Additive Manufacturing Glossary

This glossary defines commonly used additive manufacturing terms in the context of real defense, aerospace, and regulated industrial programs. Definitions are written for engineers, procurement teams, and program managers who need terminology that maps to actual RFQs, qualification plans, inspection workflows, and certification packages.

Core process terms

Additive Manufacturing (AM): A family of processes that build parts layer-by-layer from digital data (typically a CAD model). In aerospace/defense sourcing, “AM” often implies more than printing—expect an integrated route: build → depowder → stress relief → support removal → HIP (when required) → machining → inspection → documentation.

Powder Bed Fusion (PBF): AM category where a heat source selectively fuses regions of a thin powder layer. Common metal variants include laser powder bed fusion (L-PBF, often called DMLS/SLM) and electron beam powder bed fusion (EB-PBF). Procurement implication: PBF is sensitive to powder quality, atmosphere control, scan strategy, and build orientation—these should be controlled variables in a qualified process.

Directed Energy Deposition (DED): AM category where powder or wire is fed into a melt pool created by a laser/arc/e-beam. Used for larger near-net shapes, repairs, and features added to forged/cast substrates. Engineering note: DED typically has larger melt pools and thicker layers than PBF, which affects surface finish, microstructure, and machining allowance.

DMLS / SLM: Common industry terms for laser powder bed fusion of metals. “DMLS” (Direct Metal Laser Sintering) and “SLM” (Selective Laser Melting) are often used interchangeably in purchasing, but the critical requirement is not the label—it’s the qualified parameter set (laser power, scan speed, hatch spacing, layer thickness, atmosphere, recoater method) tied to a specific machine model and material.

Build Envelope: Maximum printable volume of a machine. For RFQs, confirm whether the part must be printed in one piece within the envelope, printed on an angle, or printed in sections and later joined—each option changes risk and inspection burden.

Build Orientation: How a part is placed in the machine (e.g., X/Y plane vs Z direction). Orientation drives support strategy, distortion risk, surface finish on critical faces, fatigue performance (due to anisotropy and defect distribution), and where witness coupons can be placed.

Layer Thickness: The height of each deposited powder layer (or deposited bead in DED). Thinner layers typically improve detail and surface finish but increase build time and cost; thicker layers may reduce cost but can increase roughness and limit thin-wall fidelity.

Scan Strategy / Toolpath Strategy: The pattern used to fuse each layer (e.g., stripes, islands, rotations between layers). It materially influences residual stress, distortion, and porosity. In controlled aerospace production, the scan strategy is part of the frozen process definition.

Supports / Support Structures: Temporary features printed to anchor overhangs and manage heat flow. Support removal is a real cost driver and can introduce surface damage; for RFQs, define which surfaces are “as-printed acceptable” vs must be machined.

Recoater: Mechanism that spreads powder layers in PBF. Recoater type (blade vs roller) affects risk of collisions and layer quality. A recoater crash can scrap a build and may trigger additional inspections depending on quality procedures.

Inert Atmosphere (Argon/Nitrogen) & Oxygen Level: PBF metal builds are executed in controlled atmosphere to limit oxidation and defects. Oxygen limits are typically specified internally by the supplier; for critical applications, buyers may request build logs showing O₂ levels and alarm events.

Relative Density / Porosity: Measures of how much void content remains in a printed part versus fully dense material. Requirements depend on application: pressure-containing, fatigue-critical, or fracture-critical hardware typically demands higher density and may require HIP plus NDE verification.

Hot Isostatic Pressing (HIP): A post-processing step using high temperature and isostatic gas pressure to close internal voids and improve fatigue performance. In aerospace AM, HIP is commonly specified for Ti-6Al-4V and nickel alloys when internal porosity and fatigue are key concerns. HIP changes microstructure, so it must be accounted for in mechanical testing and heat treat condition.

