1. Scope

This standard covers the methods used to measure the density of additively manufactured (AM) materials. Due to process-induced defects in the AM parts, measuring the overall parts density is crucial to evaluate fabrication quality. Some density measurement methods cannot account for the process-induced defects (e.g., lack of fusion (LoF)). In addition, there is operator-to-operator and organization-to-organization variability in density measurement procedures which could be reduced by standardized methodology and procedures. This investigation is intended to compare the efficacy of various methods for measuring the overall density of AM parts that incorporate the process-induced defects. This is a guide for AM users to follow any specific density measurement method according to the desired application.

Keywords

Process-induced defects; Density; Density measurement methods; Archimedes; X-ray computed tomography (XCT); 2D imaging; Additive manufacturing; Laser powder bed fusion

Rationale

Fabricating fully dense parts has been a challenge since the emergence of additive manufacturing (AM). Additively manufactured (AM) parts encompass unavoidable volumetric defects inherent to the manufacturing process, which can reduce the parts density. The quantity, size, and shape of the volumetric defects influence the mechanical performance of the fabricated part, specifically under cyclic loading conditions. Such defect aspects (i.e., quantity, size, shape, etc.) are mainly governed by the employed process and design parameters for manufacturing as well as feedstock and geometrical factors. The very first step in understanding an AM material's quality is to measure its density. Afterward, characterizing the defects aspects may help AM users to assess the process window for fabricating parts with an improved density, and consequently, achieve enhanced mechanical performance. While measuring the density of the material can give beneficial information regarding the health of the fabrication, there is still no specific method to measure the overall density of the AM parts. There are some standards for non-destructive density measurements (e.g., ASTM E1935, and ASTM 3166-20); however, there is no standard for destructive inspection and qualification. Moreover, different institutes use self-customized guidelines for density measurement, resulting in company-to-company and even operator-to-operator variations. In addition, some specific characteristics of volumetric defects (e.g., slit-shaped morphology of lack of fusion defects) may result in an inaccurate overall density evaluation. Therefore, it is crucial to develop a standardized practice for measuring the overall parts density, which may also account for individual characteristics of AM volumetric defects.

The title and scope are in draft form and are under development within this ASTM Committee.