Application driven advances in laser micro-machining technology

Le, Hoang (2023). Application driven advances in laser micro-machining technology. University of Birmingham. Ph.D.

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Abstract

The use of a laser as a machining tool in micro manufacturing has several distinct advantages, including high speed non-contact processing, high accuracy, repeatability, and reproducibility, excellent control flexibility, and no restrictions on the types of materials that can be machined. Possibilities for further improvement of laser material processing are still in progress and facing challenges. There are limitations that prevent laser micro-machining from improving performance and expanding the range of manufacturing applications for this technology, such as the poor removal rate of ultrashort pulse processing and the tapering effect at side walls of microstructures. Therefore, the primary goal of the thesis is to address these important issues, thus, to advance this technology, i.e. achieving quality and process efficiency improvements in machining of various materials.
The research focuses on implementation and investigation of generic solutions to improve quality of fabricated products and process efficiency, as well as demonstration of the laser micro-machining capabilities in various industrial applications. Firstly, a refractive beam shaper was deployed to attain top-hat intensity profile at the focus position of a nanosecond pulsed laser source for micro-machining of blind structure. The top-hat processing was able to reduce taper in range from 4% to 15% and surface roughness in range from 15% to 21% for different scanning strategies. Advantages of top-hat profile over Gaussian profile also presented at various machining conditions. Secondly, MHz burst mode of ultrashort laser pulses was proven to scale-up material removal rate in laser micro-machining of stainless steel and copper. Specifically, material removal rate was increased by 2 to 6.5 times when machining copper and by 5.7 to 16.3 times when machining stainless steel. This technique allows the laser power to be fully utilised while laser fluence is kept closely to optimum level. The advantages of MHz burst mode in removal rate consequently led to the improvement of surface quality in some cases due to less required number of scanning layer in comparison to single mode. Thirdly, a novel fabrication process, called precession laser machining, was investigated and employed to produced THz devices. The use of this technology was able to reduce taper angle at the sidewall by 3 times (from 4.1° to 1.6°) and 6 times (from 11.5° to 1.9°) in producing through structure on 300 µm and 600 µm thickness, respectively, when compared with conventional laser machining process. The performance of fabricated THz devices satisfied all requirements with 1% error. Fourthly, the precession laser machining was investigated systematically to study its capabilities and limitations. The results showed that it was possible to drill hole with zero or even negative taper angle on 0.6 mm and 1 mm Nickel alloy substrate for hole diameter from 100 µm to 500 µm. It was not possible to achieve zero tapering when drilling on 2 mm substrate thickness. However, there still is a significant reduction in hole’s taper angle when machining on 2 mm substrate, where aspect ratios were up to 20:1. The precession beam is clipped at the hole entrance when beam is refocused downward that indirectly limits the machining capability of this technique on thick substrate.
In summary, the obtained results clearly demonstrated the capability of employed technologies in enhancing the material removal rate and quality of microstructures. In addition, the limitations of these technologies were also discussed and clarified. The research advances the knowledge in laser-based manufacturing technology and contributes to broaden the use of this technology in industrial applications.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):