Powder Bed Fusion and EBM Quiz

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).
• 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.