So you’re interested in qualifying that new product design that holds liquid but dreading the required post-processing? Keep calm and Insight.
There seems to be an endless amount of applications as Additive Manufacturing (AM) technology evolves. Nonetheless, those looking to AM for functional prototyping and end-use parts continue to get the job done with a 25 year-old workhorse – Fused Deposition Modeling (FDM) technology. A whopping 85% of the market is FDM based and it’s no surprise. It produces accurate and functional parts in a wide array of engineered production plastics.
Aside from all of its advantages, FDM is also inherently porous. For many applications this doesn’t come into play at all. If you’re thermoforming, you’d embrace this flaw. However, if you’re trying to hold a gas or liquid (in or out), this is a glaring limitation. So when porosity is a concern, starting with Insight processing software is the best way to ensure that your application is successful.
Geometry will greatly impact which technique, or combinations of techniques, are required to seal the part for testing, and then end use. Employing Stratasys’ Insight software, included with Stratasys’ Fortus line, is an easy way to solve porosity issues on most geometries; conversely, some complex geometries may potentially require labor intensive post-processing. So if you’re the frugal type, you should put your efforts into processing STL’s upfront with an Ultem fist to ensure those manual operations aren’t necessary. And guess what? Unlike most post-processing methods, this strategy won’t change the part geometry.
If you’re already familiar with FDM, you may be aware of why porosity is often necessary. If not, here’s why: the model may have areas that aren’t self-supporting so the supports need to be removed and dissolved. The natural porosity allows the soluble solution to reach the support material as well as drain from those same areas that may be concealed. In other words, sometimes leaching is helpful. Just keep that in mind.
Sealing with Insight
With Insight, you have the ability to control or even eliminate the porosity concern, especially with simple geometries. This is true as long as the application requirements are to hold a gas or liquid around atmospheric pressures. It won’t be as effective at higher pressures/vacuum, or with complex part geometries.
The first step is addressing the orientation of the build on the platform. This will require your judgment and the application needs. The most important rule is to orient the part so that most surfaces are oriented vertically.
Once you’ve determined the optimal orientation, the next step is to add multiple contours to the vertical walls (bottom image). Fundamentally, this technique relies on using additional contours and in turn reduces or eliminates rasters from these layers. The existence of rasters within a model increases the risk of leakage, due to the air gaps they create as shown below (top image).
From the Groups toolbar, you can setup the parameters to reduce air gaps following these steps:
- Determine your wall thickness by measuring at each layer and then do the math, so wall thickness is equal to the number of contours multiplied by contour width. You can select a range of layers that have the same wall thicknesses.
- Set up Custom Groups for each thickness and add the layers to the groups. Within each group, you’ll be able to control the number of contours and their respective widths.
- Select the Link Contours feature and add a slight negative contour-to-contour air gap whenever possible. This feature will create continuous toolpaths by eliminating start and stop points between each contour.
In this example, shown in the parameters for a custom group, I have a 0.100 wall thickness. I’ve used five (5) contours with a 0.020 contour width. I also have the Link Contour box checked and gave it a -0.001 air gap. Alternatively, you can apply Contour Width and Link Contours globally if it suits your needs through the Toolpath Setup menu.
Note: Modifying some of these parameters may vary your build time and material usage. Best practice is to run a “green flag” as a control and take note of the estimated time and material before modifying parameters.
Next, we’ll look at rasters, because you’re likely to have some areas that will require them. By default, raster angle controls are set to start at 45° and alternate by 90° delta (see above). These alternating turnaround areas leave pathways or airgaps through the layers, i.e. the black triangles where the rasters meet the inside edges of the contours.
By selecting Parallel Offset Rasters, Insight will modify three parameters.
- Varies the number of contours on each layer in order to conceal the raster turnarounds. This will still apply even if you’ve already setup multiple contours.
- Positions the raster toolpaths parallel with adjacent layers (0° delta).
- Offsets the rasters toolpaths so that they cover the seams of the previous layers.
So that about seals the deal. This should give you an excellent starting point in processing STL’s in preparation for FDM sealing applications.
Here is an article on some other post-processing techniques that will take sealing to the next level. But be careful, because they will affect your geometry.
Tags: FDM Technology, Ultem, Thermoforming