Additive Manufacturing Testing: A Complete Guide
Additive Manufacturing TestingWhat Is Additive Manufacturing Testing?
Additive manufacturing (AM) testing evaluates the mechanical properties, internal integrity, and dimensional accuracy of 3D-printed parts, addressing quality concerns unique to layer-by-layer manufacturing – build orientation dependence, internal porosity, and support structure artefacts – that don’t arise with traditional subtractive or casting processes. ASTM F3122 serves as the primary guide, directing users to existing mechanical test standards while flagging the AM-specific factors that must be recorded alongside results.
Specimen Preparation Considerations
ASTM F3122 identifies several factors that can meaningfully influence reported AM mechanical properties and must be documented: material, material anisotropy (properties often differ substantially by build direction), method of material preparation, porosity, specimen preparation method, testing environment, specimen alignment and gripping, testing speed, and testing temperature. Because AM parts are inherently anisotropic, a specimen’s build orientation relative to the load direction is not optional metadata – it’s a primary variable that must be reported alongside every result.
Mechanical Test Types
- Tensile testing: dog-bone shaped specimens, following existing tensile standards (E8 for metals) but with AM-specific reporting of build orientation and post-processing state
- Compression testing: cylindrical or rectangular prism specimens, evaluating compressive strength and modulus
- Flexural and impact testing: beam-like specimens, evaluating bending strength and toughness
Porosity Evaluation
Internal porosity – voids introduced during the layer-by-layer deposition or fusion process – is one of the most significant AM-specific quality concerns, since it directly reduces mechanical properties in a way conventional manufacturing rarely introduces at comparable magnitude. X-ray computed tomography (CT) is the primary non-destructive method for characterising porosity, resolving pore size, shape, density, and spatial location in three dimensions without damaging the part. CT scanning parameters for metal AM parts commonly use voltages around 150-200 kV, with voxel resolutions in the 50-150 micron range depending on part size and required detail.
Post-Processing Effects on Properties
Hot isostatic pressing (HIP) is commonly applied to metal AM parts specifically to reduce internal porosity and improve mechanical properties, effectively closing voids under combined heat and pressure. Heat treatment alters microstructure and mechanical behaviour similarly to its effect on conventionally manufactured metal, while surface finishing (sanding, polishing, or chemical treatment) affects surface-dependent properties like fatigue life. Any post-processing step can also introduce new residual stresses, which should be accounted for when interpreting mechanical test results.
Industry Specifications Referencing Additive Manufacturing Testing
- ASTM F3122: primary guide for mechanical property evaluation of metal AM materials
- ASTM F2971: practice for reporting data for test specimens prepared by AM
- ASTM E8, A370: referenced tensile and mechanical testing standards applied within the AM context
Conclusion
The biggest mistake in AM part testing is treating it like conventionally manufactured material with a different production method – build orientation, porosity, and post-processing state are first-order variables in AM mechanical performance, not secondary details, and any test report that omits them is missing the context needed to interpret the numbers correctly.
Why is testing important for additively manufactured parts? Additive manufacturing can produce complex geometries, but part quality may be affected by powder condition, layer bonding, build orientation, machine settings, thermal history, and post-processing. Testing helps identify porosity, incomplete fusion, cracking, distortion, poor surface finish, and inconsistent properties before the component is approved for service.
What materials can be tested? Testing can be performed on additively manufactured metals, polymers, ceramics, composites, and multi-material systems. Common materials include titanium alloys, stainless steels, aluminum alloys, nickel-based superalloys, engineering thermoplastics, photopolymers, and fiber-reinforced polymers. The required test methods depend on the material, printing process, and intended application.
What non-destructive testing methods are used? Common non-destructive testing methods include X-ray computed tomography, ultrasonic testing, radiography, liquid penetrant testing, visual inspection, and dimensional scanning. Computed tomography is particularly useful because it can reveal internal pores, cracks, inclusions, and dimensional features within complex parts without cutting them open.
How are porosity and internal defects evaluated? Porosity can be measured using microscopy, density methods, image analysis, or X-ray computed tomography. Testing may determine pore size, shape, volume fraction, and location. Irregular lack-of-fusion pores and cracks are often more damaging than small rounded gas pores because they create higher stress concentrations and may reduce fatigue life.
What should be included in an additive manufacturing test report? The report should include the material and feedstock details, printing process, machine identification, build orientation, specimen location, layer thickness, processing parameters, support strategy, heat treatment, surface finishing, test methods, results, and acceptance criteria. Photographs, scan data, micrographs, defect measurements, and deviations should also be included when relevant.
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