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Questions and Answers
Selective laser sintering (SLS) was the first commercialized PBF process.
True
All PBF processes utilize lasers as the thermal source.
False
LS processes were originally developed to produce metal prototypes.
False
Non-laser thermal sources require significantly different machine architectures than laser sintering machines.
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True or false: Loose powder sintering always has a negative effect on the build process?
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True or false: Loose powder sintering can help minimize part curling by providing tensile and compressive strength to the powder bed?
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True or false: Thermally induced fusing of the desired cross-sectional geometry can cause the just-formed part cross section to be quite hot?
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Parts produced using polyamide powders have mechanical properties approaching those of injection molded thermoplastic parts, with reduced elongation and unique microstructures.
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Polystyrene-based materials with low residual ash content are suitable for making sacrificial patterns for investment casting using pLS.
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Porosity in an investment casting pattern aids in melting out the pattern after creating the ceramic shell.
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Elastomeric thermoplastic polymers with rubber-like characteristics are resistant to degradation at elevated temperatures and chemicals like gasoline and automotive coolants.
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Flame-retardant polyamide and polyaryletherketone (PAEK or PEEK) are commercially available polymers for 3D printing.
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Biocompatible and biodegradable polymers processed using pLS include polycaprolactone (PCL), polylactide (PLA), and poly-Llactide (PLLA).
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Composite materials consisting of PCL and ceramic particles have been investigated for bone replacement tissue scaffolds.
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Polymers in PBF can have fillers that enhance their mechanical properties, such as glass bead filled polyamide materials.
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Metals processed using PBF include stainless and tool steels, titanium and its alloys, nickel-base alloys, some aluminum alloys, and cobalt-chrome.
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RapidSteel was one of the first metal/binder systems, developed by DTM Corp, and consisted of a thermoplastic binder coated 1080 carbon steel powder with copper as the infiltrant.
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LaserForm ST-100 had a broader particle size range, allowing for lower temperature sintering and infiltration in a single furnace run.
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EOS marketed proprietary nickel-based powders and Cu-based powders for direct tooling applications and parts requiring high thermal and electrical conductivities.
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mLS and EBM technology have made some alloys obsolete in favor of engineering-grade alloys.
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Titanium alloys, steel alloys, nickel-based super alloys, and CoCrMo are widely available for PBF production.
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Alloys that crack under high solidification rates are not suitable for mLS.
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Crystal structures and mechanical properties differ in mLS due to high solidification rates.
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Advancements in mLS and EBM processes will lead to the development of new alloys tailored for PBF production.
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Ceramics consist of metal oxides, carbides, and nitrides, and are available commercially.
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Phenix Systems in France, acquired by 3D Systems, developed commercial machines for ceramics.
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Ceramics and metal-ceramic composites have been demonstrated in research.
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Biocompatible materials like calcium hydroxyapatite have been processed using PBF for medical applications.
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Four fusion mechanisms are present in PBF processes: solid-state sintering, chemically induced binding, liquid-phase sintering, and full melting.
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Solid-state sintering occurs at elevated temperatures without melting, driven by the minimization of total free energy of powder particles.
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Sintering is important in most thermal powder processes, but few AM processes use sintering as a primary fusion mechanism.
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Powder Bed Fusion processes are only used with polymers and composites.
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Powder Bed Fusion processes involve the use of a counter-rotating powder leveling roller.
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The part building process in Powder Bed Fusion takes place in an open chamber.
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Infrared heaters are used to cool down the part being formed.
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A focused CO2 laser beam is directed onto the powder bed to fuse the material.
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After each layer is completed, the build platform is raised by one layer thickness.
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Powder Bed Fusion processes can be used with all materials, including those that cannot be melted.
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Thermoplastic materials are not suitable for powder bed processing due to their high melting temperatures.
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The most common material used in Powder Bed Fusion is polyamide, commonly known as nylon.
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Powder Bed Fusion processes are not widely used globally.
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Powder Bed Fusion processes can be used for the direct manufacturing of end-use products.
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Thermal sources are not utilized in Powder Bed Fusion processes.
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Study Notes
Powder Bed Fusion Processes in Additive Manufacturing
- Powder Bed Fusion (PBF) processes have been extended to metal and ceramic powders, with various thermal sources being utilized.
- PBF processes are widely used globally and can be used with a broad range of materials, including polymers, metals, ceramics, and composites.
- The process is increasingly used for the direct manufacturing of end-use products due to comparable material properties to engineering-grade polymers, metals, and ceramics.
- Powder Bed Fusion processes involve thin layers of powder being fused using a counter-rotating powder leveling roller.
- The part building process takes place in an enclosed chamber filled with nitrogen gas to minimize oxidation and degradation of the powdered material.
- Infrared heaters are used to maintain an elevated temperature around the part being formed and above the feed cartridges to preheat the powder.
- A focused CO2 laser beam is directed onto the powder bed to thermally fuse the material to form the slice cross-section.
- After each layer is completed, the build platform is lowered by one layer thickness and a new layer of powder is laid and leveled using the roller.
- A cool-down period is required to allow the parts to come to a low enough temperature that they can be handled and exposed to the ambient atmosphere.
- PBF processes can be used with all materials that can be melted and resolidified.
- Thermoplastic materials are well-suited for powder bed processing due to their low melting temperatures, low thermal conductivities, and low tendency for balling.
- The most common material used in PBF is polyamide, a thermoplastic polymer, commonly known as nylon, which has distinct melting points enabling reliable processing.
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Description
Learn about the mechanical properties of pLS parts produced using polyamide powders and their suitability for investment casting. Explore the unique microstructures and sacrificial pattern making using polystyrene-based materials in investment casting process.
