Influence of pulsed and continuous wave emission on melting efficiency in selective laser melting

A wide proportion of the industrial Selective Laser Melting (SLM) systems are operated with high brilliance fiber laser sources. These sources are most commonly operated in continuous wave (CW). A smaller fraction of these systems employs pulsed wave (PW) emission by power modulation, resulting in pulses with μs level durations, kHz level repetition rates and comparable peak powers to CW emission. Clearly, the laser temporal emission mode can have an impact over temperature fields, which in return control the melt pool size, stability and densification behaviour. The aim of this paper is to investigate the effect of laser emission regime on the melting efficiency in SLM. In particular, an analytical model was developed to investigate the process efficiency in single track formation at fixed energy input when employing different emission modes. A single mode fiber laser installed on an in-house developed prototype powder bed fusion system was used as the experimental setup with AISI 316 L metallic powders. The effect of duty cycle was evaluated starting from CW (i.e. 100% duty) moving towards PW, at fixed energy density levels. Results show that at constant energetic input, CW increases process melting efficiency up to 3 times whilst the deposition stability is reduced with lower duty in PW regime. Although less efficient, at stable conditions the use of modulated emission produces narrower tracks providing higher process resolution.