Double-pulse laser micro sintering: Experimental study and mechanism analysis aided by in-situ time-resolved temperature measurements

Abstract

Laser micro sintering (LMS) is a process of manufacturing microscale parts and/or features by laser sintering. Small powder particles (e.g., on the order of ~1 μm) are often used for good spatial resolutions. Besides, pulsed lasers are often employed due to related potential advantages. For good mechanical properties, pulsed laser-based LMS typically desires high densification of sintered material, which is, however, often more difficult to achieve than conventional macro selective laser sintering or melting. A new double-pulse laser micro sintering (DP-LMS) process was recently proposed by the corresponding author, which is a novel approach to potentially achieve good densification of sintered material in pulsed laser-based LMS. It employs laser pulse groups, each of which contains “sintering laser pulse(s)” followed by “pressing laser pulse(s)” at a certain delay time, which are used to sinter (melt and coalesce) the powder particles and generate a high transient pressure onto the material, respectively. This paper reports a study of the DP-LMS process for single-track sintering. The related fundamental mechanisms are analyzed with the help of in-situ time-resolved measurements of powder bed surface temperatures during DP-LMS. Under the conditions studied, it has been found that DP-LMS can produce better sintering results than those by LMS only using the sintering or pressing laser pulses. For a good sintering result in DP-LMS, the “pressing laser pulse” needs to have a sufficiently high intensity and follow the last preceding “sintering pulse” close enough such that the irradiated surface region is still in a molten state (or partially so to a sufficient extent). The fundamental mechanism for good sintering results in DP-LMS is expected to be that the “pressing laser pulse” can induce (likely via laser ablation and plasma generation) high pressures on the powder bed surface, which can promote melt flow, reduce balling and/or enhance material densification and/or continuity. In addition, a thermal accumulation effect between adjacent “sintering laser pulses” during DP-LMS has been revealed by the in-situ temperature measurements.