A design engineer in Germany ordered 12 titanium brackets from a metal 3d printing service for a drone prototype. The parts arrived at 22 grams each, the dimensions matched the drawing, and the team was happy for two weeks. When the brackets were loaded on the test drone, three of them cracked at the root. The vendor had skipped stress relief annealing and did not report the powder batch. The engineer had compared price per part, not process control. Before you upload your STEP file, run the six checks below.
Material Grade and Powder Traceability
Start with the powder, not the printer. A metal 3d printing service that buys cheap 316L powder from a commodity trader will ship parts with inconsistent chemistry. Ask for the material grade (316L, 17-4PH, AlSi10Mg, Ti6Al4V Grade 23, Inconel 718), the powder lot number, and the Certificate of Conformance. A medical device startup in Sweden once received titanium parts that failed the biocompatibility test; the vendor had used Grade 2 powder instead of Grade 23, and no traceability record existed. Rule of thumb: only work with a metal 3d printing service that can show you the powder COA for the exact batch your parts were printed from.
Tolerance and Surface Roughness
Tolerance decides whether the part fits the assembly. A metal 3d printing service that quotes ±0.1 mm on a 100 mm part sounds fine, but on a 5 mm pin that tolerance is 2% and will not fit. Ask for the tolerance per feature, not per part size. Surface roughness matters too: as-printed Ra runs 8 to 12 micrometers, while a CNC-finished face drops to Ra 1.6. A pump manufacturer in Italy ordered 40 AlSi10Mg housings from a metal 3d printing service; the sealing face leaked because the vendor had not specified which faces were machined after printing. Ask which faces are as-printed, which are bead-blasted, and which are CNC-finished, in writing.
Post Processing Capability
Post-processing decides whether the part actually survives service. As-printed metal parts have locked-in internal stress. A drone maker in the Netherlands printed 20 Ti6Al4V brackets that warped by 0.4 mm after two weeks on the shelf; the metal 3d printing service had skipped stress relief annealing. Ask whether the vendor offers stress relief annealing, hot isostatic pressing (HIP), solution treatment and aging, and CNC post-machining on site. If they outsource HIP to a third party, ask for the turnaround time; a part that waits six weeks for HIP can delay your whole program.
Certifications and Quality Reports
Certifications decide whether the part can enter aerospace, medical, or food equipment. A metal 3d printing service without ISO 9001 is a job shop, not a supplier. AS9100 is required for aerospace, ISO 13485 for medical devices, and NADCAP for some prime contractors. An automotive Tier-1 in Mexico once sourced a suspension bracket from a vendor with no AS9100 equivalent; the part passed the lab test but was rejected at the customer audit. Ask for the certification numbers and verify them on the registrar website, not just on a PDF. Also ask whether the metal 3d printing service holds NADCAP accreditation for heat treatment and non-destructive testing, because prime customers will ask for it on every lot.
Minimum Order and Lead Time
Lead time decides whether you hit your trade show or production window. A metal 3d printing service that quotes 7 days for one prototype is fine, but the same vendor may take 21 days for 50 production parts because the machine queue fills. Ask for a written lead time at three volumes: 1 part, 10 parts, and 100 parts. A robotics company in Japan once waited 14 weeks for a batch of 60 stainless steel impellers; the vendor promised 4 weeks then stacked the job behind a larger customer. Confirm the lead time on the PO and add a late-delivery penalty clause. Also ask whether parts from one build plate ship together, or whether the vendor splits your batch across machines to hit the date; mixed builds can show up as color and roughness differences on the same part number.
Non Destructive Testing and Inspection
Inspection decides whether the hidden defects stay hidden. Metal 3D printing can hide porosity, un-melted powder, and internal cracks that never show up on a caliper. A aerospace subcontractor in Canada once accepted a batch of Inconel 718 vanes; CT scanning at the customer plant found 12% porosity in the cooling channels. Ask the metal 3d printing service whether they offer CT scanning,显微 hardness testing, and tensile coupons from the same build plate. A tensile coupon from the same build is the single most valuable document you get; without it, you have no evidence the part meets spec. Ask also whether the vendor provides a build report showing the laser power, scan speed, and layer thickness for your lot; those parameters decide the fatigue life of dynamic-loaded parts.
Run these six checks and the metal 3d printing service you pick will ship parts with traceable powder, finished faces that seal, stress relief that holds, and reports your customer audit will accept. For related background, read our automotive cnc machining materials article and our precision cnc milling article before you shortlist; when the quotes come back, cross-check the plastic prototype angle in our vacuum casting prototypes article and the small-part precision in our brass cnc milling article, so the 12 titanium brackets do not turn into a drone crash. Ask for two sample parts before you commit to a batch of 50, have them tested by your own lab, and only then release the PO; that 2-week sample cycle saves you a 3-month rework later.
