The Top 10 Tips You Should Consider When Designing Your FDM Part

Fused Deposition Modeling (FDM) is one of the most popular 3D printing technologies for hobbyists, service bureaus, and OEMs alike. From cost-effective prototyping to functional parts, FDM is suitable for a wide range of applications and offers great design flexibility. However, to achieve higher accuracy and successfully printed FDM parts, designers and engineers should consider the possibilities and limitations of design for FDM. To help you achieve the best printing results, we have compiled a list of the 10 most important points to consider when designing for FDM.

FDM 3D printer Fused Deposition Modeling works by extruding a filament through a heated nozzle onto a build platform. As the material is deposited, it cools down and solidifies, forming a solid layer of material. This process is repeated layer by layer until the final object is completed. FDM typically works with a wide range of production-grade thermoplastic materials, although some metal filaments can also be used. It should also be noted that 3D-printed FDM parts usually have a rough surface finish and therefore require some form of post-processing to achieve a smoother surface.

It is important to ensure that the FDM design is watertight, i.e., that there are no holes on the surface of your 3D model. A watertight design can affect the printability of a part - non-watertight models cannot be 3D printed. Therefore, it is important that you check your design before sending it for printing.

Your FDM designs can often contain complex features such as steep overhangs, bridges, holes, and hollow profiles. To avoid build failures, these features require support structures. In general, it is easier to reduce or avoid supports since they add time and cost to the production process and leave traces after removal. However, the use of support structures often cannot be avoided since complex geometries can be printed. When designing parts for FDM, it is recommended to apply the 45-degree rule: features with angles less than 45 degrees must be supported to ensure that a part does not break during the printing process. Another thing you should keep in mind is that the walls for supports should be at least 1.2 - 1.5 mm thick to provide your part with sufficient strength.

The minimum wall thickness for FDM parts is determined by the filament size as well as the nozzle diameter of a 3D printer. To ensure successful printing, a rule of thumb is to design walls with twice the thickness of the nozzle diameter, with a minimum thickness of 1.5-2 mm. Although thicker walls result in stronger parts, designing walls that are too thick will increase your production times and costs and lead to printing problems such as warping. However, if your part requires thick walls, you can design cross-hatched internal structures instead of solid walls, which save material and reduce print time.

The FDM process typically produces undersized holes. This means that, for example, a hole with a diameter of 5 mm can be printed with a diameter of approximately 4.8 mm. Therefore, it is recommended to design oversized holes. It is generally recommended to increase the hole diameter by 2% to 4% for holes up to 10 mm. If the accuracy of a hole diameter is critical, the hole can be 3D-printed undersized and then drilled to achieve the correct diameter.

When developing threads, sharp edges and 90-degree angles should be avoided. The recommended thread type for FDM is 29-degree threads (also known as ACME threads) with a thread pitch of at least 0.8 mm. Also keep in mind that holes for threads should be larger than 3 mm in order to be 3D printed.

When developing small features for FDM, the recommended feature size for engraved details is 1 mm thickness and 0.3 mm depth to ensure readability. The minimum size for columns and pins must also be considered during the design phase: these features should not be less than 2 mm in diameter to be printable.

Since the material in FDM is heated during the printing process, temperature changes that occur can lead to deformations in your part. Fortunately, these problems can be avoided with design features such as fillets and chamfers. By adding a chamfer along the bottom edge of a part, thermal stresses can be distributed more evenly, which reduces warping and shrinkage. Adding chamfers also means that your part can be easily removed from the build platform. In addition to chamfers, fillets can be incorporated into a 3D model to reduce stresses during printing and increase the strength of a part. They can also be added to overhang surfaces of more than 45 degrees, which eliminates the need for supports.

Part orientation is an important point that must be considered, as it can affect the surface quality and strength of your part as well as the number of supports required. First, it should be noted that upward-facing surfaces tend to have better surface finish. Second, since curved and angled surfaces are often susceptible to stair-stepping effects (rough surface texture), you can orient such surfaces parallel to the build platform to minimize this effect. Finally, you can eliminate supports for holes by orienting them in the vertical direction. If parts have multiple holes in different directions, you should first pay attention to blind holes and then to holes with the smallest diameter. FDM parts are highly anisotropic, meaning that parts are much stronger in the XY axis than in the Z plane. To ensure strength, it is advisable to design the part so that brittle features are oriented parallel to the surface.

It often makes sense to break down complex 3D models into several parts, print them separately and then assemble them. This not only reduces the number of supports and simplifies post-processing, but also accelerates the printing process while saving material at the same time.

FDM is perhaps the most cost-effective technology for affordable prototyping and functional parts. To get the most out of your FDM printing process, however, design guidelines for the FDM printing process should be considered before sending print jobs to production. While FDM involves a certain degree of trial-and-error approach, these considerations can reduce the complexity of your processes and significantly increase efficiency.