dmld direct metal laser deposition - procédés et...
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DMLD
Direct Metal Laser Deposition
TP Techniques ExpérimentalesDirect Laser Metal Deposition
Cyril GORNY2
What’s the DMLD ?It’s a laser additive technique which allows to manufacture metal prototypes or small industrial series.
The DMLD process can be described as follows (Fig.1):
- The three dimensional geometry of the parts is first represented by a CAO file, then “sliced” into 2-D layers used
to control the relative motion between a vertical laser head and a planar substrate;
- The laser path follows motion program, creates a melt-pool at the surface of the substrate, where local powder
feeding (coaxial or not to the laser) creates a layer. The melt-pool characteristics and the resulting layer
morphology depend on the powder – laser – melt-pool interactions;
- The juxtaposition and superposition of DMLD solidified layers form a 3-D fully dense complex shape.
(a) (b)
Figure 1 : (a) Basics of the Direct Metal Laser Deposition process
(b) example of a DMLD stainless steel structure (electric connector : source = Sandia Lab, USA)
TP Techniques ExpérimentalesDirect Laser Metal Deposition
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Type of tool used to transform the matter ?
LASERLight Amplification by
Stimulated Emission
of Radiation
TP Techniques ExpérimentalesDirect Laser Metal Deposition
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What is the stimulated emission ?
(Source MELLES GRIOT)
TP Techniques ExpérimentalesDirect Laser Metal Deposition
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LASER description
Active middle
Totally reflectivemirror
Partially reflectivemirror
Output Beam
CAVITY
Pumping device
Amplifier
GAIN > LOSSES
Population Inversion
TP Techniques ExpérimentalesDirect Laser Metal Deposition
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Usual light versus LASER beam
Luminous waves in all directions
Disorderly luminous waves
Polychromatic
Two operating modes :
- Continous Wave (CW)- Pulsed Wave (PW)
Important Energizing Irradiance (W/m²)
monochromatic
Luminous waves in the samedirection
Coherent luminous waves
TP Techniques ExpérimentalesDirect Laser Metal Deposition
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Main LASER types• Semiconductor LASERS
• Gaz LASERS :� Ne-He Laser : Visible (CW)� Ionized Argon Laser : Visible (CW or PW)� Carbon Dioxyde Laser : Mid Infrared (CW or PW)
• Solid State LASERS :� Ruby Laser (Maiman – 1960)� xx-YAG (Yttrium Alumina Garnet) Laser : Near Infrare d (CW or PW)
YAG LASER disk example
TP Techniques ExpérimentalesDirect Laser Metal Deposition
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Spatial characteristics of LASERS beams
Monomode GaussianBeam
Laser CO2: scellé 400 WSlab kW
Laser Nd:YAG Q switch qqs WLaser Yb:YAG: continus < 1500 W
Multimode BeamLaser CO2: 12 –15 kW
‘Top Hat’ beam
Laser Nd:YAg: diamètre 600 microns: 4.5 kWLaser Yb:YAG: diamètre 200 microns, 8-10 kW
jusqu’à 50 kW, techno fibre.
TP Techniques ExpérimentalesDirect Laser Metal Deposition
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Beam analyzer
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Irradiation types• Continous wave P(W)
t
PCW
• Pulsed wave Duty Cycle :α = TH / T
Relation between PC and <p> :PC=(<p>*T)/TH
In each case, we must have :<p> = PCW
TP Techniques ExpérimentalesDirect Laser Metal Deposition
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« SAFETY FIRST ! »
WARNING !
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LASER dangerousness
Why the LASER is dangerous ?- Powerful (energizing beam).- Monochromatic radiation (visible and invisible).- The beam is very directional.
What the body parts are feeling ?
The eye
In our case, focusing on the retina.
Visible and near IR
The skin
Burns.
In our case, the radiation penetratesin depth to the under epidermal
tissue.
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LASERS classes (French Version)
EN 60825-1:2007
extract
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Indirect risks to the LASER use
- Electrical risks- Mechanical risks (motions)- Thermal risks- Physico-chemical risks (tooling particles smokes)- Noise risks (discharges of high-power pulsed lasers)- Fire risks- Explosion risks (excitation flashs, laser bars)
Solutions : « LASER Zone » and Individual Protection
Equipment
- Laser eye-protectors (EN 207)- Laser adjustment eye-protectors (EN 208)
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Optical Fiber
Optical Fiber Connector
Optical Head
Coaxial Camera
Shielding Gaz Tubes
Throwing Nozzle
Water Cooling Tubes
Pinch Solenoid Valve
Shielding Lateral Nozzle
Substrate
Powder Feeder Tubes
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Nozzle description
Gas outlets description :• a : powder holder gas.• b : optical shielding (PFP position influence).• c : local shielding.
PFP
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Process parameters
LASER PARAMETERS :• Diameter• Power• Beam distribution (Gaussian, annular, Top Hat)• Irradiation type (Continous, pulsed)
POWDER FEED PARAMETERS :• Powder feeder (measure tray : rotation velocity and height groove)
→ Mass feed rate D m (g/min)• Powders granulometry and goemetry
• Spatial powder distribution
OTHER :• Scan speed• Material
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Instantaneous temperature and thermal cycles
V = 100mm/minP = 400Wε = 0,36
Ti6Al4V substrate reloaded by 20 Ti6Al4V layers
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Surface finish (3D Profilometry)
Ti6Al4V / P = 450W – Dm = 2g/min
V = 200mm/min V = 400mm/min
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Ti6Al4V + 7% TiC / P = 450W – Dm = 2g/min
V = 200mm/min V = 400mm/min