26 May 2017 16:23
3D Printing Support Structures: The Key Things You Need to Know
Many AM professionals consider support structures a necessary evil and look forward to the day when printing technology makes them unnecessary. However, their intelligent application opens up a wide range of opportunities for printing complex models that would not be achievable otherwise. For example, with the right support structures, it is now possible to produce a sophisticated front-piece for a sports car in a single print run.
Support structures, as the name implies, support your part throughout the printing process, ensuring each element can print cleanly and accurately, with no deformation caused by sagging. They provide a stable platform on which further layers can be printed and ensure the part remains firmly attached to the printing bed throughout the entire process.
Regardless of which methods of 3D printing your operation makes use of, you will have to consider support structures as part of the process as some point, so in today’s tutorial we will be looking at the support elements required during the most widely used printing processes and how to utilise them effectively.
Now, let’s look at what support structures will be required for different printing methods:
Selective Laser Sintering and Binder Jetting
Support structures will not be required when printing with these technologies. During the printing process, the powder bed itself provides support for the model, after which it can be lifted out and cleaned. In order to minimise material wastage, be sure to build escape holes into your finished design, so any excess powder on the inside of the part can be removed during post-processing.
Direct Metal Laser Sintering
Although DMLS utilises a powder bed in the same way as SLS, support structures will still be required to ensure the part remains securely attached to the printing bed. They will also help prevent any deformation and ensure heat is properly dissipated — essential with the high temperatures used in DMLS.
Optimal part orientation is key here, and can help to minimise the need for support structures by avoiding overhangs. As a general rule, any overhangs with an angle less than 45° will require a support structure, so consider this when determining the ideal printing angle. As a bonus, this can also help to minimise visible layers in the finished part.
Ideally, the need for support structures should be minimised with any DMLS project, as they can prove quite difficult to remove, and often require wire cutting or CNC machining to achieve a professional result. If they prove unavoidable, offset support structures will usually be easier to remove, as they can reduce the number of surfaces that must be cut when removing the part from the printing bed.
Fused Deposition Modelling
For FDM printing, support will be required for any overhangs of more than 45° and any bridges of greater than 5mm. In terms of the actual support structures, it has become common practice to utilise specially designed support materials, which are added to the build during printing via a separate extruder. Once printing is complete, they are simply dissolved in water or a suitable chemical. This process has the advantage of being totally hands-free, and means that no further sanding and polishing will be required to remove the marks typically left when support structures are removed. However, it does require the use of a multi-head printer, and fully dissolving the supports usually takes several hours.
Alternatively, certain support materials are designed to simply break away from finished part, without the need for a water or chemical bath. This is potentially faster, but the removal of the support structures will need to be factored into the part’s design to ensure they can be removed cleanly, without any material left behind.
The two most common dissolvable materials for FDM support structures are Polyvinyl Alcohol (PVA) and High-Impact Polystyrene (HIPS). PVA dissolves in water, but bear in mind that it is quite susceptible to temperature changes, which can affect the time it takes to dissolve and may even lead to blockages in the printer head. HIPS, on the other hand, is less affected by temperature, and dissolves in limonene (a readily available household cleaner) rather than water. If you are planning on using HIPS, be sure to factor the cost of limonene into your budget, as it could potentially become a significant ongoing expense, depending on your printing volumes.
Support structures are always necessary when printing with SLA, both to avoid any deformed areas, and to ensure your part stays properly affixed to the printing bed until it is complete. The good news is that supports are quite easy to remove compared to other processes, and can usually be clipped away with little trouble. Bear in mind that the right part orientation can limit the number of support structures that are needed during an SLA print. Alternatively, it may be possible to print a part as several individual pieces that can then be clipped or glued together, minimising or eliminating the need for supports.
As SLA parts are considerably more delicate than parts produced using other methods, use a delicate approach when sanding away any marks left by support structures. As an alternative to sanding, consider a light bead blast as a way of achieving a smooth, clean finish.
When printing with material jetting, all overhangs will require support materials, regardless of the angle. However, these supports are far easier to remove than with other methods, and can usually be simply clipped off after printing, with relatively little sanding and polishing required to remove any marks that remain.
Finally, a few general guidelines to bear in mind:
- Consider which areas of the part need to be the most visible (e.g. the parts of a prototype that will be seen most by its intended audience), and avoid attaching any supports there, to ensure they look as clean and attractive as possible.
- Avoid redundant support structures, as these will only serve to increase the printing time and lead to material wastage
- Check that all support structures will be accessible after printing. Any supports that are difficult to reach will be hard to remove cleanly.
- Remember that the internal areas of a model may also require support structures, so consider how these will be removed after printing. It may be necessary to split the design into two parts that can be printed separately, then glued together.
- Don’t attach support structures to delicate structures, or anywhere with fine details, as this can lead to a loss of detail when they are removed
- Certain printers have the facility to add support structures automatically. Alternatively, you can add them in your preferred software platform, either by hand or using an integrated tool that calculates where supports will be required. Consider the level of control you want over your support structures before making your decision.
- Invest in a set of quality needle-nose pliers and flush cutters, as this will make removing support structures far easier. Use pliers where parts can simply broken away, and cutters for supports that require more precision to achieve a clean result. Some people prefer to use a knife for this purpose, or to remove very small supports, although bear in mind that this can scratch more delicate materials, so work carefully
- When smoothing out any marks left when structures are removed, sand carefully to avoid any unwanted dimensional changes. More information on sanding can be found in our last tutorial.
When working with support structures of any sort, the most important rule is to exercise caution and work carefully. If you do this when adding supports in your CAD software and when removing during the post-processing stage, you will achieve great results from your 3D prints.