A Review: Melt Pool Analysis for Selective Laser Melting with Continuous Wave and Pulse Width Modulated Lasers

Abstract

Selective laser melting (SLM) is a promising additive manufacturing technique applied to various areas such as aerospace and biomedical industries. Because product characteristics can be controlled by SLM process parameters, several investigations have been conducted to clarify the relationship between process parameters and product characteristics. Melt pool, controlled by process parameters, is a suitable resource to determine the product profile accuracy and mechanical property. Two laser types, continuous wave (CW) and pulse width modulation (PWM), are typically used in SLM processes, and each has distinct advantages depending on the purpose of the process. While CW maintains its power constant, PWM presents a repeated pattern with a pulse width. Herein, the main differences in the process parameters between the two laser types and their effects on the melt pool formation during the SLM process are explained. The results demonstrate that CW and PWM are favorable for dense and fine structures, respectively.

Towards an understanding of the functional properties of NiTi produced by powder bed fusion

“…Despite the same energy density, the melt pool formation can be different depending on the examined laser process parameters as well as the profile of the laser beam. In case of a pulse wave mode, rapid cooling rate and higher curvatures of melt pools are registered, resulting in finer columnar dendrite structures with relative high tilting angle [34]. A further experimental evidence that is worth to highlight, is the effect of h and v with respect to the laser energy on the thermo-mechanical properties.…”

“…These regions derives from the overlapping of two consecutive laser spots (pulse overlap). The pulse overlap occurs only for pulse wave emission lasers [34] and it principally depends on the point distance d and on the exposure time t parameters. Since d was kept constant in the present study, pulse overlap was mainly ascribed to t parameter.…”

“…For NiTi alloys, values of E in the range of 55 to 222 J/mm 3 provide high density and low porosity level within the produced samples [22 -25, 27, 29 -31]. Some selective laser melting machines use pulse wave emission laser, which present unique process parameters due to the laser pulse mechanism [32][33][34]. For these devices, the laser energy density can be approximated to [35]:…”

Improvement of Part Accuracy by Combination of Pulsed Wave (PW) and Continuous Wave (CW) Laser Powder Bed Fusion

“…During the laser off-time, the generated melt pool cools down and (partially) solidifies before the next melt pool is generated by the following laser pulse. Due to the discretized energy input and intermittent solidification of the melt pools in comparison to cw emission, smaller melt pool volumes are generated and Marangoni flows are reduced, limiting uncontrolled melt pool movements and therefore geometric deviations [8,14,[16][17][18].…”

In-Situ Characterization of Pore Formation Dynamics in Pulsed Wave Laser Powder Bed Fusion

“…One of the primary distinctions between commercial LPBF systems is the type of laser emission mode employed [ 2 ]. In continuous wave LPBF (CW-LPBF) systems, the laser delivers energy continuously without interruption; while in pulsed wave LPBF (PW-LPBF) systems, the laser power is fast modulated to turn on and off repeatedly, delivering energy in pulses [ 3 , 4 ].…”