AM Post-Processing

Also: Support Removal, Powder Recovery, Build-Plate Cutting

Depowdering removes unfused powder from metal AM parts after the build cycle. For LPBF and EBM, loose powder fills the build chamber, internal channels, and lattice voids. Removal involves: (1) initial evacuation of bulk powder by gravity and vacuum; (2) automated multi-axis vibration and rotation (Solukon SFM series) to dislodge powder from complex internal geometries; (3) high-pressure air or gas purging of residual powder from channels; (4) powder sieving and oxygen-level testing for recycling. Build plate separation follows depowdering: wire EDM (preferred for AM — no mechanical vibration) or bandsaw (risk of part damage) cuts the part from the steel or aluminium substrate plate.

Also: Stress Relief, Annealing, Solution Treatment

Heat treatment encompasses a range of controlled thermal cycles applied to AM metal parts after printing: stress relief (reduces residual stress without phase change), annealing (recrystallisation, grain growth), solution treatment (dissolves precipitates), and ageing/precipitation hardening (forms strengthening precipitates). Each cycle targets a specific metallurgical outcome — from relieving the high residual stress inherent to LPBF rapid solidification to achieving peak hardness in age-hardenable alloys.

Also: HIP

Hot Isostatic Pressing applies simultaneous high temperature (800–1250 °C depending on alloy) and isostatic pressure (100–200 MPa, argon atmosphere) to eliminate internal porosity and micro-cracks in AM metal parts. The combined thermo-mechanical driving force closes voids that form during LPBF or EBM solidification — achieving relative densities >99.95% and mechanical properties that approach or match wrought equivalents, particularly fatigue strength.

Also: WEDM, Wire Electrical Discharge Machining, Wire-Cut EDM

Wire EDM (Electrical Discharge Machining) uses a continuously fed thin wire electrode (typically 0.1–0.3 mm diameter brass or coated wire) to cut electrically conductive parts via controlled spark erosion. The wire never contacts the workpiece — material is removed by plasma discharges across a dielectric fluid gap (deionised water). Kerf width is 0.12–0.35 mm. Wire EDM achieves tolerances of ±0.005 mm and surface finishes of Ra 0.05–0.8 µm in finishing passes.

Also: Die-Sink EDM, Ram EDM, Sinker Electrical Discharge Machining

Sinker EDM erodes a cavity into a conductive workpiece using a shaped electrode (graphite or copper) that is the mirror image of the desired feature. Spark discharges across a dielectric gap remove material without cutting force, producing sharp internal corners, deep slots, blind cavities, and fine features that milling cannot reach. Unlike wire EDM (which cuts through-profiles with a wire), sinker EDM sinks a 3D electrode form into the part.

Also: CNC Milling, 5-Axis Milling, CNC Turning

CNC machining removes material from near-net-shape AM parts to bring critical features — datums, mating faces, bores, threads, sealing surfaces — to final tolerance and surface finish that the AM process alone cannot hold. Milling (3- and 5-axis) addresses prismatic and freeform features; turning addresses axisymmetric features (shafts, flanges, bores). Because AM tolerances are typically ±0.1–0.3 mm and as-built Ra is 5–25 µm, machining is required wherever drawings call for tight GD&T (±0.01–0.05 mm) or fine finishes (Ra <1 µm).

Also: AFM, Abrasive Flow Finishing, Extrude Hone

Abrasive Flow Machining (AFM) forces a semi-solid viscoelastic abrasive medium through or across workpiece surfaces under hydraulic pressure (5–60 bar). The medium — abrasive particles (SiC, Al₂O₃, or B₄C, grit 60–220 mesh) suspended in a silicone or polyborosiloxane polymer carrier — acts as a self-conforming lapping tool. Material removal is highest at flow restrictions (channels, passages, corners), naturally concentrating abrasion where it is most needed. One bidirectional stroke (media extruded through and back) constitutes one cycle. Typical processes: 5–50 cycles at 5–30 bar for internal channel finishing; 50–200 cycles for precision surface finishing.

