3D Printing – Truths and Myths of 3D Printing with Support Material
Our knowledge of FDM additive manufacturing is mostly derived from the past 25+ years of industrial-style 3D printing. Over this time period, we’ve tended to print small (less than 8”x8”) parts and it’s become commonplace to create “dissolvable” support structures from a second extrusion head.
The support structures are designed to hold up “overhangs” so that the part does not collapse as it is being layered. Afterward, the support material is dissolved, usually in a caustic sodium-hydroxide mixture in a circulating heated tank, leaving the main material forming the desired part.
Today, we are tending to print larger parts (up to 12”x12”x 22.75” in the case of the EVO) for not only prototyping purposes, but also for applications such as jigs and fixtures. In other words, these parts must not only look good, they should also be large and functional. As large prints can take significantly more time, machine reliability and print repeatability is coming into sharp focus in the next cycle of additive manufacturing.
While we still use support structures for overhanging model geometry, support generation has matured significantly. It is now possible to use one material for both print and support material. Today’s same-material supports, such as those generated in Apex software, are easily removable from the main part and leave little to clean up after the print. This tends to play a significant role in the generation of larger models where fine details (less than .5mm) are not as critical as overall appearance, print time, and functionality
Dissolvable support has also matured with the advent of materials such as Hydrofill. This type of support dissolves in warm water rather than by using chemicals. As with traditional additive manufacturing, these dissolvable supports are extruded from a secondary nozzle. The advantage over less user-friendly support materials of the past is that Hydrofill is safe to work with, environmentally friendly, and compatible with most printers.
When and Where to Use Soluble Support Material
Cases where soluble support material like Hydrofill really shine are with prints that feature internal geometry or extremely delicate features. Since single-head support material must be taken out by hand (usually using a set of pliers, etc.), there may be internal features that are completely inaccessible with a hand tool, and thus unsuitable for single-head support.
Conversely, as long as there is an entry point for water, soluble support may be dissolved out, without the use of hand tools. For delicate models (ie characters, architectural, etc), you may have features — such as fingers — that are extremely gentle and can be easily broken if too much force is used with a hand tool. Models that are suspended within each other, have internal threading, and moving models can also be more easily printed with a soluble support structure, and some models can only be printed this way.
With the introduction of this water-soluble support material, the process of creating soluble support has become easier than ever before. The cost of the extra equipment needed to dissolve the material is eliminated, and the safety is no longer a factor as these materials (like Hydrofill), are usually completely non-toxic and safe for the environment.
However, keep in mind that soluble support is usually more costly than printing with a single material. The cost of dedicated support materials is usually 1-2 times that of the main printed material (i.e., ABS). Those of us familiar with 3D printing understand that models are frequently iterated at least 2-3 times and as such, consideration must be given to the cost of using this more expensive material in your workflow, at least during the initial stages. Accordingly, it is wise to make sure your print will benefit from using soluble support material.
Ease of Use
While a few desktop 3D printers, such as the EVO and Axiom, utilize soluble support material well, adding a second material of any type to a 3D printer introduces another layer of complexity to the print. With more complexity comes more possibility of error. Specifically, two heads now have to work together to build the part correctly (vs. a single-head print). If either head jams, it can cause the entire print to fail. Failures in dual-head prints are frequently more costly than single-head failures because of the added cost of the secondary support material. In addition, by using two heads most of the time, a prime or wipe tower will be used to create a purge for one head when the other is printing. Creating the prime tower adds complexity and significant time to the print.
A job that may take only 3 hours in single-head printing mode, may take twice as long using primary and secondary extruders. In addition to adding prime towers as set forth above, soluble support material is generally more delicate than conventional materials and therefore tends to be printed at a slower speed. Also, it will frequently be printed at thicker infill rates requiring further time. Build time will also increase because the dual print heads will need to switch for most every layer, such switching including prime cycles for both nozzles. Conversely, harder and more easily workable base materials such as ABS can usually be printed with single-head support quickly because the settings for Airwolf printers are optimized to print ABS as fast as possible in a reliable fashion.
