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Questions and Answers
What is a primary reason an electron beam is used in a low-partial-pressure vacuum environment?
Laser beams can be absorbed by gas if the gas is transparent at the laser wavelength.
False
Name one benefit of using powder-based additive manufacturing processes compared to liquid-based processes.
Wide variety of materials can be processed.
During part building in polymer PBF, loose powder serves as sufficient ______ material.
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Match the following particle sizes with their effects on part quality:
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What is a drawback of using powders in additive manufacturing?
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Accuracy and surface finish of PBF processes are generally superior to those of traditional subtractive manufacturing.
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What significant factor influences the accuracy of powder-based additive manufacturing?
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What are Polymer Laser Sintering (pLS) machines primarily designed for?
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Selective Laser Sintering (SLS) machines can handle pure metals directly.
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What is the primary advantage of Electron Beam Melting (EBM) over laser-based systems?
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Nylon polyamide materials are the most popular __________ in Polymer Laser Sintering.
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Match the following processes and their characteristics:
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Which of the following materials cannot be directly processed by Polymer Laser Sintering machines?
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The primary difference between electron beams and laser beams is their composition, with electron beams made of streams of electrons.
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What is one of the main benefits of using a nitrogen atmosphere in pLS machines?
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Which of the following processes utilizes a point-wise laser scanning technique originally developed for plastic prototypes?
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Thermoset polymers are commonly processed using Powder Bed Fusion into parts.
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What is the typical thickness of powder layers used in the Polymer Laser Sintering process?
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The build process in pLS takes place in an enclosed chamber filled with __________ gas to minimize oxidation.
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Match the following materials with their classification:
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Which of the following materials can be processed using Powder Bed Fusion?
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Irregular molecular structures are typically found in crystalline thermoplastic polymers.
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What thermal source can be used in the Powder Bed Fusion process other than lasers?
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The primary characteristic of ceramics is that they are generally composed of __________, __________, and __________.
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What is one of the main benefits of using Powder Bed Fusion processes?
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What does the extrusion process primarily use for material state control?
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Bioextrusion primarily uses temperature for material liquefaction.
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What is the primary benefit of using chemical changes in the extrusion process?
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In the context of extrusion-based systems, the process of __________ involves the melting of material to allow it to flow out through a nozzle.
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Match the following extrusion principles with their descriptions:
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Which of the following is a limitation of Fused Deposition Modeling (FDM)?
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Contour crafting is one of the alternative systems to Fused Deposition Modeling.
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What might be utilized in industrial applications of the extrusion process instead of thermal effects?
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Study Notes
Electron Beam Melting (EBM)
- EBM utilizes a high-energy electron beam to fuse metal powder particles.
- EBM is practiced in a low-partial-pressure vacuum environment.
- Electron beams are inherently different from laser beams as they are made up of electrons moving near the speed of light.
- In contrast, laser beams are made up of photons moving at the speed of light.
Powder Bed Fusion (PBF)
- PBF is a 3D printing process that uses a heat source to fuse powdered material layer by layer.
PBF Processes
- PBF can process a wide variety of materials, including polymers, metals, ceramics, and composites.
- PBF processes involve one or more thermal sources to induce fusion between powder particles.
- PBF uses a method for controlling powder fusion to a prescribed region of each layer.
- PBF processes use mechanisms to add and smooth powder layers.
- PBF is increasingly being used for direct digital manufacturing of end-use products.
Laser-Based Systems
- Laser-based systems use a laser to melt and fuse the powder particles.
- Laser-based systems are commonly called Selective Laser Sintering (SLS) or Laser Sintering (LS) machines.
- 3D Systems’ low-temperature machines are designed to run a large variety of powdered material types.
- Nylon polyamide materials are the most popular pLS materials.
- Laser-based systems have been extended to metal and ceramic powders, with variants for layer-wise fusion of powdered materials being introduced.
- Lasers used in PBF include CO2, Nd-YAG, and other types.
Polymer Laser Sintering (pLS)
- pLS is a common PBF approach that fuses thin layers of powder.
- pLS machines use infrared heaters to maintain an elevated temperature around the part being formed.
