Reason: Some contents in my dissertation have been submitted to Journals, which are currently under review.
until file(s) become available
Experimental Study, In-situ Measurement and Modeling for Laser Based Additive and Subtractive Manufacturing
thesisposted on 17.09.2021, 17:33 by Hanyu SongHanyu Song
Research work on laser sintering of carbon nanotube (CNT)-metal composites on a polymer substrate is reported, using a continuous-wave laser or a nanosecond (ns)-pulsed laser. Multiple approaches are employed, such as in-situ temperature measurements through fast pyrometry, in-situ reflected probe laser beam measurement, and post-process electrical resistivity measurement and microscopic characterizations for sintered material. The results are analyzed and discussed.
A novel laser micro sintering (LMS) process, with the name of “double-pulse laser micro sintering” (DP-LMS), has been studied. DP-LMS utilizes laser pulse group(s) consisting of
“sintering laser pulse(s)” followed by “pressing laser pulse(s)” at a suitable delay time. Under the studied conditions, DP-LMS can produce an improved sintering result than those by LMS under similar conditions without using the “double-pulse” approach. The underlying mechanism for the effect of the “pressing laser pulse” delay time has been analyzed with the help of in-situ time resolved
measurements of powder bed surface temperatures during DP-LMS.
A preliminary experimental study on a laser metal deposition (LMD) process, called warm ultrasonic impact-assisted laser metal deposition (WUI-LMD), has also been reported (such a study has been rarely seen in literature to our knowledge). During WUI-LMD, in-situ ultrasonic impact treatment is applied on laser-deposited material at elevated temperatures. The preliminary results show that for the conditions and samples studied, the WUI-LMD process can effectively reduce the porosity of the deposited material. This implies its great potential for improving the LMD process without obviously increasing the total production time.
A novel laser-induced plasma deburring (LPD) process was reported in a previous preliminary experimental study. However, the burr removal mechanism in the previous LPD
experiment still requires further study to understand. In this study, a physics-based model is developed for laser-induced plasma flow and plasma-burr interactions. Under the conditions studied, it has been found that the plasma-induced thermal effect on the burr is unlikely to play a major role in the burr removal. Instead, the high pressure induced by the plasma on the burr can induce stresses potentially large enough to remove the burr. Therefore, the burr removal should be mainly through a mechanical mechanism instead of a thermal mechanism during the LPD process under the conditions studied.