If the objective is a final prototype for a presentation to potential investors or upper management, soluble support may be beneficial, at least for the final iteration, as you will have a cleaner surface where the primary material is mated with the support structures. However, when using materials such as ABS, a bit of light support sanding could make nearly as nice of a part in far less time. Further, it must be remembered that the dual-head print will still need at least a small bit of post-processing to optimize the clean mating surfaces.
Soluble support material such as Hydrofill, usually dissolves by soaking the part in hot water for several hours. Agitation and heat will generally speed up the process. Since these materials are developed to work this way, they are susceptible to moisture from the surrounding air and can degrade if not properly re-packaged after use. This can be a costly mistake with a $100+ roll of material. Proper handling and storage techniques are needed when using these materials. However, with single-head printing, no extra material is needed. This eliminates the issues that can arise during storage, the cost of storing filament correctly, and the space it takes up in the workplace. Generally with either material, if it kept inside an enclosed printer like the EVO, the filament will tend to stay dry as the chamber is heated.
While dual-head prints have reached a level of quality that is accepted in the industry, a single-head print, using intelligent single-head support structures, such as those generated in Apex, can also achieve very high quality. Things like chamber temperature and bed temperature can be optimized for that one material, rather than possibly compromised for two different types of materials. Any time a second head is introduced, it is usually using a different material and will need different, or slightly different settings to work properly. This complexity can lead to poor quality prints if settings are not correct.
Many machines have complex dual-head systems that tilt or close up an inactive nozzle to prevent it from dripping filament. While these methods try to prevent the two print heads from contaminating each other, they also add more complexity to the hardware, and in most cases can cause reliability issues. The best way to prevent material contamination within a dual print is to work with the correct settings, especially if the manufacturer provides software with presets for their machine (Airwolf 3D has many dual-head presets written into APEX).
Single-Head Support Structures
As a general rule, single-head support structures come with more benefits than drawbacks. Our experience is that most users who purchase a dual-head printer don’t often use the second head for support. However, dual-head printers are very useful for optimizing workflow by printing with different settings for primary and secondary nozzles. For example, with the EVO and Axiom Dual Direct, users can place different size nozzles on different print heads and use optimized settings for each. Apex allows users to select nozzle sizes and thus allows one printer to print a part in two completely different ways from primary and secondary heads (i.e., fast with a 1.0mm nozzle on one head, and slower and more precise with a .35mm nozzle on the other).
Single-head support structures have also greatly improved over the past few years, mostly due to software development. For these supports to be broken off easily, but also have the ability to leave somewhat clean surfaces, the software has to be able to not only create the support where needed but also set the spacing correctly for it to be broken off with little effort. When printing large models, single material support tends to work well as most imperfections arising from support material tend to be overshadowed by overall part appearance.
Having the ability to use different support patterns is also becoming common practice. In this case, for example, the single-head support structures utilized in APEX printing software use the “line” pattern. This only lays support structures down in one direction — enabling the user to more easily remove the structure. For soluble printing, the “Grid” pattern is used in order to provide more support for the print (since it will not be removed by hand).
The ability to use a secondary head for creating soluble support structures remains a powerful tool in the belt of the creator. Featuring the ability to support inaccessible part geometry and to minimize post-processing time, dual soluble support will continue to be a staple of FDM additive manufacturing. However, single-head support needs to be factored into more purchasing, design, and manufacturing considerations. When it comes to repetitive iteration, experimentation, and large part making, the cost and time efficiencies associated with same-material support are worthy of consideration.
Download our white paper "Support Material, Truths and Myths"
This white paper discusses the options and process involved in the use of support material in FDM additive manufacturing. Read this white paper to learn: - When and where to use soluble support material - The pros and cons of same material support - The pros and cons of soluble support