I ❤️ FDM

If you talk to me for more than five minutes, then you are going to find out that I love FDM. Well, maybe that is an exaggeration. Usually, "hello" is enough for me to get started. Suitable for mass manufacturing, industrial quality, most flexible of all the additive manufacturing processes, safe to use, giant material selection, multi-material-capable - you know the drill. This article is about something else.

This article is about the ❤️ shape itself, and how to reproduce it in FDM. Read on, and you might also pick up a few details about designing for FDM. Also, at the end of this article, I am sharing the 3D model I created here.

Autodesk has recently released an AI assistant for its Fusion software. I am currently testing it, to see how suitable it is for practical purposes. My application example: a sandmould toy for kids to play with in a sandbox. We usually make functional components, but I wanted something simple to test.

My initial prompt was:

Can you design a sand mold for me that a child can use to play in a sandbox?

The AI selected for itself a star shaped mould:

A CAD model of a star shaped mould generated by an AI.

While this result was okay - and quite good actually given the simple prompt, I was not quite satisfied. I was curious about printing a seashell-shaped mould, even though the staircase effect in FDM makes curved horizontal surfaces difficult. I added a prompt:

Change the shape to a shell.

While the AI did its best, it did not remove the original shape. The resulting design also went further away from what I was looking for:

A CAD model of a rough sea shell mould and a star shaped mould overlaid, generated by an AI.

This is where I stopped trying to get the whole design from the AI, and started over. I could have continued with this shape, and I actually succeeded in asking the AI to purge all the old shapes from the document. But it seemed to me that to get all the details of the sand mould right, to the degree that I wanted it, would probably involve a lot of back and forth. I knew how to get to the mould shape anways, what I need the most was the base shape pattern for my mould. I started over, decided on a new shape, and created a new prompt:

Create a 2d sketch of a heart shape.

Here, I immediately received a valuable result. It sped up my work a lot:

The AI generated a beautiful, heart-shaped 2D sketch for me, after a simple prompt. I especially like that it uses one of my heart equations to create it:

x = 16*sin^3(t)
y = 13*cos(t) - 5*cos(2*t) - 2*cos(3*t) - cos( 4*t)

You can head over to Wolfram Alpha to get its plot:

Now that I had the base shape, getting to a sandbox mould well suited for an FDM design was straightforward. I had to do the following:

1. Remove any sharp corners from the sketch. As the sketch would define the slices, and FDM cannot print sharp corners (0 width is impossible if your shaping tool has a non-zero diameter), these would not show up on the part. Also, sharp corners cause decelerations, which increase build time - even though here this would probably be negligible. Also, shar corncers can be uncomfortable to touch, and this is a toy for children, after all.

2. Extrude upwards with a decent wall thickness. I ended up with 5mm wall thickness after scaling the base shape. If walls are too thin, there is no infill, and parts are very suspectible to shear forces. I used the Extrude command, followed by the Shell command.

3. Fillet the inner, bottom corner: This allows for easier de-moulding as the sand separtes more easily from the mould.

4. Fillet the top corners. This makes the part comfortable to touch, and fillets work well on horizontal edes of upskins.

5. Chamfer the bottom corners. Fillets do not work well on horizontal edges of downskins, as the change in curvature creates a strong staircase effect.

And voilà, here is the finished product:

Of course, the design is only the intermediary step. If I was ordering the part from Gramm now, I would download the CAD model as 3MF, STL or STEP, head over to the Gramm website, upload it, select a material and color, place my order, and wait a few days until the finished part shows up at my doorstep.

But since I work at Gramm, I can skip right to production, or rather, the build preparation (slicer). I downloaded the CAD model as a 3MF file, and loaded it into our build preparation software:

As you can see, the higher wall thickness allows for infill generation, which greatly adds to part stability. If this was an engineering part, we would have applied our standard settings for functional components (3 walls, 20% grid infill), but this is a toy, and I was in a hurry. Increasing the wall count increases build time.

As the material, I chose PLA, since it is a bioplastic, so it would have the least amount of chemicals in it. PLA does not automatically mean your part is suitable to be used or sold as a toy. But it is a good start. And luckily we have an entire factory at Gramm, so I could choose between dozens of colors I oped for marine blue. And here is the result:

It took me only around an hour from opening up my CAD tool to starting the print, and the print itself took around two hours. I could have sped it up by increasing the layer thickness, but I wanted to minimize the staircase effect.

If you are interested in the CAD mould for this little sand mould toy, you can download it here: https://a360.co/3RtICXO

This is how you create a heart shape in CAD, a complex 2D shape, and then use it create a part manufacturable in FDM! I used essentially the same process we apply when designing parts for our customers. I hope this simple example helped give you an idea how we work when designing parts optimized for FDM. If you work with us, and you hire us to design and manufacture your part, you can be sure to get an optimized design manufactured in excellent quality.

Do you have an application but you need a manufacturing solution that includes design? Then head over to https://www.gramm.online/inquire to get in touch with us.

If you are designing the part by yourself, then we are happy to produce it for you: https://www.gramm.online/order .