- pLS processes have a build platform that is lowered layer by layer.
- pLS processes use a counter-rotating powder leveling roller to spread and level powder layers.
- The powder is maintained at an elevated temperature just below the melting point and/ or glass transition temperature of the powdered material.
Materials Used In PBF
- Polymers: Thermoplastic or thermoset.
- Metals: Stainless steels, tool steels, titanium and its alloys, nickel based alloys, some aluminum alloys, and cobalt-chromium.
- Ceramics: Metal oxides, carbides, and nitrides, and their combinations.
Advantages of PBF
- PBF can produce complex geometries and intricate designs.
- PBF is a relatively faster process compared to other additive manufacturing processes.
Disadvantages of PBF
- The accuracy and surface finish of PBF are typically inferior to liquid-based processes.
- PBF processes can be influenced by operating conditions and powder particle size.
- Build materials typically exhibit 3-4% shrinkage, which can lead to part distortion.
- Materials with low thermal conductivity can result in better accuracy.
- Total part construction time can take longer than other additive manufacturing processes due to preheat and cool-down cycles.
Extrusion-Based Systems
- A method for generating 3D structures by extruding material through a nozzle.
- Two primary approaches:
- Temperature Control: Material is liquefied, extruded through a nozzle, and solidifies, bonding with prior material - similar to conventional polymer extrusion.
- Chemical Change: Solidification occurs due to a curing agent, solvent evaporation, reaction with air, or simply drying. This approach is more suitable for bio-compatible materials.
Basic Principles
- Material Loading: Raw materials are loaded into the system.
- Liquification: Material is heated to liquid form – using thermal melts or chemicals.
- Extrusion: The liquefied material is pushed through the nozzle.
- Solidification: The material solidifies upon exiting the nozzle.
- Positional Control: The nozzle is precisely moved to maintain a path and shape of the object.
- Bonding: Solidified material bonds with previously extruded material.
- Support Generation: Supporting structures are created to prevent sagging or deformation during the extrusion process.
Plotting and Path Control
- Describes how the extrusion process is controlled to create a desired 3D geometry.
- Involves precise movement of the nozzle along a predefined path.
- This path is often described by a computer aided design (CAD) software.
- Slice-based Printing: The design is sliced into 2D layers. Each layer is then extruded.
Fused Deposition Modeling (FDM)
- A widely used extrusion-based 3D printing technology.
- Developed by Stratasys.
- Materials are thermoplastic filaments (e.g., ABS, PLA).
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FDM Machine Types:
- Desktop FDM: Compact size, affordable, ideal for prototyping and small scale production.
- Industrial FDM: Larger scale, high precision, used for production of large parts.
Materials
- Thermoplastics are commonly used:
- ABS (Acrylonitrile butadine styrene)
- PLA ( Poly-lactic acid)
- Nylon
- PEEK (Polyetheretherketone)
- Other materials used for FDM include:
- Composites
- Metals
Limitations of FDM
- Layer Visibility: Visually identifiable layer lines, can affect surface smoothness.
- Mechanical Strength: Can be directionally dependent, with weaker strength perpendicular to the layers.
- Limited Material Options: Not all materials can be effectively used in FDM.
Bioextrusion
- Focuses on creating three-dimensional structures for biomedical applications (e.g., tissue engineering and drug delivery).
- Gel Formation: Biopolymers are suspended in water, and form gel structures during printing.
- Melt Extrusion: Thermoplastics are extruded using controlled temperatures.
- Scaffold Architectures: The printed structure acts as a scaffold for cell growth and tissue regeneration.
Other Systems
- Contour Crafting: A construction printing technology that uses a robotic arm to deposit concrete and building materials.
- Nonplanar Systems: These systems are capable of printing structures in multiple directions.
- FDM of Ceramics: Extrusion of ceramics, enabling the creation of complex ceramic structures.
- Reprap and Fab@home: Open-source 3D printers designed for affordability and accessibility.
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Description
Test your knowledge on Electron Beam Melting (EBM) and Powder Bed Fusion (PBF) processes. This quiz covers key concepts, differences between EBM and laser systems, and materials used in PBF. Suitable for those interested in advanced manufacturing technologies.
