DMLD Direct Metal Laser Deposition
What’s the DMLD ? It’s a laser additive technique which allows to manufacture metal prototypes or small industria...
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;
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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 Expérimentales Direct Laser Metal Deposition Cyril GORNY
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Type of tool used to transform the matter ?
LASER Light Amplification by Stimulated Emission of Radiation TP Techniques Expérimentales Direct Laser Metal Deposition Cyril GORNY
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What is the stimulated emission ?
(Source MELLES GRIOT) TP Techniques Expérimentales Direct Laser Metal Deposition Cyril GORNY
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LASER description Totally reflective mirror
Partially reflective mirror
CAVITY Population Inversion Pumping device
Amplifier
Active middle
Output Beam
GAIN > LOSSES TP Techniques Expérimentales Direct Laser Metal Deposition Cyril GORNY
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Usual light versus LASER beam monochromatic
Luminous waves in the same direction Polychromatic
Coherent luminous waves Luminous waves in all directions Important Energizing Irradiance (W/m²) Two operating modes : Disorderly luminous waves
- Continous Wave (CW) - Pulsed Wave (PW)
TP Techniques Expérimentales Direct Laser Metal Deposition Cyril GORNY
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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 Infrared (CW or PW) YAG LASER disk example
TP Techniques Expérimentales Direct Laser Metal Deposition Cyril GORNY
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Spatial characteristics of LASERS beams Monomode Gaussian Beam
Multimode Beam
‘Top Hat’ beam
Laser CO2: scellé 400 W Slab kW Laser Nd:YAG Q switch qqs W Laser Yb:YAG: continus < 1500 W
TP Techniques Expérimentales Direct Laser Metal Deposition Cyril GORNY
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Beam analyzer
TP Techniques Expérimentales Direct Laser Metal Deposition Cyril GORNY
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Irradiation types •
Continous wave
P(W)
PCW
t
•
Pulsed wave
Duty Cycle : α = TH / T In each case, we must have : = PCW Relation between PC and : PC=(*T)/TH
TP Techniques Expérimentales Direct Laser Metal Deposition Cyril GORNY
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« SAFETY FIRST ! »
WARNING !
TP Techniques Expérimentales Direct Laser Metal Deposition Cyril GORNY
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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
The skin Burns. In our case, the radiation penetrates in depth to the under epidermal tissue.
Visible and near IR In our case, focusing on the retina. TP Techniques Expérimentales Direct Laser Metal Deposition Cyril GORNY
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LASERS classes (French Version) EN 60825-1:2007 extract
TP Techniques Expérimentales Direct Laser Metal Deposition Cyril GORNY
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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)
TP Techniques Expérimentales Direct Laser Metal Deposition Cyril GORNY
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Optical Fiber
Water Cooling Tubes
Optical Fiber Connector
Coaxial Camera Pinch Solenoid Valve
Optical Head
Powder Feeder Tubes
Shielding Gaz Tubes Shielding Lateral Nozzle
Throwing Nozzle
Substrate TP Techniques Expérimentales Direct Laser Metal Deposition Cyril GORNY
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Nozzle description
PFP
• • •
Gas outlets description : a : powder holder gas. b : optical shielding (PFP position influence). c : local shielding.
TP Techniques Expérimentales Direct Laser Metal Deposition Cyril GORNY
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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 Dm (g/min) • Powders granulometry and goemetry • Spatial powder distribution
OTHER : • Scan speed • Material
TP Techniques Expérimentales Direct Laser Metal Deposition Cyril GORNY
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Instantaneous temperature and thermal cycles Ti6Al4V substrate reloaded by 20 Ti6Al4V layers
V = 100mm/min P = 400W ε = 0,36
TP Techniques Expérimentales Direct Laser Metal Deposition Cyril GORNY
