Additive Manufacturing Techniques
7 different Additive Manufacturing techniques each with their own benefitsAdditive Manufacturing at its summary level involves adding material to create a form, rather than the traditional machining techniques that remove material from a block to form the shape, that or assemble multiple parts.
To add material to the base and create the designed part, thin layers are fused on top of each other, the layers determined by slicing the design model into the correct thickness.
Additive Manufacturing processes determine how these layers are built on top of each other. There are 7 of these additive manufacturing processes:
Powder Bed Fusion
This is the process adopted by Freeform Technology, and enables us to deliver highly accurate and versatile additive manufacturing capabilities to our clients.
Powder Bed Fusion involves spreading a fine powder across the base of the build plate, in our case we use a fine Aluminium powder in our SLM 280 print machine, using a blade. 2 Laser beams then melt/sinter the powder to fuse together. The powder is melted as dictated by the layer slice of the part design file.
Once fused, the base is then dropped to allow the next layer to be spread and sintered in the form required.
Eventually, the part is formed and the excess powder scraped away to be used on the next run.
We have chosen to invest in the Powder Bed Fusion process because of the versatility of the process in effectively printing complex geometries and delivering a part that is highly accurate and requires minimal post-print finishing.
What does this mean for you? It saves you time and money.
Direct Energy Deposition (DED)
Directed Energy Deposition (DED) does not use a layer of powdered material on the base plate, instead it melts wire, filament feedstock or powder using a laser, electric arc, or electron beam gun directly on the arm, depositing material on a layer by layer approach with the baseplate moving vertically to accommodate the multiple layers.
DED has the ability to control the grain structure of the part to a high degree, ultimately being useful for repair applications of high-quality parts. A balance is needed between surface quality and speed, the latter being sacrificed for accuracy and the required microstructure.
One downside to DED is that the finish can vary depending on material, and material selection is limited to only a few.
Sheet Lamination
There are two forms of sheet lamination; Laminated Object Manufacturing (LOM) and Ultrasonic Additive Manufacturing (UAM).
UAM uses sheets or ribbons of metal, including aluminium, titanium, copper and stainless steel. These sheets are fused together using ultrasonic welding as the design dictates, with the unfused material being removed post-printing.
The metal is not melted during the UAM process which leads it to being fast, low-cost and easy to handle.
LOM is a very similar approach using paper and adhesive instead of the ultraviolet welding used in UAM. Laminated Object Manufacturing is often used within construction for visual and aesthetic models that aren’t suitable for structural use.
Binder Jetting
An Additive Manufacturing process similar to Powder Bed Fusion, Binder Jetting lays a fine layer of material on the baseplate. A second print head then moves across and deposits an adhesive layer onto the powdered material in the areas that need to be fused.
The base plate then moves vertically and the cycle repeats. Once completed, the part is heated in an oven to cure the binding agent.
Binder Jetting can accommodate many materials, including metals, ceramics, and polymers. In the instance a polymer and a ceramic is used, different colours can be included on different layers to make a part more aesthetically pleasing.
There are multiple benefits to Binder Jetting. It’s generally faster to print a part, and different variations of the powdered material and the adhesive gives rise to variations in mechanical and structural properties.
However, parts made using the Binder Jetting process are not normally used for any structural parts due to a lack of strength caused by the binder material.
There is often also a requirement for multiple post-printing processes that can add to overall delivery time and cost including heat treatment, vulcanising etc.
Material Extrusion
Trademarked by the company Stratasys, Fuse Deposition Modelling (FDM) is a common material extrusion process.
Similar to all other additive manufacturing processes by constructing the part layer by layer, it perhaps has most in common with DED. Material, often spooled, is fed through a nozzle and placed onto the part structure layer at a time.
The difference being that the material is heated at a constant temperature and fed at a constant pressure to achieve its result, rather than DED which uses an energy source to melt the material as it is added as a layer.
FDM is inexpensive relative to other additive manufacturing processes, and it can deposit ABS plastic as a material which has good structural properties.
However, the accuracy and finish of the final piece are relatively poor, controlled by the nozzle thickness and the constant pressure requirement.
VAT Polymerisation
Possibly the most different Additive Manufacturing process to the others is VAT Polymerisation (also known as stereolithography) , which constructs the design from a vat of liquid resin that is hardened as needed by an ultraviolet light.
The UV light builds the part layer by layer as the bedplate is moved vertically downwards on the completion of that curing of the preceding layer.
One limitation of this process is the requirement to include support structures within the print profile, dissimilar to other methods that are supported by the material itself.
Only available to be used with photo-resins, this expensive process does deliver a high level of accuracy relative to other processes.
Material Jetting
Often compared to an inkjet printer, Material Jetting, instead of jetting drops of ink it jets tiny droplets of liquid plastic on a layer by layer basis to form the shape.
A UV light cures and hardness the plastic after the printer head jets the liquid into place to produce a structurally sound part.
Limited to plastics and polymers, Material Jetting enables engineers to print parts which contain multiple materials and multiple colours at high accuracy and with low waste.
At the same time as printing the part, the process also prints out support structures using different materials that are then broken off after the process is complete.
