A closer look at 3D Printing Support Structures and their effect on part wash time

Soluble Supports

The use of soluble support material lifts one of the biggest barriers in designing for Additive Manufacturing (AM), which is the generation of complex structures and embedded channels within parts. Soluble 3D Printing Support Structures are designed to dissolve in a wash station, leaving only the model material behind.

For context, the “wash station” that I’m referring to represents any circulation tank system which involves submerging a printed part in a heated bath with a specific amount of added cleaning solution.

The cleaning process is naturally very slow, and it’s not that easy figuring out how much time it will take to clean your specific part. Unfortunately there is no tried-and-trusted method you can follow to accurately determine wash times for parts. You can make very broad estimates, but there are many factors that are constantly at play that could affect the dissolving process. The ones we’ll cover in this blog include:

• Wash station temperature
• Part complexity
• Support structure type (Basic, sparse, box, surround, SMART)
• Support structure density in relation to model

Wash Station Temperature

Wash station temperatures are set according to the support material used in the printing process. Stratasys offers documentation regarding FDM support removal on their website. The full document can be found here. The document includes a table showing the recommended temperatures for cleaning parts with each type of support material:

Setting the wash tank to higher temperatures than the ones listed in this table could potentially damage parts.

Part Complexity

Take a look at this part:

Filleted cube with a series of holes on the top.

Looking at this part, it’s evident that there shouldn’t be that much 3D Printing Support Structures in the first place, meaning the wash time will be very short. But if we look at the part a little closer, we can see that may not be the case:

There are lots of little channels within the block that need to be filled with support material.

Every single one of these small channels will be filled with support material during the printing process:

Support material used to fill in the channels. You can see an isolated view of support structures using GrabCAD Print.

These support structures track the inner surfaces of the channels all the way through the part. Channels like these take a lot longer to clean out, as they don’t get as much exposure to the wash solution. As I mentioned before, there is no accurate way of determining wash times, but from my experience with printing parts like these, I would expect at least a 6-hour cleaning process.

Now lets look at this next part:

This is a simple cradle for a phone. It has no inner channels or complex structures.

A part like this doesn’t have any super intricate features that require concealed support placement. The wash solution can chew away at the structures relatively easily, meaning the total wash time is significantly decreased.

The supports for the cradle are easier to clean, as they’re out in the open.

This specific part took about 2.5 hours to clean.

Part complexity is the biggest factor when determining wash times, but it’s not the only factor. The next thing to take a look at is the type of 3D Printing Support Structures used for the printing process.

Types of 3D Printing Support Structures

3D Printing Support Structures are generated by software but is based on user input. There are a few options available for support generation, mainly “sparse”, “surround”, and “SMART”. A few other structure types exist as well, such as “basic” and “box”, which are variations of “sparse” and “surround” respectively.

• Sparse support uses the simplest support generation method to build structures based on layer overhang. Overhang angle is different for every printer, but the average tends to be around 45 degrees.
• Surround support engulfs the entire model within a support shell in order to maintain stability during the printing process. This type of structure is great for parts that are tall and have small surface areas.
• SMART support uses a series of optimization algorithms to determine the best possible support generation while using the least amount of material. It’s the best option for most 3D printing applications, and is set as the default support type in GrabCAD Print.

One model can have many types of support structures.

SMART supports take the least time to dissolve, purely due to their material optimisation. Surround supports, on the other hand, take the most time to dissolve, as they engulf the entire part with support material. A good example of this can be seen below:

Here you can see the comparison between two extremes of support structures.

You can probably infer which of these parts will have a shorter wash time. I highlighted a layer of the part to show the toolpaths for each print job. Notice how the toolpaths for Surround support structure look more dense than the SMART support? This leads into the next factor for determining wash times.

Support Structure Density

Looking at the image above one more time, you can see a significant difference in the densities of material that is being laid down for each layer. SMART supports are “lighter”, whereas Surround supports are a lot “heavier”. These densities cannot be changed in GrabCAD Print, however can be manipulated using Insight. Insight’s toolpath customisation parameters allow you to set distances between parallel and adjacent contours and rasters. It’s not a perfect compensation strategy to reduce wash time, but the availability is there nonetheless.

Final Thoughts

For most applications, leaving parts to wash for around 3 to 4 hours (with the recommended temperature) does the trick. However, there are some cases where the amount of support material being used can be drastically decreased with a quick part reorientation or change of support type. The key is to understand the behaviour of soluble support material and part geometry. Of course, every printing application has a unique purpose, but knowing some of the information stated in this blog, you might be able to clean your parts and implement them faster than before.