The Evolution of Strength in FDM 3D Printing

Fused Deposition Modeling (FDM) is one of the oldest and certainly the most widespread 3D printing process across the additive manufacturing user base (professional and hobbyist) today.

FDM is actually a trademarked term, coined by Stratasys, when the company’s founder, Scott Crump, pioneered the technology in the 1980’s. The filament extrusion process has expanded greatly, thanks in large part to the emergence of the open source RepRap project (2007) that has spawned a far-reaching community of users of these open-source machines as well as a high number of commercial operations developing 3D printers and/or filament materials based on this process — often also called FreeForm Fabrication or Fused Filament Fabrication.

From the earliest days, 3D printing has always involved an inter-dependent relationship between hardware and materials. This is true of any manufacturing processes, actually, whereby material selection is based on application functionality in relation to how the manufacturing processes will influence the material properties of the final product specifically with regard to its intended application.

Breaking down application areas into the three most basic categories — prototyping, tooling and manufacturing / production — the FDM process, from its earliest origins, has demonstrated huge capacity for reducing the time and costs involved in determining form and fit prototypes. However, due to material limitations, notably around strength, functional capabilities remained limited for many years in terms of prototyping, tooling and manufacturing.

The mechanical properties of 3D printing materials within an industrial manufacturing context are still often cited as a limitation for the FDM process (indeed many 3D printing processes), however, this belies the real progress that is being made and the evolving range and capabilities of FDM materials available on the market today.

Two of the most common filament materials used for the FDM/FFF 3D printing process are acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA). These are generally favored due to their compatibility with desktop extruder set-ups and (relative) ease of use. Alternative filament material types such as Nylon variations and Polycarbonate (PC) are increasing in use with 3D printers, with specialist filament manufacturers also developing PET and other composite variations. This is true for both desktop 3D printers and industrial focused 3D printers. However, if we narrow the scope down to industrial 3D printers, the materials palette for FDM/FFF particularly with regards to mechanical properties and strength is interesting to consider.

The desired “strength” requirement, as ever, is application dependent and like ANY manufacturing application, trade-offs are involved, in terms of other desired material properties and/or functionality demands, such as weight, chemical resistance and ESD etc.

Beyond the material properties themselves, however, the FDM process is also crucial in determining the final output, including the strength of the resulting part. This can be controlled, to a certain degree, by the specified density of the printed part; whether solid, partial, or hollow. The notable limitation of the FDM process, in terms of strength, is the nature of the fused layers in the Z axis, where inherent weaknesses can exist.

Strong Materials for FDM

As the pioneer of FDM, Stratasys, unsurprisingly, offers a range of functional materials and materials blends, two of which are focused primarily on strength. Under the trade name of ULTEM, which is actually a thermoplastic named Polyetherimide, or PEI, ULTEM 9085 and ULTEM 1010 have been developed.

ULTEM 1010 offers the highest heat resistance, chemical resistance and tensile strength of any FDM thermoplastic, according to Stratasys, and the certified grade (ULTEM 1010 CG) of this material is biocompatible and approved for food contact with NSF 51 and ISO 10993/USP Class VI certifications. Full mechanical properties can be viewed here.

In addition to notably high tensile strength, ULTEM 9085 is also FST rated, which means it satisfies flame, smoke and toxicity standards, characteristics that remain unchanged throughout the FDM process (FORTUS). ULTEM 9085 also offers a high strength-to-weight ratio and is produced in accordance with strict procurement requirements for documentation and traceability. Full mechanical properties can be viewed here.

As mentioned earlier, required material properties for a given application require trade-offs. This is true for all manufacturing processes and materials and often no single material offers a perfect solution. To this end, composite materials (blends) can offer suitable answers for specific applications.

One such solution is PC-ABS for FDM, which provides the most desirable properties of both PC and ABS materials. According to the company, it offers the superior mechanical properties and heat resistance of PC — including one of the highest impact strength ratings of all FDM materials — and the flexural strength, feature definition, and surface appeal of ABS.

A white paper from Stratasys provides insight on another interesting material from the company focused on thermoplastic strength, in combination with electrostatic discharge (ESD) safety, namely ESD PEKK (dissipative polyetherketoneketone). This is an R&D material and not commercially available, but the material does indicate further progress, building as it does on Stratasys’ existing experience with ULTEM 9085 and ABS-ESD7. Effectively, the PEKK material combines the favorable mechanical properties of both materials.

Final Word

Probably needless to say, but this post is focused solely on the FDM process and the advances made around this singular 3D printing technology. Similar evolutionary developments are also visible for other additive techniques when it comes to strong and stable materials. But, as always, the application is the key, and finding the right solution in terms of strength but aligned with economic viability and added value is the goal.

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