PM-HIP (Powder Metallurgy + HIP): A densification route where metal powder is consolidated in a sealed canister and HIP’d to near-fully dense billet or near-net shape. PM-HIP is not “printed,” but it is often evaluated alongside AM for complex parts requiring superior isotropy and predictable properties. Procurement note: PM-HIP can reduce supply risk for large cross-sections, but requires disciplined can design, powder cleanliness, can removal, and subsequent machining.

Stress Relief: Heat treatment intended to reduce residual stresses from printing. Typically performed before major support removal or machining to reduce distortion. For RFQs, specify whether stress relief is required and whether it is in addition to or replaced by HIP/solution/age cycles.

As-Printed / As-Built Condition: The state of the part immediately after printing (and often after depowder and stress relief), before machining or finishing. “As-built” surfaces are usually rougher and dimensionally less accurate than machined surfaces; engineering drawings should clearly identify where as-built is acceptable.

Buy-to-Fly Ratio: Ratio of starting material weight to finished part weight. A driver for adopting AM and PM-HIP in titanium and nickel alloys. Programs track buy-to-fly because it impacts cost, lead time, and strategic material consumption.

Quality and inspection terms

AS9100: Aerospace quality management standard built on ISO 9001 with additional requirements (configuration control, risk management, traceability, etc.). For buyers, AS9100 certification indicates a baseline system, but you still need process-specific qualification (e.g., PBF parameter control, heat treat approvals, NDE capability).

NADCAP: Industry accreditation for special processes (e.g., heat treating, NDT, chemical processing) widely required by aerospace primes. If HIP, heat treat, or NDT is outsourced, procurement should confirm whether the sub-tier is NADCAP-accredited when required by customer flow-downs.

ITAR (International Traffic in Arms Regulations): U.S. export control rules for defense articles and technical data. Practical implication: the supplier must control access to CAD files, build files, process parameters, inspection data, and even part photos depending on program requirements; also confirm where data is stored and who can access it.

DFARS Compliance: U.S. Department of Defense acquisition regulations including requirements that may impact sourcing and documentation (e.g., specialty metals, cybersecurity clauses, counterfeit parts prevention). Procurement teams should identify DFARS clauses at RFQ stage to avoid rework in supplier onboarding.

Material Traceability: The ability to trace a delivered part back to the specific material heat/lot and processing history. For metal AM, traceability typically includes: powder lot, powder reuse history (if allowed), build ID, machine ID, parameter set revision, heat treat/HIP batch, and final inspection records.

Certificate of Conformance (CoC): Supplier statement that parts meet drawing/spec requirements. In regulated programs, the CoC is supported by objective evidence (test reports, inspection results, lot traceability, special process certs). Buyers should define what must be in the certification pack to prevent delays at receiving inspection.

First Article Inspection (FAI) / AS9102: A structured verification that the first production part meets design requirements. For AM parts, FAI planning should include: ballooned drawing, build ID, revision control, special process certs (HIP/heat treat), and NDE/CT results when required.

Process Qualification: Demonstration that a specific machine + material + parameter set can repeatedly produce acceptable parts. In practice, qualification includes coupon builds, density/chemistry verification, mechanical testing in relevant orientations, dimensional capability, and definition of in-process monitoring/acceptance criteria.

Witness Coupons / Test Coupons: Samples printed alongside parts (or in the same build) used for mechanical testing, density, microstructure, or CT. Coupon strategy matters: location in the build and orientation should represent the most critical geometry and thermal conditions of the part.

NDE (Non-Destructive Evaluation): Inspection methods that do not damage the part. Common AM-related NDE includes CT scanning, fluorescent penetrant inspection (FPI), and sometimes ultrasonic testing (UT), depending on geometry and acceptance criteria.

CT Scanning (Computed Tomography): X-ray based volumetric inspection used to detect internal porosity, lack-of-fusion defects, and internal geometry deviations (e.g., lattice integrity, internal channels). Practical considerations: CT capability depends on part size/density; acceptance criteria must be defined (e.g., maximum pore size, pore population, region of interest).

