FDM cannot handle overhanging structures with much success. Therefore, systems are often equipped with a second extrusion head for depositing 'sacrificial' material. This is commonly dissolved in a solvent that does not affect the properties of the build material.
FDM is essentially a rapid prototyping technique that with careful control can be used to create functional parts. Consideration needs to be given to the following:
- Molten or semi-molten material is exposed to oxidising atmosphere (i.e. air). An inert atmosphere such as nitrogen or argon can be used to reduce oxidation and improve layer-to-layer adhesion.
- Unsupported material can be supported by sacrificial structures.
Limited to thermoplastics. Common examples include:
- polycarbonates (some grades can be sterilised and used for implantation applications)
- ABS (available in many solid and translucent colours)
- polyphenylsulfone (selected for high-strength applications)
- PETG (impact resistant, but higher density than ABS).
Component design is limited by the following:
- Strength and thoroughness can be influenced by many factors including time of build, atmosphere and even polymer colour.
- Overhanging regions need extra designing.
- Structures requiring more than a single filament width require care to ensure voids are not created between filaments.
- Support structures can only be placed where they can be removed (i.e. not inside internal voids like those required to create a ball).
This article is a part of Manupedia, a collection of information about some of the processes used to convert materials into useful objects.