How do we join parts together permanently or so they can be taken apart?
Permanent joining methods (welding, brazing, soldering, adhesives, riveting) and temporary methods (nuts and bolts, screws), and when each is used.
A focused answer to AQA GCSE Engineering on permanent joints (welding, brazing, soldering, adhesives, riveting) and temporary joints (nuts, bolts and screws), with the choice between them.
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What this dot point is asking
AQA wants you to sort joining methods into permanent and temporary, give examples of each, and choose the right method for a situation, explaining whether the joint ever needs to come apart. Questions often give a product and ask you to justify a join, so reasoning matters more than a list.
Permanent joining methods
- Welding: melts and fuses the parent metals themselves into one continuous piece; very strong and used for steel frames and structures.
- Brazing: joins metals with a melted filler (a brass or bronze alloy) above 450 degrees C; the parent metals stay solid, so it suits joining dissimilar metals or thin sections.
- Soldering: like brazing but below 450 degrees C; the low temperature makes it ideal for electronics and small pipework where heat would damage components.
- Adhesives: glues such as epoxy bond a wide range of materials, spread load over a large area and add no heat, but cure slowly and can be weak in peel.
- Riveting: a rivet is passed through aligned holes and its end spread (headed over) to clamp the parts; permanent because it must be drilled out to remove.
The key contrast within this group is whether the parent metal melts. In welding the parts themselves melt and fuse; in brazing and soldering only the filler melts and flows into the joint by capillary action, while the parts stay solid.
Temporary joining methods
Choosing a method
Use a permanent joint where strength, sealing and a one-piece result matter, for example a welded bicycle frame. Use a temporary joint where parts must be removed later, for example a panel that has to be unscrewed to reach the components behind it. The deciding question is always "will this ever need to come apart?"
Try this
Q1. Name one permanent and one temporary joining method. [2 marks]
- Cue. Permanent: welding, brazing, soldering, adhesive or rivet. Temporary: nut and bolt, or screw.
Q2. State one advantage of a temporary joint over a permanent one. [1 mark]
- Cue. It can be undone for maintenance, repair or replacement.
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 20194 marksCompare a welded joint with a bolted joint for fixing two steel plates together.Show worked answer →
A good answer contrasts permanence, strength and maintenance.
Welding fuses the two plates into one piece, giving a very strong, permanent and sealed joint with no extra parts. However it needs skill and equipment, distorts the metal with heat, and cannot be undone without cutting.
A bolted joint clamps the plates with nuts and bolts. It is a temporary joint that can be undone for maintenance or replacement, needs no special skill or heat, but adds weight and parts, can work loose under vibration and may let water in at the gap.
Markers reward at least one clear advantage and disadvantage of each, linked to whether the joint must be permanent.
AQA 20226 marksA manufacturer assembles a metal access panel that must be unbolted for servicing but must not rattle loose in use. Discuss the joining methods and features they could use.Show worked answer →
A good answer chooses a temporary method and explains how to keep it secure.
The panel must come off for servicing, so a permanent joint (welding, riveting, adhesive) is wrong; a temporary joint is needed. Nuts and bolts or machine screws into threaded holes allow the panel to be removed with hand tools.
To stop it rattling loose under vibration, the manufacturer can add a locking feature: a spring washer or nylon-insert (nyloc) nut increases friction on the thread, a thread-locking adhesive holds the thread, or a tab washer is bent against the nut. These keep the joint secure while still allowing removal with the right tool.
Markers reward selecting a temporary method for the servicing requirement and naming a sensible anti-loosening feature with a reason.
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Sources & how we know this
- AQA GCSE Engineering (8852) specification — AQA (2017)