RETURN II - EU Project

Closed loop in the additive-subtractive manufacturing of titanium components

The aim of the RETRUN II project was to develop and optimise a closed-loop recycling process for titanium scrap to produce high-quality spherical alloy powders for additive manufacturing processes. The process development was accompanied by the creation of a digital twin to predict the powder quality on the basis of varying process parameters.

The aim of the RETURN II project was to develop a closed-loop recycling process for titanium waste from subtractive manufacturing to produce spherical metal powders for additive manufacturing processes. The project considered the entire product lifecycle from chip production to the processability and quality of the metal powders produced. As part of the project, strategies and solutions were developed with the objective of ensuring that the titanium chips are provided in pure form, with as few impurities as possible. This enabled the recycling of titanium chips and powder for the production of new high-performance additively manufactured titanium components. An environmentally friendly and efficacious washing medium was successfully tested on an industrial scale for the removal of adherent cooling lubricants. The subsequent compacting of chips of other materials is already a state-of-the-art process, and as anticipated, demonstrated a high level of effectiveness when applied to titanium chips.

An innovative approach has been introduced for the recycling of titanium chips from machining and powder residues, with the objective of producing electrodes. The recycled titanium chips are compacted into electrodes via hot isostatic pressing (HIP). The recycled hot isostatically pressed titanium electrodes were found to be suitable for use in powder atomisation processes, with no discernible differences in the resulting powder quality. In particular, the level of impurities was reduced to a degree that enabled compliance with the specification for titanium grade 5. The subsequent evaluation of component properties of additively manufactured parts produced from recycled powder also demonstrated no significant differences in mechanical properties when compared to components produced from standard powder. The machinability of additively manufactured parts produced from recycled powder was also examined, and the findings indicate comparable levels of tool wear and edge zone characteristics following machining when compared to samples created from standard powder.