FDM 3D Printing is a best entry-level technology for enthusiasts, hobbyists, designers, and engineers. Designing for FDM 3D printing is simple but a designer must know the limitations in order to have a successful 3D printing experience and higher success rate for prints.
Here, we explain 9 important tips for designing for FDM 3D Printing.
Generally, FDM 3D printers have a Z-axis resolution of 100 microns (0.1 mm) and an X-Y resolution of 500 microns (0.5 mm). These can be the guiding principles for designing for FDM 3D printing. By a rule of Thumb, the feature size in the X-Y direction should be equal to the nozzle diameter and the wall thickness should be two times the nozzle diameter.
Even though the feature size also depends on the capability of the 3D printer and the material, several general guidelines are established for new learners to achieve a higher print success rate.
Minimum Thickness: 1 mm
Minimum feature Size: 0.8 mm
Minimum Emboss Details: 0.1 mm
Minimum Engraving Details: 0.4 mm
In FDM 3D Printing, the first layer acts as a base for the next layer to be printed upon. Without a base, the material will be deposited in thin air and the printing will never form the desired shape. To avoid such instances, FDM 3D printing uses support structures for layers which have a partial base like in case of overhangs and bridges.
The support material, most of the times, is hard to remove and leaves unnecessary marks on the printed parts. Moreover, supports mean added material and increased cost along with extra printing time. It is important to understand the rules governing designing for FDM 3D Printing, so the best practice is to reduce or avoid the support structures in the design.
45 Degree Rule: Walls with more than 45-degree angle (horizontal perspective) will need to be printed with supports. If the wall has an angle less than 45 degrees then there is no need for support structures.
Note: Angles more than 45 degree but close to 45 degrees can be printed without supports but by keeping a close watch on the print and adjusting the print speed and monitoring it.
Edges with Fillet’s and Chamfers
The FDM 3D printer nozzles have a circular cross-section, so the deposited material will also have a radius. The corners will never be perfectly edgy. This means a square printed in an FDM 3D printer will never be a perfect square.
Considering this limitation, either the design must include such a tolerance to accommodate the curvy edges, or the design must be modified to include fillets and chamfers.
Fillets and chamfers not only help in eliminating supports structures in some cases but also helps in increasing the strength of the parts at the sharp edges. It also aids in easy removal of parts and gives a nice aesthetic smoothness and flow to your design.
Also Read: How To Strengthen 3D Printed Parts in 5 Simple Ways
Designing to 3D Printer Size
Designing for FDM 3D Printing has some limitations and restriction which have to be taken into consideration. But most designs are designed in isolation and the manufacturability is not taken into consideration. This is crucial when the part is to be manufactured in a 3D printer. Existing 3D printers are quite small and many parts are to be broken down into smaller segments and then assembled later.
Considering the size of the 3D printer to be used for printing the product, the design has to accommodate the size of the complete part, or the smaller segments it is broken down into.
Companies like BigRep and Massivit manufacture large 3D printers but not every company will have these big machines at their disposal.
Generally, FDM 3D printers print undersized holes. So a 5 mm diameter hole will measure around 4.8 mm. It is a general rule of thumb to consider a 2-4% of undersized for a hole of up to 10 mm diameter. For bigger holes, the correction percentage will be smaller.
Through post-processing techniques, the holes can always be made bigger so for tight tolerances and the undersized hole is preferable so it can be post-processed to increase the diameter.
It is important to ensure that the model is watertight. Watertight models are those which are completely solid. Non-watertight designs are not printable and hence it should be checked before you try to print it. Models can be tested in Netfabb or using free Sketchup plugin like Solid Inspector.
Breaking down the model
Often times it is easier to print the model in broken down pieces and then joining/assembling them together. For example, in case of a sphere, the complete sphere may need supports but if the sphere is divided into two separate hemispheres then individually they will not require any support structure.
The hole orientation should preferably be in a vertical direction. A vertically printed hole will not have any support, unlike the horizontal hole where the support removal can prove to be pretty tedious.
Due to layer-by-layer deposition of the material FDM 3D printing round edges formed at the ends. This creates a stress concentration t the joints and can lead to cracks. So, the build direction has to be considered during designing itself.
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