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CMfgE: Additive Manufacturing

CMfgE · Work through your exam, one topic at a time.

All guide sections

Additive Manufacturing

Additive Manufacturing tests the seven ASTM/ISO 52900 process categories, how each behaves with materials, and the design and cost consequences of orientation, supports, anisotropy, and post-processing.

The seven categories

  • Vat photopolymerization (SLA, DLP): UV-cured resin, fine features and smooth surfaces, but brittle and UV-degrading parts.
  • Material extrusion (FDM): thermoplastic filament, low cost, pronounced Z-direction weakness, supports needed for overhangs.
  • Powder bed fusion (SLS, DMLS, EBM): laser or electron beam fuses powder; the powder bed supports the part, enabling lattices and nested geometry; residual stress and warping are the main risks.
  • Material jetting: droplets of photopolymer, multi-material and smooth, inkjet-like.
  • Binder jetting: binder printed into powder; fast and inexpensive, but the green part needs sintering or infiltration and shrinks.
  • Sheet lamination: bonded or ultrasonically welded sheets.
  • Directed energy deposition: nozzle-fed powder or wire with a laser or arc, used for repair and large metal structures.

Design rules

Orientation fixes build time, support volume, surface finish on critical faces, and strength direction. Extruded parts typically reach only 50–80% of XY strength in Z. Design rules include minimum feature size, overhang limits near 45°, and drain paths for trapped powder or resin in internal channels. Post-processing - support removal, sintering, HIP, machining of critical faces - often dominates cost and lead time.

Worked example

An FDM part 60 mm tall at 0.2 mm layers is 300 layers. At 45 s per layer, build time = 300 × 45 s = 13,500 s = 3.75 h. Reorienting to 30 mm height halves it to about 1.9 h, but changes support placement and the finish of the critical face. The exam wants that trade stated, not just the arithmetic.

Traps

Assuming AM parts are tolerance-free; most polymer processes still need machining for fits. Forgetting SLS needs no part supports but does need depowdering. Confusing binder jetting with powder bed fusion. Ignoring anisotropy and orienting the load path across layers.