3D Product Design for Additive Manufacturing 2 — Questions and Answers
Question 1: When designing holes for press-fit inserts in an FDM part, what is the recommended approach?
- Design holes exactly to nominal size
- Design holes 0.1–0.2mm undersized, then drill or ream to final size (Correct answer)
- Design holes 1mm oversized to allow shrinkage compensation
- Avoid printed holes entirely and always drill post-print
Correct answer: Design holes 0.1–0.2mm undersized, then drill or ream to final size
FDM holes tend to print slightly undersized due to material shrinkage and layer geometry; designing them slightly undersized and finishing to size yields the most accurate press fits.
Question 2: What is the primary engineering benefit of incorporating lattice structures into a 3D printed product?
- Increasing part weight for added stability
- Significantly reducing mass while maintaining structural stiffness (Correct answer)
- Improving electrical conductivity of the part
- Enabling easier post-processing and sanding
Correct answer: Significantly reducing mass while maintaining structural stiffness
Lattice structures are open-cell frameworks that remove bulk material from low-stress regions, dramatically reducing weight while preserving the structural integrity demanded by the application.
Question 3: When designing snap-fit joints for FDM printed parts, which material property pair is most critical?
- Thermal conductivity and hardness
- Electrical resistance and density
- Flexural modulus and elongation at break (Correct answer)
- Tensile strength and thermal expansion
Correct answer: Flexural modulus and elongation at break
Snap fits must deflect under load (requiring low flexural modulus) and return without fracturing (requiring high elongation at break), making these two properties decisive for reliable snap joints.
Question 4: What does 'functional integration' mean in Design for Additive Manufacturing?
- Adding electronic components inside a 3D printed shell
- Consolidating multiple traditionally separate components into a single printed part (Correct answer)
- Integrating software simulation into the design workflow
- Using multiple filament materials in one print job
Correct answer: Consolidating multiple traditionally separate components into a single printed part
Functional integration leverages additive manufacturing's geometric freedom to merge several parts into one, reducing part count, assembly time, and potential failure points.
Question 5: Why must designers account for anisotropic mechanical properties when creating press-fit assemblies with FDM parts?
- Anisotropy increases overall part density
- FDM parts are stronger and stiffer along the Z (build) axis than the XY plane
- FDM parts are stronger in XY than along Z, so fit forces in the build direction may cause layer delamination (Correct answer)
- Anisotropy only affects surface finish, not mechanical performance
Correct answer: FDM parts are stronger in XY than along Z, so fit forces in the build direction may cause layer delamination
FDM parts are weakest in the Z (layer stacking) direction due to incomplete inter-layer bonding; interference fits that apply stress along Z risk delamination failure.
Question 6: How does layer height selection affect the design of curved surfaces on an FDM part?
- Layer height affects only print speed, not surface geometry
- Thicker layers exaggerate the staircase effect on curved surfaces, which designers must consider for functional or aesthetic requirements (Correct answer)
- Smaller layer heights always reduce part strength
- Layer height only matters for flat top and bottom surfaces
Correct answer: Thicker layers exaggerate the staircase effect on curved surfaces, which designers must consider for functional or aesthetic requirements
Larger layer heights create a more pronounced staircase stepping effect on angled or curved surfaces; designers should orient critical curved features or specify finer layers when surface quality matters.
Question 7: What is the 'staircase effect' and how can part orientation in the slicer help mitigate it?
- Skipped layers from filament runout; prevented by using a runout sensor
- Visible layer stepping on angled or curved surfaces; mitigated by orienting critical curved features closer to vertical (Correct answer)
- Uneven first-layer adhesion; corrected by bed leveling
- Warping on large flat surfaces; corrected by using an enclosure
Correct answer: Visible layer stepping on angled or curved surfaces; mitigated by orienting critical curved features closer to vertical
The staircase effect is visible stepping on non-vertical surfaces caused by layer-by-layer deposition; rotating the part so important curves lie closer to vertical reduces the apparent stepping.
3D Product Design for Additive Manufacturing 2
When designing holes for press-fit inserts in an FDM part, what is the recommended approach?