Powder Bed Fusion

Powder bed fusion (PBF) is a form of additive manufacturing (AM) in which a heat source (such as a laser or a thermal print head) is used to consolidate powdered material into three-dimensional (3D) artifacts. When each coating is completed and new powder is distributed over the build area, heat is applied to particles found inside a powder bed, which eventually indexes down. PBF techniques share common advantages such as cost-effective customization and reduced assembly with all AM techniques (e.g., layer-by-layer fabrication directly from 3D model data). However, unlike many other AM processes, polymer PBF processes do not require support structures since the surrounding unfused powder bed supports overhangs and unconnected islands.

Powder Bed Fusion (PBF) is a cutting-edge AM technology that has developed through several years of research and development. Because of this advancement in technology, PBF technology is now widely used in commercial applications, especially for the production of high-value goods that are not technically feasible using conventional manufacturing processes.Commercial opportunities exist, in particular, for the manufacture of highly complex geometry in limited production quantities, such as those needed for medical and aerospace applications. Despite major contributions to technological advancement for PBF applications, there are numerous commercially important DFAM research opportunities.

Process optimization for well-known engineering alloys, the development of novel PBF-optimized materials, toolpath optimization to reduce thermal defects, and advanced topology optimization methods that use PBF processes as an optimization variable are among them

Types of Powder Bed Fusion

 

 

 

 

 

 

This technique can be used to make both metal and plastic pieces, and it can be divided into four classes based on the energy source used to melt the material.

  • Laser Fused
  • Electron Beam fused
  • Fused with agent and energy
  • Thermally fused

 

 

Furthermore, the Laser Fused technique can be divided into two types: Selective Laser Sintering (SLS), which allows only plastic parts to be printed, and Direct Metal Laser Sintering, also known as Selective Laser Melting (SLM), which allows metal parts to be printed.

Electron Beam Melting, also known as EBM, is a form of electron beam fusion in which metal powder is fused using an electron beam in a high-vacuum setting. HP’s Multi Jet Fusion (MJF) falls into the third group, in which the powder bed is uniformly heated at the start and a fusing agent is used to bind the powder to form 3D geometrical components. Selective heat sintering (SHS) technology from Blueprinter, a Danish company, uses a thermal print head to sinter thermoplastic powder to produce 3D parts that fall into the fourth group, thermal powder bed fusion.

How Powder Bed Fusion Works?

Powder bed fusion printers have two chambers: the build chamber and the powder chamber, as well as a coating roller that moves and spreads the powder around the build chamber. To prevent the molten material from corroding, the above setup is often put inside a partial vacuum chamber and filled with inert gas. You can read more about why an inert environment is preferred and why it’s relevant.

Furthermore, some manufacturers have two powder chambers on each side or on the same side of the build chamber, which are used as excess overflow chambers. A linear z-axis perpendicular to the top horizontal plane allows both the powder and create chambers to travel up and down.

While the form of powder bed fusion technique described above differs in terms of the technology it employs to create 3D components, they all follow a similar process to produce the final part.

  1. 3D CAD models are translated into cross-sections of objects and saved as.stl files. 

  1. Via the printer user interface, this stereolithographic file of the part or parts is loaded and oriented correctly. This program could be used on a computer or on a printer.

  1. The build area can be filled with multiple parts to maximize efficiency, as seen in the image below.

  1. The powder chamber is either manually or automatically loaded with powdered build material (material in powder form). This could be achieved with a hopper or a build material cartridge.

  1. A thin layer of powder is then applied to the build platform by the coating roller. The thickness of the layer defines the resolution of the pieces. After the coating roller, a scraper, a blade, or a leveling roller can be used to ensure uniform thickness of the material top layer.

  1. The energy source, such as a laser or an electron beam, is then used to selectively melt the deposited thin top layer of metal powder based on digital 2D cross-sectional data from the.STL register.
  1. The construct platform is incrementally lowered down by the resolution of the bed z-axis after that layer has been scanned and fused. The powder chamber is elevated by the same volume at the same time. This determines the component resolution as well as the powder coating thickness.

  1. On top of the fused portion of a sheet thickness, the coating roller deposits another thin layer of powder over the created chamber or base.

  1. The energy source scans and fuses the sheet once more. This layering and fusing process is repeated until the 3D object is complete.

  1. The component will be buried within the powder build chamber at the end of the print process. The powder will be extracted as shown below, leaving the fused component attached to the build plate. Although part support is not needed for powder bed fusion, the part still requires an anchor point to build from, so the part will be built onto the built plate.

  1. Wire eroding or other machining methods are then used to remove parts from the build plate. As a consequence, it’s important that the parts are built and loaded in the most acceptable orientation to prevent build errors and save time and money.

  1. The chambers may be either a separate replaceable cartridge or built-in hoppers, depending on the size of the unit.

 

Typical Characteristics and Applications

PRO

    • Low-cost – Low-cost in comparison to other options. Manufacturing costs have decreased in recent years as the cost of powder bed fusion machines has decreased.

    • No or minimal support – In most cases, no support systems are required because the powder acts as an integrated support system. However, to increase accuracy, the bottom build plate is often used as a support
    • Various materials to choose from – Ceramics, glass, plastics, metals, and alloys are only a few of the materials that can be used to create 3D artifacts.
    • Recycling powder – Powder may be recycled in some situations, but in order to get better bits, it is often important to preheat the powder, which may cause the powder to bind together.

