AM post-processing: the complete guide for metal parts

A metal AM part leaves the machine in a state that is almost never usable as-is. The build plate needs to be removed. Supports need to come off. Residual stress needs to be managed. Surface finish may need improvement. And for critical applications, microstructure needs to be verified.

Post-processing is often the most expensive part of the total AM workflow — sometimes exceeding the build cost itself. Understanding what each step does and when it's actually necessary is essential for cost-effective AM manufacturing.

The standard post-processing sequence

Most LPBF metal parts go through some version of this sequence:

Build complete
   ↓
Stress relief (optional, sometimes required before removal)
   ↓
Wire EDM / bandsaw — part removed from build plate
   ↓
Support removal
   ↓
Heat treatment (anneal / HIP / precipitation hardening)
   ↓
Surface finishing (blasting, polishing, machining)
   ↓
Inspection (dimensional, NDT, mechanical test coupons)
   ↓
Functional use or further coating/assembly

Not every step is required for every part. The sections below explain what each step does and when it applies.

Step 1 — Stress relief before build plate removal

LPBF generates large temperature gradients (thousands of °C/s) during solidification. The resulting residual stresses can be significant — in titanium LPBF, residual stress can approach the yield strength in some regions.

Why stress relief before removal matters: When a part is still attached to the build plate, the plate constrains the part. Removing the part without stress relief can cause significant elastic spring-back distortion, and in extreme cases, cracking.

Typical stress relief cycles:

When you can skip it: Low-residual-stress geometries (thin planar parts, short builds) may be removed directly from the plate without significant distortion. EBM parts are built in a hot sintered powder bed and emerge nearly stress-free — stress relief before plate removal is typically not required.

Step 2 — Build plate removal

The standard methods:

Wire EDM: Precise, no mechanical force on the part. Preferred for thin walls, complex geometry, and parts where support contact surfaces are close to functional features. Leaves a thin re-cast layer (~5–15 µm) on the cut surface — relevant for fatigue-critical applications.

Bandsaw: Faster and cheaper. Acceptable when the cut is well away from functional surfaces. The blade forces can distort thin parts.

Milling: Used when tight positional control of the cut location is needed. Slower but high precision.

Leave 0.5–1.0 mm of material above the cut line on the part to allow for the cut tolerance and any subsequent machining.

Step 3 — Support removal

Support structures are the most labour-intensive post-processing step. Methods depend on material and support geometry:

Manual breaking: For accessible steel and titanium supports with thin contact areas (0.1–0.3 mm contact distance). Pliers or flathead screwdriver. Fast when designed correctly — slow and damaging when supports are over-engineered.

Machining / grinding: When supports are at tolerance surfaces. A ball-nose end mill removes support stumps cleanly and leaves a machined surface in one step.

Chemical removal: Not commonly used for metal AM supports (unlike FDM soluble supports). However, electrochemical polishing or acid etching of support witness marks is sometimes used for medical implants.

EDM: For difficult-to-reach internal supports in titanium and Inconel. Expensive and slow — this is a design failure. Internal supports should be eliminated by design wherever possible.

Keys to easy support removal (design recommendations):

• Use perforation patterns in support skin layers (reduces contact area by 50–80%)
• Set contact gap: 0.1–0.2 mm for titanium, 0.05–0.15 mm for steel
• Avoid supports on curved surfaces — use contour supports that follow the part surface
• Never put support on a bore or channel that has a tight diameter tolerance — it will be impossible to achieve the tolerance after support removal

Step 4 — Heat treatment

Heat treatment for AM parts serves several distinct goals. Understanding which goal you need determines which treatment is appropriate.

Stress relief (low-temperature anneal)

Goal: relax residual stress without significantly changing the as-built microstructure or strength.

Best for: parts where as-built mechanical properties are acceptable and distortion control after machining is the concern.

Typical effect: 10–20% reduction in yield strength, marginal improvement in ductility. For aluminium (AlSi10Mg at 300°C), effect on strength is minimal.

Solution anneal + age (T6 / precipitation hardening)

Goal: dissolve the as-built microstructure, re-precipitate a controlled dispersion of strengthening phases.

Best for: aluminium alloys (AlSi10Mg T6), martensitic stainless steels (17-4PH H900), nickel superalloys (IN718 SA+DA).

Example — AlSi10Mg T6:

• Solution: 520°C / 1 h / water quench — dissolves the fine Al-Si eutectic network
• Age: 160°C / 4 h — precipitates Mg₂Si, restores strength

Effect: Yield strength drops ~25% from as-built, but ductility doubles and properties become near-isotropic. Thermal conductivity increases ~20%.

HIP (Hot Isostatic Pressing)

HIP applies simultaneous high temperature and isostatic gas pressure (argon, typically 100–200 MPa at 900–1200°C for metals). It closes internal porosity and sub-surface pores that are inaccessible to other methods.

