rapid prototyping techniques - FDM


This article is contributed by Joe Pizzo, an experienced FDM specialist.


FDM stands for “Fused Deposition Modeling”. This method is the best choice when we need a part with low volume of details and high structural integrity.
The method is based on melt extrusion of thermoplastic material of the styrene family - usually ABS. ABS along with other styrenes is known first of all for its durability. Styrene parts are easy to machine, drill, glue, sand and paint, they serve for a long time without a sign of deterioration. Since the beginning of “Plastic Age” styrene was a first choice in professional model making.

The material is being melted in the nozzle tube and being deposited, layer by layer, along the trajectory of the contour nozzle. An extruded material is curing rapidly as its temperature goes down, instantly bonding with the underlying layer. A thickness of each layer plays role and has its limitations. With the minimum line width (wall thickness is .020” (.5mm) FDM machinist can set a layer thickness to .007, .010, or .014 inch thick, according to complexity of the part and required resolution.

A basic FDM bed is 10” x 10” x 12” high, which is enough for most of the parts. These parts longer than 10 - 12” can be built in sections and fused together. As was mentioned before ABS is great to glue or screw, so assembling a part’s sections does not pose a problem.

As the height of the built increases it needs to be supported in order to keep the shape of the future part in accordance to the CAD design. In order to provide adequate supporting structure, the FDM software automatically designs a secondary structure identified as "SUPPORT" providing not only support but also an orientation for the main built, and only where it is needed. So there is a second nozzle from which a support material is extruded during the process, building a secured structure in holes and cavities of the main part and around it. An appropriate layer’s thickness also can be set for the support built.

The support material is water solvent. After a built is completed, it is being easily removed off the part using sonically driven hot water bath. Because a support material is being “washed” off the part and not removed physically, it preserves the integrity of the part’s surfaces, especially in holes, cavities and undercut areas.

In conclusion, when we need parts with fewer details but of higher structural integrity, FDM method is the answer. This technique cannot be seen as an alternative to SLA – it is a mistake being made often. FDM has obvious weaknesses in comparison to SLA, such as poor representation of details or more effortful surface finish. On the other hand, ABS material is far superior to SLA resin due to its durability and other characteristics and the technique itself is less expensive than SLA. There is no doubt that FDM method has its rightful and respectful place in the world of rapid prototyping.

As we stand for diverse and combinatory rapid prototyping strategy, we determine which parts and components are better to produce by FDM while planning a dispatch of digital tooling.


Samples of the Parts produced by FDM Technique

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All-FDM chassis for 1:6 scale model of up-armored HMMWV

All-FDM chassis for 1:6 scale model of up-armored HMMWV

All-FDM hood for 1:5 scale model of MaxxPro Dash MRAP

All-FDM rope boxes, antenna mast posts and tilting mechanism

Rear view of all-FDM antenna mast post/tower

Tilting System. All components are produced by FDM, durable and articulating

1:144 scale Hangar replica produced by FDM

FDM made 1:144 scale Hangar replica, side view

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