Today’s hearing aids are more advanced than ever before. In addition to their primary function of selectively amplifying specific frequencies to improve speech intelligibility, modern devices increasingly suppress unwanted background noise and enable phone calls and music streaming via Bluetooth connectivity with smartphones.

Despite these advancements, hearing aids still require a trade-off between wearing comfort and acoustic performance. Soft, open-fit domes reduce the occlusion effect and improve wearing comfort and perceived sound naturalness. However, they allow low-frequency sound leakage, which negatively affects bass response during music streaming and reduces speech intelligibility in noisy environments. In contrast, closed systems enhance low-frequency amplification and noise control, but often cause discomfort due to occlusion.

The only commercialised product currently addressing this challenge is the Phonak ActiveVent, which automatically switches between open and closed vent states based on environmental sound analysis. Despite its innovative approach, the electronic miniature components required for the automated mechanism reduce cost-effectiveness and durability, while limiting user control. This graduation project addresses these limitations through the development of a more robust, user-friendly, manual open/closed venting mechanism for Receiver-in-Canal (RIC) hearing aids.

Through desk research, user interviews, iterative prototyping and testing, an innovative manual alternative was developed. Fugai, the final proposed concept, is a RIC hearing aid featuring a manual adaptive venting mechanism that allows users to actively control their listening experience across different acoustic environments. By integrating a manual mechanism rather than an automated one, the design enhances robustness and durability while improving cost efficiency. Providing direct user control further increases perceived reliability and usability.

As a result, Fugai presents an innovative RIC solution that balances user autonomy, ease of use, robustness and cost-effectiveness, without compromising acoustic performance.

This research provides a recommendation for Sonion, a company specialised in the development and production of hearing aids, on the production of moulds for the injection moulding machine.

The goal was to develop a process that reduces the cost and the time to manufacture an injection mould while maintaining a similar accuracy as in conventional mould production. Usually, Sonion outsources the production of injected moulded parts, resulting in parts with a tolerance of ~ ±10 µm that cost €15.000 for a 1000 pieces with a delivery time of 6-8 weeks. For Sonion’s development process, which is prototype heavy, this is too expensive and takes too much time. A micro injection moulding machine is acquired to shorten the iteration time of their design process and to reduce cost.

Before and during this research, the possibilities of 3D printing the moulds with a thermal resistant resin were being explored. For that reason, 3D printing with these materials was left out of the scope of this project. Although the accuracy for this method is sufficient, it struggles with the high pressure and temperature it is exposed to while injection moulding.

After identifying many possible manufacturing methods, the most promising techniques capable of withstanding the injection moulding temperature were chosen and validated through testing, research and consulting experts. For a total of six methods, the physical performance (a combination of accuracy, surface roughness and tool life) and the feasibility (iteration time, cost, form freedom and ease of execution) was determined. From the selected six methods, two were recommended for further exploration and investigation; Micro Metal Casting and Powder Injection Moulding. The other methods fell short due to a lack of accuracy, causing iteration time to be too long and the inability to manufacture certain parts of the mould.

The Micro Casting method works on the principle of the lost wax casting and is taken to a higher level by increasing its ability to replicate a shape. Both fully outsourcing the production and in-house production have been tested with similar results; the in-house production being slightly more accurate with a lower surface roughness. Metal moulds can be produced with a tolerance of ±25 µm for a price of around €750 within one to two weeks. It is recommended that for the continuation of this method, first the already acquired moulds are tested and future designs are fully outsourced until higher accuracy and lower surface roughness are required.

Powder Injection Moulding is a method capable of moulding metal parts at a temperature of 190 °C by mixing a fine metal grain with a polymeric binder and therefore could be used to produce a metal injection mould. In theory, the 3D printed moulds should be able to resist this temperature since it is relatively low. After moulding, the part goes into the oven for the polymer to debind and the grains to be sintered together.
A collaboration with the Powder Injection Moulding company Demcon had been setup for testing, but due to misaligning agendas it could not be set in motion. A test with a similar material has been conducted with highly detailed results. It is suggested to explore the possibilities of this method further.