FDM 3D Printing - Fused Desposition Modelling

FDM printers are the most common 3D Printing technology. Quick and cheap prints, make them ideal for prototyping. They are also used for custom thermoplastic parts.

FDM printers are the most common 3D Printing technology. Quick and cheap prints, make them ideal for prototyping. They are also used for custom thermoplastic parts.

FDM printers are the most common 3D Printing technology. Quick and cheap prints, make them ideal for prototyping.

FDM 3D Printing - Pros

Fast Print Times
Cost Competetive prints
Wide range of materials

Fast Print Times
Cost Competetive prints
Wide range of materials

Fast Print Times
Cost Competetive prints
Wide range of materials

FDM 3D Printing - Cons

Visible build lines
Supports needed
Post processing often neccesary

Visible build lines
Supports needed
Post processing often neccesary

Visible build lines
Supports needed
Post processing often neccesary

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What is FDM 3D Printing

 

FDM printing works in the same way as conventional 2D printers. Producing an image by moving from one side to the other, line by line. However with FDM 3D printing the 3D object is built, layer by layer. One on top of another. This is achieved by heating a material to a desired temperature and extruded through a nozzle. This follows a pre-determined path until the object is complete. The minimum layer hieght for FDM is 0.1mm.

Fused deposition modelling Materials

 

Thermoplastics, in the form of filament on spools, are used for FDM 3D printing. There are normally 1.75mm or 3mm in diameter. FDM filament are generally the cheapest materials used in 3D printing. In addition they start at around $20 – $40 per roll for PLA and ABS. These come in a range of different colors. However, for higher performance filaments like PEEK, you can be looking at upwards of $500.

 

As shown in the pyramid, the higher the temperature required to melt the plastic, the higher the engineering properties. Futhermore the higher the cost. This is due to increased quality of machinery used. Finally, for filaments like PEEK industrial machines must be used. This is because they provide better control over the printing environment.

Traingular chart comparing performance over cost of FDM 3d printing materials

Common Material Properties

ABS

Good mechanical properties

Good temperature resistance

Susceptable to warping

PLA

Most common 3D printing plastic

Easy to 3D print with

Lower impact strength, elongation and temperature resistance than ABS

Nylon (PA)

Suitable for finished prints

Good flexibility

Excellent chemical resistance

PETG

High impact and chemical resistance

Good heat resistance

Susceptable to warping

TPU

Flexible rubber like parts

Good elongation

Difficult to print accuratly

PEI

Excellent strength to wight ratio

Fire and chemical resistance

High cost

FDM technology illustration - fdm 3d printing

FDM Perameters

 

This image shows the general mechanics of most FDM printers. There are many variable parameters. These include:

 

 -Build speed

-Max build Volume

-Nozzle temperature

-Layer height (microns)

– Build density (Infill)

– Heated bed

 

The nozzle diameter and layer height (microns) are the variables that determine the dimensional accuracy of a model. So, a small nozzle and low layer height are required for a smooth finish, and furthermore high detail.

 

The maximum build volume must be considered for any 3D printed part or model. The average volume for a desktop printer in 200 x 200 x 200 mm. Whereas, larger industrial machines can have up to 1000 x 1000 x 1000 mm. Sometimes it makes sense to break down large models into smaller components.

FDM Warping

 

Warping, or distortion happens because different parts of the build layers cool at different rates. As this occurs, the cooler sections create internal stresses that pull on the sections close by. Long flat objects are prone to warping because the perimeter of the shape cools first. This image is a prime example of distortion in FDM 3D printing. A good bed adhesion and a heated bed are the best ways to anchor model. Therefore, giving the best chance of avoiding warping. 

 

A good CAD designer should be able to mitigate these issues, before they happen. Furthermore, they can save you money, through getting the print right first time round.

Example of fdm warping, on the corner of a rectangular print.
FDM warping illustration
Photographic example of why supports are needed in FDM. Using a model of the letter T
FDM Supports
 

As you already know, FDM Printers print one layer on top of the other. But how would you print a raised layer that has nothing to print on to? This is where supports come in.

Much like scaffolding in construction, supports are structures that can be built upon. Furthermore, like scaffolding, they are removed post construction.

 

Supports are neccesary if a section ‘overhangs’ by more than 45 degrees. You can still print overhangs, below this angle, only they will suffer in quality. There are two types of supports: Standard and dissolvable. 

FDM 3d printing supports illustration. Overhangs needed for anything overhanging more than 45 degrees
Standard Supports
 

Standard Supports can be added to any CAD file. They are automatically generated in any 3D printing software. The supports must be removed by hand. In addition, sanding down is necessary if a smooth finish is required. Visible marks will appear, after it is finished. However, it is cheap to do, because the same filament is used. Therefore, making standard supports ideal for form and function testing.

Dissolvable  supports
 

Dissolvable supports are added in the same way as standard supports. However, these require a dual nozzle FDM printer. This is because, a dissolvable wax filament is used for the support structure. These can be removed in either water or solvent. In addition, no marks makes them great for high detail, quality prints. However, the process is expensive due to multiple filaments being used.

FDM Infill

 

FDM parts are rarely printed solid. Parts are printed with an internal structure, known as infill. This is one of the variable perameters in FDM 3D printing. There are several different infill structures to choose from. To the right, are a few examples.

 

A parts application determines the percentage of infill used. For example, a high percentage infill, is neccesary for high strength prints. Whereas, form and fit testing, only requires a low percentage infill.

 

Print times and costs, go up in tandem with Infill percentage. You can save yourself a lot of money with a good CAD designer with hands on 3D printing knowledge. This is because, there is a minimum cost price for most 3D printing services. This is especially relelvent, when printing small component parts.

FDM infill variations. Honeycomb, triangular, square and zig-zag.
4 Different examples of FDM 3d printing infill, ranging from 5% to 80%

FDM strengths and weaknesses

Fused deposition modelling’s greatest strength is it’s accessability. Firstly machines and materials are relatively cheap. Moreover, there is a wide range of materials and colors available. FDM is the popular choice for rapid prototyping and form, fit and function testing.

The main weakness of FDM is the anistropic nature, of parts. This is due to the layer structure, which makes parts weaker in on direction. In addition, infill has an effect on strength. The default infill, for most machines, is 20%. You can raise this percentage. However build time and costs will increase.

FDM Image Gallery