New Specification for Additive manufacturing -- Non-destructive testing and evaluation -- Dimensional measurements on Xray Computed Tomography images
1. Scope
This document specifies guidelines and recommendations to be followed prior to carrying out
dimensional measurements on three-dimensional (3D) volumetric X-ray Computed Tomographic (XCT)
images of additive manufacturing (AM) series production parts. It is applicable to cone beam XCT
systems. However, these guidelines and recommendations can easily be transposed to fan beam XCT
systems.
The process to be followed prior to performing dimensional measurement on 3D volumetric XCT
images of AM series production parts, in this standard, is divided into two steps:
Step 1: Quantification of an XCT system performance, in terms of image quality and basic
dimensional measurement accuracy, with a reference object and eventually a Representative Quality
Indicators (RQI), with the specific part (part chosen from the AM series production parts) XCT setting
under certain environmental conditions. This step leads to the determination of the image quality, the
voxel size and the basic dimensional measurement accuracy of an XCT system;
Step 2: Validation of the XCT system compliance, in terms of dimensional measurement accuracy,
with the specific part, with the chosen XCT setting under the specific environmental conditions. This
step leads to a simplified determination of the dimensional measurement uncertainty of each
measurand of the specific part.
If step 1 does not comply with the set requirements, the XCT system cannot be used for step 2.
This document does not claim to provide a definitive method to determine XCT dimensional
measurement accuracy, which, given the complexity of an XCT process, is not yet established. For the
same reason, it is addressed to qualified XCT operators with the support of metrology experts.
This document is dedicated to AM series production parts and its aim is to provide a methodology for
controlling the geometric specificities associated with AM (internal shapes, lattice structures). It is
applicable on parts that are fabricated by any type of AM categories of processes and material
provided the X-ray penetration lengths are sufficient to scan the test part.
These prior quantification and validation processes, which allow dimensional measurements to be carry
out on 3D volumetric XCT images of AM series production parts, are valid for a specific part geometry
in a given material associated with a chosen XCT setting (magnification & XCT acquisition and
reconstruction parameters of the specific part) under specific environmental conditions for the
measurands specified. The quantification and validation processes are reconsidered when different
geometry of the part or material or XCT setting or environmental conditions or measurands are taken
into account.
Keywords
AM,
Rationale
X-ray Computed Tomography (XCT) spreads out for quality control of parts in industry, i.e. threedimensional (3D) visualisation in volume for function testing, non-destructive inspection for
flaw
analysis, but also metrology for nominal/actual comparison, tolerance analysis, and
dimensional
measurements. This spreading can be explained by the fact that additive manufacturing
(AM),
producing parts with complex geometries that may contain internal features, is becoming
increasingly
popular in industry. Parts conventionally manufactured, without internal feature, are
dimensionally
measured by surface methods, providing a 3D surface point cloud (such as coordinate
measurement
method (CMM)). As a complement, this standard allows the dimensional measurement of
internal
features for AM parts to be performed with XCT, enabling the visualisation of the whole volume of
a test part (geometric 3D representation of the inside and
outside).
