Joining Metals

METALS PPT 4

oxy-acetylene welding

uses
characteristics
advantages
disadvantages

the metal is prepared by grinding an angle on the edges of the two pieces to be joined by forming a v shape. this is to ensure that the weld runs through the entire thickness. the join area is heated to form a melt pool and at the same time, a steel filler rod is introduced to the joint area. the melt pool is extended to form a continuous bead along the length of the joint. the molten metal will flow to the hottest part of the metal - forming a continuous seam.

quick repair jobs with no access to electricity or carried out remotely. portability and lack of electricity. relatively slow speed and require skilled operator.

used to weld low carbon steel sheet, tube or plate. mixes two very high pressure gases (oxygen and acetylene) forming a very hot and intense flame (3500C). flame is adjusted by changing the gas and oxygen mixture to - flame cut / weld / brazing.

ferrous metals - low carbon steel, cast iron, stainless steel
non ferrous metals - copper, brass, aluminium, bronze

portable / cost effective / versatile for small scale

slower / less efficient for thick materials / requires skilled operator / larger heat affected zone / cause distortion

MIG welding

uses
characteristics
advantages
disadvantages

MIG welding uses a filler wire as an electrode. the wire electrode melts in the arc and fills the gap between the two metals. the welding torch is gently swirled to form a bead of weld. the electrode wire is stored on a reel and is fed through the nozzle as the trigger is pressed. inert gas shields the area being joined to prevent oxidization in the weld. heat is generated in a localized area - if not done well it can burn or distort the metal. workpiece is clamped to the negative connection and the positive electrode is called the electrode.

wield thin gauge metal such as aluminium and some steels. used for - aluminium, copper, stainless steel, magnesium, nickel, iron, most alloys.

uses - climbing frames, bike frames, vehicle exhausts. automotive, construction, manufacturing, aerospace, railroad, shipping industries.

simple to learn, efficient, high productivity.

high set up costs and replacement nozzles are expensive.
limited positions. cannot be used outdoors. fast cooling rates. cannot be used for think materials.

brazing (hard soldering)

uses
characteristics
advantages
disadvantages

the materials to be joined are cleaned and degreased. the two pieces are clamped together. a flux is applied to stop the metal from oxidizing. the joint is then heated. the brazing rod is then applied to the area. the brazing “spelter” will flow along the joint.

uses a oxy-acetylene flame or a gas and compressed air brazing hearth. brazing rod is made from brass and finishes well with wire wool.

make a steel framework, etc - low carbon steel sheet, aluminium, copper, nickel.

can be used to join dissimilar metals.

needs lower temperature than welding as the brazing rod melts at around 850C, so it is not as strong.

hard soldering

uses
characteristics

higher temp than soft soldering (590C - 870C). the material is cleans and has to finished to leave no gaps between the areas joining. flux must be applied to prevent the metal oxidizing which enables the solder to flow.

join precious metals like gold and silver.

soft soldering

uses
characteristics

uses lower melting points (solder) to join othe rmetals together - 320C. new solder variants are lead free and RoHS compliant (restriction of hazardous substances directive)

used in plumbing and electronics where damage may be caused by high temps.

screws

Joining wood to wood, metal to wood and sheet polymer. ​

Self-tapping screws can be used to join sheet metal. ​

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A clearance hole is drilled following a pilot hole into the bottom part this directs the screw to make an accurate join. ​

nuts / bolts and washers

Joins materials for disassembly, or allows access for repair. ​

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The bolt sits in a clearance hole before both parts are joined, A washer is used on the nut to create a tighter join. ​

Washers spread the load and prevent material damage when being tightened​.

rivets

Generally used to join sheet metal together. Pop rivets are great for when you can't access the other side of the material. ​

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Two pieces of material are overlapped, drilled and hammered to join. Pop rivets use a rivet gun. ​

pop rivets

Pop rivets are used to create a semi-permanent fixing between two thin sections of metal​

• The pop rivet gun is used to apply pressure to ​
  the rivet by pulling the shank until it breaks​

• This action splays the inserted end​
  to create the bond​

press joining

Joins thin ductile sheet metals together, more for bulk sheet metal applications. ​

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Material is joined placed in a machine and pressed between a punch and a die. Under pressure the sheet deforms interlocking the shape. Press joining is not as strong as riveting. ​