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Novel aluminium welding methods

Exploitable results

Welding baselines have been established. Joint efficiencies and fatigue performance has been much higher than expected. For example, for 2024 alloy welded by TIG, CO2 or Nd-YAG lasers both static and dynamic joint efficiencies were about 70% or greater Good weld bead geometry was found to be essential for good fatigue performance. This has necessitated the use of filler wire in all cases. Two novel laser sources were developed and tested. These were a high average power CO2 TEA laser and a CW+pulsed Nd/YAG laser. However during the course of the project new CW Nd/YAG laser sources of high power (>3kW) were developed that supersede the requirement to use a pulsed source.. Both excimer and ND-YAG lasers were investigated for their ability to provide surface cleaning prior to welding. The excimer laser cleaning was very effective. Relatively pore free welds were obtained even when the welding process was carried out several weeks after the excimer cleaning. For some applications, such as laser welding, it is a viable on line process that could be used. The Nd/YAG process has been shown to be suitable for Nd/YAG laser welding but gave a different result from the excimer laser for the TIG welding. The reason for this discrepancy between the two pulsed laser systems has not yet been established. A study of the low power (100W) q-switched Nd/YAG laser enhancement of the TIG welding process was made. Large changes in penetration depth due to the addition of the laser have been observed but this has always been an additive effect. Adding 100W of TIG power will produce the same change. No constriction of the arc has been observed. Theoretical welding models were produced. They are suitable for welding process simulation and optimization. Five demonstrator components were fabricated. Two were realized using TIG welding whilst the others utilized laser welding. In all cases weld quality was sufficient to allow adoption of welding technology. However, the TIG welded components suffered from unacceptable distortion. For four of the demonstrators the economic assessments were favourable, and in some cases very much so. For one of the demonstrators the production rates were not high enough to amortize the cost of the capital investment in a reasonable time. There was also a weight saving of about 10% in favour of the welding processes compared to other metal joining processes. The main conclusion of this project is that high quality welds can be produced in aerospace alloys. Provided correct procedures are applied, they are defect free and have static and dynamic joint efficiencies about 70%. The welding processes appear, in most cases, to be economically beneficial. Providing distortion is sufficiently well controlled, or managed, the processes are practically realizable for large components. This was shown by the production of five industrial components.