Plasma-Involving Laser-based Manufacturing, Laser Fabrication of Metal Composites and Ceramics

This dissertation presents research work related to laser micro sintering, laser-induced plasma deburring, laser fabrication of ceramics and CNT-metal composite.

Firstly, we present the development of a physics-based model for double pulse laser micro sintering (DP-LMS), which typically utilizes long nanosecond (ns) laser pulses to melt metal powders and a followed short ns laser pulse to generate plasma-induced high pressure that promotes melt flow and fills voids. Chapter 2 shows a thermal model that predicts the temperature history in the power bed under ns laser irradiation. The model has been validated by comparison with the measured temperature. Chapter 3 shows an integrated physics-based model that simulates the thermal and hydrodynamic processes in DP-LMS. The model is used to evaluate the effect of plasma-induced pressure on the densification enhancement, and also reveals the effects of the long ns laser pulses on the plasma generated by the following short ns laser pulse.

Secondly, we present extensive experimental studies of laser-induced plasma micro-deburring (LPD). Chapter 4 shows LPD on an aluminum-alloy workpiece using plasma generated from sacrifice plates made of different materials. Residual effects of LPD on the workpiece have been discussed. Chapter 5 shows time-resolved imaging and optical emission spectroscopy (OES) measurements of the plasma generated by high intensity ns laser in a channel with and without burrs on the channel sidewalls. The effects of the burrs on laser-induced plasma have been revealed.

Thirdly, in Chapter 6 we present preliminary work on an additive manufacturing process for ceramics, which is called pulsed-continuous dual-beam selective laser melting (PC-DB-SLM). In this process, a pulsed laser beam is used to generate melt pool, and a CW laser beam is used to reduce the temperature gradient. The work shows that the PC-DB-SLM process has a great potential to address challenges associated with SLM of ceramic parts.

Finally, we present the experimental work on laser fabrication of carbon nanotube-metal composite in Chapter 7, showing high densification and hardness.