Choose 3D printing over traditional manufacturing for runs below ~5,000 per year, complex or organic geometry, or when you cannot wait weeks to months for tooling. For simple parts in large runs, injection moulding and CNC are often cheaper. For variety, iteration or speed, 3D printing almost always wins.
Four drivers for 3D printing
Time to market. Serving the first 100 customers is possible within weeks. Building a mould takes 2-3 months.
Design flexibility. Every iteration goes straight into production, no tool rework, no NRE per revision.
No minimum order. One part costs the same per unit as a hundred. With SLS bundling, per-unit price even drops as volume rises.
Inventory-free. On-demand printing means no capital tied up in stock, no risk of obsolete components.
Four cases where traditional wins
Large runs of stable designs. From ~10,000/year, injection moulding wins on per-part cost.
Metals. Stainless, aluminium, steel, brass: CNC or casting. SLS offers no metals.
Block-material geometries. Flanges, plates and brackets with flat faces are cheap on CNC out of aluminium block.
Ultra-tight tolerances. Below ±0.05 mm needs CNC precision or finishing.
The hybrid strategy
You do not have to choose. Most common: SLS for the first 6-12 months of bridge production during market validation, injection moulding once the design settles and volume justifies it. Or: SLS for exceptions and variants (colours, left/right, customer-specific) alongside a moulded mainstream.
Talk to an engineer if you want to know where the tipping point sits for your case.