Printing can produce a working assembly in one build, either by consolidating several parts into one solid component or by printing separate parts already interlocked and moving. Both are genuinely useful and both are frequently done for the wrong reason, because a part that can be printed as one piece is not automatically better as one piece.
Printed in place mechanisms
Hinges, ball joints, chain links, captive fasteners and enclosed gear trains can all be printed already assembled, with a designed clearance between the moving surfaces. The clearance has to suit the process: too small and the surfaces fuse or the powder does not clear, too large and the joint is sloppy. Sintered nylon is the most forgiving because unfused powder can be blown out.
Part consolidation and what it buys
Replacing an assembly of several machined parts and fasteners with one printed component removes joints, leak paths, fasteners, inspection steps, part numbers and inventory. On a manifold or a bracket assembly the saving is often larger in the supply chain than in the manufacturing, which is where the real business case for additive frequently lives.
When to keep it an assembly
When one component wears and should be replaceable. When different regions need different materials. When the consolidated part becomes too large to print economically. When inspection of an internal feature becomes impossible. And when consolidation makes the part unrepairable, since a one piece part that fails is scrapped rather than serviced.
Practical design points
Provide escape paths for powder or resin from every internal cavity. Design clearance to the process rather than to a nominal fit. Break the mechanism in first while it is still on the bench, because printed in place joints are often stiff until the first movement. And test the mechanism at the size you will build it, since clearance behaviour does not scale linearly.
Questions people ask about 3d printing assemblies
Can 3D printing produce a working assembly in one build?
Yes. Hinges, joints, chains and gear trains can be printed already interlocked, with a designed clearance between the moving surfaces.
What clearance is needed?
It depends on the process. Sintered nylon is the most forgiving because unfused powder can be cleared; resin and filament processes need more careful clearance design.
What does part consolidation actually save?
Fasteners, joints, leak paths, inspection steps, part numbers and inventory. The supply chain saving is often larger than the manufacturing saving.
When should a part stay an assembly?
When a component wears and should be replaceable, when different materials are needed, when inspection of an internal feature would become impossible, or when repair matters.