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The reduction of microstructural damage during the drilling of ceramics by high power laser

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posted on 2022-06-09, 09:36 authored by Andrew J. Murray

The key problems associated with laser processing of ceramics are centred on the induction of high temperature gradients. These temperature gradients are typically in the order of magnitude of 1000°C, and in turn give rise to tensile strain, which in the case of ceramic substrates cause microcracking, or catastrophic failure.

Numerical analysis techniques were developed to quantify the thermal damage, and to assist in the characterisation of the process using microscopy and image processing. As part of this development, uncertainty analysis was completed to identify the errors involved in imaging, mechanical sectioning of the substrates, and measuring features. In addition to the post process measurements systems, high-speed imaging was used to monitor the process of laser beam interaction, and hole breakthrough with respect to the assist gas dynamics for the laser drilling process.

Systematic experimental studies were completed to assist in the characterisation of the issues associated with laser beam interaction during drilling and cutting. Experimental methods were developed and applied to overcome the temperature gradient problems by attempting to balance the thermal shear between the laser beam, the assist gas and the substrate. These included pre and post process substrate heating and localised in-process non-transferred plasma arc heating. The final advancement made in this area, was the development of a novel technique for the in-process heating of the assist gas. The application of the new combined gas and substrate heating method to the laser drilling and cutting processes led to significant reductions in thermal damage. This development cumulated in a patent application being made.

The final stage of this research, was the application of this experimental knowledge to the formation of theories with regard to the. perepsSion laser drilling process. This work put forward new concepts which described the process in the context of laser beam focus, laser beam pulse characteristics, beam wave-guiding, assist gas dynamics and substrate conduction properties. These driving mechanisms were broken down into groups which described the different stages in hole growth and how they contribute to the features of a laser drilled hole. These were: the shallow hole, intermediate hole, deep hole, breakthrough, and post-penetration hole phases. Conduction modelling was used to highlight the thermal issues associated with each of these hole growth phases, and how they contributed to the generation of strain and cracking within the substrate.

Funding

National Physical Laboratory

History

School

  • Mechanical, Electrical and Manufacturing Engineering

Publisher

Loughborough University

Rights holder

© Andrew Murray

Publication date

2001

Notes

A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of the degree of Doctor of Philosophy of Loughborough University.

EThOS Persistent ID

uk.bl.ethos.392515

Language

  • en

Supervisor(s)

John Tyrer

Qualification name

  • PhD

Qualification level

  • Doctoral

This submission includes a signed certificate in addition to the thesis file(s)

  • I have submitted a signed certificate

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