27 Design Tips for 3D Printing

Bas Koper
03 aug 2018

Additive Manufacturing (AM) or 3D Printing is a production method which offers unique characteristics and possibilities. It allows for designing more freely without having to take into account machining restrictions. In order to be able to design optimally for 3D printing and get the most out of this technology, it is crucial to have a good understanding of the process, its restrictions and its possibilities. At Mobius 3D Technologies (M3DT) we can help you with product design or making adjustments to existing products in order to optimize them for 3D printing. In this text, we offer a list containing 27 design tips and considerations that will help you along.

  1. Try to minimize the amount of supports needed

Surfaces at an angle of 45deg or less with the build plate will require print supports. Try to make sure that the least amount of print supports are required during the print process. This will reduce the amount of post processing work and result in a lower price.

  1. Combine parts in to one part to avoid assembling.

Review your assemblies and consider if it might be possible to combine various parts into one part. The form freedom of AM might make it possible to produce such complex combined parts as one product.

  1. Make full use of the design freedom that this technology offers.

You do not need to worry about free form surfaces like aerodynamic surfaces or optimized free form flow channels. With AM, it is just as easy to manufacture free from surfaces and complex shapes as printing cubes!

  1. Make sure that hollow parts have a hole to remove the powder after printing.

Thin and asymmetrical shapes are at the highest risk to deform. Deformations can be largely prevented with proper heat treatment. Stress relieving heat treatment is applied to the 3D printed products while they are still attached to the build plate with print supports. This ensures that internal stresses are relieved before the print supports are removed such that deformation that could result from these stresses are mitigated.

  1. Holes with diameters larger than 7 mm require internal supports

The maximum diameter for supportless, vertically oriented, holes or channels is about 7mm. Holes or channels with a larger diameter will require print internal print supports which could be difficult to remove. A possibility is to design channels with a droplet shape. In this case, the top of the circular cross section of a channel is replaced by two lines at 45deg with a smaller half circle (diameter less than 7mm) on top. It is, of course, required to know how the product will be oriented on the build plate.

  1. Do not create overhangs of more than 0.5 mm without supports

The maximum unsupported overhang length is about 0.5mm. A larger 90 degrees overhang will require print supports.

  1. Avoid to make contacts between surfaces by keeping a clearance of 0.2 mm

It is advised to allow for a minimum of 0.2mm clearance between surfaces. The advised minimum hole diameter and maximum pin diameter are 0.5mm.

  1. For one-offs: try to design with minimization of build height in mind

The cost for print machine hours is the main contribution to the product price. Therefore it is important to make efficient use of the machine’s build volume. For one-off’s. if possible, design the product such that it can easily be orientated with a minimal print height. In order to make this feasible, one must apply the print support rules to that product orientation. For larger batches, this is less important. As long as the build volume is efficiently used.

  1. Take into account build volume limitations

At Mobius 3D Technologies the largest print volume we currently offer is 250x250x280mm. It is possible to print a product in parts and weld them together afterwards. Since the AM process is similar to a welding process, AM materials are usually well suited for welding. However, this is not done often.

  1. Think about the surface roughness and if it can be modified after printing

What surface roughness can be expected? Straight out of the printer, a surface roughness of about 6Ra can be expected. After some tumbling and/or media blasting, a roughness of 2-3Ra is attainable. With proper polishing, a mirror finish (<0.8Ra) can be achieved on AM produced parts.

  1. Know what tolerances can reasonably be expected from the AM production method.

Take into account a dimensional accuracy of about +/- 0.1mm per 100mm. When in doubt if certain dimensional tolerances be achieved, contact your AM manufacturer. 3D printing can, for now, not achieve micrometer level precision. If such tolerances are required, post machining will be necessary. In such a case it might be smart to add attachments to the print design which can be used for clamping during the machining process.

  1. Be aware that holes often turn out slightly smaller than the dimensions indicated.

Holes often turn out slightly smaller than the dimensions indicated in the print file due to material deformations. Especially for small holes, the shrinkage can be a significant percentage of the diameter. It is difficult to directly determine what percentage of shrinkage to take into account since this is dependent on the hole diameter, orientation and the amount of surrounding material. At M3DT we apply scaling to the hole diameters in the print files to counteract shrinkage.

  1. Long, slender products might deform during printing, if not properly designed & positioned.

During the AM process, a significant amount of heat is applied in order to build up the product. This heat will create material stresses which can result in product deformations. The way in which a product deforms and the magnitude of the deformations is very dependent on the specific product’s shape, product orientation, proper placement of print supports, machine settings and heat treatment.

  1. If your product will be part of an assembly, take into account the previous few tips on what tolerances can be expected.

Consider sharing information on how the product will be used and how it will be assembled with your manufacturer in order to get to best result.

