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Friction stir welding of combat vehicles

All friction welding of metals is conducted in the solid phase, i.e. below the melting point of the workpieces. This results in high integrity joints with very high strength, especially when being tested using ballistic impact tests. TWI can conduct confidential feasibility studies, parameter development and optimisation, on-site consulting and operator training for companies that want to apply friction welding in the manufacture or repair of armour vehicles or tanks, mobile bridges, munitions and missiles. 

Friction stir welding can be used for the manufacture of lightweight military tanks from high strength aluminium alloys. Some of the existing joints developed for MIG welding have to be re-designed to apply the friction stir welding process. On-site operator training using existing milling machines of US tank manufacturers has been conducted, and the process was successfully demonstrated to designers, production engineers and management of manufacturers of aluminium tanks. The process is being considered for the following applications:

  • Lightweight tanks from aluminium alloys or aluminium based metal matrix composites (MMCs)
  • Military bridges and amphibious personnel carriers
  • Steel tanks that could be friction stir welded from extra high strength armour plate using two passes from two sides after further tool and parameter development
  • Titanium lightweight field howitzers
WhorlTM FSW tool in front of a section taken from weld in 75mm thick AA 6082-T6
WhorlTM FSW tool in front of a section taken from weld in 75mm thick AA 6082-T6

A second generation of Whorl™ friction stir welding tools has been developed through TWI’s Core Research Programme. These tools have sophisticated profiles on the pin and shoulder and are made from wear resistant materials. Aluminium alloys of up to 50mm thickness can be welded in one pass. Thicker plates, of up to 75mm thickness, are typically welded in two passes from both sides. The benefits are as follows:

  • Very encouraging tensile, fatigue, deformability and ballistic impact properties
  • No joint preparation is necessary, even when butt welding 75mm thick plates
  • The welding speeds are higher than those of mechanised MIG welding when welding plates of more than 10mm thickness
  • Low distortion and high reproducibility

Rotary and linear friction welding can be used for joining high-strength or wear resistant alloys as they are used in military high-performance applications. The rotary friction welding process can be exploited for the following applications:

  • Track rollers for tracked vehicles
  • Bimetallic tipping of projectiles and armour piercing shells
  • Machine gun barrel liners
  • Fuse liners (e.g. joining of thin-wall deep-drawn canisters to thick-wall tubular rings)

  

Friction surfacing can be used for depositing corrosion resistant layers on high-strength aluminium alloys. Modern aluminium alloys now being considered for the manufacture of aluminium tanks often have insufficient corrosion properties and need cladding to fulfil the demands of the army.

Radial friction welding has been developed for the attachment of driving bands to artillery shells. For this application, a gilding metal ring is compressed onto the outer diameter of a rotating steel shell. The weld time is approximately 15 seconds. The joint quality can be assessed by ultrasonic inspection using P-scan.

Friction stud welding procedures have been developed for military rockets. The studs are used to keep the solid fuel of the rocket in place and maintain distance between the shells of the rocket.

For more information please email contactus@twi.co.uk. 

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