Colour is normally considered a visual requirement. For a rugged navigation device, it became an RF performance issue.
Dudley Associates was asked to support the development of a component combining a rigid engineering-polymer substrate with a soft TPE overmould. The part needed to withstand physical testing, provide the required feel and protection, and avoid materials that could interfere with radio-frequency transmission.
The application
The product forms part of a navigation system intended for demanding field use. Its construction required insert moulding and overmoulding within a 1+1 aluminium tool. Makroblend PC/PBT was selected for the rigid substrate, with a Kraiburg TPE used for the overmoulded section.
The two polymers needed to work together mechanically and through the moulding process. The substrate had to remain dimensionally stable, the TPE needed to form consistently around it, and the finished assembly had to tolerate 27 J drop testing.
“This is exactly the type of challenge our team is experienced in. With insert moulding and overmoulding, success depends on much more than selecting two suitable materials. The interface, tooling, moulding sequence and final performance requirements must all be engineered together.”
Why the masterbatch mattered
The colour system could not be treated as a standard masterbatch choice. Carbon black and certain metallic constituents can absorb, reflect or otherwise affect RF signals. A visually acceptable colour could therefore undermine the performance of the device.
We sourced a bespoke masterbatch formulated without carbon or metallic content. This allowed the colour requirement to be addressed while protecting the device’s RF transparency. The masterbatch also needed to remain compatible with the base polymer and the moulding process, including dispersion, appearance and repeatability.
Designing the manufacturing route
The project combined material selection, DFM, toolmaking and process development. The 1+1 aluminium tool was selected to support the expected volumes and the required insert-moulding and overmoulding sequence.
Following DFM approval, the tool was manufactured within four weeks. T0 followed one week later, with T1 components available one week after that. Keeping design, toolmaking and moulding within one working team allowed issues to be reviewed without long handovers between separate suppliers.
“Because the design, tooling and moulding teams work together under one roof, from each stage can be acted on immediately. What we learn during tool manufacture or sampling can be reviewed directly against the DFM and tool design, without information being lost between separate suppliers.”
Validation before production
The finished product progressed through drop testing and was successfully validated. The project is now moving into its first production order of 500 units.
The result was not created by one isolated decision. The substrate, TPE, pigment system, gate strategy, tool construction and test requirements all had to work together. That is the practical value of treating a rugged enclosure as a complete manufacturing system rather than a CAD model followed by a tool order.
Discuss an RF-sensitive enclosure
If you are developing a navigation, telemetry or wireless product, the polymer and colour system can affect more than appearance. Dudley Associates can review material compatibility, RF considerations, overmoulding and tooling before the manufacturing route is fixed.
Frequently asked questions
What is RF transparency?
Why can masterbatch affect RF performance?
What is a 1+1 mould tool?
A 1+1 tool contains two different cavities, normally producing one of each related component during a moulding cycle.
Why use aluminium tooling?
For suitable geometries and lower production volumes, aluminium can provide a faster and more proportionate tooling route. The decision still depends on material, complexity, expected life and production conditions.
