Recent developments in welding techniques has led to the development of a high-speed, solid state joining process, particularly used to fabricate titanium alloys. Welding titanium alloys through linear friction welding is commonly used within the aerospace industry, titanium is favoured due to it’s high strength to weight ratio and durability. Despite the process showcasing dynamic results, the technique is still being perfected and is only currently possible within blisk manufacturing processes. This article will give insight into the continually developing techniques and the benefits of using linear friction welding.
The original patent for the process was first filed in the 1920s, however, little detail was recorded on the intended function and procedure. No progress was reported on linear friction welding until the 1960s when a group of Russian engineers investigated the process, but added that they thought it was ‘very doubtful’ the technique could be used in manufacturing. Further work was carried out by both Ohio State University and the University of Bristol as well as The Welding Institute in the 1980s, but little information on their findings was ever published. It wasn’t until the March 2018 volume of Progress in Materials Science that the benefits of linear friction welding were explored.
Linear friction welding helps to join two solid-state materials by moving the two metals over each other under a large and compressive force. As the materials move over each other, in a process called oscillation, the surfaces produce heat which causes the materials to become plasticised and mouldable. Due to large amount of pressure pushing the two surfaces together, material is expelled from the centre in the direction of the force, this is called the ‘burn-off’. As the ‘burn off’ is produced, any foreign particles or other contaminants are removed from the weld surface, helping to improve on the quality of the weld. As the surface no longer contains impurities, the process allows pure metal on metal contact, helping improve the integrity of the bond.
The process can be segmented into four main phases:
* Initial Phase – the two metal surfaces have microscopic contact and heat begins to be generated through friction. The material around the surface begins to soften and deform, this allows the area of contact to increase. As the materials move over each other, the ‘burn off’ is produced in the area of the movement.
* Transition Phase – As the materials continue to pass over each other they become increasingly viscous, this causes the area of contact to increase to 100%. Heat spreads away from the interface causing more of the metal to become malleable, increasing the amount of ‘burn off’ produced.
* Equilibrium Phase – Through continuous oscillation, a steady state is found where the amount of ‘burn off’ produced is constant.
* Deceleration and Forging Phase – The movement of the materials is stopped and the surfaces are aligned, additional force can be added to help stabilise the weld.
One of the main advantages of linear friction welding is the reduction of distortion and imperfections. Pores and solidification cracks are commonly seen in fusion welding which melts and re-solidifies the metal. The process uses lower temperatures than fusion welding, this reduces the amount of intermetallic formation and allows more dissimilar materials to be joined. Linear friction welding does not require filler metal, flux or shielding gas and the process can be easily automated. However, the machines used during the process are large and expensive and the maximum weld size is limited by the size of the machine.
Orbital Fabrications is a leader in specialist welding services including orbital welding, high-tech fabrication and manual welding. Made up of a team of welding specialists, Orbital Fabrications has become renowned for delivering welding services and providing support with welding contracts and projects. With over 25 years’ of experience, Orbital Fabrications has become one of the UK’s leading welding companies.
In addition to specialised welding, Orbital Fabrications provides a number of machining services and quality procedures including helium leak testing. With recent expansions to their facilities, Orbital Fabrications now boasts Class 5 and Class 6 cleanroom facilities and workstations. Continuous investment into training and facilities allows Orbital Fabrications to continue to offer high-quality welding services.
If you would like to find out more information about any of Orbital Fabrications’ services, speak to a member of the team on 01480 464 066 or contact us here.