GlossaryKind of term: Manufacturing termAdditive manufacturing (AM)
What is additive manufacturing?
Additive manufacturing makes a part by building material up layer by layer from a 3D model, rather than cutting it away as machining does.
On the shop floor it is usually called 3D printing. What defines it is joining material from 3D model data; layer upon layer is the usual way of doing that, not the only one. It stands apart from machining, which removes material, and from forming processes such as casting and forging. It covers plastics and metals, prototypes and end-use parts. The terminology standard ISO/ASTM 52900 uses this term and groups the processes into seven categories.
Which processes fall under additive manufacturing?
For metal, two families are common. In powder bed fusion a laser or electron beam melts a thin layer of powder locally, layer after layer; the part grows on a build plate and usually needs supports under overhanging faces. In directed energy deposition a head feeds wire or powder and melts it onto an existing part or substrate; this builds faster but coarser. Other categories include material extrusion and vat photopolymerisation, mostly for plastics, and binder jetting, which is also used for metal parts and sand moulds. Dimensional accuracy, roughness and material properties depend on process, machine, layer thickness, orientation in the build chamber and heat treatment. Steep thermal gradients and rapid cooling often leave residual stress, which shows up as distortion when the part comes off the plate or is machined.
How does additive manufacturing work in practice?
A printed metal part is usually a starting shape, not a finished size. Fits, sealing faces, toleranced bores and threads are often machined, while the rest of the surface stays as printed or blasted. With powder bed fusion that adds steps a milled part does not have: stress relieving on the build plate, sawing or EDM cutting the part off the plate, support removal, and a setup on a free-form shape, often with a dedicated fixture or printed-on clamping lugs and a datum probed on each part. Whether printing beats machining from solid depends on shape, quantity, material and that post-machining; internal channels and shapes that cannot be milled shift the balance.
What is additive manufacturing often confused with?
Additive manufacturing is not rapid prototyping: prototyping is a use, printing one way to get there, and printed parts also go into service as end-use parts. Nor is it the same as machining printed parts: that is the cutting step that follows the print.
Frequently asked questions
Does a metal 3D printed part still need machining?
Usually, on the functional surfaces: fits, toleranced bores, sealing faces and threads. Which surfaces may stay as printed follows from the drawing and from the size and roughness the print process achieves.
Is 3D printing cheaper than CNC milling?
It depends on shape, quantity and material. A prismatic part with a few pockets is often cheaper from solid. Printing can win on internal channels, lattices and shapes you cannot mill, provided the post-machining is counted.
Which metals can be 3D printed?
Common choices include stainless steels such as 316L, titanium Ti-6Al-4V, aluminium-silicon alloys, nickel alloys and tool steels. How the part machines afterwards depends on the alloy, the print process and the heat treatment.
How do you fixture a 3D printed part?
With a fixture that follows the free form, or on clamping lugs printed on as part of the design and machined off later. The datum is usually probed on the part itself, because the printed shape can depart from the model.