Since its inception in the 1980s, additive printing or 3D printing technology has evolved into various technologies. Today in this article we will compare the two currently most popular and versatile 3D printing methods: the hugely popular FDM printing and the Multi Jet Fusion technology which, presented in 2016 by HP, represented the most important step forward in additive technology of the last decade.
1. 3D printing with FDM technology
1.1. What is an FDM 3D printer?
An FFF or FDM printer (the acronyms of Fused Filament Fabrication and Fused Deposition Modeling basically mean the same technology) is a 3D printer that is most often used in early concept development and prototyping. The material (molten plastic) is deposited by a three-axis system in single layers and multiple layers are fused together to form the 3D model. The low purchase costs, on Amazon you will find FDM printers starting from just over €/$ 100, and the relative ease of use make this technology the most widespread among makers.
In FDM technology, a filament a) of plastic material is fed through a heated moving head b) which melts and extrudes it, depositing it, layer by layer, in the desired shape c). A mobile platform e) lowers after each layer has been deposited. For this type of 3D printing technology additional vertical support structures are required d) to support the protruding parts. Source: Wikipedia by Paolo Cignoni
1.2. How does an FDM printer work?
The 3D file of the model you want to print is processed by a slicing software (the most used and simple to use are Cura, Simplify3D and PrusaSlicer) which literally "slices" it into layers of the desired thickness and simultaneously generates a file in G- code that describes to the printer the movements of the axes necessary to create the piece itself. Then the FDM printer melts the solid plastic filament and extrudes it from a layer-by-layer nozzle thus forming the 3D object on the build plane. The layers generally have a thickness ranging from 0.1 mm to 0.5 mm but which can also be outside these values depending on the purpose of use of the object being created.
1.3. What are the most used materials in FDM printers?
The two most used materials in FDM printing are ABS (acrylonitrile butadiene styrene) and PLA (polylactic acid). Both are inexpensive and available in a variety of colors.
PLA: it offers a surface quality among the best in FDM printing, it is one of the easiest materials to print and is also biodegradable but it is not resistant to shocks and temperatures above 60/70 degrees Celsius.
ABS: it offers good resistance and thermal characteristics, but needs good ventilation as it emits strong odors when printed. Requires a heated build platform to prevent warping.
FACT: professional FDM printers with prices starting from 25K € and which have heated chambers, nozzles that print at over 500 degrees and have adequate mechanics can create functional high-performance technical pieces among which the most popular are Peek, Carbon Peek, Pekk and other materials suitable for industrial use and metal replacement.
1.4. What are FDM printers typically used for?
Without prejudice to the functional solutions of the previous point, in general, designers and engineers use FDM printers in the early stages of concept exploration and in the medium fidelity prototyping stages.
Initial Concept Exploration Phase: FDM printing allows users to easily print multiple concepts to examine the shape and fit of the actual part before pursuing detailed features.
Mid-fidelity prototyping phase: FDM printing is a good compromise for testing or for prototypes that look like real production parts. In these cases, thin layers of 0.1 / 0.2 mm are generally used. This option is ideal for getting feedback on feel and performance.
Production of print runs: although it is possible to see online images of printing farms made up of dozens if not hundreds of FDM printers, this appears to be a niche solution as the low mechanical versatility of the entry materials, the slow production (10cm3/h on average for machine against about 300cm3/h of MJF technology), the need for supports, the fact that the pieces are not 100 filled, limit the applications.
Fact: there are printing farms with over 500 FDM printers!
FDM printing farm: the Prusa printing farm has over 300 FDM printers in a single room
1.5.What are the advantages and disadvantages of FDM printers?
Advantages: The most significant advantage offered by FDM printers is the low cost of purchase and operation. Because they are popular in the consumer market, low-end FDM printer models start at € 100. FDM printers are easy to use and offer fast turnaround times from concept to prototype.
Disadvantages: FDM printers do not offer the high quality, dimensional accuracy or reliable operation that other 3D printers offer. Reliability can be an issue with frequent part remakes and nozzle clogging. Ultimately, FDM is not the best choice for printing parts that need to be very good.
2. 3D printing with MJF technology
2.1. What is an MJF 3D printer and how does it work?
Multi Jet Fusion is an additive manufacturing method developed by the Hewlett-Packard (HP) company and presented in 2016. The final parts feature quality surface finishes, excellent resolution and more consistent mechanical properties than processes such as selective laser sintering or FDM.
Multi Jet Fusion uses an inkjet matrix to selectively apply fusing agents and details onto a bed of nylon or other material powder, which are then melted by heating elements into a solid layer. After each layer, the powder is spread over the bed and the process repeats until the part is completed.
At the end of the printing process, the build box is removed from the printer. An operator carefully takes parts out of the build box and removes residual dust with various shot peening systems.
Multi Jet Fusion (MJF) process scheme: (a) stages 1-5 of the fusion process); (b) 3D construction unit; (c) processing station. Source: research gate
2.2. What materials can be used with MJF printers?
MJF printing technology offers a limited range of materials but they are very versatile from a mechanical point of view. Currently there are five materials available. These materials are PA11, PA12, PA12GB, TPU and polypropylene. For an in-depth discussion we recommend you to read: HP Multi Jet Fusion (MJF) 3D Printing Materials and Properties
Being able to produce at low cost 100% filled, functional parts with complicated and detailed designs without the need for any support, this technology offers a wide range of solutions, here we will limit ourselves to the main ones:
Rapid Prototyping: Although prototypes can be created with any 3D printing technology, MJF can create robust prototypes with excellent mechanical properties to really test function and form.
Run Production: The scalability of this technology is becoming a real contender to move low-volume production away from other production methods and in particular injection molding (see the article Injection Molding vs. 3D Printing. Which is Better?) . This is particularly true for complex parts: in fact, not only with MJF technology obviously there is no need for expensive molds but besides this there are practically no design constraints normally associated with the production of injection parts.
A question that must be asked when asking whether one technology is better than another is: better for what?
Surely the arrival of MJF technology has marked an epochal leap forward in the simplicity of construction, in the quality of truly functional industrial pieces and in the ability to concretely compete with injection molding.
But it must also be said that FDM printers, albeit with a limited range of professional uses, can provide visually acceptable parts and a considerable range of materials with an investment that starts at around € 150 against the € 500,000 needed to set up a single MJF.