Porosity Measurements and Analysis for Metal Additive Manufacturing Process Control

Abstract

Additive manufacturing techniques can produce complex, high-value metal parts, with potential applications as critical metal components such as those found in aerospace engines and as customized biomedical implants. Material porosity in these parts is undesirable for aerospace parts - since porosity could lead to premature failure - and desirable for some biomedical implants - since surface-breaking pores allows for better integration with biological tissue. Changes in a part’s porosity during an additive manufacturing build may also be an indication of an undesired change in the build process. Here, we present efforts to develop an ultrasonic sensor for monitoring changes in the porosity in metal parts during fabrication on a metal powder bed fusion system. The development of well-characterized reference samples, measurements of the porosity of these samples with multiple techniques, and correlation of ultrasonic measurements with the degree of porosity are presented. A proposed sensor design, measurement strategy, and future experimental plans on a metal powder bed fusion system are also presented.

Proof of Concept of Crack Localization Using Negative Pressure Waves in Closed Tubes for Later Application in Effective SHM System for Additive Manufactured Components

“…Fatigue and crack propagation properties of additive manufactured materials are not very well known yet [1], because a lack of process understanding and a lack of in situ process monitoring and control, especially in metal AM systems, currently results in unknown porosity levels and distributions [2]. Multiple sources report a reduced fatigue lifetime.…”

X-ray computed tomography for additive manufacturing: a review

“…This monitoring aimed to provide an in-situ pass/fail status for parts, defined by tolerancing of the resultant part porosity as measured post-process by XCT. Slotwinski et al [73] developed a method of in-situ porosity monitoring by ultrasonic sensing, correlating ultrasonic porosity data to porosity data gained using three other methods; mass/volume, the Archimedes method and XCT. The authors in this instance noted that porosity values varied significantly between measurement procedures and so further destructive testing would be required to ascertain the "true" porosity value.…”

Effects of Void Array Orientation on Compressive Properties of Cellular Structures

“…Slotwinski et al used finite element analysis (FEA) and micro-CT scanning of Co-Cr samples manufactured by selective laser melting (SLM) to show that the intrinsic porosity itself did not lead to elastic anisotropy. [11] Leicht & Wennberg found only small differences in the elastic modulus of SLM Ti-6Al-4V in the build plane and normal to the build plane, but these disappeared after stress relief of the samples. [12] Simonelli et al found no variation in elastic modulus of SLM Ti-6Al-4V with build orientation due to the weak a 0 texture of the as-built material.…”