Metal 3D Printing

What it does

Metal additive manufacturing builds a part up out of metal instead of cutting it out of a block. Several different processes share that description and they are not interchangeable. Laser powder bed fusion melts thin layers of powder with a laser. Binder jetting glues powder together and then sinters it in a furnace. Directed energy deposition, including wire arc, lays metal down through a nozzle or a welding torch and is closer to automated welding than to printing.

How it works

In powder bed fusion a recoater spreads a layer of powder a few tens of microns thick across a build plate inside an inert gas chamber. One or more lasers melt the cross section of the part into the layer below. The plate drops, the recoater spreads again, and the cycle repeats for the height of the part. Everything is then cut off the plate, heat treated to relieve stress and usually machined on the surfaces that matter. Binder jetting prints a binder instead of melting, so the machine runs faster and cooler, but the green part has to be debound and sintered, and it shrinks while that happens, which the model has to allow for. Wire arc builds much larger and much rougher shapes quickly and is then machined back.

The numbers

Layer thickness in powder bed fusion is typically in the 20 to 100 micron range, and build envelopes on production machines commonly run from roughly 250 mm cubed up to about a meter on the largest multi-laser systems. As-built surfaces are rough enough that any sealing or bearing face gets machined afterwards. The cost that surprises people is not the machine time: it is powder handling, inert gas, support removal, heat treatment and the machining that follows. Compare quoted build rates carefully, because makers measure them differently.

Who uses one

Aerospace, medical implants and instruments, motorsport, oil and gas, tooling shops printing conformal cooling channels into mold inserts, and any plant that needs a discontinued part that nobody will tool for again.