| Optimising Tooling Materials by Stephen Leonard-Williams - Plastech Limited.
"Composite tooling has been well proven as a successful route toward cost effective Resin Transfer Moulding (RTM). At Plastech we have developed and refined our toolmaking procedures continually over the last 15 years. This work has entailed evaluating new materials and processing options whilst continuing to offer a viable and effective system to customers. Plastech offers both an in-house tool building service or training to enable customers to manufacture their own tooling.
As part of the continual drive to optimise the materials used in tool building we have concentrated our development work into a formal project. Plastech has employed Advanced Composite Graduate, Jonathan Smith, under a project administered by the Department for Business Development at the University of Plymouth which is part funded by the European Social Fund through its Unlocking Cornish Potential programme. This programme is designed to encourage graduate engineers to remain in the county and to make technical resources available to manufacturing industry.
The targets set by the project were as follows:
- Evaluate various tooling gel coats;
- Evaluate various tooling resin systems;
- Measure the thermal conductivity of available tooling systems and assess their suitability for thermal transfer in moulds heated by liquids;
- Measure the shrinkage of all the materials used and optimise their use for maximum stability and accuracy within the finished mould structure.
Perhaps the most interesting results, so far, have been in the areas of thermal conductivity and shrinkage. We have taken as our benchmark existing commercially available tooling systems, developed to give good thermal conductivity. These systems are often heavily filled with aluminium particles and are designed to be mass-cast around the master pattern. This approach, although effective and fast on a small scale, can be extremely impractical and costly on larger applications.
Plastech's aim has been to design a tooling structure that is readily scaled up to any tool size, that has good thermal conductivity to enable a good surface spread of heat to be achieved, has excellent stability and yet is cost effective and easy to work with. Resin systems ranging from polyester and vinylester to epoxy have been tested with a wide range of conductive fillers. All resulting mixtures have been compared with the existing aluminium particle filled systems.
Test panels have been made using all the options identified with various permutations of laminate structure, thickness and heater matrix design. Thermal conductivity of the sample laminates has been tested with the use of thermal imaging equipment at the University of Plymouth to record their exact behaviour during the heating and cooling cycle. The thermal images are video recorded in real time and give a perfect graphic picture of the surface spread of heat.
Relative Heat: (Coldest) Black - Purple - Red - Orange -Yellow - White (Hottest)
As a result of this work we have been able to optimise the thermal response of the tooling structure using a standard resin system and a low cost filler mixture. The exact mix ratio was found to be of vital importance when balancing good conductivity against low shrinkage. The resulting tooling structure displays outstanding stability, enabling the continued production of accurate moulds with greater confidence and without any extra build-complexity or expense."
Extract from Plastech's 'RTM Newsletter' - Spring 2000
|
