FFF vs FDM 3D Printing Explained
What is the Difference?
When most people think of 3D printing, they usually think about filament manufacturing Deposition Modeling (FDM) which has existed since 1988. However, it wasn't until over 20 years later that 3D printing gained traction and popularity.
In 2009 the patent on FDM 3D Printing expired, paving the way for new, lower cost 3D printers using a similar printing process called Fused Filament Fabrication (FFF). With the advent of these low cost printers, 3D printing became both tangible and accessible to everyone, making it possible for consumers to own their own 3D printer. This sparked conversations about 3D printing and its capabilities as more and more tinkerers were adding them to their home workshops which lead to a media buzz in 2014 that made 3D printing more common place.
Unbeknownst to the average consumer - this new lower cost printing process is very different than what has been on the market for the past two decades. Early adopters of 3D printing like GE, Airbus, BMW & Ford have been using FDM 3D printing for decades as a tool for designing low volume specialized manufacturing jigs, fixtures & parts using large industrial grade additive manufacturing machinery. While this new 3D printing technology was superficially similar to FDM, the actual results were wildly different.
If these low cost FFF consumer printers serve as initial exposure to 3D printing for engineers, designers and other professionals there is the potential for a negative perception about 3D printing especially if they receive a part output that is not up to the mark. This may lead them to refrain from choosing 3D printing again if they find the FFF 3D printed parts have a poor quality, strength, surface finish, or are "just not there yet" as we hear commonly in the industry. Those settling for a subordinate process (FFF) are not exposed to the scope and potential of other 3D printing technologies.
The FFF 3D printing process being touted during this media buzz was actually a very simplified version of what global companies have relied on for the past two decades to fuel their manufacturing process. Consequently this led to an incongruous expectation of what FDM (and other industrial printers) can really achieve, thereby inadvertently undermining these larger industrial machines & their applications.
What Makes FDM Better than FFF?
Fused Depositon Modeling (FDM) are large enclosed machines that cater to part applications requiring high quality, engineering-grade prototypes that can withstand mechanical loads. Parts printed in FDM are capable of achieving an accuracy of ± .127 mm (± .005 in.) which is one of the highest tolerances of any 3D printer on the market. Fused Filament Fabrication (FFF) usually caters to part applications requiring prototypes for form and visual validation and are not capable of holding consistent tolerances. While not everyone may require parts with high tolerances, or mechanical properties, here we explore what makes these printers different.
In FDM the deposition process is contained in a print chamber that is maintained at about 90ºC for ABS (or higher for advanced materials). This oven is completely isolated from the ambient environment allowing the filament to flow from a hot extruder of about 320ºC through a heated environment onto a hot build platform. This hot-hot-hot transition leads to better mechanical properties, significantly increases layer to layer adhesion strength and prevents warping and curling during filament deposition.
FFF printers have no heated chamber, and as a result the material filament traverses from a hot extruder through a cold or unevenly heated ambient environment onto a hot build platform. This transition from a hot-cold-hot medium results in the generation of residual stresses in the part being printed and makes the part output and quality very different. This difference in part output quality is due to the immediate cooling of plastic during the extrusion processes as it leaves the print head, negatively affecting both mechanical properties and tolerances.
Fused Filament Fabrication 3D printers do not have enclosed ovens because of a patent that Stratasys owns on thermal separation between the heated build chamber and a gantry that controls motion. In Stratasys FDM printers, the motors sit on the outside of the enclosed space whereas FFF printers use heated beds to increase the ambient temperature of the chamber and increase bed adhesion. This "hack" however is less that perfect, and causes uneven cooling often results in uncontrollable tolerances, and surface defects.
This ultimately limits what plastics can be printed effectively with PETG and PLA being very popular because of its minimal shrinkage - but outside of these materials, most advanced material is very difficult to print on anything less than a FDM machine.
FDM is capable of printing in some of the strongest plastic materials commercially available, including Polycarbonate, Nylon, ULTEM & PEEK. This is made possible by FDM's enclosed ovens, as well as very strict quality control in their filament manufacturing process. While FDM filaments tend to cost a bit more than hobbyist filaments, there is a significant amount of strict ISO guidelines quality & traceability guidelines that these manufacturers follow. If you look at 3D printing filament head-on it should be a circle, but along a stretch of filament the cross section can change from a circle to an oval. If filament is inconsistent across its either its’ diameter or length , this will change the rate of material extrusion resulting in poor surface quality, mechanical properties & part accuracy
One of the trade offs made in low cost filament is consistency in cross sectional area which is often quite variable due to much lower standards of filament producing for FFF 3D Printers. FDM filament manufacturers use a laser as part of a quality control mechanism to ensure correct diameter, whereas the quality control process for FFF filaments is often much more lax.
Barring minimum feature size or wall thicknesses, you will rarely find a geometry impossible to 3D print with FDM due to the dual extrusion technology. FDM 3D printers always use a soluble support material that dissolves in minutes inside of a heated ultrasonic tank. This means no damage to the part and no waiting for PVC to dissolve in water. Each FDM support material is specially designed to print with a specific thermoplastic ensuring perfect results no matter what oven temperature.
FFF printers are only recently starting to develop dual extrusion, often using a support material called PVA which is an abbreviation for polyvinyl alcohol, a water-soluble material. This support material was specifically designed to print with PLA and generally works fairly well as it it requires the same operating conditions and temperature of PLA. However issues of delamination, warping and surface quality issues become apparent when using PVA to support higher temperature materials such as ABS, PC or other more advanced filaments.