The main objective of this project is to develop a functional composite overwrapped pressure vessel (COPV), using Omnidea’s cold forming process to manufacture the metal liner.
During this project the liner manufacturing process was tuned, so that the manufactured product would comply with its design specifications.
A methodology for the COPV dimensioning using FEM analysis tools was implemented in the design process and it was validated by testing real life specimens on a laboratory-controlled environment.
The greatest challenges found in this project were concerned with the manufacturing processes settings and the FEM model correlation with the experimental results.
The liner manufacturing method combined with design specifications led to the development of special equipment that had to be fine-tuned in order to produce satisfactory results.
Since it was used wet winding technique in the carbon fibre overwrapping process, the parameters had to be adjusted to prevent carbon fibre slippage.
The COPV dimensioning required experimental data in order to validate the model. This was accomplished on the final specimens.
The traditional liner manufacturing methods involve welding two tank halves at the cylindrical section, which is the tank’s most stressed zone. The fact of having a structural weld in this area means that expensive non-destructive inspection methods must be carried out in these areas to ensure that welded areas do not have defects. The cold forming process developed by Omnidea allows to produce aluminium liner shells without welded areas on the most stressed zones (cylindrical zone).
In terms of manufacturing easiness, the welding process at the cylindrical section is not a straightforward operation since it must assure the proper alignment/concentricity between each tank half. Omnidea’s cold forming operation assures the proper alignment between each end of the tank, being only required to weld a set of end caps at each end in order to close the liner. In terms of manufacturing difficulty, non-destructive inspections and cost, it is much better to perform the weld at the bottleneck than in the cylindrical section of the liner.
The COPV features an aluminium liner without girth welds and its specifications are:
Volume range: 5-15 L
MEOP: 200 bar
Burst: 300 bar
Liner material: AA 6063
Carbon Fibre: Toho Tenax UTS50
Epoxy Resin: Araldite LY 556
The COPV in development is divided in two main components, the aluminium liner and the carbon fibre overwrap.
The aluminium liner has three main functions:
to provide a gas barrier;
to serve as an interface for the propulsion system piping/spacecraft;
to act as a mandrel for the carbon fibre overwrapping process;
Most of the structural strength is given by the carbon fibre overwrap, so that the tank withstands the required working loads.
The project plan is to develop manufacturing method for COPVs that is supported by a reliable design methodology. This methodology is validated by testing real life specimen in laboratory environment and assessing the materials properties.
Following the successfully testing of the tanks, the next step will be towards qualification. The main goal is to use the innovative cold forming process developed by Omnidea to produce a flight model for the future INFANTE constellation.
A COPV capable of achieving the required pressure thresholds has been successfully tested in laboratory environment, and a design methodology for COPV design has been developed and validated with experimental data.
The welding process of the end caps of the liner need further improvement.
Due to the successful results obtained during the Aluliner project, Omnidea proposes as a continuation of this project to use the innovative cold forming process internally developed to continue the production and development of small tanks according to the market needs.
The purpose of the follow-up activity is to use the innovative cold forming process developed by Omnidea to produce a flight model for the future INFANTE constellation.
The requested tank is a pressure vessel for propulsion gas storage made from aluminium alloy AA6063, with a diameter of approximately 98 mm and a volume of approximately0.8 L. Other important goal of the follow-up project is to improve the current TIG welding machine prototype, focusing in achieved a higher TRL. This development will allow Omnidea to obtain, in near future, a certificated TIG aluminium welding process.