Aluminium is used for many industrial applications. Such things as bulk road tankers, tipper trucks, beer barrels, overhead pylon cables, window frames, aircraft components, fast ferries, trains, vehicles both private and military and military bridges.
Aluminium is the most abundant material on Earth after oxygen and silicon. And is desirable for its inherent mechanical and its rustproof properties,
and is one of the most ubiquitous metals in the modern world, thanks to properties like high strength-to-weight ratio, high thermal and electrical conductivity, atmospheric corrosion resistance, workability and formability. These properties make it an ideal choice in applications as varied as the aerospace and construction industries, high-tech electronics, high voltage power lines, and more. These characteristics, along with its high recyclability, help improve life-cycle management, and reduce the overall economic and environmental impact of its application.
WFEL use aluminium special armour plate because of its strength and lightness. DGFVE 232B. Which is a Defence Standard defines the material and performance requirements for a weldable aluminium alloy armour plate, 6mm and above, of nominal 4% Zinc 2% Magnesium Aluminium alloy in the solution treated and aged condition for the protection of crew and mechanism of armoured fighting vehicles and bridges against ballistic attack, similar alloy is 7019.
Welding of 232B on bridge building is carried out using GMAW ( Gas Metal Arc Welding) or its older term MiG Metal Inert Gas welding.
GMAW is a semi automatic welding process. Meaning that you use spool of aluminium welding wire and electrical power source and special welding torch which has copper contact tip and a gas shroud to blanket the weld whilst welding from porosity and oxidisation.
An Earth lead had to be connected to create an electrical circuit. The welding torch has trigger switch when you press it the shielding gas usually of pure Argon comes on and the reel aluminium wire feeds through the welding torch to the weld pool.
Aluminium has a tenacious surface oxide which needs to be removed prior to welding. Also aluminium melts at relatively low temperature as compared to carbon steel at 660 degree Celsius. When welding Aluminum there is no visual colour change like carbon or stainless steel. Therefore if you’re not careful the Aluminum weld can collapse on you. Because the oxide skin melts at 2000 degree Celsius.
What’s really important when welding aluminium is ensuring that the base metal is clean. Use rotating wire brushes degreaser wipes. Ensuring you don’t allow the base material from getting too hot. Each finish weld needs to be dressed and cleaned. It’s important to work in a methodical way to reduce flaws in the finished welds such as porosity lack sidewall fusion. Gas flows welding torch angles weld speed and weld settings are all critical for successful welds.
After your time in the welding school to carry out weld test pieces, multi run fillet and a root and cap butt weld which must pass Non destructive testing examination. Once these test pieces pass examination you’re put out onto the shop floor to shadow another experienced aluminium welder.
Shadowing gives you the opportunity to careful watch another welder in action and to make personal notes of welder setting and weld procedures. Each weld has its Weld Procedure Sheet WPS which clearly states the weld settings amperage and voltage wire type and size, gas flows. These must be adhere to for successful fault free completed welds.
Each part of the fabrication process has weld procedures and Fabrication procedures. Welding school welding inspector will do random checks to check the welder is adhering to laid down weld procedure. Weld size, pre cleaning, temperatures, weld sequencing to ensure reduce distortion during welding.
Armoured Aluminum is special alloy when welding your putting concentrated heat into the base metal this does change the base metal properties. Aluminium alloys can be treated by heat to create a harder stronger material. It changes the inter granular properties. Such as precipitation aged hardening.
E.G. Precipitation hardening is a heat treatment process used to help some aluminum alloys reach maximum hardness. It is performed after solution heat treatment is complete. This process allows for the dissolved elements from the solution heat treatment to fully precipitate out. Quite a technical metallurgical issue.
New welders or an old welder in my case have to learn the ropes, so to speak, in the welding of aluminium armour plate. Most or the majority of welding is carried out on rotating jigs and fixtures. These also act as restraints against welding distortion. During the welding fabrication process in regular basis you need to check heat import and allow the welds to cool.
Otherwise the aluminium will distort so patience is needed during the welding process. As the jig/fixtures are able to rotate to enable all the welding to be done in the down hand welding position. PB position for fillet weld which carried out the 45 degree angle.
The welder, Ian, I was shadowing has been with the company over 14 years and had worked on the launch beam for the past 10 years. He has it off to fine art and produces very high quality aluminium welding workmanship!
First he uses a degreaser WipeMaster Wipe 9 from (IPA Isopropyl Censol Ltd ) to degrease the base metal. Once thats been degreased he uses a rotating air tool with a circular stainless steel wire brush to clean off all the surface oxide. This has be carried on all the welded parts.
He always checks his welding setting that are laid down on the Weld procedure sheet first I.E On a Miller incision 459MPa power source and wire feeder.
Ian the welder is extremely methodical with his welding. Which he says reduces weld defects and aluminium wire feed problems. 5556a wire is fairly hard wire but it’s still soft as compared to steel welding wire.
The welding gun or torch has a Teflon liner inside to reduce wire feed problems. The welding torch has gas diffuser and outer Cooper nozzle and a contact tip that picks up the electrical circuit.
The gun needs to be blown out with an airline on a regular basis and the contact tips need to be changed regularly and the out gas shroud needs to be cleaned of aluminium debris.
Before welding Ian always clips the wire to ensure a good electrical contact at the start of the weld when welding. Welding torch angle inert gas flow rates of the argon are critical 55 cubic feet per hour or 26 lites per minute. This to blanket the weld to prevent oxidation. The argon gas blankets the weld to stop porosity and helps stabilise the arc during welding. Ian always presses the pre gas button when switching on the welding machine and checks his weld settings for the 1.6mm wire diameter approx machine setting was 300A 28.3V (10.3).
Ian stated if you stick to his basics it will reduce weld defects and aluminium wire feed problems. The welding gun or welding torch has a Teflon liner inside interconnecting cable to reduce wire feed problems. The welding torch has gas diffuser and outer Cooper nozzle and a contact tip that picks up the electrical circuit.
The gun needs to be blow out with an airline on a regular basis and the contact tips need to be changed regularly and the out gas shroud needs to be cleaned of aluminium debris
Welding torch angle inert gas flow rates of the argon are critical 55 cubic feet per hour or 26 lites per minute. This is to blanket the weld to prevent oxidation. Also keeps the weld nice and clean giving good root penetration. Sound of the arc is an important indicator you have the correct torch angle and speed of travel.
Depending upon type of weld fillet or butt he varies the power setting to suit material thickness and weld joint. Torch angle is critical fillet 45 degrees with 15 degree back slope of the torch use a push or forward technique.
GMAW is semi automatic process press the weld torch trigger the aluminium wire reel rotated (Din 300) and the wire makes contact with base metal and forms a weld pool. With aluminium GMAW you have to move quickly as the base metal gets hot. Completed welds need to be allowed to cool to prevent distortion or to minimise it! Before Ian starts welding he died a trail run on piece of scrap aluminium to ensure everything is okay prior to carrying out the full weld on the job. Ian’s advice was if you stick to his method of working you won’t go far wrong!