CMM (Coordinate Measuring Machine): High-accuracy dimensional inspection using tactile probing or scanning. CMM results can be influenced by surface roughness and probing strategy; many AM programs machine datums/features first, then CMM critical dimensions after finish machining.

Gage R&R (Measurement System Analysis): A method to confirm that the measurement process is repeatable and reproducible. For high-consequence hardware, buyers may ask suppliers to demonstrate measurement capability for critical dimensions or surface finish.

SPC (Statistical Process Control): Use of data trends to maintain process stability. In AM production, SPC may be applied to powder properties, oxygen level, laser calibration checks, density on coupons, and key machined dimensions after a stable process baseline is established.

Nonconformance (NCR) & MRB (Material Review Board): Formal control of out-of-tolerance conditions and disposition decisions (use-as-is, repair, rework, scrap). Procurement and program managers should require timely notification and disposition approval pathways, especially for ITAR-controlled programs.

Post-processing terms

Depowdering: Removal of unfused powder from a build and internal cavities. For parts with internal channels, depowdering is a design-for-AM constraint and a quality risk; RFQs should specify whether “powder-free” internal passages are required and how verification is performed (mass check, borescope, CT).

Support Removal: Mechanical separation of support structures (sawing, machining, EDM, hand tools). Plan for stock allowance and protect critical surfaces; aggressive removal can introduce nicks that later fail FPI or reduce fatigue life.

Heat Treatment (Solution, Age, Anneal): Thermal cycles used to achieve required microstructure/properties. The sequence matters: some alloys require stress relief before HIP; others require HIP followed by solution/age to hit strength targets. Drawings should call out the required material condition (e.g., “Ti-6Al-4V, HIP + anneal”).

HIP + AM Workflow (typical step-by-step): (1) Print part and coupons to a controlled build plan; (2) depowder and record powder lot/build logs; (3) stress relief if required by internal procedure; (4) remove from build plate and remove supports to a defined interim condition; (5) HIP parts/coupons with documented cycle and load map; (6) perform post-HIP heat treat if required; (7) rough machine datums and critical interfaces; (8) NDE (often CT pre- or post-machining depending on what you need to see); (9) finish machine to print; (10) final inspections (CMM, surface finish, FPI as applicable); (11) compile certification pack (CoC, material certs, HIP/HT certs, NDE reports, dimensional report, FAI if applicable).

CNC Machining: Subtractive finishing used to achieve tight tolerances, surface finish, and datum control that AM typically cannot meet directly. For procurement, the key question is whether the supplier controls both printing and machining under one quality system or whether handoffs occur between suppliers (each handoff adds risk and traceability requirements).

5-Axis Machining: CNC capability allowing complex access and reduced setups. Often essential for AM parts because near-net shapes can have compound angles and internal clearances that require multi-axis toolpaths. It also helps maintain positional tolerances by reducing re-fixturing.

EDM (Electrical Discharge Machining): Material removal using electrical spark erosion. Useful for removing parts from build plates, cutting supports in hard alloys, and creating sharp internal features that are difficult to machine conventionally.

Surface Roughness (Ra, Rz): Quantified texture of a surface. AM as-built surfaces often have higher roughness; fatigue-critical surfaces are typically machined or chemically polished. Drawings should specify surface finish where it matters and allow looser finish where it doesn’t.

Shot Peening / Bead Blasting: Mechanical surface treatments used to clean or improve surface condition. Note: blasting can hide defects or change surface texture; if FPI is required, sequence must be controlled. Shot peening may improve fatigue but must be qualified for AM microstructures and geometry.

FPI (Fluorescent Penetrant Inspection): NDE method for detecting surface-breaking flaws. Common on titanium and nickel hardware. Ensure the supplier controls surface preparation and masking because rough as-built surfaces can create false indications.

Passivation: Chemical treatment (often for stainless steels) to improve corrosion resistance by removing free iron and enhancing the oxide layer. If required, it is a special process that should be controlled and documented in the certification pack.

Coating (e.g., anodize, thermal spray): Applied to improve corrosion, wear, or thermal performance. Coatings can change dimensions and may require masking and final thickness verification; for AM parts, confirm coating compatibility with as-built vs machined surfaces.

