One of the main advantages of metal 3D printing is that it allows for a whole new approach to design in which complex and unique shapes can be created. For manufacturers, this means that highly detailed geometric parts can be produced as a single piece while being lighter yet stronger than the ones produced with traditional methods – without additional costs and with a reduction on material waste. However, this requires the design of existing parts to be optimized for additive manufacturing. In order to help engineers achieve those optimizations, we compiled a list of the best practices on how to design for metal 3D printing.
#1 Avoid overhangs larger than 0.5 mm
In order to avoid the deformation of your part, you should support the overhanging geometries with additional structures. This can be done through a small modification between the vertical face and the out-sticking wall, which will distribute the strength further from the inside corner. This modification consists of applying a fillet or a chamfer at the intersection point where the overhang is located. In our opinion, a chamfer works better because you can extend the overhang at by the depth of the chamfer. As for the fillet, it will allow you to extend the overhang at by ½ – 1x the radius of the fillet.
You can compare this situation to building a ceiling and roof without enough supporting pillars between the outer walls.
Overhangs are the elements of the design that are unsupported by the rest of the part. If no other geometry in the design supports it, the bottom surface may begin to collapse, resulting in the deformation of the whole geometry.
The distance from the rest of the mass should therefore not exceed ±0.5 mm.
When designing your part for metal 3D printing, try to avoid overhangs and, if necessary, support them with additional geometries.
#2 Improve the surface quality
The optimal position of the part in the printer can be best explained by an example of a circular hole. If printed in parallel to the build plate, the perfectly circular shape will be maintained. If turned by 90°, so perpendicular to the build plate, the hole might change shape into an oval and be much less functional.
Another issue is that the direction in which the part is printed may significantly affect the quality of its outer surface. Orienting the most crucial planes of the part horizontal to the build plate will improve its appearance.
Depending on the printer, you can achieve good surface quality on faces angled as little as 20 – 30° from the build plate. However, remember that the walls angled less than ±45° with reference to the build plate might have a poorer surface quality. To achieve greater smoothness, you should avoid narrow angles in your design.
An experienced metal 3D printer operator will know how to achieve the highest surface quality in your part. Nevertheless, remember about positioning your model well.
#3 Adjust the wall thickness
Printers which use metal powders can reach the printing resolution of 100-150 μm in the XY plane parallel to the build plate. In the Z plane or print direction, the tolerance is 1 layer thickness. However, it does not mean that all the features can be made to such tight tolerances. Your print may lack an acceptable degree of details fidelity if they are too fine.
In 3D printing, wall thickness refers to the distance between one surface of your model and its opposite sheer surface. Minimum wall thickness is defined as the minimum thickness your model should have at any point of the geometry.
Bear in mind that no elements or walls thinner than 0.5 mm are recommended. Selective laser sintering or melting may cause the distortion of the shape due to the high heat. Both thin walls and small elements (for example, letters engraved on the part) are also more difficult to successfully post-process.
Remember not to demand too much precision of fine details in parts 3D printed in metal.
#4 Create gaps in the correct sizes
The printability of gaps and voids differs between various metal 3D printers. Generally speaking, those details should not be thinner than 0.5 mm. If the distance between neighboring walls is lower than that, the gaps show poor resolution and the elements may just merge together.
Round holes or threads may lose their concentricity or collapse if their diameter is lower than the advisable 0.5 mm.
Of course, you can further drill out and machine your 3D printed parts, but this option introduces additional costs and delays in production.
In the case of big parts, you may print threads with quite a high accuracy. It varies between designs, parts, and materials, though.
When designing for metal 3D printing, remember to design proper sizes of round holes and spacings.
#5 Add bridges and supports suitable for metal 3D printing
There are two ways of designing the part in order to avoid the collapse of double-sided overhangs. This might be necessary if the distance between the vertical connected walls in your part is greater than 1mm. With supports like chamfers or fillets, you can extend the overhang up to 2x the chamfer depth or fillet radius.
To add structure, you can round the double-sided overhangs with an arch, as it was done on ancient bridges. The structure will get stronger as mass accumulates on top and can be more visually appealing.
Another design trick you might apply is to create a pointed profile on the bottom surface of the overhang. You can achieve that by adding double-angled chamfers meeting in the center and forming a triangle.
If none of the tips above is an option for your design, cut-out structures can be also held by conventional support elements. These are typically thin, high cylinders or cuboids which you can remove in the post-processing phase.
When designing the overhanging elements of your part, remember to design them in a way that strengthens the corners.
#6 Avoid the caves
If you are creating a hollow model in order to reduce the weight and amount of material used, it is important to leave more than one hole in the design. This will allow the removal of remaining unused powder in post-processing.
Since the parts are made by melting, or sintering, the metal powder in the build box, some powder will become encapsulated in the inner cavities.
The minimum opening should be 2 – 4 mm and will serve as an exit allowing to remove the rest of the powder from the inside of your part.
Conclusion
When designing your part for metal 3D printing, it is best to keep in mind these basic design guidelines. A good design will let you make the most of metal 3D printing and its possibilities, and improve the quality of your parts.
Remember to avoid the overhangs and, if necessary, support them with additional geometries. Also, do not demand too much precision from fine details in 3D printed metal parts.
When designing for metal 3D printing, remember to make holes and spaces the proper sizes, and modify overhangs to strengthen and support corners.
Last but not least, remember that the excess powder will be encapsulated in your design after printing, and needs to be removed.
An experienced metal 3D printer operator will know how to bring the highest quality to your part, nevertheless remember about positioning your model and its outer walls correctly.
At Beamler, we find metal 3D printing a very promising technology allowing to revolutionize many industrial solutions.
Read the other article on the benefits of using 3D printing instead of conventional technologies, for example, to reduce material waste and create complex, unique structures that cannot be casted.