  1. Combine printing with machining, printing before machining or machining before printing.

Some products are relatively easy to manufacture with other methods for the most part, but might have a small feature which is very difficult to make. In such a case it might be worth considering machining a half product, placing this half product in the 3D printer and adding the feature with Additive Manufacturing.

  1. Keep in mind that the loose powder needs to be removed after printing.

If a product contains internal features like cooling channels, the print powder will have to be removed after the printing process is completed. This is usually no problem. Mobius has experience with clearing a nearly 1 meter long curled channel with a diameter of just 1mm by simply using air pressure. It is also possible to print hollow structures to create lightweight components (and possibly reduce print time). Do take into account that, if the powder has to be removed from the cavity, a small hole will have to be placed somewhere in order to have access. If required, the hole can be closed with welding.

  1. When designing a product with internal channels or cavities do take into account the design constraints for support-less printing.

Supports might be required inside the internal structure. These supports can either remain inside the product or be removed. If they must be removed, it is important to think about if and how this can be done. Specialized tooling may be required.

  1. Internal channels can be treated to improve their surface finish to 0.8 Ra.

As discussed in tip 10, untreated surfaces will have a roughness of about 6 Ra. The same goes for internal channels. However, often a better surface finish will be required in order to improve flow characteristics. This can be achieved with extrude honing. During the honing process, a thing paste is pumped through the channels and acts as a polishing agent.

  1. Use Meta-material characteristics without additional manufacturing costs.

An exciting new possibility which Additive Manufacturing has unlocked is the development of previously only theoretic meta-materials. Meta-materials are porous materials which are usually structured as repeating unit mesh structure. By changing the geometry of the mesh it is possible to tweak the effective material properties. We will not go in depth on this subject here, but there is a lot of interesting literature available on this subject.

  1. Get topology optimization to work for you!

Topology optimisation can help you design mass optimized structures efficiently. Topology optimisation programs are iterative solvers that make use of finite element methods (FEM) to determine material stresses given a certain part geometry and loading conditions. After each FEM cycle, some material is removed from the regions with low stresses. This process results in a usually somewhat organic looking shape which is optimized for handling specified loading conditions with minimal use of material. Manufacturing such shapes is very challenging with production methods other than Additive Manufacturing.

  1. Make sure that you have sufficient wall-thickness, at least 0.3 mm

3D printing with metals does need a wall thickness of at least 0.3 mm. Everything thinner than that is critical. It is not impossible, but one has to keep in mind that it will take extra efforts to come to the right finishing.

  1. Consider the layer thickness to define the quality you would like to achieve

In principle, any shape can be produced with AM. Some things, however, should be taken into account when designing for Additive Manufacturing. The product is build up layer by layer. These layers usually vary from 20 to 100 micrometres. Using the right machine settings, smaller layers will result in a higher quality product with a more smooth surface and less micro-porosities. Well manufactured AM product can reach a density of more than 99.9%.

  1. Be aware of the build settings & build orientation

Quality products made with AM have material properties that are very similar to machined or casted products. However, the quality of the product depends on using the right machining settings, smart product placement and proper print powder material management. Often, the ductility of AM materials is higher when compared to the same material in bulk or casted form. This can be beneficial or not, depending on the product’s function and specifications. Most AM suppliers will have material datasheets available.

  1. Know where you would like to place the supports on

In order to create sufficient support while building up a product layer by layer, print supports are required that attach the product to the build plate. These supports are removed during post processing. Surfaces which have had these print supports attached will usually require more attention during post processing in order to improve the surface quality. This is one of the factors to take into account when determining the best way to position a product on the build plate. Sometimes, an extra margin is taken on a downwards facing flat surface. This allows for removing some material from the surface such that the required surface finish can be achieved. Some of the “rules” which determine if supports are required on a certain surface are described in the following tips.

  1. Be creative!

Give your mind the freedom to innovate: there are no restrictions on the shape of the product that will bring extra costs. A freely shaped product can be easier to manufacture than a simplified geometry.

  1. Make sure that you have a detailed 3D drawing!

No need for detailed 2D drawings: For complex products, creating proper technical drawings can be a time consuming task. This is not necessary for the AM process since the 3D file itself is used to determine the laser pattern that needs to be followed in order to build up the product. So make sure that your file does not contain undefined edges or unsmooth surfaces. Every single detail will be exposed in the 3D print, so it has to be smooth and defined. If you are unfamiliar with 3D printed products, it is best to specify requirements on surface roughness’s and important tolerances. It might be necessary to perform extra surface treatment or post machining for tight tolerances.

  1. Combine 3D scanning and 3D printing!

Do you need a spare part, but you no longer have any drawings? Think about doing a 3d scan and using the scan as production file for 3D printing!

  1. Don’t worry about your final design: Iterations do not bring additional costs for 3D printing

Changing a small design feature is unlikely to have a significant impact on the manufacturing process. No new machining programming or new casting mould is required. This makes AM a very adaptable process.