Thermal modeling and validation via time-resolved temperature measurements for nanosecond laser irradiation of a powder bed of micro metal particles

Abstract

Continuous-wave (CW) lasers are often used in selective laser sintering or melting; but short-pulsed lasers (e.g., with a pulse duration on the nanosecond scale) have their own potential advantages, such as high resolutions and small residual thermal effects. Compared with CW lasers, nanosecond lasers involve additional parameters (such as the pulse frequency) and more complicated relations between laser parameters and the powder bed thermal responses in laser sintering or melting. To help fundamentally understand the relations and guide efficient parameter selections, it is highly desirable to develop a thermal model for nanosecond laser irradiation of a metal powder bed and directly validate the model via in-situ transient temperature measurements. However, research work integrating such model development and validation has been rarely reported to the authors’ best knowledge. In this paper, a thermal model has been developed for nanosecond laser irradiation of a powder bed of micro metal particles. The model-predicted transient surface temperature history of the powder bed agrees reasonably well with that measured by a fast pyrometry system. Under the conditions studied, the model simulations show that high-frequency nanosecond laser pulses can induce a significant thermal accumulation effect in a metal powder bed due to its lower thermal conductivity than that for a bulk metal. With the same time-averaged laser power, by changing the pulse frequency, a nanosecond laser can induce very different temperature histories, melt pool evolutions and lifetimes, suggesting the laser has a potential advantage of good adjustability and flexibility in laser sintering. It also means a parameter-selection challenge due to the complicated parameter-thermal response relations, implying the importance of a thermal model validated by time-resolved temperature measurements.