- Title
- Optimisation of laser welding for thin-walled Ti6Al4V glider pressure hull
- Creator
- Nel, Matthew Ryan
- Subject
- Laser welding
- Subject
- Welding
- Subject
- Mechanical engineering
- Date Issued
- 2024-04
- Date
- 2024-04
- Type
- Master's theses
- Type
- text
- Identifier
- http://hdl.handle.net/10948/64739
- Identifier
- vital:73882
- Description
- Laser welding is a type of fusion welding process characterised by deep penetration, low heat input and high welding speed. This dissertation investigates the suitability of this process for the fabrication of an underwater glider buoyancy engine from thin Ti6Al4V alloy sheet. Areas of interest include the effect of process parameters on weld microstructure, static properties (microhardness, tensile and bend tests) and dynamic properties (fatigue tests). The effect of welding speed and laser defocusing were evaluated considering experimental matrices consisting of four different travel speeds and three defocus distances. These were narrowed down to three travel speeds and a single defocus distance, resulting in a final test matrix delivering three different heat inputs. Thereafter, the effect of heat input on static and dynamic properties was investigated. Vickers microhardness tests were carried out to predict weld response during tensile testing, with the expectation being that harder welds would offload more strain. This was confirmed using digital image correlation, which allowed for virtual measurement and visualisation of strain offloading. Bend tests were carried out on parent and welded samples to confirm whether Ti6Al4V could be formed to the correct geometry. Forming Ti6Al4V into a U-shape was the first consideration, since dynamic testing required samples of this geometry with longitudinal weld orientation. A two-stage forming methodology was developed from these experiments. Formed samples were subjected to fatigue tests in a custom designed fatigue platform for testing weld orientation as it would appear in the final component. Prediction of the welded buoyancy engine life was the goal behind these tests. Fracture surfaces were analysed to gain understanding of where crack initiation and final fracture occurred. Porosity served as the primary cause for crack initiation in failed samples. Pore distribution was heaviest in low-heat weldments and decreased with increasing heat input, while pore size increased with increasing heat input. This resulted in medium-heat weldments exhibiting superior performance to that of low- and high-heat ones. It was concluded that the laser welding process is able to produce weldments of sufficient integrity in thin Ti6Al4V sheet-formed components intended for use in glider buoyancy engines.
- Description
- Thesis (MEng) -- Faculty of Engineering, the Built Environment and Technology, School of Engineering, 2024
- Format
- computer
- Format
- online resource
- Format
- application/pdf
- Format
- 1 online resource (XXX pages)
- Format
- Publisher
- Nelson Mandela University
- Publisher
- Faculty of Engineering, the Built Environment, and Technology
- Language
- English
- Rights
- Nelson Mandela University
- Rights
- All Rights Reserved
- Rights
- Open Access
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | SOURCE1 | Nel, MR.pdf | 10 MB | Adobe Acrobat PDF | View Details Download |