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 low-cost 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 designing 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.

The FDM printing process

FDM 3D printers Fused Deposition Modeling works by extruding a filament through a heated nozzle onto a build platform. As the material is deposited, it cools 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.

10 tips when designing for FDM

1. make your design waterproof

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.

2. support structures

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

3. wall thickness

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

4. holes

The FDM process typically produces undersized holes. This means, for example, that a hole with a diameter of 5 mm can be printed with a diameter of around 4.8 mm. Therefore, it is recommended to design oversized holes. It is usually recommended to increase a 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.  

5th thread

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 of at least 0.8 mm. Also keep in mind that holes for threads should be larger than 3 mm to be 3D printed.

6. minimum size for details

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

7. radii and chamfers

Since the material in FDM is heated during the printing process, any temperature changes that occur can lead to deformations in your part. Fortunately, these issues can be avoided with design features such as curves and chamfers. By adding a chamfer along the bottom edge of a part, heat stresses can be distributed more evenly, reducing warpage and shrinkage. Adding chamfers also means that your part can be easily removed from the build platform. In addition to chamfers, curves can be designed 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, eliminating the need for supports.  

8. partial orientation

Part orientation is an important point to consider as it can affect the surface quality and strength of your part, as well as the number of fixtures required. Firstly, it should be noted that upward facing surfaces tend to have a better surface finish. Second, since curved and angled surfaces are often prone to stair-step effects (rough surface texture), you can align such surfaces parallel to the build platform to minimize this effect. Finally, you can eliminate the brackets for holes by aligning them in a vertical direction. If parts have multiple holes in different directions, you should first look for blind holes and then for holes with the smallest diameter. FDM parts are highly anisotropic, which means 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 the brittle features are aligned parallel to the surface.  

9. design for assembly

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

Summary

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