Also: Electrochemical Polishing, EP, Electrolytic Polishing

Electropolishing selectively dissolves surface asperities from metal parts by making the workpiece the anode in an electrolytic cell. Peaks dissolve faster than valleys — levelling the surface and reducing Ra without mechanical contact or stress. Three main variants exist for AM parts: (1) Wet electropolishing — immersion in acid electrolyte (typically H₂SO₄/H₃PO₄ for stainless; H₂SO₄/HF for titanium) with DC current; achieves Ra <0.4 µm from Ra 5–10 µm input; (2) Dry electropolishing (DLyte / GPainnova) — solid granular electrolyte medium in a rotating drum; geometry-uniform material removal without liquid waste; (3) Hirtisation® (Hirtenberger) — pulsed electrochemical machining combined with support removal; single-step process for AM internal features.

Also: Shot Peening, SP, Laser Shock Peening

Shot peening bombards a surface with small spherical media (steel shot, glass bead, ceramic bead, or cast iron) at controlled velocity, inducing a compressive residual stress layer 0.05–0.5 mm deep. This counters the tensile residual stresses inherent in as-built LPBF and DED parts — which are fatigue crack initiation sites. Laser Shock Peening (LSP) uses high-power pulsed laser beams (nanosecond pulse, confined plasma) to introduce compressive stresses 2–6 mm deep, significantly deeper and more uniform than conventional shot peening, without surface roughening.

Also: Tumbling, Vibratory Finishing, Drag Finishing

Mass finishing processes improve the external surface of AM parts by placing them in contact with abrasive media in a controlled motion environment. Variants: vibratory (parts + media vibrate in tub), drag finishing (parts moved through stationary media at controlled speed — preferred for AM due to no part-on-part impact), centrifugal disc (parts in high-g rotating disc). Isotropic Superfinishing (ISF — REM Surface Engineering) adds a chemically accelerated step: a reactive chemistry converts surface asperities into a soft passivating film that media removes gently, achieving Ra <0.2 µm with no directionality.

Also: Chemical Vapour Smoothing, Vapour Polishing, PostPro

Vapor smoothing exposes polymer AM parts to a controlled solvent vapour that briefly reflows the outer surface layer, eliminating the staircase/layer texture and reducing roughness to injection-moulding levels. The vapour condenses on the surface, lowers the local viscosity, and surface tension pulls the molten skin smooth before it re-solidifies. The process is dimensionally near-neutral (typical change <50 µm) and seals the porous surface, improving cleanability and (often) elongation at break.

Also: X-ray CT, Computed Tomography, Industrial CT

Industrial computed tomography rotates a part in an X-ray beam and reconstructs a full 3D voxel volume of its interior. It is the only non-destructive method that reveals internal porosity, lack-of-fusion defects, cracks, inclusions, and the geometry of internal channels — none of which are visible from the outside. Analysis software (Volume Graphics VGSTUDIO, others) quantifies pore size/distribution, measures internal dimensions, and compares the scanned geometry to the nominal CAD (nominal/actual deviation).

Also: CMM, Coordinate Measuring Machine, Structured-Light Scanning

Dimensional inspection verifies that an AM part's external geometry meets its drawing tolerances. Coordinate Measuring Machines (CMM) use a touch probe to measure discrete features (bores, datums, GD&T callouts) to micrometre accuracy. Structured-light and laser 3D scanners capture millions of surface points to build a dense mesh that is compared against nominal CAD (colour-map deviation) — ideal for the freeform surfaces AM produces. The two are complementary: CMM for tight-tolerance functional features, scanning for whole-surface form and first-article CAD comparison.

Also: PVD, CVD, Thermal Spray

Coating and surface-treatment processes deposit or convert a surface layer on AM parts to add wear resistance, corrosion resistance, thermal protection, electrical properties, or dimensional build-up. Key families: PVD/CVD hard coatings (TiN, TiAlN, CrN, DLC) for tooling and wear surfaces; thermal spray (HVOF, plasma) for thick functional layers and dimensional reclamation; electroless nickel for uniform corrosion/wear layers on complex geometry; anodising for aluminium; and chemical passivation for stainless corrosion resistance.