Welding of metals is used in almost all architectural and interior design projects, whether it be a desk with metal legs, metal ceiling panels, balustrades, staircases or external facades.
However, there are a number of considerations that need to be taken into account when welding is required on a product or project. It requires an understanding of what the desired finish is for the finished product or element of work.
Understanding and discussing what the final desired finish on a project or product will be from the outset will save significant time later on. Everything during the manufacturing process is geared around the finish, and certain finishes will require specific tools or techniques to be utilised to permit the desired outcome.
What is welding?
The fundamental concept of welding is that it is a fabrication process where two materials, usually metal, are joined by using high heat to melt the parts together and then allowing them to cool, causing fusion. Welding is distinct from lower temperature techniques such as brazing and soldering, which do not melt the base metal.
Welding is an essential process for architectural metalwork, where certain metallic materials need to be joined together to create a finished product. There are several welding types for metal and the most common are MIG and TIG.
Arc welding is a type of welding process that uses an electric arc to create heat to melt and join metals. A power supply creates an electric arc between an electrode and the base material using direct or alternating currents. Two common types of arc welding are MIG welding and TIG welding.
The power supply provides AC or DC power to create the arc, and the electrode is moved along the joint in the base material to create the weld. The electrode can either be consumable (used up in the process) or non-consumable (remains intact throughout the process).
The welding arc that melts and fuses the metal reaches a temperature of around 3500°C (6500°F), which can cause the molten metal to react with the air. This causes problems like porous and weak welds, excessive spatter, and reduced productivity.
To eliminate these welding defects, it is common to provide some form of protection to the molten pool when arc welding. This usually comes in two forms: flooding the hot weld with an inert shielding gas, which keeps the atmospheric air away from the molten metal and so prevents it from reacting, or using flux, which creates its own shielding gas and slag when exposed to the high arc welding temperature.
MIG welding (Metal Inert Gas) is an arc welding process that uses a continuous solid wire electrode that’s heated and fed into the weld pool from a welding gun. The two base materials are melted together forming a join.
The electrode wire is consumed in the welding process, which allows the wire to also act as a filler material for the weld. So, the wire alloy is usually matched to the metal being welded.
MIG welding uses a shielding gas such as argon, carbon dioxide, or helium, which is pumped to the gun to prevent the materials from being contaminated.
TIG welding (Tungsten Inert Gas) is also a welding process that uses electricity to melt and join metals. However, unlike MIG welding that involves the use of a continuously fed wire that’s consumed during the welding process, TIG welding uses a non-consumable tungsten electrode to generate an electric arc.
The tungsten electrode employed is not consumed while welding. As such, a separate filler rod must be fed with your second hand, making TIG welding a two-hand process.
Like MIG welding, TIG welding requires the addition of a shielding gas to protect the weld from the air.
The most common method that we use in most of our architectural projects is TIG welding, because of its suitability to weld a wide range of different metal thicknesses. The welding process can be undertaken in any position: vertical; horizontal and overhead, and it creates minimal smoke and a colourless gas, meaning it is easier for the welder to see the workpiece being welded. The major benefit of TIG welding is that the welds are extremely ductile and are stronger and more corrosion resistant than other welds.
TIG welding is also extremely precise. The process provides more precise control of the weld than any other arc welding process because the arc heat and filler metal are independently controlled.
There are certain occasions, though, where MIG welding is preferred, such as with certain materials and thicknesses. When used in combination with DC arc welders, which offer a smooth, easy-to-control arc, MIG welding can work better on thin materials. You also get less spatter, and in general, DC beads are “prettier”.
As mentioned above the final finish needs to be considered from the outset when specifying certain products that require welding. Whilst architects and designers do not necessarily need to know all of the intricacies of each type of welding process, they should ideally have an understanding of the advantages and disadvantages of welding when it comes to applying different finishes. So, identifying a finish such powder coating, PVD (physical vapour deposition) coating or anodising will dictate how that product needs to be manufactured and subsequently welded.
In our experience, the most common types of finishes for our projects and products are anodising and powder coating, and as a bonus to the must-know welding information provided thus far, the below is something that every architect and designer who is working with metallic finishes should also know and understand.
Anodising increases resistance to corrosion and wear, and provides better adhesion for paint primers and glues than bare metal does. It involves an electrolytic passivation process, where the material becomes the ‘anode’ of an electrolytic cell, and is used to increase the thickness of the natural oxide layer on the surface of metal parts.
Anodised finishes are most commonly applied to aluminium products, typically from the 5005 grade of aluminium, which is more expensive than the standard 1050 grade.
If an anodised finish is needed on a product, it is not common to actually weld the aluminium together, as the welded areas can often result in a darker colour than the parent material during the anodising process.
In order to join two parent pieces together and retain the colour throughout the material during the anodising process, the only option is to fold the parent material as tightly as possible, and this is nowhere near as strong as actually welding the materials together.
Aluminium is a softer material than mild steel and stainless steel and can sometimes leave visible heat marks that do not get hidden by the anodising process. During the anodising process, any damage or marks on the parent material may still be visible after anodising and you do get colour inconsistencies between batches of anodising.
Anodised surfaces often require a sealing process to achieve corrosion resistance. Anodic films are generally much stronger and more adherent than most types of paint and metal plating, but also more brittle. This makes them less likely to crack and peel from ageing and wear, but more susceptible to cracking from thermal stress.
Cutting or drilling the item should be done prior to anodising. The anodised surface is brittle – it may fracture if it’s cut or drilled.
Anodising is a more time-consuming process. Lead-times for architectural applications tend to be longer than for powder coating.
Powder coated finish
Powder coating is a dry finishing process created by an electric charge that causes a dry powder (usually a thermoplastic or a thermoset polymer) to fuse to the surface of the metal. Unlike conventional liquid paint, which is delivered via an evaporating solvent, powder coating is typically applied electrostatically and then cured under heat or with ultraviolet light. It is usually used to create a smooth, hard finish that is tougher than conventional paint.
If a powder coated finish is required, then welding can be used to join materials together, as the welds, heat burn marks and most surface imperfections can be hidden by the powder coat finish. Different metals in a fabrication, once coated, will have
the same appearance, and lower grade aluminium or steel can be used.
Having a powder coat finish opens up a plethora of different manufacturing options, and the most cost effective raw materials can be used.
Therefore, by designing products with a powder coated finish, a far greater range of fabrication options become available. You are able to hold colour better between batches and do not get such varied colour inconsistencies, which can occur when anodising.
If it’s the look of an anodised finisholutions such as Anomatch™ by Powdertech are powder coat finishes that have been specially designed to represent architectural anodising on both aluminium and galvanized steel, enabling architects and designers to match the look and finish of anodising fairly closely, while providing all of the benefits of powder coating.
The most successful architectural metalwork projects make design considerations including welding requirements at the start.
By working backwards from the desired finish, it’s possible to plan the materials and processes that can be used, and avoid having to change the design of a product due to the wrong materials being specified for a project that needs to utilise welding.
Finishes of exceptional quality can be applied to welded metal, but you must take into account what the desired outcome is before choosing the material and welding method.
This information about welding forms part of a series of ‘Meet The Expert’ videos by Amron Architectural.
You can see the rest of the videos in the series by visiting the Amron Architectural YouTube channel.
The Amron Architectural website contains more information about the different finishes that can be applied to architectural metalwork, and you can contact Jonathan Reed on LinkedIn or via email if you have any further questions.