Topic 4 of 6 · Form 5
Fabrication and welding technology
Butt, lap, tee, corner and edge joints; flat, horizontal, vertical and overhead positions; edge preparation (single-V, double-V).
Notes for this topic 1 file, in order
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Welding processes
- Manual metal arc (MMA/stick): flux-coated electrodes; versatile, used for gates, frames and structures.
- MIG/MAG: continuous wire with shielding gas; fast, good for sheet and production work.
- TIG: tungsten electrode with argon; high-quality welds on stainless steel and aluminium.
- Oxy-acetylene: gas welding and cutting; flame types (neutral, carburising, oxidising).
- Resistance (spot) welding for sheet metal; brazing and soldering for lower-temperature joins.
Weld joints and positions
Butt, lap, tee, corner and edge joints; flat, horizontal, vertical and overhead positions; edge preparation (single-V, double-V).
Weld defects
Porosity, slag inclusions, lack of fusion, undercut, cracking, distortion. Causes include wrong current, dirty surfaces, poor technique and moisture in electrodes. Distortion is reduced by tack welding, clamping, balanced welding sequences and pre-setting.
Inspection
Visual inspection, dye penetrant, magnetic particle, ultrasonic and radiography.
Mechanical fastening
Bolts and nuts, rivets (solid and pop), self-tapping screws; thread forms (ISO metric).
Safety
Eye and skin protection (UV radiation), ventilation (fumes), fire prevention, gas cylinder storage, electrical safety.
Check yourself
- Which welding process is best for thin aluminium?
- What causes porosity in welds?
- How can welding distortion be reduced?
Show answers
- TIG welding (MIG is also used).
- Gas trapped in the weld from moisture, contamination or poor shielding.
- Tack welding, clamping/jigs, balanced welding sequence, pre-setting parts, controlled heat input.
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