CONS

    • Powder preheating, vacuum generation, and cooling off time all add to the build time, making it one of the slowest in the additive manufacturing industry.

    • Post-processing – Before being used, printed parts must be post-processed, which adds time and cost.

    • Weak structural properties – Due to the layer-based manufacturing process, these have poor structural properties as compared to other manufacturing processes.

    • Surface texture – Since the parts are made by fusing metal powder together, surface consistency is determined by the powder grain size and is very close to manufacturing processes such as sand casting and die casting.
    • Help the build plate – While it theoretically does not include supports, it may be necessary to provide support to prevent issues such as warping due to residual stress. In addition, most printers use a build plate to produce the pieces, which necessitates post-removal and post-processing. It is possible to reduce this by designing with it in mind.
    • High energy consumption – It takes a lot of energy to make pieces.

    • Powder recycling – Powder is expensive, but throwing away partially melted or unused powder is even more so. The powder is often preheated to speed up the printing process. This means that some powder, despite not being in the final portion, is affected by the sun.
    • Thermal distortion is another issue, which is primarily a problem with polymer parts. Fabricated parts can shrink and warp as a result of this.

Different Types of Powder Bed Fusion?






PBF is classified into many types based on the heat source used and the form of material entered. Laser beam (PBF-LB) and electron beam (PBF-EB) are the two most common styles, each with its own set of trademarked technologies. Each variant has its own set of benefits and drawbacks, so suitability can be determined on a case-by-case basis. The following are some examples:

 

SLS - Selective Laser Sintering

The SLS procedure starts with the heating of a bin of polymer powder to a temperature well below the melting point of the nylon (polyamide) or polymer. A recoating blade drops a very thin layer of powdered material onto a build platform (typically 0.1 mm).The 3D model is then used to direct a CO2 laser beam at points identified by the model. The laser fuses the nylon or polyamide powder together, solidifying a cross-section of the component.The building platform descends one layer thickness in height until the entire cross section has been sintered. The recoating blade puts a new layer of powder on top of the recently scanned layer, and the laser proceeds to sinter the part’s successive cross sections onto the prior solidified cross-sections.

The end result is a bin full of powder and  The method can be used for batch production so many parts can be manufactured at the same time. The powder bin is unpacked after the printing process is completed and the powder bin and pieces have cooled. Compressed air and a blasting medium are used to separate the solid materials from the unsintered powder. The unsintered powder is collected and reused in 50% of the cases. After that, the pieces are either ready to use or undergo additional post-processing to enhance their appearance.

Selective Laser Melting(SLM)?

SLM is a trademarked concept that is similar to SLS in that it uses a laser to provide heat (thus falling under PBF-LB), but the laser completely melts rather than sinters the powder. Metal powders such as aluminum alloys, titanium and its alloys, and stainless steel are used in this process. Exotic metals (such as tungsten) can be processed, but they are more application specific. To avoid oxidation and/or nitriding of the consolidated material, the build chamber is filled with an inert atmosphere (typically argon).

 

Direct Metal Laser Sintering (DMLS)

DMLS is a trademark of EOS GmbH, a German additive manufacturing firm, and it operates in a similar way to SLM. Despite the use of the term ‘sintering,’ absolute melting is achieved. TWI holds the distinction of becoming the first company in the United Kingdom to have a certified method for using this technology in manufacturing.

Electron Beam Melting (EBM)

EBM is a similar method to SLM, but it uses an electron gun instead of a laser (hence a PBF-EB process). The construct chamber uses a vacuum instead of an inert atmosphere due to the use of an electron beam, but a limited amount of inert gas (typically helium) is used to enable better process control.

 

 

 

 

Post Processing

PBF parts are often subjected to post-processing in order to enhance their suitability for their intended applications; this is particularly true for metals and alloys. This could happen for a number of reasons:

  • Enhance the mechanical properties (via heat treatment)
  • Reduce the stress levels (via heat treatment)
  • Improve the finish of the surface (using chemical or laser polishing, as well as abrasive grit blasting)

What are the Advantages Of Melting
Powder Bed Fusion?

PRO

  • Material waste and prices are minimized (superior buy-to-fly ratio)
  • Production cycle times have been reduced.
  • Rapid prototyping and low-volume manufacturing are now possible.
  • able to build functionally graded parts
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  • Parts that are completely customized on a batch-by-batch basis, obviating the need for set designs.
  • As opposed to other additive manufacturing techniques, it has a high resolution.
  • Powder that hasn’t melted can be recycled effectively.
  • Ability to join a variety of materials such as ceramics, glass, plastics, metals, and alloys.
  • The need for machining fixtures is no longer needed.
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What are the Applications of BF?

PBF processes are used in a variety of industries for a variety of applications. The medical industry, for example, uses the process to create customised orthopaedic components like titanium alloy cranial or acetabular implants. PBF processes are gaining a lot of interest and use in the aerospace industry, both for military and commercial aircraft. The PBF-made fuel nozzle on General Electric’s GE9X engine, which is used on Boeing 777 aircraft, is an example of this. The GE9X is the world’s largest turbofan engine, and the additively manufactured nozzle is five times more durable than previous versions; the Boeing 777 has 300 additively manufactured parts for its two GE9X engines. PBF techniques were used in the manufacturing phase of Koenigsegg’s new hypercar, the “One:1,” from rapid prototyping to ensure various details of the car looked and worked as planned to incorporate it to produce metal parts for production vehicles.