Materials terms

Ti-6Al-4V (Grade 5 / Grade 23 ELI): Common titanium alloy used in aerospace AM. Grade 23 (ELI) is often used where improved fracture toughness is needed. For AM, oxygen pickup and microstructure control are critical; HIP is frequently used for fatigue-critical applications.

Inconel 718 (Nickel Alloy 718): Widely used nickel superalloy for high-temperature applications. AM 718 typically requires solution/age heat treatment to achieve target strength. Processing and heat treat must be aligned to the specific specification revision required by the customer.

Stainless Steels (17-4PH, 316L): Common AM materials. 17-4PH properties depend strongly on heat treat condition (H900, H1025, etc.). 316L is often used for corrosion resistance but has different strength expectations. RFQs should state required condition and any corrosion testing requirements.

Aluminum Alloys (AlSi10Mg, others): Common in AM but more sensitive to fatigue and surface condition. Also consider powder handling and oxidation risks. For aerospace, confirm whether the specific alloy and condition are approved for the intended environment and certification basis.

Cobalt-Chrome (CoCr): Used for wear and high-temperature corrosion resistance. More common in medical and some aerospace wear applications. Machinability and finishing approach differ from steels and nickel alloys.

Powder Morphology: Shape and surface characteristics of powder particles (often spherical for gas-atomized powders). Morphology affects flowability, packing density, and layer quality; suppliers typically control and verify morphology via incoming inspection.

Powder PSD (Particle Size Distribution): Distribution of powder particle sizes. PBF requires a controlled PSD range to ensure stable spreading and melt behavior. Procurement note: a supplier’s allowable powder reuse policy (and how PSD shifts over reuse) should be defined in their process controls.

Powder Reuse / Recycle Ratio: The practice of reusing powder from prior builds after sieving and blending. Reuse can be acceptable when controlled, but it must be documented because it can affect chemistry (oxygen/nitrogen pickup), PSD, and defect rates. For critical hardware, buyers sometimes require “virgin powder only” or strict reuse limits.

Chemistry (Heat/Lot Certification): Chemical composition verification of raw material (powder) and sometimes post-process material. Aerospace programs typically require mill certs for powder and traceability to a lot; for AM, confirm whether additional in-house chemistry checks are performed for reused powder.

Anisotropy: Direction-dependent properties (e.g., Z direction may behave differently than X/Y). AM parts can exhibit anisotropy due to thermal history and microstructure. Engineering teams should place critical load paths and test coupons to validate the required orientations.

Microstructure: The arrangement of phases/grains in the metal. AM microstructures can be finer and more directional than wrought products. HIP and heat treat modify microstructure; therefore, mechanical allowables must correspond to the exact post-processing route.

Residual Stress: Internal stresses locked into a part due to rapid heating/cooling during printing. Residual stress drives distortion and can promote cracking; stress relief and smart orientation/support strategies mitigate it.

Mechanical Properties (Tensile, Yield, Elongation, Hardness, Fatigue): Key performance metrics. In AM procurement, the question is not only “did it meet minimum tensile?” but also “were properties validated in the correct condition, orientation, and location representative of production parts?”

Drawing/RFQ terms

RFQ (Request for Quote): The package a buyer sends to suppliers to solicit pricing and lead time. For AM, a strong RFQ includes: drawing/model revision, material and condition, quantity/lot size, inspection requirements, special process requirements (HIP/heat treat/NDE), ITAR/DFARS flow-downs, and required certification pack contents.

Model-Based Definition (MBD): A CAD model containing PMI (Product Manufacturing Information) such as GD&T, notes, and surface finish callouts. For AM, ensure the supplier can consume MBD reliably and that revision control for both model and drawing is explicit.

GD&T (Geometric Dimensioning and Tolerancing): A symbolic language defining allowable geometric variation. AM parts often require machining of datum features to make GD&T measurable and achievable. When tolerances are extremely tight, assume machining and inspection costs dominate.

