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This lesson covers the methods used to join materials together in product manufacture, as required by AQA GCSE D&T (8552), Section 3.2.5. Joining is essential because most products are assembled from multiple components. The choice of joining method depends on the materials being joined, the strength required, whether the joint needs to be permanent or temporary, and the production volume.
Joints are classified as either permanent (cannot be taken apart without damaging the components) or temporary/semi-permanent (can be taken apart for repair, maintenance, or disassembly).
| Classification | Examples |
|---|---|
| Permanent | Welding, soldering, brazing, adhesives (most), rivets |
| Temporary / Semi-permanent | Screws, bolts and nuts, clips, press-fits, knock-down (KD) fittings |
Adhesives are substances that bond two surfaces together. Different adhesives are suitable for different materials and applications.
| Adhesive | Type | Materials | Setting Time | Strength | Common Use |
|---|---|---|---|---|---|
| PVA (polyvinyl acetate) | Water-based | Wood, paper, card | 30 min to 24 hrs | Moderate | Timber joinery, paper crafts, school use |
| Epoxy resin (e.g. Araldite) | Two-part thermosetting | Metals, ceramics, glass, composites | 5 min to 24 hrs (depending on type) | Very high | Structural bonding, filling gaps, repairing metal |
| Superglue (cyanoacrylate) | Chemical cure | Most materials (not PE or PP) | Seconds to minutes | High (brittle) | Small, precise bonds; model making; quick repairs |
| Contact adhesive (e.g. Evostick) | Solvent-based | Laminates, rubber, leather, wood | Apply to both surfaces, leave to become tacky, then press together | Good | Applying laminate to worktops, shoe repair |
| Hot glue (from a glue gun) | Thermoplastic | Card, fabric, wood, some polymers | Sets in seconds as it cools | Low to moderate | Quick prototyping, craft, temporary bonds |
| Tensol cement | Solvent-based | Acrylic (PMMA) only | Minutes; full cure 24 hrs | Excellent on acrylic | Joining acrylic components (actually dissolves and fuses surfaces together) |
| Fabric adhesive (e.g. Bondaweb) | Heat-activated or solvent | Textiles | Varies | Moderate | Hemming, applique, bonding fabric layers without sewing |
AQA Exam Tip: When selecting an adhesive in the exam, match it to the specific materials being joined. PVA is for timber and paper; Tensol cement is for acrylic; epoxy resin is for metals and mixed materials. If you suggest PVA for joining metal, you will lose marks because PVA does not bond effectively to metal surfaces.
Mechanical fixings use physical interlocking or clamping to hold components together. Most are temporary or semi-permanent, allowing disassembly.
| Fixing | Type | Description | Application |
|---|---|---|---|
| Wood screws | Semi-permanent | Tapered, self-tapping screw driven into timber | Joining timber components, attaching hinges and fittings |
| Machine screws and nuts | Temporary | Screw passes through a clearance hole and is secured with a nut | Joining metal and plastic components; easy to disassemble |
| Bolts and nuts | Temporary | Stronger than machine screws; hexagonal head tightened with a spanner | Structural connections, machinery, furniture |
| Rivets (pop rivets) | Permanent | A mandrel is pulled through a tubular rivet, expanding it to clamp two sheets together | Joining sheet metal; replacing traditional solid rivets; aircraft skins |
| Knock-down (KD) fittings | Temporary | Cam locks, barrel bolts, cross dowels | Flat-pack furniture assembly; designed for repeated assembly and disassembly |
| Nails | Semi-permanent | Driven into timber with a hammer | Simple timber joints, construction framing, attaching trim |
| Clips and press-fits | Temporary | Plastic clips snap together | Electronic enclosures, car interior trim, cable management |
KD fittings are specifically designed for flat-pack furniture and allow the end user to assemble and disassemble the product without specialist tools.
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