Managing the Limitations of FDM Printers

We just discovered that additive manufacturing is quite an incredible technology, capable of creating any shape. But despite being very flexible, 3D printing is still bound to limitations that we must consider when approaching a new part study.

In this chapter, we are going to try answering the following question: can an FDM 3D printer create every imaginable geometry? The answer is… almost. We must understand that this type of printing technique has some limitations – some related to part shape, others to material properties.

In this chapter, we will cover the three main limitations of FDM printers that we have to consider:

• The first limitation is printing overhang areas; some geometries can be a bit challenging to print if not properly supported
• The second limitation is bed adhesion, which is related to the first layer placement; if the contact area between the printed part and the build platform is not large...

Technical requirements

The only requirement for this chapter is to have read and understood Chapter 14 – in particular, the section about FDM printers.

Printing overhang geometries

Overhang areas are sloped faces that protrude beyond the base of our model. We actually already faced a similar concept, undercuts, when studying milling issues:

Figure 15.1: Undercuts for milling

As we may recall, undercuts are geometries that cannot be reached by the cutting tool, they are a huge limitation to milling processes even if we already found several possible solutions to fix undercuts in Chapter 7.

In this section, we will focus on additive manufacturing to find out whether undercuts are an issue that affects FDM printing as well, and if so, how.

Facing overhangs (undercuts) in 3D printing

Before jumping to the answer, let’s get back to basics – additive manufacturing, instead of removing material from a solid block, creates a shape by stacking multiple layers one on top of the other.

For this reason, generally speaking, 3D printers don’t suffer undercut-related issues nearly as...

Understanding bed adhesion

Every FDM printing process relies on printing the part from the build platform of the 3D printer and stacking layers on top of it. As you can imagine, having the object perfectly glued to the build surface is super-important. It must not detach from the platform nor vibrate while printing; otherwise, the printing process will fail miserably.

Usually, the best prints are achieved when the area of contact between the build platform and the part is large enough to give perfect adhesion to the latter.

This is probably the most important rule for a successful print, and luckily, it is also quite simple to understand – we always have to put the larger and flattest area of our component in contact with the printing bed.

The reason behind this rule is quite intuitive; since the part, while printing, has to remain perfectly fixed to the printing bed, a larger contact area will grant better adhesion forces to counteract vibrations and local deformations...

Understanding anisotropies of the printed part

FDM prints feature anisotropies along the printing direction. Typically, the mechanical strength between stacked layers is weaker than the strength in other directions; therefore, the higher loads should always be applied along the layers, not perpendicular to them.

We should always consider these anisotropies when studying part placement, especially if we are about to print a functional prototype that will be loaded by forces and deformations. Let’s take the following component as an example; this part is similar to a circlip ring and will act a bit like a spring:

Figure 15.7: Another example of different printing orientations

As you can see, there are two different part placements for this part; the first one on the left features the part standing up, while the second shows the part laid on its side.

Both part placements are feasible from a printing perspective. However, since this is a component...

Choosing the first layer placement and part orientation

After reading the previous suggestions, you may find yourself a bit disoriented with all of the different limitations. So, considering those, let’s try to find the best part placement for the following component:

Figure 15.9: Choosing the best printing orientation

Here, we can find all the possible printing orientations for the given part. Let’s analyze them and test whether the given rules are respected.

First, let’s look at placement 1:

• This placement requires quite a large volume of support material; therefore, the first rule is not really respected
• The first layer is quite large, and it will grant a good adhesion to the part; therefore, the second rule is respected.
• This type of layer placement will make the thin vertical wall very fragile; therefore, the third rule is not respected

Let’s look at placement 2:

• This placement requires...

Summary

That’s the end of the chapter. Let’s quickly recap what we explored.

First of all, we discovered overhangs in 3D printing and why they can cause trouble to printed parts. Then, we moved on to the most common approach for handling undercut-related issues, using support structures.

Lastly, we discovered how layer orientation and part placement can change the mechanical behavior of our components, and we gave a few practical suggestions on how to optimize orientation choice.

Getting an overall idea of the covered subjects is super-important for the proper use of additive manufacturing (and, in particular, FDM printers).

Now that we have a better understanding of FDM printing’s potential and its limitations, we can move on to the next chapter, where we are about to start our part setup and slicing journey!