joining metals

when joining metals the order from hottest to coolest methods is oxyacetylene, hard soldering, brazing and soft soldering

PERMANENT METHODS

MIG welding - metal inert gas welding used to weld thin metal such as steel or aluminium where an electric arc to generate heat without burning or distorting the metal, the workpiece is clamped to a negative connection and the positive electrode is in the nozzle. it is used for climbing and bike frames. it is used for one-off production or on a production line. first the wire electrode melts in the arc and fills a gap between the metals and the welding torch is swirled to create beads, the wire is fed through the nozzle controlled by a trigger an inert gas shield is used to stop oxidation

TIG welding - tungsten inert gas is used to weld stainless steel, aluminium and copper. is uses and electrical arc where the electrode is made from tungsten and does not melt instead a filler metal is used. the gas used is argon or helium. in TIG there is a better control for stronger and more accurate welds than MIG, however it is slower and more complicated

spot welding - spot welding is quick with no filler, neater and it can be automated, it welds using heat and pressure. the metal surfaces are joined from heat made by resisting electrical currents. during spot welding the piece is held between two electrodes, this can be highly automated for mass production

oxyacetylene welding - oxyacetylene uses gas instead of a current to weld low carbon steel. it mixes two high pressure gases to make a very hot flame at around 3500°C. this flame can be adjusted by controlling the gas flow allowing welding, brazing and flame cutting

soft soldering - used for low melting point metals often in workshops, some solders contained lead but this was stopped by the restriction of hazardous substances directive. this can use a blowtorch or soldering iron. it is used in electronics and plumbing to avoid damage from high temperatures and places where lots of equipment can’t be taken. wave soldering is used for mass production

hard soldering - hard soldering is used at around 600-800°C for precious metals such as silver and gold, it is neater than soft soldering and requires clean metal with no gap, flux is applied to prevent oxidisation and to enable the solder to flow

brazing - brazing can use oxyacetylene or compressed air, it uses a brazing rod that melts around 850°C making a weaker joint than soldering, it is used for joining different metals

riveting - this is semi permeant as is used for sheets and plates with fasteners and a shaft or tail, this is often used for quick assembly of industrial pieces. riveting is semi permanent as the rivets can be cut and removed

cold formed rivets - used when you have access of both sides of a piece with a set and snap which pressurises the rivet to hold in place

pop riveting - pop riveting is used when you only have access to one side of a piece, it uses a gun and is used for aluminium in plane manufacture. this is used for thin pieces where the pop rivet is inserted and snapped

NON-PERMANENT METHODS

self tapping screws - self tapping screws create their own thread and are quick to install into sheet metal, they are used for pieces that may require maintenance. some screws can make a hole for themselves but some require a pilot hole

machine screws - these are used with a bolt with a fine thread for motors or casings, they have different heads, threads, and diameters

nuts and bolts - these don’t screw into the material but into each other around a piece, some nuts are designed to hold and others to be loosened easily, washers are also used in conjunction with nuts and bolts for moving parts