Steel panels were traditionally fastened in place with standard nut and bolt fixings, the removal of which was complex and time consuming. Making the nacelle panels out of composite materials opened up better ways of fastening which could simplify the operation, improve safety and reduce costs. and designing the optimum composite panel fastening became a key project focus.
Early in the process, bigHead worked with the composite designers and fabricators in the Siemens supply chain. This ensured that all the various elements of the design, manufacturing and final assembly steps were considered. This is particularly important for multi-material fastening where many stakeholders play a part and where many variables will influence the outcome and there are no standards or guidelines to rely on
As an outcome of the design review, some key application requirements were agreed:
- Assembly access from one side only
- Sealing against water ingress
- Discrete appearance, with colour matched to nacelle panels
- Additional protection from a harsh offshore environment
- High load and torque-up performance
Several pre-production prototypes were trialled to make sure the key application requirements were met.
As an outcome of the collaborative design process, a bigHead design, joint configuration and installation method were all finalised for Siemens. They consisted of a bigHead surface bonding fastener product featuring M16 thread size, and marine grade 316 stainless steel construction, with polymer over-moulding and encapsulation of the head component, whose colour matched to the nacelle. In addition, serviceable assembly connection points were created using the bigHead product with a threaded-stud fixing functionality in a through-material configuration. The bigHead product was installed with adhesive bonding into composite components.
The nacelle panel can be easily secured or removed by a single person from the interior of the structure. Despite using a through-bonded configuration, the bigHead composite panel fasteners were colour matched over-moulding ensures the fasteners are discrete, as well as safeguarded against lightning strikes.
Like all bigHeads produced at its UK factory, every production batch is tested and documented as part of an ISO 9001:2015 certified quality management system.
Due to the heavy weight of the M16 bolt, special packaging was created to protect the threaded part from damage in transit and before installation.
Since then, the solution has been field-proven around the world.