How metal 3D printing actually works
Metal additive manufacturing, most often powder bed fusion, builds a part by spreading a thin layer of metal powder about 20 to 60 microns thick and fusing the cross-section with a fiber laser or electron beam, then lowering the build platform and repeating. The part is grown from the bottom up rather than carved from a solid block.
The result can be fully dense, often 99.5 percent or better after hot isostatic pressing, with mechanical properties approaching those of wrought material. Because support structures are added only where geometry overhangs, the process wastes little material compared with machining a solid billet down to a fraction of its mass.
Why choose metal printing over CNC machining
The headline advantage is geometry. Internal cooling channels, conformal lattices, and organic topologies print as a single piece, eliminating welds, brazes, and assemblies that would be impossible or uneconomic to mill. Engine manifolds, heat exchangers, and lightweight brackets are classic wins.
Consolidation is the second win. A ten-part assembly becomes one printed component, removing fasteners, mating surfaces, and potential leak paths. For low volumes where tooling does not yet exist, printing also skips the long lead time of casting patterns and dies.
When metal printing is the wrong choice
If the part is a simple solid shape made in the hundreds or thousands, CNC machining is usually cheaper and faster per piece once setup is amortized. Machined stock also arrives isotropic, whereas printed layers can retain slight directional differences unless post-processed.
Printing is also slower for a single dense part than many buyers expect. A metal build can run from several hours to days, and the part then needs depowdering, support removal, heat treatment, and often CNC finishing. When speed to a few parts is critical and geometry is simple, machining or even a printed polymer may fit better.
Stainless steel 316L
316L is the workhorse marine and medical grade. Its low carbon content improves corrosion resistance and weldability, and it prints with good ductility, making it ideal for housings, valves, and brackets exposed to water or sterilizing cycles.
Expect roughly 500 to 600 MPa ultimate tensile strength and excellent resistance to chlorides compared with 304. It is the default choice when you need real metal performance and corrosion resistance without the cost premium of titanium or nickel alloys.
Titanium Ti6Al4V
Ti6Al4V offers the best strength-to-weight ratio of the common printable metals, around 900 to 1100 MPa tensile strength at roughly half the density of steel. It is also biocompatible and resists corrosion in body and seawater environments, which is why it dominates aerospace brackets and orthopedic implants.
The trade-offs are real. Titanium powder and machine time are expensive, the laser process is slow, and the metal reacts with oxygen, demanding an inert build atmosphere. Reserve it for parts where weight savings or biology justify the premium over steel or aluminum.
Aluminum AlSi10Mg
AlSi10Mg prints light, stiff, and thermally conductive, with a silicon content that improves laser weldability and reduces hot cracking. It is a favorite for enclosures, ducts, heat sinks, and drone or robotics parts where every gram matters.
Typical tensile strength lands near 300 to 450 MPa with density around 2.7 grams per cubic centimeter, so it undercuts steel on mass while keeping useful stiffness. It is the economical metal option when you need metal properties but must control cost and weight.
Nickel alloys such as Inconel 718 and 625
Nickel superalloys hold strength and oxidation resistance at temperatures where aluminum and steel would soften. Inconel 718 retains useful properties past 650 degrees Celsius, making it the material for turbine blades, exhaust manifolds, and downhole oil and gas hardware.
625 adds superior corrosion resistance in aggressive chemical and seawater service. These alloys are the most expensive to print because powder is costly and the high melting point demands more laser energy and slower scan speeds, so they are reserved strictly for thermal or corrosive extremes.
Tolerances, density and surface finish
As-printed metal parts carry roughly plus or minus 0.1 to 0.3 millimeter accuracy, with visible layer lines and a slightly rough surface, typically Ra 6 to 12 microns. Dimensional drift comes from residual stress, thermal warping, and support removal, so critical features are usually machined after printing.
Post-processing defines the final part. Stress relief or aging controls distortion, hot isostatic pressing closes internal pores, and bead blasting or machining delivers the required finish. Plan for this work up front, because the quoted print price rarely includes full finishing.
Cost and the break-even with machining
Metal printing is priced by build volume, material mass, and machine hours, plus the cost of virgin powder that often cannot be fully reused. For a single complex part it beats casting, which needs tooling, but it rarely beats CNC for simple shapes made in quantity.
A useful rule is to print the first article to prove a hard-to-machine design, then evaluate CNC or die casting once volumes rise above a few dozen. The crossover depends on part size, alloy, and how much post-machining each method needs, but printing stays competitive mainly below low hundreds of units.
Typical industry applications
Aerospace uses printed titanium and nickel for brackets, ducts, and engine components where weight and heat dominate. Medical printing delivers patient-specific implants, surgical guides, and sterilizable instruments in 316L and titanium.
Automotive and motorsport print manifolds, turbo housings, and tooling inserts with conformal cooling that cuts cycle times. Consumer and robotics teams use aluminum and steel for functional prototypes and low-volume end-use parts that would be too costly to tool.
How FabProto supports your metal parts
FabProto runs powder bed fusion for the major alloys and pairs it with in-house CNC machining, heat treatment, and inspection, so a printed part can be finished to drawing in one place. Send a model and we will flag where printing beats machining and where it does not.
Our team returns a clear material and tolerance recommendation for your application, including the volume at which CNC or casting takes over. That end-to-end view is why product teams use us from first article through low-volume production.