• Jordan

What is FDM?

Updated: Jan 19

Imagine a regular 2D printer, you can print any shape or design onto a flat piece of paper and the printer will deposit ink on any part of the paper to produce your design. Now imagine doing this repeatedly over and over again on the same piece of paper to build up layers, this is essentially what a Fused Deposition Modelling (FDM) printer does.

Monocolour photo of a 3D printer building a small support structure

However rather than depositing ink like a traditional paper printer, a FDM printer deposits filament material. A FDM printer produces a 3D object gradually using layers, each layer printed is 2D just like a paper printer.

For example imagine a Cube, and slice it into 2d layers - each layer would be a square. A FDM printer will print the “square” layer and then print the next layer on top of the previous. This is repeated for all the layers which would result in a 3D cube.

In order for a FDM printer to deposit material, the material is heated up to its printing temperature within a hotend, which consists of an extruder, heater element and nozzle. The print head can move within the X-Y-Z space precisely using highly accurate stepper motors.

The nozzle in a hotend is what the filament is extruded from, the nozzle diameter in a FDM printer will determine the average layer height and wall thickness. The material that is extruded is in the form of a blob, for good layer adhesion and print quality the shape of this blob should ideally be spherical. The height and width of the extruded blob will depend on the layer thickness and extrusion thickness.

A typical desktop FDM printer offers a printing area of around 220 x 220 x 220mm, whereas an industrial FDM printer can be scaled up and print very large objects. Larger designs can also be broken up into smaller parts, printed separately and then assembled afterwards.

Materials that are used on a FDM printer can vary from the Semi-crystalline and Amorphous categories, ranging from commodity plastics to high performance materials. Desktop FDM printers typically can only print commodity plastics whereas industrial FDM printers are designed with a suitable environment that can print engineering and high performance grade polymers.

The characteristics of an FDM printed part consists of layer lines for the outer perimeter, the core of the 3D printed parts is semi-hollow as an infill percentage is typically used, resulting in lighter and cheaper parts. A limitation of a FDM printer is that it can’t print on thin air, therefore the slicer program calculates whether support structure is required for the floating geometry to be printed upon. Therefore once a part is printed a post processing step requires removing support material from the object.

As the material is extruded from the nozzle, the material cools at different rates and therefore causes some inconsistencies such as shrinkage and warping within the 3D printed component. Also as the extruded material is pushed against the previous layer in a FDM printer the extruded material is squeezed from its initial circular shape to an oval shape, decreasing the dimensional tolerance to approximately ± 0.5mm. The shape of the extruded material is roughly circular and therefore the outer perimeter of the 3D part will create an uneven surface finish, to remove the uneven surface a post finishing process would be required. As the material is extruded from the nozzle, the previous layer that is printed upon is also heated up. This stretches and shrinks the material at varying rates, causing the layer underneath to warp upwards slightly.

#fdmprinting #3dprinting #additivemanufacturing

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