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002
Laser Seam Welding
• Battery casings, Pace maker casings• Car bodies, Transmission parts• Sub assemblies in ship building• Plastics (overlap penetration welding)
Seam weld
KeyholeGap / slit
Movement
Laserbeam
Top view seam welding Cross section seam welding
Undesiredporosity
Laserbeam
Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002
Laser Seam WeldingProcess monitoring - Direct delivery system
Focussing mirror
Optical emissionfrom processing area* Photo diode* spectrometer
Processgas
workpiece
Input powermonitoring
2-D thermal imaging
Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002
Laser Seam Welding
LaserCollimatorlens
Work piece
Scanningmirrors
Fibre
Temperature
Plumeemission
ReflectedLaser power
Inputlaser power
Process monitoring - Fibre delivery systemSensing implemented in processing head
Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002
Overlap fillet
Spot Weld Geometries
Overlap penetration
Nose weld
Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002
ProcessMonitoring
in spot welding
200 micronfibre
CCDcamera
Work piece
Laserinput power
Reflectedpower
Plumeemission
Surfacetemperature
Nd:YAG filter
Acousticemission
Eddy currentlosses
X/Y scanningmirror
Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002
Signal ProcessingExample of measured signals
Spot welding of 2 x 100 micron copper sheets400 micron spot, 4000 Watt square pulse
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
-1 0 1 2 3 4 5 6 7 8
Time [ms]
Volts
LMO
Plume
Temp lin
Temp log
Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002
Signal ProcessingExample of measured signals
Spot welding of 2 x 100 micron copper sheets400 micron spot, 3500 Watt square pulse
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
-1 0 1 2 3 4 5 6 7 8
Time [ms]
Volts
LMO
Temp lin
Temp log
Eddy
Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002
Automatic Classificationbased on multi sensor process monitoring
• The complete set of sensors provides a broad information range about the performance of the process
• Realisation of data reduction by extraction of specific features from the recorded signals
• The features are recognised as being related to certain process events
• The relations between features and a good or bad performing process have to be established through a large set of verification experiments