Joining Techniques Continued...

Fusing Fusing is the process whereby two or more materials are joined by either: 1.Heating them until they melt and run together 2.Heating a third material until it melts and forms a join.

Fusing Metals Metals can be fused by the following processes – 1.Brazing 2.Soldering 3.Welding

Brazing & Soldering You can join two metals by using a different metal with a lower melting point as the “adhesive”. When you heat the joint, the low melting point metal melts and flows into the gap. As the joint cools this metal turns solid, joining the other two pieces of metal together in a rigid, permanent joint. It is important to clean the pieces of metal to be joined. Use a flux to keep them clean when heating the joint. If they are dirty, the liquid metal will not stick to them properly so the joint will be weak or will not stick at all.

Brazing

Soldering

Welding Welding is used when we need to join two, or more, pieces of the same metal and we need to produce a very strong joint. There are three forms of welding: 1.Arc Welding 2.Gas Welding 3.Spot Welding

Arc Welding Arc welding relies on the intense heat produced from an electrical arc. An arc forms when a current flows through two electrodes that are separated. The electricity arcs through the air, or another gas, between the electrodes and gives off light and heat. A protective viewing plate allows the welder to view the welding process without fear of damage to the eyes.

Gas Welding In gas welding the required heat is produced by burning a gas (often acetylene) in an oxygen rich environment producing an extremely hot, blue flame.

Welded Joints

Fusing Plastics Plastics can also be joined using fusing techniques. Many plastics adhesives produce a welded joint as the solvent actually melts the plastic which runs together and fuses in a similar way to more traditional welds. In addition to solvent welding plastics can also be fused by: 1.Frictional Welding 2.Hot Gas Welding

Frictional Welding This technique is only suitable for similar thermoplastic material. The heat required for welding is produced by pressing the two pieces together and spinning or rotating one of them. This process is most suited to applications where the appearance of the joint is not critical and one of the parts is circular in section. We’ll now experiment with this technique in the workshop.

Hot Gas Welding This is a process that is very similar to gas welding for metals. In this case the plastic is heated using a stream of hot gas, usually air which is normally heated electrically. A filler rod is used to close the gap between the plastics.