The big idea: Joining puts two or more pieces together, and the first design question is not which process but: does this joint ever need to come apart?
A temporary joint can be opened for repair, upgrade, battery replacement and recycling. A permanent one is stronger, lighter, sealed and cheaper to assemble — and turns the product into a single object at the end of its life.
Five techniques drawn as how each one holds — and sorted by whether the joint can ever be opened.
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| Technique | Permanent? | How it holds | What it suits |
|---|---|---|---|
| Adhering | Permanent | An adhesive bonds two surfaces, spreading the load over the whole joint area | Dissimilar materials that cannot be welded, thin sheets a rivet would tear, and joints that must be sealed as well as held |
| Fastening | Temporary | Screws, bolts, rivets, clips and snap-fits hold parts mechanically at discrete points | Anything serviceable, anything assembled from different suppliers' parts, and anything shipped flat |
| Stitching | Permanent | Thread passes repeatedly through both layers, holding with a flexible line of small points | Textiles and leather, where the joint must bend with the material and survive washing |
| Weaving | Permanent | Strands are interlaced so friction and geometry hold them with no separate joint at all | Textiles, baskets, cane furniture, carbon and glass fibre reinforcement, wire rope |
| Welding | Permanent | The parts are melted together, so the joint becomes continuous parent material | Metals and some thermoplastics, where the joint must be as strong as the material and completely sealed |
Riveting is fastening, and it is not removable in practice: A rivet is a mechanical fastener, so it is classified with fastening — but it has to be drilled out to remove it.
That is worth saying explicitly, because "temporary" in this topic means the joint can be opened, and a rivet is at the edge of that.
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| Technique | The cost that has to be accepted |
|---|---|
| Adhering | It cannot be undone without destroying something, surfaces must be clean and prepared, and the bond ages — so an adhered product is effectively unrepairable and hard to recycle |
| Fastening | Load is concentrated at each fastener, extra parts must be bought and fitted, holes weaken the material, and assembly takes labour or a machine |
| Stitching | Every stitch pierces the fabric, so a seam is a line of small weaknesses — which is why stressed seams are doubled, taped or bound |
| Weaving | The join IS the material, so it cannot be undone — though it also has no fastener to fail and no adhesive to age |
| Welding | It needs compatible materials, heat distorts and weakens the area around the joint, it takes skill or a robot, and it cannot be reversed |
The end-of-life consequence: A glued-shut product is one object at the end of its life, and can only be shredded. A screwed one is a pile of materials that can be sorted.
That single decision, made early and for assembly-cost reasons, decides whether the product can ever be repaired or recycled — which is the link to design for disassembly.
How this is tested — explaining how components are assembled using joining techniques. It comes up two ways:
Paper 1 — multiple choice
- Classify a named joint as temporary or permanent.
- Choose the joining technique suited to two dissimilar materials.
Paper 2 — analysing a product
- Explain the joining techniques used in a named product.
- Justify a joining technique against an alternative.
The trap: Choosing a joint on strength alone. Repairability, recycling, the two materials involved, and whether the joint must be sealed all matter as much.
IB-style questionJustify[6 marks]
A laptop manufacturer glues its battery in place and rivets its hinges. Justify each choice, then argue against one of them.
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