Joining Methods for Metal (Temporary & Permanent)

Design & Technology students must be familiar with a range of temporary and permanent joining methods for metals. This article helps students revise this information and concludes with sample examination questions from the Cambridge AS/A Level syllabus.

Temporary joining methods for metal

Nuts & Bolts

  • Bolt sits in a clearance hole drilled through both parts
  • Uses a washer, sometimes on both sides to spread the load and prevent damage to material when tightened
  • Nut is threaded on end and tightened

Note: Screws can be used to join sheet metal to another material, such as wood, but cannot be used to screw directly into metal.

Slot-in parts

Permanent joining methods

Rivets

rivets
  • Typically used to join thin sheets of metal together
  • Rivets are hammered to close (or put in with a rivet gun), so cannot be undone

Press joining

  • Metal is placed between a punch and a die, pressing the metal into an interlocked shape
  • Not as secure as riveting

Welding

  • Melts and fuses edges of metal together, typically using high heat
  • Creates a strong permanent bond
  • Common types include arc welding (using electrical current), gas welding (using flame), and newer techniques like laser welding
  • Sometimes uses a separate metal rod or wire that acts as a filler materials to melt and add to the joint (the filler is usually the same material as the item being welded)
  • Different metals are sometimes hard to weld together and some are impossible
gauntlets and spats
Safety precautions: Welding is a very hot and dangerous activity – with little bits of molten metal flying everywhere called “spatter” which can burn through regular clothing. It is important to wear gauntlets (heavy-duty protective heat-resistant gloves that extend up the forearm), spats (protective coverings worn over shoes and lower legs), a welding helmet with dark filter lens, fire resistant jacket/apron, steel-toe boots, and long pants.

Soldering

  • For light use applications (much weaker than welding)
  • Commonly used to join circuit wires together using a soldering iron
  • A filler rod made from low-melt-point metal called “solder” (often made from tin or silver alloys) is melted and used to connect two pieces, without melting the materials that are joined themselves
  • The molten solder flows between the joint surfaces and hardens when cooled, creating a mechanical and electrical connection.
  • Requires clean surfaces and often needs “flux” – a chemical to remove oxidation/rust/tarnish (although this can be built in to the solder)

Tweet
Share
Share
Pin