Abstract
Quality concerns in laser powder bed fusion (L-PBF) include porosity, residual stresses and deformations during processing. Single tracks are the fundamental building blocks in L-PBF and their shape and geometry influence subsequent porosity in 3D L-PBF parts. The morphology of single tracks depends primarily on process parameters. The purpose of this paper is to demonstrate an approach to acoustic emission (AE) online monitoring of the L-PBF process for indirect defect analysis. This is demonstrated through the monitoring of single tracks without powder, with powder and in layers. Gas-borne AE signals in the frequency range of 2–20 kHz were sampled using a microphone placed inside the build chamber of a L-PBF machine. The single track geometry and shape at different powder thickness values and laser powers were studied together with the corresponding acoustic signals. Analysis of the acoustic signals allowed for the identification of characteristic amplitudes and frequencies, with promising results that support its use as a complementary method for in-situ monitoring and real-time defect detection in L-PBF. This work proves the capability to directly detect the balling effect that strongly affects the formation of porosity in L-PBF parts by AE monitoring.
Highlights
Metal additive manufacturing (AM) has grown significantly in recent years in industries such as aerospace, medical, automotive, and other high-tech areas
Since a layer consists of multiple tracks that are next to each other, depending on the position of the single track, varying amounts of solid and powder material will be involved in the melt pool and affect the progression of the acoustic emission (AE)
The results show to be similar in that: the AE energy increases with powder layer thickness; the same peaks are present at ∼6–8 kHz and for no powder the energy is low at higher frequencies (Figure 11)
Summary
Metal additive manufacturing (AM) has grown significantly in recent years in industries such as aerospace, medical, automotive, and other high-tech areas. Manufactured parts can be produced with high resolution and excellent mechanical properties, in some cases even superior to cast or forged metal alloys, as described in detail in the review paper (DebRoy et al, 2018). The L-PBF process involves many variables and a non-optimal setting (or variation) of these variables can result in reduced part quality, and these quality changes cannot always be detected. This is further complicated by the fast-growing field with different types of systems and the general lack of standards (Seifi et al, 2016; Seifi et al, 2017). The current state is such that published reports on mechanical and especially fatigue
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