This proposal addressed the fibre winding manufacturing of a sleeve structure (rotor part) for an aircraft cooling unit, which is subjected to a highly variable environment, e. g. a large temperature range, and has excellent mechanical properties to withstand mechanical loading from high speed rotations. The replacement of existing metallic structures with continuous fibre reinforced polymer parts shall allow a weight reduction and higher rotational speeds at elevated temperatures. The proposal included a detailed analysis of requirements, current designs, and constraints to allow the proposal of a suitable manufacturing concept including material and cost assessment.
A new siphon impregnation system developed at IVW allows a complete wet-out of fibres with stable processing conditions and can further improve laminate quality. Cyanate esters are high sophisticated thermoset polymer resins suitable to be used in high temperature environments with highly desirable properties and encompass characteristics of epoxy resins, e.g. benzoxazines, bismaleimides or phenolic resins, but are sensitive to processing conditions, i.e. moisture uptake before and during curing. Therefore, this proposal addressed the development of a monitoring of gelation and curing of the matrix resin during processing e. g. by ultrasonic transducers, via dielectric analysis with rheological correlations, and indentation tests. Also, monitoring of filament tension, moisture and void content are addressed. The monitoring is included in or accompanies an automated and CNC-controlled fibre winding process. An optimum design for the structure was achieved via structural analyses including mechanical and thermo-mechanical stress analyses, design and ply book generation. Fabrication was set-up and prototypes manufactured and mechanically tested under near-operation conditions. Finally, manufacturing was optimised and 5 demonstrators manufactured and TRL-5 readiness assessed.
This project suggested fixed starting date to comply with the Eco Design program.
Project HiTemComFil covered the development of a composite sleeve for an aircraft cooling unit, including process and methodology development. Due to the extremely high thermal and structural requirements, Cyanate ester resin was utilised in a filament winding process. As this resin poses high demands for the control of moisture and heat generation during the winding process, a methodology was developed and the winding process was optimized for achieving the desired laminate quality. In-depth analysis of the chemical and physical processes during curing and utilization of these findings for process optimization led to a reduction of the void rate of the laminate by 78 % during the project. As a result of this optimisation, high quality composite parts with superior properties at elevated temperatures are available for the current application as well as for various high-technology applications in other fields.
In order to achieve a design with minimum weight while fulfilling all mechanical requirements, finite element simulation was performed alongside experimental validation, resulting in two alternative designs for the sleeve, based on two different manufacturing methods. The commonly used press-fit design, requiring the assembly of several individually produced components, was compared to a novel, one-step production process using pre-strained filaments in a winding process. During the project, this latter method emerged as a highly efficient, reproducible manufacturing method for the given part as well as for general components subjected to high-speed rotation or internal pressure, e.g. pressure vessels, pressure lines or fly-wheels.
The development of the manufacturing alternatives allowed for a significant reduction in production time. When the manufacturing efficiency for press fit solution using conical glass fibre inner layer and carbon fibre sleeve with conical inner shape is set to 100%, manufacturing effort using direct winding solution is about 40%. In other words, the manufacturing efficiency for the developed direct winding would be about 60% more efficient than the press fit solution mentioned before.
As a result of the simultaneous optimization and adaption of the component design as well as the process control, the utilisation of cyanate ester resin with its demanding processing properties was established in the series-production- worthy filament winding process. The unique adaption of the filament winding process with introduction of high pre-stress values in the fibres by an especially developed brake allows for the systematic adjustment of built-in stresses in the cured laminate.
The project success was demonstrated by successful manufacturing and application-related testing of five demonstrator parts. The project results were presented at various exhibitions, among them Composites Europe and JEC, and were received with interest by potential customers across industries.