Polyamide (MJF)

In general, we recommend a wall thickness of at least 1 mm. Large parts may require larger wall thicknesses or added ribs or fillets for reinforcement. It is possible to have thinner features with walls of only 0.5 mm for living hinges, but here the length needs to be limited to 10 mm when they are only attached at one end or 25 mm when attached from two sides. Although hinges can be positioned differently without the risk of breaking (thanks to the isotropic mechanical characteristics of the material), it is advisable to avoid making the thinnest sections of your living hinges parallel to the Z plane.

We advise hollowing out a solid model as much as possible, and when the wall thickness exceeds 20 mm. This will save material and prevent sink marks. We recommend a wall thickness of 2-3 mm and the inclusion of at least two holes with a minimum diameter of 2 mm for powder removal. It is possible to create holes or perforations and ducts. The recommended diameter size of these holes is 2 mm, with a minimum of 1 mm, but some post-production will be needed to remove excess powder. Some residual powder may be stuck on the inside of complex ducts. It is advised to design a strip or chain through the duct to help in dislodging the powder once the part has been printed. In general, complex holes or ducts require larger diameters in order to achieve thorough removal of the unfused powder.

It is possible to print interlocking parts and assemblies in a single build. Parts that are printed together should have a minimum clearance of 0.5 mm.

For embossed or engraved textures, we advise a minimum thickness of 0.25 mm. For legible engraved or embossed text, we recommend letters with a minimum line thickness of 0.5 mm, a depth of 1 mm, and an overall height of at least 2.5 mm.

We strongly recommend that you do not design large, flat plains in dimensions like an A4 page. In most cases, your model will deform. This process is called “warping”. Even if you create support ribs under your plane, it doesn’t solve the problem. It increases the chance of deformation even more. The key here is to avoid big flat planes.

One way of making sure all the shells in your design stay together and can be processed as one part is to connect the different shells with support beams. It is important that the parts are well connected and that the connection beams are strong enough. Use a minimum wall thickness of 3 mm as anything thinner will not be strong enough to support the different parts of your design.

The heavier/bulkier your individual parts are, the thicker the connecting beams should be. If the connections between the parts are too weak, there is a risk that your parts might get lost. You can prevent bulkier shells by hollowing them out. Just don’t forget to provide several large drainage holes so that the powder on the inside can be removed – otherwise, your part will not become lighter. The part’s wall should be less than 5 mm thick.

It’s also advisable to have 4 firm connections per shell. The larger the shells, the more difficult they are to connect properly. That’s why the sum of the dimensions of the imaginary box (X+Y+Z) around your design should be less than 350 mm.

Another option that will allow you to have multiple shells printed in one go is to place all of your parts into a container. This means that you will need to design a container around you parts. Here are some basic things to take into account when designing that container. Always engrave your container with a unique label identical to the filename of your design so we can easily identify your box as we won’t be able to check the contents of your container. Use a clearly readable font such as Arial Black for the engraved text. We recommend using letters with a minimum line thickness of 1 mm, a depth of 0.8 mm, and an overall height of at least 3 mm.

It is advised to use a perforated container because that will allow us to remove most of the excessive powder from your parts. We recommend the following minimum feature sizes for your container: at least a 1.5 mm thickness for the grid lines; and a minimum of a 4 x 4 mm square up to a maximum of 10 x 10 mm. Make sure the parts on the inside of your container cannot pass through the perforations of the container to ensure that all your parts stay together. Parts that pass through the holes might get lost.

In addition to your container features, you also need to keep a minimum spacing distance of 3 mm between each individual part and between the sides of the container and the parts. If the distance is smaller than this, parts might get sintered together.

If the overall volume of your container is larger than 1700 cm³, you should limit the density in the container because parts that are too dense can cause an irregular cooling down process. This may cause deformation of your parts. Limit the total volume of the model to 10% of the overall volume of the container.

If you have fragile parts in the container, we recommend connecting the individual parts to the container. This will prevent fragile parts from hitting each other during shipment. Otherwise, your parts will be loose in the closed container and may damage each other by moving around during the shipping process.

Once printed, each model will need to be cleaned with a brush and sandblasted to remove the excess powder stuck to your model. This is the same for grouped models but in these cases, access to all of the parts is more difficult. Because parts will be connected to each other as well as a container, this may prevent every edge and corner from getting sandblasted. Please be aware that some residual powder might be present when receiving your parts. To clean your parts further, the residual powder can be removed with a brush or compressed air.

Please be aware that grouped models are only offered in natural finish. Because of the limitations stated above for these types of files, a good result cannot be guaranteed. Other finishes can be achieved through various post-processing techniques but will require perfectly cleaned and fully accessible parts, which is not possible for grouped models enclosed in a container immediately upon printing.

Several factors make it hard to fully predict the outcome of the polishing process. One of them is the geometry of your model, which can act differently each time it is put in the tumbling machine. In general, you should have wall thicknesses of at least 1 mm throughout your model. Although we carefully place and orientate your models in our printers to minimize “weak points” created by the layered buildup of your model, certain elements of your design may be more sensitive to the impacts of the polishing stones than others. Therefore, we suggest adding some extra wall thickness if your design can allow for it. Polishing is not advised when your model has tiny details like pins because they will break off during the polishing process.

As already mentioned, small polishing stones are used to make the surface of your model smoother. However, because of the size of the stones, they can easily get stuck inside small holes. Therefore, we recommend that any openings that need polishing be larger than 6.5 mm in diameter. This helps avoid the problem of the stones getting stuck inside your model. Also, note that the inside of your model will always be less polished than the outside - in fact, your model will not be polished at all on the inside if the holes are smaller than 6.5 mm because the stones won't be able to enter.

If your model contains sharp edges, these will be rounded off. Rounded corners and smooth transitions between surfaces will have a higher degree of polishing than sharp edges. Polishing will take 0.1 mm of material off your model, so add extra wall thickness to avoid any problems.

Embossed details on your model tend to be worn away by the polishing stones. Make sure to raise these details by at least 1 mm, otherwise they may disappear when your model is polished. Engraved details are less of a problem because, in most cases, the stones won’t be able to reach the inside of the engraving; however, the edges may still be affected. To be on the safe side, make sure your engravings are deeper than 1 mm.