Datums: Reference features used to locate a part for measurement and assembly. AM designs should include machinable datum pads or interfaces; relying on rough as-built surfaces as datums creates inspection ambiguity and repeatability issues.

Critical-to-Quality (CTQ): Features that materially affect function, safety, or downstream assembly. Procurement should ensure CTQs drive the inspection plan (e.g., 100% CMM on CTQ dimensions, CT on CTQ internal channels) rather than blanket inspection that adds cost without reducing risk.

Machining Allowance / Stock Allowance: Extra material intentionally printed so that final dimensions can be machined. AM designs should specify where stock is included and how much; insufficient stock can lead to scrap after HIP/heat treat distortion.

As-Built vs Finish-Machined Callouts: A clear separation of which surfaces are allowed to remain as-built and which must be machined. Ambiguity here is a common RFQ failure mode that leads to change orders, delays, and mismatched expectations.

Inspection Plan / Control Plan: Document describing what will be inspected, how, and at what frequency. A practical AM control plan ties requirements to stages: incoming powder checks, in-process machine checks, coupon testing, post-process inspections, and final dimensional/NDE verification.

FAI Package / Certification Pack (typical contents): (1) CoC; (2) material certs for powder and any canister material (PM-HIP); (3) build record (build ID, machine ID, parameter set revision, orientation/support notes); (4) heat treat/HIP certs with cycle details and load identification; (5) NDE reports (CT/FPI/UT as required); (6) dimensional inspection report (CMM); (7) objective evidence for any deviations or approved concessions; (8) traceability matrix linking serial/lot numbers to all above records.

Supplier Qualification (practical step-by-step): (1) Verify quality system fit (AS9100, ITAR controls, cybersecurity/DFARS clauses); (2) confirm machine/material capability and whether the process is already qualified for your alloy/spec; (3) review sample certification pack for completeness; (4) align on inspection methods and acceptance criteria (especially for CT); (5) run a pilot build with coupons and FAI; (6) lock configuration (machine, parameter set, post-process route, inspection plan); (7) establish change control—any machine move, software update, parameter change, or powder policy change triggers review.

Quick FAQ

What’s the difference between DMLS and SLM?
In most RFQs they refer to the same L-PBF process. The meaningful differentiators are the specific machine platform, the qualified parameter set, and the post-processing route (stress relief, HIP, heat treat) that produces the required properties and inspection outcomes.

When should we specify HIP for AM parts?
Specify HIP when internal porosity and fatigue performance are critical, when CT reveals pore populations that must be mitigated, or when program standards require it for the alloy/part class. Also specify the final required material condition (e.g., HIP + solution/age) and ensure your acceptance criteria and testing are based on that condition.

Can we accept as-printed surfaces on flight hardware?
Sometimes, yes—when the surface is non-critical, does not interface with seals/bearings, and is not fatigue-critical. The drawing should explicitly identify acceptable as-built zones and include a realistic surface finish requirement (or “as-built allowed”) to avoid assumptions.

Is CT scanning always required for metal AM?
No. CT is powerful for internal defects and internal geometry, but it adds cost and may be limited by part size and density. Use CT strategically: focus on critical regions, first articles, new builds, or high-risk geometries (thin walls, internal channels, lattices). Define defect acceptance criteria up front.

What should procurement ask for to reduce AM sourcing risk?
Ask for a complete certification pack definition, powder traceability and reuse policy, machine/parameter set qualification evidence, post-processing control (HIP/heat treat/NDE), and a clear change-control process. For regulated programs, confirm ITAR/DFARS flow-downs and how the supplier protects technical data throughout printing, inspection, and subcontracted steps.

How do we avoid surprises on tolerance and cost?
Assume tight tolerances require machining and robust datums. Provide a clear drawing/model with GD&T tied to machinable datums, specify stock allowance where needed, and align with the supplier on which features are printed vs machined. Early DFM feedback (orientation, supports, distortion risk, inspection access) is often the fastest path to lower cost and lead time.