How to Review a Metal 3D Printing Company

Most review pages compare brand names. That is the least useful part. A supplier's name tells you nothing about whether your part will hit its tolerance, whether the heat treat was done in-house, or whether the build plate was cut off square. Those are the things that show up in your incoming inspection report.

Start with the process itself. Metal parts are usually built by laser powder bed fusion (LPBF, also sold as DMLS or SLM). A laser melts 20–60 μm layers of gas-atomized powder in an inert chamber. That gives you internal channels and lattice structures that no milling cutter can reach. It also gives you as-built surfaces around Ra 8–12 μm, residual stress in the part, and support structures welded to downward-facing faces.

The second item is post-processing. A printed part is a near-net shape, not a finished component. It needs stress relief before the build plate is cut, then support removal, then heat treat if the alloy requires it, then often machining on the critical faces. If the supplier subcontracts any of those steps, you lose traceability and add days.

The third item is metrology. Ask what gets measured, on what machine, and whether the report comes with the shipment. A CMM report on three critical dimensions is worth more than a certificate that says the shop is ISO 9001 registered.

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  Process controlLayer thickness, laser parameters, and powder lot records for the build.
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  In-house post-processingStress relief, support removal, heat treat, and finish under one roof.
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  Inspection dataCMM or optical reports for the features you actually tolerance.
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  Material traceabilityPowder lot number tied to the part serial and the heat lot.

Metal AM pays off when geometry is the problem. Conformal cooling channels in a mold insert, a manifold with internal passages, a bracket that needs to be 40 percent lighter through topology optimization, or a small run of 20 complex parts where tooling would cost more than the parts. Those are good candidates.

It is a poor fit for anything prismatic. A plate with holes, a shaft, a housing with flat faces and a few bores: those run faster and cheaper on a 3-axis or 5-axis mill. Printing them also gives you worse surface finish and a heat treat step you did not need. If a supplier quotes printing for a part that a CNC shop could run in an afternoon, that is a signal about how they qualify work.

Size is the other hard limit. Most LPBF machines build inside a 250–400 mm cube. Larger parts must be printed in segments and joined, which adds a weld or a bolted joint and a new set of tolerances. If your part is 600 mm long and mostly solid, subtractive manufacturing is the sane route.

Wall thickness matters too. Thin walls below about 0.4 mm are difficult to hold consistently across a full build. Thick solid sections above roughly 20 mm trap stress and can warp during cooling. Both cases call for a design review before the file is released, not after the first build fails.

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  Good fitInternal channels, lattices, organic brackets, low-volume complex geometry.
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  Poor fitPrismatic blocks, shafts, flat plates, anything a mill cuts in one setup.
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  Watch the sizeMost builds fit a 250–400 mm envelope; larger means segments and joints.

Ask for the build orientation and support plan. Orientation sets anisotropy, surface finish on the critical face, and how much support has to be cut away. A supplier who cannot show you a build layout is guessing.

Ask who does the heat treat and what the cycle is. For Ti-6Al-4V, a stress relief before plate removal and a subsequent anneal or HIP step change the fatigue behavior. For 17-4PH, the aging temperature decides whether you get the hardness you specified. These are process steps, not paperwork.

Ask how critical faces are finished. Printing gets you close, then a 5-axis machine cuts the sealing face, the bearing bore, or the thread. A shop with both capabilities controls that handoff. A shop without a mill sends the part out and the tolerance chain grows.

Ask about the powder. Gas-atomized powder is reused in most shops, and reuse changes oxygen content and flowability. A serious supplier tracks reuse cycles per alloy and retires powder on a defined schedule. That is the difference between a repeatable part and a lucky one.

Finally, ask what happens if the first build does not meet the drawing. Conforming and non-conforming parts should be separated and identified, and the rework path should be defined before the order, not negotiated after.

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  Build layoutOrientation, support strategy, and nesting on the plate.
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  Heat treat cycleStress relief, annealing, HIP, and aging parameters by alloy.
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  Critical face finishingWhich surfaces get machined, and to what tolerance.
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  Powder policyLot tracking and reuse limits per alloy.

A part rarely stops at printing. It gets stress relieved, cut off the plate, supports removed, critical faces machined, then anodized, bead blasted, or laser marked. Each handoff adds a queue, a shipping box, and a chance for the wrong revision to move forward.

GreatLight runs additive work inside a machining operation. Printed parts move to the 5-axis department for face and bore finishing, then to finishing for anodizing or electroless nickel. The same team reads the drawing end to end, so a tolerance stack does not get lost between vendors.

The equipment matters here. 16 simultaneous 5-axis machining centers, 16 mill-turn centers, and 127 high-precision CNC machines in total handle the subtractive side, with work envelopes up to 4,000 mm. That covers everything from a printed manifold that needs two sealing faces skimmed to a large fixture plate.

Inspection closes the loop. We inspect 100 percent of parts before shipment, with raw material checks, in-process monitoring, and final reports on request. For a printed part, that means dimensional checks on the machined features plus visual and, where agreed, dye penetrant or CT checks on the printed geometry.

The point is not that printing beats machining. It is that the two belong in one process plan. When a supplier can quote both, the conversation shifts from 'can you print this' to 'what is the cheapest reliable way to make this part'.

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  One process planPrint, machine, and finish steps defined together before the build.
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  Tolerance handoffMachined datums established on the printed blank for later setups.
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  Fewer shipmentsPost-processing stays in-house instead of moving between vendors.