Support structures are a necessary evil of 3D printing. They can be frustrating and time-consuming, but they are required to keep many parts from collapsing or becoming distorted. In a paper entitled “Support Structures for Additive Manufacturing: A Review,” a group of researchers take a close look at supports and their various forms and functions, and evaluate some of the research that has been conducted on them already.
The purposes of support structures, according to the researchers, can be divided into three types:
- Supports that act as a heat diffuser and rigidity enhancer, preventing shape distortion and residual stresses due to excess heat accumulation, particularly in metal 3D printing
- Supports that are necessary in processes like FDM so that material isn’t being deposited in midair
- Supports that act as a tether to keep parts from shifting and/or collapsing
Support structures, while necessary, also have plenty of disadvantages, including creating excess material that often cannot be reused, as well as creating lots of extra work to remove. They also result in longer print time and additional work and expertise required to generate them properly. The paper discusses how to circumvent some of these obstacles, including optimizing the orientation of the part and the structure of the supports, as well as using sacrificial or soluble supports or support baths.
In the study, the researchers take a look at other publications that have been dedicated to 3D printing support structures, and find that the majority of them are focused on FDM 3D printing, rather than metal 3D printing processes.
“The reason for this is most probably because of the unavoidable and higher requirement of support in FDM, and the popularity of the printing technique,” the researchers state. “FDM needs material beneath the printed layer as it is extrusion-based, while for powder processes, the powder could take the role of support. In addition, the unused powder which acts as the support can be reused, to an extent, in the future. However, the supports fabricated in extrusion-based processes are generally unable to be reused, unless the supports are re-manufactured into filaments. For powder bed processes, the support material is generally for ameliorating against thermal stresses during manufacture and to anchor the printed part within the build volume.”
Many of the studies reported focus on the optimization of part orientation in order to minimize support usage, but others are dedicated to eliminating support usage altogether. One research team tried to use an inclined deposition method for FDM, but the method is a bit complex and involves control over the direction of the nozzle. Another proposal involved using water or ice as supports for SLA builds.
“Though this strategy seems to eliminate using the part material as support, it instead requires the repeated heating and cooling of water to induce the necessary phase change, which may be less energy efficient,” the researchers point out.
The design of support structures should be based on several principles. The support should be able to prevent the part from collapsing or warping, especially the outer contour area; for metal processes, stress and strain need to be considered and thermal simulation modeling can be considered for design. The connection between the supports and the final part should be the minimal strength needed, in order for removal to be as easy as possible, and the contact area between the support and final part should be as small as possible to minimize damage. Material consumption and build time should also be considered.
Support structures are unavoidable in many 3D printing processes, the researchers conclude, but more effort should be made to minimize the negative effects of supports. In the research that they evaluated, there were a few gaps that they pointed out, including the lack of a comprehensive method for reducing support material while keeping the mechanical strength and surface finish quality.
“In addition, some innovative and creative methods which can largely minimize or even achieve zero-support for AM are urgently necessary,” the researchers conclude. “Support structure modeling needs to be adopted in the future, especially for metal processes. Further, a standardized model and uniform criteria need to be made in the future for fairly comparing different support methods and choosing the most economical strategy. Lastly, topology optimization is necessary to be integrated into support structures for further reducing materials used, making AM a more sustainable technology.”
Authors of the paper include Jingchao Jiang, Xun Xu, and Jonathan Stringer.
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