One of the classifications of additive manufacturing process is powder bed fusion process (PBF). PBS process works when a powder bed layer is selectively fused by using any one of the energy sources namely a laser or an electron beam for production of a 3D object.
In order to understand PBF process it is evident that we know the difference between sintering and melting. Sintering basically combines all the materials by heat and pressure. Sintering is a process wherein any form of melting is not involved, melting on the other hand combines the particles by heating them till the time they liquefy and form into a single substance
Powder Bed Fusion 3D printing technology is best known for its ability to generate photorealistic products with utmost accuracy. The PBF 3D printing technique allows the manufacturing of complexly shaped products, using a laser, to fuse powder particles one over the other in the form of layers, therefore forming a solid chunk. This is one of the most mature metal additive systems. Powder bed fusion is apt for designing a new component, and is useful in iterating on designs rapidly This is one of the most accurate ways in dealing with a more efficient process in manufacturing of highend 3D parts.
This technique encompasses of the following commonly used printing techniques, on the basis of the energy source it uses to melt the material, these are as follows-
Selective laser sintering (SLS)
Selective laser sintering (SLS) is a very well known process for 3D printing of polymer powders. The powdered material is then spread across the bed, and is selectively melted using a laser beam. The process is repeated till the time the entire procedure is completed
Direct metal laser sintering (DMLS)
DMLS is widely utilized 3D printing process, almost same as SLS which uses a computer-controlled, high-power laser beam to melt and fuse layers of metallic powder together. The only difference between SLS and DMLS is the material used for the process.
Selective laser melting (SLM)
In Selective laser melting, the powder particles are melted completely. In this process a laser is used to melt the powder particles.
Electron beam melting (EBM)
This is another powder bed fusion process for metals. This is similar to SLM the only difference is that EBM uses electron beam as energy source. This requires a vacuum that can be used with metals and alloys for creating a functional part.
Selective heat sintering (SHS)
This is a comparatively lesser known technique for 3D printing. In comparison to any other approach to 3D printing, SHS works mainly by applying heat to the various layers of powdered thermoplastic, with the help of a thermal printhead.
Table of Contents
Working of Powder Bed Fusion
To begin with the PBF process we have to spread the powder layer, the powder is loaded into a reservoir in the machine. Similar to any other 3D printing process, even in powder bed fusion, a 3D CAD file is generated and is filled up into the machine.
Then comes the procedure of scanning, every layer is sorted into a number of segments called “islands”. The system uses one fiber layer to selectively fuse the powder bed layer. This entire process is performed under a built chamber, which has inert gases mostly argon or nitrogen gas.
The powder chamber is filled with powdered build material either manually or through an automated process. A laser then works on the cross section of the part, with the forwarding of the process, the powder particles liquifies and fuses to one another and ends up creating a solid part.
Post creation of first layer, the print bed moves down. This process of layering is repeated many times, until the full product is generated. During the process of printing, the print volume is filled with a gas to improve the quality of the print, by displacing any reactive impurities from the air that can cause any form of quality hindrances. After the printing process is done, the remaining or the leftover powder is collected and sent for recycling.
These processes combine together and form/manufacture fully heavy metallic parts from these wide range of metal alloys namely stainless steel, cobalt chrome, aluminium alloys and tools steels etc.
Word of caution
The power mode fusion uses very fine metal powder, that has to be handled with considerable caution. The powder is a respiratory and a flammability hazard. For anyone getting into PBF process, it is highly important to focus on getting the right safety equipments and take proper precautions.
The Powder bed fusion process mainly uses the powder based materials, commonly used metals and polymers includes Nylon DMLS, SLS, Stainless Steel, Titanium, Aluminium, Cobalt Chrome, titanium, Cobalt Chrome, al and copper.
- Material which is not utilised, in the process can be recycled thus material wastage is reduced.
- Powder Bed Fusion process is apt for visual models and prototypes
- The powder part of the process portrays as an integrated support structure
- There is great flexibility in the material usage
- The process lacks structural properties in materials
- Powder Bed fusion works around with materials that are expensive and have relatively slow and long print time
- The procedure requires a lot of energy and power to create parts
- Thermal distortion causes the shrinking and warping of fabricated parts
- Post-procession of printed parts before usage adds to time and cost
Future of Powder Bed Fusion
Since its invention, powder bed fusion has been rapidly evolving and has proved to be a very necessary invention in the field of science. Its future lies to a large extent in the demands and requirements of industries such as aerospace, biomedical, defense, and automotive. This trend of utilizing powder bed fusion will continue to drastically grow into the future and will thereby assist in the transformation of manufacturing to a much smarter, fasted, and visually appealing manufacturing of products.
New advancements in PBF over the past few years have outdone all of the accumulated developments in the previous twenty years. The segment of 3D technology, that was led for so many years by a single dominant player is now transforming into an inquisitive and a resourceful marketplace of innovation and new ideas, with the help of powder bed fusion.
History of Powder bed fusion
During the years of early 1990s, several companies began exploring and experimenting with the process of Powder Bed Fusion (PBF) as a part of 3D technology. The process in the initial stages starts with melting of the metal powder particles, using a heat source, layer by layer. In 1994, EOS patented its process called Direct metal layers sintering (DMLS), not much later in 1995 the Fraunhofer Institute introduced the term SLM for Selective Laser Melting. The two techniques together comprise the process of Powder Bed Fusion.