9 Design Rules for a Successful 3D-Print

Wall thickness

Models printed using the lasersintering (SLS) or extrusion method should not have wall thicknesses below 1.0 mm. Parts that will not be subjected to mechanical force and have supporting geometry can be as thin as 0.8 mm. For both printing methods using glued powder wall thicknesses should not be lower than 2.0 mm.

In the image to the right the model has an additional wall giving a higher stability.

An example of supporting geometry would be a wall that is supported by other surrounding walls. In general wall thicknesses should not be below the minimums. This is especially true for walls that are critical for the structural integrity of the model.

Should your model include walls that are thinner than the minimum wall thickness you can either thicken them or just scale up the whole model. You can also try a different printing method that allows thinner walls.

Bounding box size

The build volume of the printer chosen defines the biggest possible bounding box for your model.

You can scale down your whole object to make it fit into the build volume of the 3D printer of your choice. Keep an eye on the minimum wall thickness and feature size though.

Removing features that stick out can accomplish the same task. Also some materials and the corresponding 3D printers have bigger build volumes than others.

For special big projects you can also contact us.

Files with multiple parts

It is technically possible to have more than one part in a model file but it can cause problems.

A very common application for multiple parts is having moving parts like for example links in a chain or ball-bearings. Here although the parts can move they can not get lost because they cling together. For many 3D-printing methods this works quite well and is one of the more interesting advantages of these additive manufacturing methods. For others methods it does not work because of technical restrictions (more information below).

Sometimes people choose to pack an array of parts in one file that do not interconnect. This can have different reasons, for example pre-packing together the number of parts in a set.

Unfortunately this often causes problems for production. First of all parts are often not positioned optimal for 3D-printing in the pre-defined arrangement in the file. This can negatively affect the 3D-print quality or can cause wasting of material and machine space. In addition, handling the parts when packing and unpacking the machine, cleaning and dyeing the separate parts and sorting them before shipping gets much more challenging and time-consuming.

Therefore we have to deny model files with too many not interconnecting parts.

The number of not interconnected parts per file that can still be handeled with acceptable effort depends much on method and used material:

Connecting parts

As having multiple parts in a file can cause problems for our production, connecting your parts with support beams can be a good idea. But beams have to be strong enough so the parts do not break or get lost.

The beams need to be 2.0 mm thick minimum for polyamide prints. For heavier, more fragile or large parts or when the beams are rather long, leverage is increasing and the beams have to be thicker. Because of that we recommend a thickness of 3.0 mm. For more fragile materials where a larger wall thickness is needed in general the beams have to be thicker as well.

We need at least 2 firm connections per part. For heavier, more fragile or large parts more connections are needed. Therefore it is recommended to have 4 connections or more.

Please also position the connected parts with sufficient distance between neighboring walls, at least 3.0 mm, so that there is enough space for easy removal of excess material. Also please do not position the parts in a nested way.

Why is this so important?

Let’s look at our process, for example for laser sintering. The printing machine is filled with many parts from different orders. Once the 3D-printing process is completed, the parts have to cool down and then be lifted from the powder bed. Then the excess powder has to be removed and the surface cleaned. This is done by suction, compressed air and glass bead blasting. Later the different parts have to be identified and sorted and may undergo additional surface finishing like dyeing or grinding. For dyed polyamid parts excess powder will lead to a poor coloring and can pollute the dye bath. So removal of excess powder is most important here.

Identification of parts can be really tricky, especially if there are multiple parts in one file, but when connection beams break during the process identifying gets nearly impossible. So it is very important that the connections withstand the whole process.

Keep in mind that besides the weight of the parts themselves the connections have to carry the weight of the excess powder while lifting from the powder bed and that for cleaning the parts 4 bar air pressure is applied.

If connections break the parts cannot be addressed to an order and can get lost. This means more work and a late or incomplete delivery for our customers.

In addition relative positioning of the connected parts may not be optimal for 3D printing. So in order to have the best quality we recommend to order the parts separately.

Engraved and embossed details

A very typical example of such a detail is text on your model. To make sure the details come out as imagined and none of the small parts break off during production or shipping, width of details should be kept thick enough.

The height or depth for embossed or engraved texts should be in a range that they are not too shallow or narrow to be clearly visible but at the same time not too much sticking out so structures do not break off easily.

For texts on models we recommend these minimal values for linewidth and height or depth:

If the height or depth is significantly larger the limitations for the wall thickness apply.

Should the details on your model be smaller than this you can increase their size, delete them or increase the size of the whole model by scaling. You can also try a different material that allows for smaller details.

Clearance

Between two parts of a model there should at least be 2.0 mm of clearance otherwise these parts might be fused together while printing. In that case holes in your model would not be fully displayed.

Even if the parts are not fused together it can happen that support material or powder plugs small gaps and holes. This can also lower the quality of dyeing.

If you want to be sure not to have much remaining material left we advise to choose clearances as big as 3.0 mm.

If your model currently does not match these parameters you can either widen the clearances or scale up the whole model.

Moving parts and fit

Certain design guidelines should be followed to achieve fit. To make sure two parts will fit, the inner diameter of one part must be bigger than the outer diameter of the other part. Usually a difference in diameter of 0,5mm to 1mm will suffice. Parts which have the same inner diameter and the outer diameter will not fit.

Not all methods are suitable for moving parts.

These methods and materials are suitable or partly suitable for moving parts:

• Plastic Sintering (Polyamide, white, dyed)
• Alumide Sintering (Alumide)
• Extruded Plastic (Thermoplastic ABS)
• Resin-bonded Plaster (Plaster)
• Resin-bonded Plastic (Grained Acrylic)
• Rubber Sintering (Thermo-PU)

These methods and materials are not suitable for moving parts:

• Resin Printing (Resin)
• Silver Casting (Silver)

Escape holes

If you do not include escape holes in your model it might get much more expensive because we can not reuse the trapped excess material. Big models should be equipped with several escape holes. If you decide to only use one it should be at least 10mm in diameter.

The cavities should be easily accessible so that the excess material can be removed without much effort. So please do not design maze-type cavities or models formed like snail shells.

If the escape holes in your model are insufficiently small you can increase their diameter or scale up the whole model. You can also add more holes or remove the cavities completely.

Warping

Especially long and thin parts of your model are affected by warping. Please try to avoid such parts if you can. The warping effect is most associated with the laser sintering method (SLS) because of the high temperatures the laser creates while melting the material.

To avoid warping effects you can increase the wall thickness of the parts in question or add some structural support by adding beams.

It is also recommended to try to avoid mixing of very thin and very thick structures in one part for laser sintering. The reason is that the laser will induce more heat into the thick structures than into the thin ones when it melts together more material for a longer time. The temperature difference can result in warping of the part as well.