Welding of stiffened panels by Friction Stir Welding
Stiffened aluminium panels are used in many industries: aeronautics, automotive, railways, naval, bridge manufacturing etc. These stiffened panels are made up of two parts: a sheet, called a “skin”, and stiffeners. Previously, two assembly techniques were favored: riveting or MIG welding. Today, FSW welding of stiffened panels is becoming increasingly popular in these industrial sectors due to the high technical characteristics of the welded components.
FEATURES OF STIFFENED PANELS
STIFFENED PANELS IN HIGH STRENGTH ALUMINIUM
Stiffened panels are used in industrial sectros with high technical and mechanical requirements such as aeronautics, automotive or shipbuilding.
LONG LENGTH STIFFEND PANELS
Stiffened panels can be up to 12 metres long. The size of the part is therefore an important factor in the choice of assembly technique.
STIFFENED PANEL GEOMETRY
Stiffeners can have different shapes: “T”, rectangular, triangular or omega. Therefore, stiffened panels are complex parts to be welded. So, the welding of stiffened panels must be perform with force control.
FEATURES OF STIFFENED PANELS
STIFFENED PANELS IN HIGH STRENGTH ALUMINIUM
Stiffened panels are used in industrial sectros with high technical and mechanical requirements such as aeronautics, automotive or shipbuilding.
LONG LENGTH STIFFEND PANELS
Stiffened panels can be up to 12 metres long. The size of the part is therefore an important factor in the choice of assembly technique.
STIFFENED PANEL GEOMETRY
Stiffeners can have different shapes: “T”, rectangular, triangular or omega. Therefore, stiffened panels are complex parts to be welded. So, the welding of stiffened panels must be perform with force control.
ADVANTAGES OF FSW FOR STIFFENED PANELS MANUFACTURING
LONGER STIFFENED PANELS
Aluminium profiles are generally lower than 400-mm wide, FSW overcomes this limit by butt welding profiles.
ONE MANUFACTURING STEP
No part preparation, no degreasing, no machining after welding.
LIGHTER AND MORE RIGID PANELS
Profile optimization associated to FSW limits the useless shapes.
LOW PRODUCTION COST
Compared to riveting or sealing & screwing.
LONGER STIFFENED PANELS
Aluminium profiles are generally lower than 400-mm wide, FSW overcomes this limit by butt welding profiles.
ONE MANUFACTURING STEP
No part preparation, no degreasing, no machining after welding.
LIGHTER AND MORE RIGID PANELS
Profile optimization associated to FSW limits the useless shapes.
LOW PRODUCTION COST
Compared to riveting or sealing & screwing.
Which application areas for FSW welded stiffened panels?
Stiffened panels welded by FSW meet many applications in several industrial sectors such as shipbuilding, construction, automotive or aerospace.
SHIPBUILDING INDUSTRY
In the shipbuilding industry, we are seeing a standardisation of aluminium panels for ship. The reason is simple: aluminium is a light, corrosion-resistant and environmentally friendly material due to its recyclability.
But aluminium is more expensive than steel and it needs requirement of optimized design structure based on extrusion. These extrusions are difficult to weld by arc welding techniques. So, one of the best way to weld aluminium stiffened panels is FSW.
Decks for fast ferries, Marine Aluminium Norway
AUTOMOTIVE INDUSTRY
In the automotive world, aluminium stiffened panels are used for the manufacturing of battery packs of electric vehicles.
Battery packs generate heat when the battery is being charged and also during usage. Therefore, serpentine heat exchangers are incorporated inside battery casings to prevent excessive temperatures. However, these systems take up space, add weight and manufacturing cost. Therefore, stiffened panels incorporated water cooling and welded by FSW are used for the floor and the frame of these battery packs.
RAIL INDUSTRY
In the railway industry, stiffened panels are used to make floors and lateral structures. Main OEM in this sector have already adopted FSW to weld their parts: Hitachi, Alstom, Bombardier.
AEROSPACE INDUSTRY
Manufacturing of low cost aircraft panels by FSW of T profiles and bending – DARPA, USA.
In the aerospace industry, FSW-welded stiffened panels are used in aircrafts panels or floors. This is the case for the Eclipse 500 for example.
The use of FSW in aerospace replaces riveting, which avoids the risk of corrosion and increases the mechanical strength of the assembled stiffened panels. Also, replacing riveting with FSW has several advantages:
One manufacturing step,
Reduction of part thicknesses,
High mechanical resistance thanks to fatigue improvement,
Waterproof panels.
These stiffened panels are also indispensable for the manufacture of aluminium tanks. They replace large tanks, freeing up space and reducing the weight of the equipment.
CONSTRUCTION SECTOR
Another sector where we can find panels welded by FSW is the construction sector and in particular the manufacturing of bridges. This allows lighter structures and increases fatigue resistance with more rigid panels thanks to stiffeners welded by FSW to the skin of the panel.
FSW welding of stiffened panels
Two steps for FSW stiffened panels:
Welding of the skin and the stiffener: FSW lap welding configuration. The stiffener is placed on the panel skin.
Welding stiffened panels together: 
FSW butt welding configuration. The stiffened panels are placed next to each other to join them together. This makes it possible to produce large panels in a simplified way.
Want to know more about stiffened panels welded by FSW? Read our article dedicated to this application.
QUALITY CONTROL OF STIFFENED PANELS WELDED BY FSW
In order to qualify your FSW weld and to be able to industrialise the process, it is necessary to carry out quality control tests following the FSW standard ISO 25239 :
Macrographic cross sections: two macrographic cuts are necessary to ensure the absence of porosity and lack of penetration in the weld beads.
S-bends: this consists of twisting the weld to check its resistance.
Stirweld FSW expertise
Our team of experts is at your disposal to qualify your weld by offering you a study of your part. This includes the co-design, the manufacturing of the clamping system, the definition of the welding parameters but also the quality control of your part. To find out more about our prototyping offer, click here.
