3D printing in the design process: from model to prototype

The education's competency goals say that you must be able to use 3D printing in connection with work on 3D models and export files for use in other CAD systems. This sounds technical, but the point is practical: A prototype in hand reveals flaws and improvement opportunities that no screen shows. Does the grip fit a hand? Can the parts actually be assembled? Is the material thickness sufficient? 3D printing makes such questions cheap to answer early.

§The three most widely used printing technologies

• 01FDM/FFF (Fused Deposition Modelling): molten thermoplastic (e.g. PLA, PETG, ABS) is laid up layer by layer through a nozzle. Cheapest and most widespread — good for design studies and functional prototypes.
• 02SLA (stereolithography): liquid resin is hardened layer by layer with UV light. Very fine details and smooth surfaces — good for small, precise parts, but requires post-curing and chemical handling.
• 03SLS (selective laser sintering): a powder (typically nylon) is melted together with a laser. Strong, functional parts without support structures because the powder carries the part — but more expensive equipment.

§File formats: STL, STEP and 3MF

For printing, the model is typically exported as STL: a pure triangle mesh that only describes the surface — without units, materials or product data. STL is the de facto standard for slicers, but unsuitable for further design work because all parametrics and precise geometry are discarded. If the model is to go to another CAD system, STEP (standardized in ISO 10303) is used instead, which preserves the precise geometry. The newer 3MF format can also contain units, colours and material information and is gaining traction as a print format.

§Tolerances and geometry in print

A printed item does not automatically hit the drawing's dimensions. Plastic shrinks when cooled holes typically become slightly smaller than drawn and accuracy depends on technology material and printer calibration. Therefore design with tolerance: fit surfaces get some play critical holes are printed smaller and bored or reamed afterwards and threads are often cut in post-assembly rather than printed. Layer thickness is a compromise — thin layers give finer surface but longer print time.

§Support, Guidance and Strength

With FDM and SLA, overhangs require support structures — temporary material that supports the workpiece during printing and is removed afterwards. The workpiece's orientation on the print bed determines both how much support is needed and where the workpiece is strong: the layers are the workpiece's weak direction so a workpiece loaded across the layers can break surprisingly easily. Think the print direction in already when you design the prototype.

§Safety and work environment

3D printing is not risk-free: Uncured resin for SLA printing can irritate skin and airways and must be handled with gloves and good ventilation, and fine powder from SLS processes must not be inhaled. Follow the supplier's safety data sheets and place printers with vapour extraction in ventilated rooms — workplace rules on substances and materials also apply in the drawing office's print corner.

“A prototype for twenty-five kroner can save a tool change worth a hundred thousand.”

— Experience from prototype work in industry.