- Practice · 5 marks
Joining processes; welded vs mechanical joints
Short answer
Joining classified as welding, brazing/soldering, adhesive bonding and mechanical fastening. Welded joints have higher efficiency (up to 100%), lighter weight and leak tightness, but are permanent and need skilled welding; bolted joints allow disassembly and simpler inspection. Brazing and soldering suit thin, heat-sensitive, dissimilar or small parts and electrical joints.
Classify material joining processes. Compare welded joints with mechanical (riveted/bolted) connections and state when brazing and soldering are preferred over welding.
Joining is the bringing together of two or more parts to make a single assembly, either permanently or so that it can be taken apart.
Classification
| Class | Principle | Processes |
|---|---|---|
| Welding | Parent metals melted (with or without filler) or forced together to form an atomic bond | Fusion: arc, gas, laser; solid state: friction, resistance, forge |
| Brazing and soldering | Filler metal melts, parent metal does not; filler flows by capillarity | Brazing (above 450 degree C); soldering (below 450 degree C) |
| Adhesive bonding | Polymer adhesive bonds surfaces | Epoxy, cyanoacrylate |
| Mechanical fastening | Parts held by fasteners or interference | Bolts, rivets, screws, press fits, seaming |
Welded and mechanical connections
| Point | Welded joint | Riveted / bolted joint |
|---|---|---|
| Joint efficiency | High, up to 100 % of parent metal | 60-80 % (holes weaken plate) |
| Weight | Lighter; no plates or heads | Heavier; cover plates, fasteners |
| Leak tightness | Good | Needs caulking, sealing |
| Disassembly | Not possible (permanent) | Possible (bolts) |
| Cost and speed | Lower labour, faster | More labour, drilling/punching |
| Residual stress, distortion | Present, HAZ changes properties | None |
| Skill, inspection | Skilled welder; NDT needed | Simple inspection |
| Fatigue | Notch at weld toe | Stress concentration at holes |
Brazing and soldering
They are preferred when parts are thin or heat-sensitive, when dissimilar metals (steel to copper, carbide tip to steel shank) or very small assemblies are joined, when low distortion and a neat appearance are needed, and for electrical joints (solder). Welding is preferred where high strength and heavy sections are required.
✓ Answer checked by Claude Opus 5.5 (high effort)
Related questions
- Gas flames, arc welding and heat input · Manufacturing and Production Processes, chapter 12
- Classification of manufacturing processes; evolution · Manufacturing and Production Processes, chapter 1
- Weld metallurgy, HAZ and heat sources · Manufacturing and Production Processes, chapter 12
- Temporary and permanent joints; soldering, brazing, welding · Workshop Technology, chapter 10
- Types of failures on riveted joints · Design of Steel and Timber Structure, chapter 4
- Bolted joints in timber · Design of Steel and Timber Structure, chapter 10
- Behaviour and detailing of bolted and nailed joints · Design of Timber and Masonry Structures, chapter 2
All Manufacturing and Production Processes chapter 12 questions →