This proposal argued that the main objectives of the undertaking, lightweight and energy-efficient tools, can be achieved by the creation of self-heating composite tools which are applicable in an RTM process. The aim was to establish a set of full-sized rotor blade tools for a low-cost and energy efficient RTM cycle. This contained two tools (upper and lower mould) for preforming, consecutively referred to as “preforming tool” and two moulds that form the impregnation and curing cavity, consecutively referred to as “RTM tool”.
Considering the RTM tool, the self-heating property was to be achieved with heating elements that are integrated into the composite structure near the cavity surface. The carbon textile heating elements were flexibly distributed in reference to the mould surface in such a manner, that temperature gradients over the entire tool can be created.
During the project alternative systems which offered the equivalent potentials for heating like electrically heat able coatings were considered and evaluated. Enhanced local heating device capable of high and homogeneous temperature for tool manufacturing was investigated.
Integration and enhancement of process simulation tools in the design process for the RTM tool provided feedback on setup variants in terms of temperature and material property distribution like glass transition temperature and degree of cure, as well as the resulting part’s shape “as built”, and thereby will help to establish a RTM tool design including the advanced heating concept “first right”. Curing simulation is the tool of choice to analyse the thermal response of the tool part setup including the energy release due to the crosslinking reaction of the resin and is vital for virtual process and tool optimization.
To verify the achievements concerning environmental impact a gate to gate life cycle assessment was performed.
Commonly used resin transfer moulding (RTM) tools made from steel show a poor performance in terms of environmental and economic aspects within the context of rotor blade manufacturing. This is mainly due to the high weight and therefore bad manageability, the intensive energy consumption for heating during the process, a high ratio of scrap when cut from solid material and high-energy expenditure for the production of raw material in the first place. Furthermore, the weight of the moulds results in undesired deflections that must be eliminated by additional material usage for stiffening the tools. On the contrary, the use of composites in tool manufacturing is known to be a solution for the above stated problems but is not yet capable of satisfying the strict requirements for RTM processing within aerospace.
The project LEEToRB comprises the development of “Lightweight, Energy-Efficient Tooling for the Manufacturing of Rotor Blades”. Carbon fiber reinforced polymer (CFRP) moulds were utilised in combination with a novel heating system introduced by the consortium partner Qpoint Composites GmbH to provide the capability of manufacuring of CFRP parts with complex geometries including highly varying cross-sections in an energy-efficient way. To do so, four major topics were addressed within the project: The manufacturing of the CFRP RTM prototype tools was carried out by Qpoint Composites GmbH. Development of process technology as well as curing simulation was accomplished by the Technische Universität München. Finally, a life cycle assessment was made by the Fraunhofer Institute. The target application of the work conducted is provided by Airbus Helicopters.
Within this project CFRP RTM tools were designed, manufactured and a proof of concept was succcessfully conducted. In three steps of development – preliminary tests, simplified demonstrator and full-scale demonstrator - design and process criteria for a CFRP RTM tool for aeronautic application were developed. Finally, a basically new tool design was necessary to ensure a robust functioning of the tool. Stiffening ribs and a steel frame were applied on the back of the CFRP shell to reduce the deformation due to compaction and injection forces. By the initial operation of the tool at the industrial partner a rotor blade could be produced successfully.
The thermal simulation performed within the project showed that temperature peaks of + 50 °C compared to the applied temperature occur during processing thick laminates. Such a thick laminate is for example the attachment area of a rotor blade. The simulated temperatures were also measured within the part laminate during curing. On basis of the simulation the temperature cycle was locally adapted through the integrated heating. As a result, a reduction of the temperature peak to + 10 °C was achieved.
Through the LCA a huge saving potential in all regarded impact categories for the CFRP tool towards the aluminium tool could be proved (about 60% to 70% for the PED and the GWP and with about 93% for the ODP). In addition, with the very small energy demand during the use-phase, the manufacturing of rotor blades for helicopters is ecologically worthwhile with a self-heated tool, out of CFRP.
Main achievements of the project are:
- 85 % lighter tool compared to metallic competitor
- 90% energy savings compared to series process
- Part quality can be improved by locally adapted heat input
- New process opportunities by low CTE of the tool