Overview
The amount of electronically controlled tasks in modern aircraft is increasing steadily and the overall weight of an aircraft has reached a magnitude that requires an analysis to obtain mass reduction. Conventional electronics enclosures are made from metal. Most of the boxes fielded today offer a monolithic architecture in the form of closed box packed with electronics and lots of connectors at the front or the back with corresponding heavy cable harness. The proper housing protects the electronics against the environment, ensures EMC and supports the thermal management. In order to reach higher power density and lower costs the optimisation of the housing is a must.
Modern structures built in composite technology are able to provide important mass savings with respect to conventional designs. The advantages of high performance composites are many, including lighter weight, the ability to tailor lay-ups for optimum strength and stiffness, improved fatigue life, corrosion resistance and, with good design practice, reduced assembly costs due to fewer detail parts and fasteners.
The objective of the present project is the development of an integrated solution for a lightweight hermetic sealed power electronic housing for unpressurised area with cost neutrality and according to DO160. The final objective is the reengineering of the flat top and bottom covers of the housing in order to demonstrate the technical and economical viability of composite materials as housing materials for extreme environments. The aluminium vertical walls providing the attachment points to the electronic components and to the covers will be maintained in the prototype design. Thus, a hybrid composite-aluminium enclosure will be developed and validated against the requirements fulfilled by the current full aluminium design. The aim is to reduce the weight of the covers made currently of anodized aluminium by 40% with electrically conductive bonding areas (Alodine 1200).
Funding
Results
Executive Summary:
The amount of electronically controlled tasks in modern aircrafts is increasing steadily and also the contribution of racks for avionics to the overall weight of an aircraft has reached a magnitude that requires an analysis to obtain mass reduction. Most of the avionics fielded today offer a monolithic architecture in form of a closed box packed with electronics and lots of connectors at the front or the back with corresponding heavy cable harness. The housing protects the electronics against the environment, ensures EMC and supports the thermal management.
Currently, housings for electronics are manufactured out of aluminium sheets. Aluminium housings tend to be quite heavy and during the machining a large amount of material is discarded, making the process not very efficient. In order to reach higher power density and lower costs, the optimisation of the housing is a must. The aluminium approach performs well, but there is still room for improvement.
SEALEDBOX project defends composite materials in electronic enclosures would provide benefits, mainly in terms of mass saving, while keeping performance. The use of composite materials in commercial airplane structures has demonstrated the technical and economic feasibility of these materials to cope with the stringent aeronautic requirements and the advantages over their metallic counterparts. Thus, it is time to transfer the composites technology and benefits to other components in order to reduce their contribution to the overall mass and improve the fuel efficiency.
Advanced fibre-reinforced composite materials have several key properties that make them especially useful in aerospace applications. Their high specific strength and stiffness, the improved fatigue behaviour and their corrosion resistance convert them in the optimum candidate materials for the design of lightweight electronic housings.
The objective of the present project was the development of an integrated solution for a hermetic sealed low weight and low cost power electronic housing for unpressurised area (DO160).
The goal is the demonstration that lightweight composite materials are a cost effective alternative for the manufacturing of hermetic sealed enclosures for housing electronic equipment to be installed in the unpressurised area of airplanes, which involves the fulfilment of vibration requirements listed in DO-160, “Environmental Conditions and Test Procedures for Airborne Equipment”.
Hermetic sealed housing has been re-engineered applying the composite approach. Specifications have been drawn and architectures, manufacturing processes and materials have been envisaged, evaluated and traded-off.
The potential problems in the composite design have been anticipated and alternative countermeasures have been evaluated. In order to keep manufacturing costs as low as possible, a design concept having infusion as manufacturing process has been selected. Regarding the materials, standard high strength carbon fibres together with aero grade infusion epoxy resin have been selected as main materials for the production of the covers. Trials at sample level have been performed in order to explore the different material solutions identified.
Detailed analyses indicate covers are able to withstand the dynamic environment. The selected laminate fulfils both lightness and stiffness requirements. Thermal results obtained are in line with the aluminium counterpart. No problems due to CTE mismatch are foreseen.
The manufactured composite structures successfully passed the electrical bonding and sand and dust tests performed. Damage of the painting was observed during the thermal testing. It was attributed to an over thickness in the EMI layer. Additional trials performed to optimize the painting procedure showed no damage in the samples.
Compared to the current aluminium approach, significant weight reductions have been obtained: 32 % reduction with respect to the aluminium covers.