Addition and Joining

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.

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Types of Joint

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

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Adhesives

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.

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Mechanical Fixings

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

Knock-Down Fittings

KD fittings are specifically designed for flat-pack furniture and allow the end user to assemble and disassemble the product without specialist tools.