Take a raw FDM print of an engineering thermoplastic part, say a PA-CF bracket, and assess it as a production article. The major surfaces are decent, the structural performance is in spec, but threaded holes are nominal at best, mating surfaces carry visible layer lines, and the part probably will not slip into a tight tolerance assembly without adjustment.
Industrial AM parts almost always benefit from post processing. The discipline is choosing the right operations to bring the part to production quality without consuming the cost and time advantage of additive manufacture in the first place.
Should I leave critical surfaces to the printer or machine them?
Machine them. The cleanest path to high tolerance features, including mating surfaces, bore IDs and datum faces, is to design them as machining stock allowances and finish on a mill or lathe. Print the part with 0.5 to 1 mm of additional material on critical surfaces, then face mill or bore to final dimension.
This combines additive freedom in shape with machining precision in tolerance and surface finish. It is particularly valuable for parts that bolt to existing mounting interfaces with tight tolerances. Our CNC machining cell handles the finishing pass in line with the print schedule.
What is the right approach to threaded holes?
There are three standard approaches, ranked by load and cycle expectation. Each has its place, and mixing them across a single assembly is normal practice. The list below sits roughly in order of cost and effort, from quickest to most involved.
Tap in print: low load, low cycle, M5 and larger in PA-GF
Heat set inserts: the standard for repeat assembly interfaces
Chemically bonded inserts: high load, high cycle, vibration prone
Helicoils: aerospace style repairs and high strength fixings
Through bolts with steel washers: structural connections
Specify per hole, not per part
Different holes on the same part can use different threading strategies. Call them out individually on the drawing so the production team does not default to the cheapest option everywhere.
How do I clean up the surface finish?
Layer line reduction is the most common surface treatment. Light sanding from 180 to 400 grit followed by primer and paint produces near injection moulded surface quality on FDM parts. Vapour smoothing with chemical solvent vapour works well for ABS and ASA but requires controlled facilities and is not suitable for every polymer.
For functional surfaces such as bearing journals or seal grooves, grinding or polishing produces sub micron finishes. These operations run on overstock material left during printing for that purpose. Surface specification should be called out per face on the drawing so production knows where to spend the effort and where a clean printed finish is enough.
Does annealing actually help?
Yes, for the right materials. Many engineering thermoplastics benefit from controlled annealing, a sustained period at elevated temperature that increases crystallinity and improves mechanical properties. Annealed PA-CF and PEEK parts can show 20 to 40 percent gains in tensile strength and stiffness versus as printed equivalents.
Annealing also relieves residual print stresses, reducing distortion risk in service. The trade off is some part shrinkage, typically 0.5 to 2 percent, which has to be accommodated in the design. We work with OzFDM on validated annealing windows for the engineering range.