Titanium: Too Valuable to Waste

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New recycling procedure could reduce CO2 emissions by up to 80 percent

In machining processes for manufacturing titanium components, a large proportion of the raw material is disposed of in the form of chips. The term "machining" refers to a group of manufacturing processes, such as milling, turning or grinding, where surplus material in the form of chips is removed in order to cut a piece of raw material into the desired shape. Material removal rates for large components used in the aircraft industry often exceed 90 percent. The research project Return II of Leibniz University Hannover intends to solve this issue. In collaboration with four specialised partners from the aircraft and recycling industry, the project is led by the Institute of Production Engineering and Machine Tools (IFW).

The project team aims to develop a comprehensive recycling concept for the production of titanium components and focuses on converting chips into powder. "By developing a process chain for converting chips into powder, we intend to improve resource and energy efficiency during the manufacturing process", explains Jonas Matthies, a member of project staff.

To date, most titanium components are manufactured from solid material. Chips generated in machining processes, where material removal rates often exceed 90 percent - for example in the aircraft industry - are not recycled for high-quality purposes, but for less demanding process chains such as additives used in the steel industry. Matthies: "During the machining process, titanium chips are heavily polluted, amongst other things through oxidation, residues of cutting fluid or tool particles. Due to these pollutants, recycling chips is quite complicated."

The current process chain for manufacturing titanium components is insufficient in terms of profitability, energy efficiency and preservation of resources. The project team aims to address these issues by creating a closed recycling loop where most chips can be reused. According to the researchers, their approach has considerable potential with regard to ecology and economics.

In preliminary research, the IFW team demonstrated that pollutants in titanium chips can be reduced significantly if specific process parameters are adjusted. By repeating the melting process, the researches produced solid and high-quality titanium for aviation purposes from recycled chips.

Within the scope of the project, which is in receipt of funding from the Federal Ministry for Economic Affairs and Energy until 2023, the researchers will investigate whether and how their findings could be applied to the fabrication of titanium powder to be used in additive production. In this context, the team aims to avoid the energy-intensive melting process via an atomisation procedure for converting chips into very fine powder. Matthies: "By using chips as a basis in powder production, we expect to reduce energy expenditure and CO2 emissions by up to 80 percent."

The anticipated improvement of profitability in additive manufacturing procedures for titanium components as well as the resulting expansion of the component spectrum could reduce CO2 emissions and energy consumption even further. Compared to machining processes, additive manufacturing provides new opportunities with regard to lightweight materials and bionic structures that increase the efficiency of the final product resulting in additional energy savings. Matthies: "The process chain developed in collaboration with our project partners facilitates ecological and cost-efficient production of titanium components from titanium that has not been recycled so far."

Subsequently, the researchers will analyse components created through additive manufacturing in order to determine how properties can be adapted within the overall process chain. "Looking into the entire process chain will enable us to analyse various effects at different stages of the production process. By adjusting these parameters, we will be able to create components with specific properties", explains Matthies.

Note to editors:

For further information, please contact Jonas Matthies, Institute of Production Engineering and Machine Tools, Leibniz University Hannover (Tel. +49 511 762 18349, Email matthies@ifw.uni-hannover.de).