Metal additive manufacturing, from powder to flight part.

What metal additive manufacturing is.

Additive manufacturing is the industrial term for 3D printing. ISO/ASTM 52900 defines it as joining materials to make parts from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing (machining) and formative manufacturing (casting, forging, moulding). Metal additive manufacturing applies that idea to engineering alloys: nickel superalloys, copper alloys, titanium, aluminium, steels.

The consequence is that geometry becomes almost free. Internal channels, lattices, thin walls and consolidated assemblies cost nothing extra to print, while they may be impossible to machine or cast. What you pay for instead is machine time, powder and post processing.

The process families, and which one we run.

The standard groups additive processes into seven categories. Five of them are used for metal in production today.

• Powder bed fusion (PBF). A thin layer of powder is spread across a plate and a laser or electron beam melts the cross section of the part. Laser powder bed fusion (LPBF, also SLM or DMLS) is the most widely used metal process and the one AME runs. It gives the finest features, the best surface and near wrought density.
• Directed energy deposition (DED). Powder or wire is fed into a melt pool made by a laser, arc or electron beam. Fast and large, with coarse resolution; used for big structures, repairs and cladding.
• Binder jetting. A liquid binder glues powder into a green part which is then sintered. Cheap and fast per part, but parts shrink 15 to 20 percent in the furnace and finish below full density.
• Material extrusion with bound metal. Metal powder in a polymer binder is extruded like a plastic filament, then debound and sintered. Small parts, limited alloys, sintered density.
• Sheet lamination and cold spray. Processes that bond solid metal without melting it; useful for specific jobs, not for intricate geometry.

We chose LPBF because the hardware our customers bring us is small enough to fit a 400 mm cube, complicated enough to need 40 micron layers and loaded hard enough to need full density. See how laser powder bed fusion works for the step by step.

Why programs use it.

• Part consolidation. A brazed assembly of twenty pieces becomes one printed part with no joints to leak.
• Internal geometry. Cooling channels that follow the wall of a combustion chamber, manifolds with smooth swept passages, conformal cooling in tooling.
• No tooling. No patterns, moulds or dies. A design revision is a new file and the next build.
• Lead time. Weeks from CAD to a part in hand, including heat treatment, rather than the months a casting can take.
• Alloys that resist machining. Inconel 718 is notoriously hard on cutters. Printing near net shape and machining only the interfaces saves hours of spindle time.

Where it is honest to say no.

Metal additive manufacturing is the wrong answer often enough that we say so. Simple geometry at volume is cheaper machined or cast. A part larger than the envelope has to be split or made another way. As built surfaces are rougher than machined ones, so sealing faces and bearing fits get finished afterwards. And every printed part carries residual stress until it is heat treated, which is a process step, not an option.

Alloys.

We qualify and run two alloys that propulsion programs fly: Inconel 718, the nickel superalloy for hot structural hardware, and GRCop-42, NASA’s copper chromium niobium alloy for combustion chamber liners and anything else that has to move heat. Other alloys that run on the EOS M 400 platform can be brought on for programs with the volume to justify a dedicated powder lot.

Standards and qualification.

Flight hardware needs more than a good looking part. The specifications below are the ones customers ask us about most.

• ISO/ASTM 52900, the terminology standard that defines the process categories.
• ASTM F3055, the specification for Inconel 718 (UNS N07718) made by powder bed fusion, including heat treatment classes and minimum tensile properties.
• ASTM F3303, the practice for metal powder bed fusion to meet critical applications: process control, parameter locking and monitoring.
• AMS 7003, the SAE process specification for laser powder bed fusion.
• NASA-STD-6030, additive manufacturing requirements for spaceflight systems, which sets out the qualified metallurgical process, part classification and witness testing.

We hold parameters, powder lots and build records for every job, put witness coupons on the plate when the program calls for them, and coordinate HIP, heat treatment and testing with partners who work to the same standards.

Metal additive manufacturing in Huntsville.

Huntsville is one of the places where metal additive manufacturing grew up. Marshall Space Flight Center matured and hot fire tested the GRCop alloys, and the engine programs on and around Redstone Arsenal print combustion devices as routine practice. AME sits a few miles from both. Our chief engineer built a GRCop-42 fuel injector with NASA and Marshall that we showed at RAPID + TCT, and the team has 35 combined years in additive. More on the shop and where we serve.