Components in an aero engine.
The aviation industry is looking for solutions that reduce carbon dioxide (CO2) emissions and reducing the weight of the aircraft is essential for success. An airplane engine weighs a lot, but through new manufacturing methods it can decrease.
One way to reduce weight is to weld several small subcomponents into a larger component instead of casting it into one whole piece. In a new doctoral thesis by Sakari Tolvanen, he presents studies that have compared the mechanical properties of welds produced with different welding processes. The aim is to gain a better understanding of how and why occasional defects occur and how the defects influence the mechanical properties of the welds.
One might imagine that welding is an old technique that has left the lab stage for a long time, but as the requirements change, manufacturing technologies need to keep up with the change. Manufacturing technologies of large aeroengine components are developed to improve material utilization, reduce cost and allow design flexibility. Welding has an important role in the development as it allows joining multiple subcomponents to produce one large structure. This approach produces less scrap material and enables design of lighter and more functional components, which in turn, results in reduced environmental impact in both production phase and the use phase of the engine.
Titanium alloys are readily joined with several common fusion welding processes such as tungsten inert gas welding (TIG), plasma arc welding (PAW), electron beam welding (EBW), and laser beam welding (EBW). Fusion welding processes can be characterized generally by the heat-source intensity. This figure illustrates the different characteristics of the aforementioned welding processes and how they affect the penetration.
Sakari Tolvanen has studied what happens when two metal components made of titanium alloys are welded together. Titanium alloys are widely used in aviation industry mainly because of their superior combination of high strength and low weight. Sakari has among other things analyzed how the chemical composition of the alloy affects the result of welding.
“The results from my studies give a better understanding of the factors that affect the microstructure and what in it leads to defects. This makes it possible to choose and optimize not only the welding process but also the base material”, says Sakari Tolvanen. “The combination of which process and material you use determines how good the result is.”
In aeroplanes, you do not want the welds to crack. By characterizing the topography of the fracture surface, information about the cause of crack initiation and fracture mechanisms can be revealed. Fatigue failure can be divided into different stages, i.e. crack initiation, crack propagation and final fracture. This figure shows a crack initiation at a pore, a relatively flat crack propagation area around the initiation and the final fracture surface. By learning the behaviour of cracks, they can be avoided.
In airplanes, titanium alloys can be found on parts for landing gear, internal components of wings, and engine components like the fan and compressor sections.
The studies carried out by Sakari Tolvanen have taken place within the framework of a research project conducted by GKN Aerospace:
Read the full thesis here:
Supervisors were Professor Uta Klement
from Chalmers University of Technology and Professor Robert Pederson from University West.
Text: Nina Silow
Images within the article: Sakari Tolvanen