In this article, 3DWhip shares with you the basic principles and an introduction to Fused Filament Fabrication (FFF) or Fused Deposition Modeling (FDM) technology. At the end of this article, you will have a better understanding of the FFF or FDM process. You will come to know the various polymer materials and the important parameters which are responsible for creating good 3D prints.
What is Fused Filament Fabrication?
Introduction to Fused Filament Fabrication (FFF) or Fused Deposition Modeling (FDM) is an additive manufacturing process. The process creates an object by adding molten plastic material (filament) layer-by-layer in a predetermined path. This predetermined part is generated from a 3D model and machine instructions know as G-Code.
FFF or FDM is the most widely used 3D printing technology found in commercial and industrial settings. The manufacturing process makes use of specific machines know as FDM 3D printers. These printers are able to create printed objects and are the first introductory level manufacturing systems people are exposed to. This article will cover the basic operations and key aspects of FFF or FDM 3D printing.
What Is An FDM or FFF 3D Printer?
An FDM 3D printer is an electro-mechanical machine designed to move in both the horizontal and vertical directions (X, Y and Z directions) using numerical controlled motors. The major parts responsible for creating physical 3D objects found on an FDM 3D printer are the extrusion nozzle (printer nozzle), the heating block and the build platform. Plastic or metal material wound into spools (filament spool) are feed to the printers heating block and the printer nozzle by the feed mechanism. At this point, the material is heated until it is molten and extruded through the printer’s nozzle and applied to the build platform. After the first layer is applied to the platform, the platform moves down to allow for the next layer to be applied. This process is continuously repeated until the final object is created.
Factors Influencing FDM or FFF Printing
There are a large number of factors which influence creating the perfect 3D printed object. The most important factors, however, include the printers parameters, print warping, layer adhesion, support structure, infill and shell thickness of the part.
3D Printer Parameters
The printers parameters are dependent on the type of fused filament fabrication (FFF) 3D printer being used. Even though there are a large number of FDM printer variations on the market, they all have a few common but important functions. These include temperature control for both the nozzle and the build platform (in some printers), the print speed, cooling fan speed, the print layer height and the printers build size.
Most commercially available FDM 3D printers have an average build size of 200 x 200 x 200 mm, while industrially available printers may have an average of 1000 x 1000 x 1000 mm. The average layer height (height of each layer of plastic or metal) ranges between 0. 005 mm to 4 mm.
The smaller the layer height (closer to the 0.005 mm range), objects created will have extremely high detail and excellent surface finish. The larger the layer height (closer to the 4 mm range), objects will have very little detail and dimensional accuracy but are cheaper to make. In general, a trade-off between layer height, print time and cost will need to be decided, depending on the purpose and type of object being created.
Print warping is considered to be a common defect in the FDM or FFF printing process. This defect is usually caused when the applied molten material applied to the build platform cools at different rates. As the cooling rates between the printed layer and the newly applied molten layer change, a build-up of internal stresses are created. These internal stresses pull the underlying printed layer upwards resulting in print warping. Warping of 3D printed objects usually occurs at the base of the object (contact between the printed layer and the build platform).
The most common object shapes which are prone to warping include:
- Sharp corners in the object’s design.
- Large flat areas.
- Thin protruding features.
- The material type used to print the object.
Simple solutions to these defects include a heated build platform, printer with a chamber and increasing adhesion between the object and the build platform.
Layer adhesion is a critical factor in the 3D printing process. This determines whether your object will firstly be securely printed to the build platform and secondly determine the strength of the final printed object due to the layers applied.
When the molten material is extruded through the nozzle, it is pressed against the previously printed layer. The molten layer melts into the underlying layer which bonds the two together. Since the layers are pressed against each other, the outer sides (object surface) are deformed into an oval shape. This creates a wavy surface finish usually called layer lines.
As the FDM or FFF process builds an object one layer at a time, objects which have overhangs (no contact with the build platform) requires supporting material. This is due to the molten material which cannot be deposited on thin air.
The surface finish, which is in contact with support material usually differs in quality when compared to the non-supported surface. This is an important factor when designing the object for 3D printing. A rule of thumb commonly used is to design the object to require the least amount of support material to achieve the best quality print.
The material used to create supports is usually the same material as the printed object. In high-end professional desktop printers, the water-soluble support material is also available.
Infill & Shell Thickness
When objects are 3D printed using FDM or FFF methods, they are normally not printed solid. This is because it increases print time and cost (using more material). Two techniques are used to create a standard 3D printed part. The first section includes the prints shell which is the outer perimeter of the object being printed. The second section is the prints infill density which forms the internal structure of the object.
The combination of infill and shell thickness will determine the strength of the 3D printed object. A rule of thumb for FDM printers is to have an infill density of 20 % and a shell thickness of 1 mm. This is considered as a good trade-off between object strength and print speed.
Common FDM Materials (Filament)
One of the advantages of the FDM technology is the wide range of available materials (filament). 3D printing materials are continuously advancing from standard material types to composites (a mixture of materials). In general, available materials are broken into three categories. These categories include commercial materials, engineering materials and high-performance materials. Printing temperature, material performance and costs increases as materials are found closer to the high-performance material category. It is important to realise the purpose of the intended object, the mechanical properties needed for the object and the available cost when selecting the appropriate material to print with.
Post Processing the 3D Print
An advantage of using FDM 3D printed objects is the ease of post-processing. Post-processing a 3D printed object can create finishes which have an extremely high standard. Various techniques and methods can be used to post-process a 3D object are summarized in the table below.
|Cold Welding (Gluing)||Vapour Smoothing|
|Epoxy Coating||Metal plating (Electroplating)|
A recap of the key points and characteristics of the FDM technology is summarized in the table below.
|Properties||Fused Filament Fabrication (FFF) or FDM|
|Materials||Thermoplastic & Metal|
|Dimensional Accuracy||+- 0.5 mm Desktop|
+- 0.2 mm Industrial
|Average Build Size||200 x 200 x 200 mm Desktop|
1000 x 1000 x 1000 mm Industrial
|Average Layer Height||0.05 mm – 4 mm|
|Support Material||Dependent on Design (Not Always Needed)|
Rule of Thumb
- Design objects that don’t require a lot of support material.
- Objects to have an infill density of at least 20 % and a shell thickness of at least 1 mm.
- Avoid large flat areas in your part to prevent warping.
- FDM can produce objects which can be prototypes and functional parts.
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