Specialised Applications and Advanced Topics
This domain tests newer and niche processes: what they do well, what limits them, and the key parameter calculations.
Advanced processes
Friction stir welding (FSW) is a solid-state process for aluminium and other low-melting metals; it avoids solidification cracking but leaves a tool exit hole and needs rigid backing and tool wear control. Laser welding gives narrow HAZ and high speed but needs tight fit-up and has high reflectivity hazards; laser safety is a major issue. Electron beam welding needs vacuum, gives deep narrow penetration and low distortion. Narrow-gap welding reduces filler volume in thick sections. Cladding and hardfacing apply a corrosion- or wear-resistant layer; dilution must be controlled. Underwater welding is either wet (higher hydrogen, quench rates) or hyperbaric dry (chamber pressure affects arc behaviour). Additive manufacturing uses wire or powder deposition with layer-wise thermal cycles.
Worked example: dilution
A cladding pass melts 1 mm into the substrate and the clad layer is 3 mm thick. Dilution = 1/(1+3) × 100 = 25%. If the specification limits dilution to 10%, the heat input must be reduced or a different process used. Reasoning: dilution is substrate melted divided by total melted thickness; it controls composition and corrosion resistance of the cladding.
Traps
Assuming FSW suits steels as easily as aluminium. Ignoring laser reflection hazards and interlock requirements. Treating EB as a field process. Confusing cladding with buttering. Forgetting that underwater welding changes hydrogen and cooling behaviour.