The global objective of the Eco-Design ITD was to reduce the product environmental impact while keeping competitiveness of the aeronautic industry. The TIFAN project addressed the manufacturing by SLM of fan wheel of an air-cooling unit that is currently made of stainless steel. New environmentally friendly fan wheels made of Titanium alloy TA6V were developed. 5 fan wheel demonstrators were fully manufactured and characterised within the project.
The TIFAN project involved the comparison between SLM and conventional bar machining process in terms of material properties (Rm, Rp0.2, E, E%, fatigue, surface roughness and corrosion resistance), environmental impact (Life Cycle Assessment) and cost.
The project was focused in the next value aspects:
- Developing at the maximum the versatility SLM manufacturing technology offers.
- Applying advanced in-process and post-built surface quality improvement strategies.
- Optimizing powder usage efficiency by defining improved powder recycling methodologies and minimizing the volume required for support structures
- Optimizing fan wheel design applying full advantage of SLM possibilities: light-weight design, lattice structures.
- Decreasing the environmental impact and manufacturing process by means of component’s weight and waste raw materials and CO2 emissions reduction.
The objective of the TIFAN project was not only to manufacture demonstrators, but to identify the critical factors that could give rise to a further manufacturing cost and weight reduction as well as mechanical performance improvement. Some of these factors comprised a significant progress beyond the state of the art.
The success of TIFAN’s goal had technical, industrial, and environmental impacts. Real impact was measured and compared to traditional manufacturing processes. On the other hand, technical conclusions of TIFAN were transferable to other components, fostering in this way the competitiveness of European Aeronautical Companies.
Titanium alloys are increasingly used because of their properties: High specific strength at elevated temperature, outstanding fracture resistance, excellent fatigue behaviour, and exceptional corrosion resistance. However, the complexity of the primary extraction process, difficulty of melting (due to its high reactivity with oxygen) and problems during fabrication and machining of titanium alloys make them expensive compared to most other alloys, limiting this way their application.
Thus, titanium alloys are especially appropriate in parts subjected to high centrifugal loads such as disks and blades, which have reduced flow diameters, as well as operate under severe fatigue conditions. Nevertheless, most titanium aero parts are manufactured by conventional machining methods, such as turning, milling, drilling, grinding, etc. In all of them, material is removed to achieve the final geometry, resulting in significant high-cost material wastage. In contrast to conventional subtractive methods, additive manufacturing (AM) is the creation of objects layer by layer. In recent years, Selective Laser Melting, an AM technology for metal parts, has gained in maturity. In theory, it has the advantage of being a cost effective and environmentally friendly and sustainable manufacturing process for producing one-off parts with high geometrical complexity structures. The manufacturing of disks, blades and in general complex geometry parts, arise as an excellent opportunity to exploit the advantages of SLM additive manufacturing technology. This was the case of the fan wheel of an air-cooling unit manufactured within TIFAN project, which is currently made of stainless steel because of the high cost of producing this part in titanium by conventional machining.
In the framework of Eco-Design ITD for Airframe application, a new generation of lightweight environmentally friendly fan wheels made of Titanium alloy TA6V were developed by means of an environmentally friendly additive manufacturing technology: Selective Laser Melting (SLM). Reduction of component’s weight, improved material usage efficiency and reduction of material wastage (saving of raw material and reduction of scrap rates) were accomplished by changing the base material from stainless steel (density 8.0 g/cm3) to TA6V alloy (density 4.5 g/cm3) and by taking full advantage of lightweight design possibilities and maximum material savings of SLM technology. It must be mentioned that SLM is considered as an environmentally friendly technology in which the scraps can be reduced to the minimum and more than 95% of the remaining material (powder that has not melted) may be recycled. The mechanical properties are equivalent to conventionally manufactured parts.
Despite the promising expectations above mentioned, it was observed that TA6V fan wheels produced by SLM have greater environmental impact than those produced by conventional bar machining (4 times higher), contrary to what was expected. This non desirable result is mainly attributable to the impact of post-treatments and transport by air of TA6V powder necessary for the SLM process.