chapter 25 - welding

welding is

a joining technique for materials with the same melting point, it fuses the materials together.

prevent oxidisation techniques

apply non-reactive gas - protective layer, apply flux - paste, powder, flux coated filler rod

oxy-acetylene (oa) welding equipment

filler rod (hand held), oxyacetylene torch, oxygen cylinder, dissolved acetylene cylinder, gas regulator

oxy-acetylene process

oxygen + acetylene are mixed and ignited to produce a very hot flame, flame melts the joint edges, fuses materials, flux coated filler rod - provides an extra material, slag layer forms over weld if flux is used.

types of oxy-acetylene flames (heat source)

neutral, carburising, oxidising

neutral flame

1:1 ratio of oxygen and acetylene, small round core, white flame, no outer feather

carburising flame

10:9 ratio of acetylene, cooler, has outer feather, large inner light, green/blue flame, alloys steels and aluminium, stops rusting

oxidising flame

1.5:1 ratio oxygen, hotter, narrow pointed inner white blue flame, weld copper, brass, bronze, bazing

uses of gas welding

light gauge metals, steel pipes, vehicle repairs

pros of gas welding

portable, easy, cheap, wide variety of metals, used for welding, cutting, brazing, soldering

cons of gas welding

rough apperance, may warp, flame can affect properties

risks of gas welding

explosion, skin burns, eye damage (arc eye), breathing

safety features of oxy-acetylene welding

colour coding - oxygen black with white cap, acetylene marron, oxygen hose blue, acetylene hose red, different screw threads - right hand oxygen, left hand acetylene, flashback arrestors - prevent flame travelling back into cylinder, pressure regulators, dissolved acetylene - dissolved in acetone for storage of large containers, as acetylene gas will explode if compressed

safety precaution for welding

wear goggles, protect eyes, protective clothing, mask

electric arc welding

uses the heat from an electric arc to melt the material, the arc is created in a small gap between an electrode and the workpiece, an earth clamp returns the current to the power supply

MMA is

stick welding, manual, for thicker steels, leaves slag, flux coated consumable electrode/filler rod

MIG/MAGS is

metal insert / active gas, semi automated, for thin and thick, clean, fast

TIG/TAGS is

tungsten inert/active gas, semi automated, percise, thin aluminium + stainless steel, non - consumable tungsten electrode feeds shielding gas, separate bare wire filler rod

SAW is

submerged arc welding, automated, for large long continuous welds, pipes, beams, hopper dispenses thick layer powdered flux, consumable filler wire electrode

ESW is

electro slag, automated, for very thick plates, tanks ships, pours flux into large vertical gap between thick plates

manual metal arc welding features

earth clamp, flux coated consumable electrode, power supply

manual metal arc process

operator holds electrode holder which clamps on to consumable flux coated filler electrode, stick brought closer to metal +hot electric arc is formed, flux and filler metal drop into the weld, slag is created on top

manual metal arc applications

heavier gauge, mild steel, gates, chairs, tables

pros of MMA

easy to learn slag layer slows down cooling - prevents brittle joints, slag layer collects impurities, windy conditions

cons of MMA

slag layer has to be chipped/machined off, not suitable for light gauge, produce a lot of fumes, short lengths

safety precautions MMA

curtain -light, protect or people, welding mask - uv light, hot metal, free from moisture environment, ventilation, fire extingushers

MIG/MAGS welding features

power supply, earth clamp, mig/mags gun, wire reel, shielding gas

MIG/MAGS process

a gun which feeds a consumable filler wire electrode from a reel, gun issues gas over the weld area - prevents oxidising, MIG uses inert gas such as argon/helium, MAGS uses mixture of gases

MIGS/MAGS electrodes

continuously feed consumable bare filler wire acts as the electrode

MIG/MAGS applications

speed, required steel, aluminium, alloy steels, thin and thick

MIG/MAGS pros

very fast, clean, no slag

MIG/MAGS cons

fumes, expensive, not suitable for wind

MIG/MAGS safety

gases are not flammable but cause suffication, physical injury

TIG/TAGS features

power supply, earth clamp, bare wire filler, shielding gas

TIG/TAGS process

non consumable electrode, separate wire filler rod, gas prevents oxidising, TIG insert gas argon/helium, TAGS mixture of gases

TIG/TAGS filler rod

seperate filler rod

TIG/TAGS applications

high precision, thin alloy steel, aluminium

TIG/TAGS pros

highest quality, control temperature this is way its suitable for aluminium as aluminium oxides very quick, very clean, no slag

TIG/TAGS cons

slower than MIG, difficult to learn need 2 hands

SAW features

earth clamp, power supply, continuous wire feed, guide rail, flux dispenser, arc submerged under flux

SAW process automated

layer of powdered flux is placed in hopper, the flux is dispenced to completely cover the joint, a continuously fed bare wire electrode fed automatically, generates an electric arc between it and the piece, a slag layer is formed, and unused flux is hovered.

SAW applications

long continuous welds, pipes, beams, plates for construction, mainly used for steel

SAW automation

fully automated, machine travels along an overhead guide rail over straight joint, or machine stays still and the pipe seam to be joined rotates underneath

SAW pros

fast, no arc flare, no smoke and fumes

SAW cons

straight joints, slag

ESW features

power supply, continuous wire feed, flux dispenser, water cooled shoes, earth clamp, starting plate

ESW process

a large gap between two thick vertical plates is filled with flux, an electric arc melts the flux forming molten slag, electric current keeps it molten, melts continuously fed filler wire and plate edges, water cooled shoes on either side.

ESW applictaions

thick steel plates, tank walls, ship plates

ESW pros

fast, unlimited thickness, low distortion

ESW cons

plates must be vertical, expensive

resistance welding -

passes a large electric current through the material to melt and fuse the parts. no shielding flux or gas is needed because the join is internal.

resistance welding suitable

for robotic control, simple process, fast, high quality, consistent, economical, efficient

resistance spot welding process

the materials to be joined are overlapped, two electrodes press in on the materials from either side, a large current is passed between the electrodes, the materials melt and fuse in one spot or nugget, the elctrodes open, and move get ready for next spot weld, portable spot welders are also available.

resistance spot applications

robotic assembly of car body parts, permanent joining of products like filing cabinets and equipment casings

ESW pros

fast, high-quality, consistent, efficient, easily automated, no filler, flux, gas, cleaning

ESW cons

joins are not as strong as other forms of welding

resistance seam welding features

power supply, roller electrodes, overlapping spot welds

resistance seam process

the material to be joined are overlapped, materials are moved between two roller electrodes, pulses of current are supplied between the roller electrodes, each pulse creates spot weld, the pulses are timed so that the spot welds overlap and create a continuous seam

resistance steam aplications

domestic radiators, fuel tanks, drums, containers

resistance seam cons

restricted to straight lines

multi run welds

welding the same joint more than once, this leads to a better, tougher joint, as each new weld re-heats the previous run, and this anneals the metal so they are less hard and brittle.

oxy-acetylene diagram

MMA diagram

MIG/MAGS diagram

TIG/TAGS diagram

SAW diagram

ESW diagram

resistance spot diagram

resistance steam diagram

power supply, for electric arc welding

a rectifier circuit is used to convert high voltage AC to low voltage high current DC