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Welding Aluminium: Design Considerations

I’m often asked the question, ‘Which is the best method for joining aluminium?’

The answer is ‘It depends’. It’s not a question of which one is best but rather understanding the pros and cons of each process and relating this to the intended application.

On this occasion we will consider welding. Welding is one of three principal methods by which aluminium parts can be successfully joined together. Bonding (structural adhesives) and using various mechanical means (cleating, folding, nuts/bots, screws, rivets, etc.) are the alternatives.

Reception Desk Fascias
Carrington House, London – Reception Desk Fascias

Welding is often rightly thought of as one of the strongest and most permanent joining methods. This heat intensive process involves fusing separate aluminium items together and then using a filler to form a joint. There are different techniques for welding aluminium (MIG & TIG). The material thickness of the parts to be welded will often determine the most suitable mode.

When considering welding, however, as a preferred joining method ‘casuality’ (cause and effect) should be borne in mind. The event of welding can change the localised form and appearance of the aluminium. For many applications these considerations are of little or no consequence, but where aesthetic considerations apply, care should be exercised. It is always good to know in advance what visual and other effects might manifest from a process.

Reception Desk Fascias
Pharmacia – Milton Keynes (Reception Desk Fascias)

One of aluminium’s primary advantages is it’s resistance to atmospheric corrosion.

This corrosion resistance is due to the oxide coating that naturally forms on aluminium’s surface.

The aluminium oxide coating has a much higher melting point (2037 C) than the aluminium base metal (648 C)and therefore needs to be removed before welding takes place. Oxide removal is usually achieved by means of using a wire brush or solvents and etching solutions immediately prior to the welding process.

Aluminium Stage Sets
Simply Red Stage Set

Satisfactory welds require a high heat input and this can cause distortion to the metal’s form and bring impurities to the surface. The filler metal used also results in producing a weld bead that stands proud of the metal and can be considered unsightly and is therefore sometimes removed.

As we know oil and water don’t mix and in most cases anodising and welding don’t either. Anodising thickens the naturally occuring aluminium oxide film, thereby preventing satisfactory weld penetration. Alternatively anodising of a pre-welded aluminium part can reveal unsightly discolouration (caused by impurities rising to the surface) around the area of the weld.

To summarise:

Weld beads can be ‘cleaned off’ if a flush surface is required (subject to adequate structural strength).

Metal grinders are normally used to remove weld beads resulting in unsightly grinding marks. These markings can be covered with a surface coating or blended in with a linished effect.

Welding Aluminium
Leeds & Bradford Airport

Avoid the welding of pre-anodised material (due to insufficient weld penetration).

Steer clear of anodising welded parts if aesthetics around the welded areas are important.

The high heat input with welding can result in material distortion. Lighter gauge materials are particularly susceptible.

You can always contact one of our helpful Project Managers who will be pleased to assist with your enquiries.

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