14 January 2005
14 January 2005
Composite Integration Ltd and Sunseeker have developed an in-house Vacuum Assisted Resin Transfer Moulding (VARTM) facility to manufacture a range of components.
The items identified initially as being ideally suited to this type of closed-mould process were mainly hatch covers and relatively small mouldings. Both the economic and engineering advantages of accurately and efficiently close moulding double-sided items were immediately apparent.
When faced with the requirement for a highly structural composite rotating roof structure on its new Predator 82, VARTM was identified as being the most obvious route to manufacture this large scale and highly complex product. The design called for a rotating circular component over 4m in diameter with demanding structural and cosmetic properties. The moulding consists of a complex fibre laminate around a foam-cored inner structure. The fibre content and orientation varies according to the specific strength requirements and ranges from a standard combination mat in the less stressed areas to unidirectional carbon and glass in the main cross beams. Various metal inserts were also required within the laminate and the completed structure had to fit within a precise target weight.
In addition to the moulding complexity, a limited time-scale added to the challenge, with the patterns, moulds and moulded component being required in less than three weeks. To meet this timescale, several processes had to be carried out concurrently.
Composite Integration worked closely with the Sunseeker design team to produce tool designs that would allow patterns to be produced of both halves of the component simultaneously. This unconventional step relied heavily on the accuracy of the initial design data and the subsequent pattern machining and finishing operation. To ensure that the required structural properties could be achieved and to confirm performance under load, test laminates were built of the various sections.
The product also required truly complex and accurately formed foam cores. Diab UK Ltd joined the project to lend their expertise in this field and to develop the hand-made prototype shapes into production-viable foam ‘kits’.
Once the product structure and tooling design was finalised, extensive use was made of Sunseeker’s exceptional in-house CAD design and large scale CNC machining facilities to produce two highly accurate patterns within the time constraints. The patterns were CAD modelled with the all necessary flange, runner and seal details so, once machined, mould halves could be rapidly taken from them with little extra detailing. On completion the moulds were constructed using a vinylester based tooling system and completed within seven days.
Considerable work had been involved in establishing an ‘injection strategy’ that would allow the mould to fill with the minimum of injection and vent ports. Resin-runner designs were devised to encourage resin to flow preferentially into the higher volume-fraction areas at the same time as the main body and thus reduce fill time.
Once complete with all seals and connections fitted, the mould was gelcoated and systematically loaded with the appropriate fibre and pre-cut foam. The mould was closed, vacuum-clamped and tested for leaks. 60kg of specially formulated resin were injected in 70 minutes and allowed to cure. Once de-moulded the component was checked, trimmed, finished and fitted to the first Predator 82 for display at the Southampton Boat Show later in the same week.
This project demonstrated that close co-operation between product designers, material suppliers, process specialists and the manufacturing team will help ensure a successful outcome in the shortest space of time.