Two-component micro injection moulding for hearing aid applications

Two-component (2k) injection moulding is an important process technique at the present state of technology, and it is growing rapidly in the field of precision micro moulding. Besides combining different material properties in the same product, two-component moulding can eliminate many assembly steps in the manufacturing process chain. One of the biggest technical challenges associated with 2k moulding is the unavailability of suitable material combinations which can meet the diverse requirement from both product and process point of views. When it comes to the point of micro application, the precise dimensional requirement and tolerance make the 2k moulding a technically challenging process. This paper presents an industrial case study of 2k micro moulding covering all the important issues like product design, material selection, moulding and functionality testing of the micro moulded 2k parts. An intensive search for suitable 2k materials is made and few combinations of plastic materials are presented in the paper which can be used for highly demanding application areas like hearing aids. By using these material combinations, a demonstrator 2k micro part has been fabricated. The moulding machine was a state-of-the-art 2k micro machine from DESMA. The fabricated micro part was a socket house integrated with a sealing ring for the receiver-in-canal hearing instrument. The test performed on the demonstrator showed the potential of the 2k moulding technology to be able to solve some of the existing problems associated with hearing instruments.