What is Fused Filament Fabrication?
Fused filament fabrication (FFF), otherwise known as fused deposition modeling, is a 3D printing process that utilizes a heated nozzle to extrude thermoplastic material into the shape of a part. FFF has been around since the 1980s and has continually been refined and innovated upon to become the most widely used 3D printing process. It is popular among both hobbyists and industrial communities due to its low cost, short lead times and ability to produce durable products with solid engineering properties.
Fused filament fabrication works by feeding a thermoplastic material, either in spools or pellets, through a drive system that extrudes the material through a heated print head (i.e. a nozzle) onto a build surface. The print head movement is computer controlled according to a set of input instructions created via both automated and manual inputs. Programmers can control the speed, temperature, layer height, infill settings and many other parameters through the slicing program. Once the print head has extruded an entire layer of material, the build surface lowers according to the layer height and the print head begins extruding material across another layer. This continues for thousands of layers until a completed 3D printed part is formed.
Some of the most common and influential input parameters on print success are infill density, shell, speed, temperature, support structures, layer height, and nozzle size. Utilizing the correct input parameters can yield crisp, high-quality 3D printed products, while incorrect parameters can quickly lead to print failures.
3D printed products are often not printed as fully dense objects, but rather, to save time and material, are printed with hollow interiors and the infill density setting determining how dense the interior of the part is. Common infill densities range from 10-20% as this provides a good balance between speed, cost, and strength of the product.
While the interior of 3D printed products are mostly hollow, the parts are still given a solid outer shell. The minimum wall thickness of most 3D printers is 1 mm, so the shell thickness is typically larger than 1 mm and is fused together with the internal infill structure of the product.
Two of the most critical input parameters for fused filament fabrication are the temperature of the nozzle head and the temperature of the build surface. Proper settings for both heavily depend on the type of material. If a high warp material is being used then the temperature of the build surface needs to be hot enough to prevent warping, while the nozzle temperature needs to be hot enough to ensure proper layer adhesion. Materials like ABS and polycarbonate are especially prone to warping and require their temperatures to be carefully monitored to achieve successful prints. However, printing at too high of a temperature can also create issues as temperatures that exceed a material’s glass transition temperature to a large degree can denature the material and not print product features properly.
Print speed and travel speed directly influence the time required to 3D print an object and would need to be inline with the temperature of the print head as a faster print speed will require more material to be liquified in a shorter period of time and thus a higher nozzle temperature would be required. The speed is limited by how much the drive system and print head can successfully extrude in a given time, if the print speed is too fast, then the product will have air gaps that can compromise the mechanical and aesthetic properties of the part.
Support structures are required when a product design requires the printer to print overhanging features. Fused filament fabrication needs to extrude molten plastic material into the previous layer of material and melt both the prior layers and current layer to create proper interlayer adhesion. The print head cannot do this if it is printing in mid-air. For this reason, support structures are required when building overhanging features. They can be made out of the same material as the product or a dissolvable support material can be used whereby the part is simply soaked in a solution after printing that dissolves the support structure. Overhang angle and overhang density are the main input parameters used to control the support structure. Supports are typically required when the overhang angle exceeds 60%, while most support structure densities are between 10-30%.
Layer height is used to determine the resolution of the product. Lower layer heights can create finer details with less visible layer lines. Layer lines are most visible in 3D printed products manufactured through fused filament fabrication techniques as the layer resolution is limited by the size of the nozzle. However, fused filament fabrication can typically achieve layer heights of 200 microns.
Nozzle size refers to the size of the opening from which the thermoplastic material can be extruded onto the build piece. Nozzle sizes can range from 0.2mm to 1.2mm in diameter and while smaller nozzle sizes can achieve higher print revolution, they will also take much longer to print complete when compared to larger 0.8-1.2mm nozzles.
Minimum Wall Thickness & Feature Size
In order to maintain a crisp part without deformities and accurate features, the minimum feature size of FFF 3D printing is 2 mm and the minimum wall thickness is 1 mm. Attempting to print smaller features and walls using FFF will result in deformities and quality defects. When finer features are required, a laser based method, such as SLA or binder jetting should be utilized.
Mechanical Properties of FFF Parts
3D printed products made with fused filament fabrication typically have good mechanical properties relative to other 3D printing techniques. Like all 3D printing methods, FFF parts are anisotropic, meaning that they are stronger in the X & Y directions than they are in the Z direction, however, programming proper layer adhesion parameters can mitigate this property.
FFF parts are also prone to warping because as the print head is adding material to the part, different areas of the part are heating and cooling at different times. This uneven cooling can add internal stress to the part which can cause deformation, or warping, of certain features. Long thin unsupported features are prime targets for warping, as are large flat features, small protruding details, and sharp corners. However, utilizing proper print parameters and design for additive manufacturing principles can mitigate warping.
Fused filament fabrication offers a wide range of materials to choose from with excellent mechanical and thermal properties including ABS, nylon, polycarbonate, and even composite materials such as carbon fiber and fiberglass reinforced thermoplastic materials.
|Material||Tensile Strength (break)||Tensile Modulus (stiffness)||Durability||Heat Distortion Temperature|
|PLA||53 MPa||3447 MPa||1 KJ/m||52 C|
|ABS||32 MPa||2265 MPa||13 KJ/m||98 C|
|Carbon Fiber||100 MPa||6000 MPa||60 KJ/m||155 C|
|ASA||40 MPa||1726 MPa||15 KJ/m||96 C|
|Fiberglass||95 MPa||4000 MPa||80 KJ/m||160 C|
|Nylon||42 MPa||1600 MPa||30 KJ/m||105 C|
|Polycarbonate||62 MPa||2048 MPa||26 KJ/m||113 C|
|TPU (Flexible)||39 MPa||26 MPa||34 KJ/m||74 C|
Fused filament fabrication is used in a variety of industries and applications including:
- Product Designers
- Consumer Products
Each of these industries and users can use fused filament fabrications to perform several different tasks throughout the product lifecycle including:
- Concept models
- Functional prototypes
- End-use parts
- Casting patterns
- Marketing materials
- Classroom and workplace visual demonstrations
Advantages and Limitations of Fused Filament Fabrication
To summarize, here are some of the main advantages and current limitations of fused filament fabrication when compared with other fabrication methods.
- Low cost
- Fast lead times
- Wide range of materials
- Visible layer lines
- Can’t print as fine of details as laser based 3D printing methods such as SLA