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How Friction Stir Welding Can Be Used In Aerospace Engineering

Aluminium and aluminium alloys are widely used materials in aerospace engineering. The material is lightweight but is very strong relative to its density. This makes the metal and its alloys ideal for applications where lightweight yet robust structures are required. Therefore, it is a prized material for aerospace engineering since weight is critical in producing effective aircraft.

However, the properties of aluminium that make it valuable for producing lightweight vehicles are also a hindrance in manufacturing. It has a relatively low melting point and is quite unreactive. This means that traditional means of welding aluminium and aluminium alloys to one another and other materials. Using conventional fusion welding approaches, welding aluminium is challenging since it is susceptible to defects, residual stresses, and deformation around the join.

Friction stir welding (FSW) is an innovative approach to joining the structural alloys used in aircraft. Read on to find out more about its applications in aerospace engineering.

What is Friction Stir Welding?

FSW is a solid-state welding approach that relies on a rapidly spinning tool. This tool is forced along the line where a join is desired between the components. This produces heat between the abutting materials through friction, resulting in a robust weld formed by the stirring of the constituent materials of both pieces.

When the tool passes over the join line, the heated material flows around the tool. This material is subject to extreme levels of plastic deformation. Once the pass is completed, the metal recrystallises into a granular structure at the centre of the weld. The area of the weld itself is often referred to as the “nugget zone”. This is surrounded by the material that constrains the zone and is deformed by the tool’s passing. The rest of the components are not subject to significant plastic strains as a result, which makes the aircraft component far more structurally robust.

FSW leader

Traditional Aerospace Joining

Until the mid-1950s, gas welding was the most common way for manufacturers to join materials used in aircraft construction. This was used for materials less than 3/16-inch thick. This process was gradually replaced by arc welding due to it being more economical.

Oxy-acetylene welding and electric arc welding have been widely used in the aerospace industry to fabricate and repair aircraft.

TIG welding was also developed in the late 1930s. This form of welding is used to join magnesium and is still widely used in the industry for this purpose. It can also be used for joining stainless steel components and for welding aluminium and aluminium alloys. This form of joining is widely used in aircraft maintenance and repair.

There are two main types of arc welding. Shielded metal arc welding (SMAW) and gas metal arc welding (MIG). These have different applications. SMAW is sometimes used when steel components need joining, and MIG welding has been used for large-scale manufacturing for some time.

However, neither of these methods are ideally suited for joining aluminium to other components. Aluminium is a challenging material for fusion welding, so using these approaches can lead to unfavourable results.

Why Friction Stir Welding is Superior

FSW has several distinct advantages over conventional fusion welding for aerospace applications. These are mostly related to how it can bond aluminium and aluminium alloys, but the process can also be significantly more economically and ecologically friendly than traditional welding.

As mentioned above, aluminium is not an ideal material for arc welding. This is especially true if an aircraft requires both steel or copper components to be joined to the aluminium.

When aluminium and steel are joined using fusion welding, the wildly different structural properties of the materials can cause problems. The most common issue is the formation of brittle intermetallic compounds between the components. These undermine the strength of a join. Since aircraft are regularly exposed to significant forces, bonds between compounds need to be as robust as possible. Therefore, arc welding is not ideal for the use of aluminium in aerospace applications.

Bimetallic inserts can be used to get around this issue. Otherwise, manufacturers can use dip coating of steel to successfully join the materials. However, these are imperfect solutions and require additional materials.

FSW doesn’t rely on any additional metals other than those that need to be joined to one another. This can make the process of joining materials intended to be used in aircraft much more cost-effective since fewer metals are required. The process can be used on thick materials, is fully automated and fast. On top of this, no shielding gases are required, significantly increasing the cost of fusion welding.

FSW is also ideally suited to aerospace engineering since it allows manufacturers to avoid using fasteners between components. Without FSW, aerospace engineers need to use millions of fasteners to join materials used in aircraft. These are redundant if FSW is used to make the joins, which leads to substantial cost and weight savings in aircraft manufacturing.

TRA-C’s Approach to Aerospace Welding

TRA-C industrie is a leading company specialising in FSW. As stated above, this method can be valuable in aerospace engineering, and TRA-C is one of the few European companies offering a fully integrated approach to producing high-quality equipment.

TRA-C has been using FSW in its manufacturing processes since 2009. During this timeframe, nearly every aspect of this approach to joining has been improved and refined. The FSW offered by TRA-C is efficient, rapid and eco-friendly. Additionally, the technique can be applied to some of the most commonly used materials in aerospace engineering, so it is possible to create robust joins between aluminium and other metals using the process. As a result, TRA-C’s innovative approach to welding is ideally suited to the aerospace industry. 

On the whole, TRA-C’s innovative approach to improving methods of bonding heterogeneous metals using FSW and its focus on robotics and automated processes are ideally suited to aerospace manufacturing. When producing aircraft, welding with high mechanical strength is essential and using TRA-C’s automated approaches, such bonds are possible with a high degree of reproducibility and efficiency.