What HIP does:

• Closes spherical gas pores and shrinkage porosity (>99.9% densification achievable)
• Partially relieves residual stress via creep at high temperature
• Coarsens the microstructure (grain growth) — reduces strength, increases ductility

What HIP does not do:

• Cannot close LOF (lack of fusion) defects with significant width — these are planar, not spherical, and do not close under isostatic pressure
• Does not improve surface finish
• Does not fix cracks that intersect the surface (pressure equalises through the crack)

When HIP is mandatory:

• Aerospace fracture-critical parts (AMS 2801 or equivalent required)
• Medical implants in load-bearing applications (ASTM F3001 / ISO 5832)
• Parts with demonstrated porosity >0.2% by X-ray CT

When HIP is not worth it:

• Parts with optimised, well-qualified LPBF parameters achieving >99.7% density — fatigue improvement from HIP is marginal
• Parts where grain coarsening from HIP would reduce fatigue life below as-built value (some aluminium alloys)
• Cost-sensitive commercial parts not in safety-critical applications

Use the HIP cycle designer tool to specify temperature, pressure, and cycle duration for your material.

Step 5 — Surface finishing

LPBF as-built surface roughness is typically Ra 8–20 µm on up-facing surfaces, Ra 15–40 µm on down-facing surfaces. For many applications, this is too rough. Options:

Shot blasting / bead blasting

The standard first step for most metal AM parts. Glass bead (soft) or steel shot (hard) bombardment:

• Improves Ra by 20–50% (from Ra 15 µm → Ra 7–10 µm)
• Introduces compressive residual stress at the surface — significantly improves fatigue life (often +30–50%)
• Gives a uniform matte finish

Cost: low. Applicable to all metal AM alloys. Most AM service bureaus include this as a standard step.

Electrochemical polishing (ECP / electropolishing)

Controlled anodic dissolution in an electrolyte. Particularly effective for internal channels and complex geometries that blasting cannot reach.

• Achieves Ra <1 µm on stainless steel and titanium
• Can polish internal channels and bores
• Improves corrosion resistance by removing iron-rich surface contamination from stainless steel
• Requires material-specific electrolyte chemistry — not universal

Abrasive flow machining (AFM)

Forces an abrasive-laden polymer medium through channels under pressure. The gold standard for internal channel finishing in hydraulic manifolds, heat exchangers, and turbine cooling channels.

• Achieves Ra 0.5–2 µm internally
• Particularly effective for conformal cooling channels in tooling inserts
• Must be designed-in: inlet and outlet ports must allow AFM media to traverse the full channel

CNC machining

The reliable path to tight tolerances (±0.01–0.05 mm) and functional surface finishes (Ra <1.6 µm) on critical interfaces: bores, threads, mating faces, sealing surfaces.

AM parts should always be designed with machining stock on functional surfaces (0.5–1.0 mm allowance). Attempting to finish AM surfaces to tolerance without machining stock risks scrapping the part if the as-built surface is at the wrong position.

Laser polishing

Pulsed laser remelting of the surface layer. Reduces Ra by 60–80% with no change in part geometry. Being industrialised for aerospace applications. Currently a specialty process — not widely available from contract manufacturers.

Step 6 — Inspection

Dimensional inspection

CMM (coordinate measuring machine) or structured light scanning verifies that the part geometry is within tolerance. Key considerations for AM:

• AM parts have higher dimensional variability than machined parts (±0.1–0.3 mm as-built for LPBF; ±0.05 mm after machining)
• First article inspection (FAI) should be 100% dimensional scan, not spot-check
• Build plate distortion and thermal gradient can cause warping of large flat sections — always include flatness in the inspection plan

X-ray CT scanning

The only method that reveals internal porosity, cracking, and dimensional deviations in enclosed features. Increasingly routine for aerospace and medical AM parts.

• Detects pores >50–100 µm (system-dependent)
• Can verify internal channel dimensions and wall thickness
• Generates full volumetric dataset — compare to nominal CAD
• More expensive than surface-only CMM but the only way to see inside the part

Destructive test coupons

Test coupons are built alongside (or as part of) the production part and removed post-build for tensile testing, fatigue, Charpy impact, or metallographic cross-section. Required by most aerospace and medical qualification schemes.

Position coupons at the extremes of the build plate (not just the centre) to capture any spatial variation in properties across the build.

Cost hierarchy

From least to most expensive (per part, typical LPBF metal):

Use the cost-per-part calculator and the TCO tool to model total part cost including post-processing labour and treatment costs.

Related tools

• HIP cycle designer — specify HIP cycle parameters for your material
• Heat treatment advisor — recommended heat treatment cycles by alloy and AM process
• Surface roughness reference — Ra values by process, condition, and surface orientation
• Cost per part calculator — model total part cost including post-processing