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FEATURE


FASTENINGS & ADHESIVES


A SOUND SOLUTION


fields of application and possibilities are highly diverse, with their use in industries such as microelectronics, electronics, RFID, automotive, mechanical engineering, machine integration and even renewable energies. In one recent application, however, the


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company’s adhesives have been specified by an award winning acoustics company, Devialet. The company is relying on DELO’s adhesives for its ultra-compact Phantom II speaker line-up.


ATTENTION TO DETAIL The company’s engineers and designers pay close attention to every single detail with specific focus on components since they affect long term sound quality. Although adhesives may seem negligible when it comes to weight or volume, their impact is critical. For anti-vibration and longevity purposes, they are used in transducers on the moving components, like the membrane, voice coil and guiding suspensions. They are also used on the static chassis (magnetic engine and basket). A typical sound box has seven or more bonding areas, and each bonding has its own requirements in terms of adhesives. The majority of high-end transducers today


are still made by hand or with low automation, because they are only needed in small quantities and because of the process-related limitations of the traditionally used adhesives. Superglues, for example, do not allow controlled curing. The curing process of these adhesives starts as soon as the adhesive comes into contact with humidity in the air. Depending on the level of humidity, the time required for the adhesive to reach final strength varies. With two-component adhesives, where curing begins by mixing resin and hardener, the challenges are different: the adhesive must be continuously dispensed so that it does not cure in the dispensing unit; and the products cure too slowly to achieve fast production processes. Devialet’s goal was to implement a fully


automated production line, with a short cycle time. To achieve this, the company involved a rich ecosystem of highly qualified partners, including DELO.


A FLEXIBLE SOLUTION DELO’s adhesives for transducers are mainly acrylate-based, can be dispensed quickly and precisely onto the corresponding component, and cure by UV light. Through exposure to UV light, the adhesives reach final mechanical strength on demand. This enables Devialet to fully control and realise automated processes. In contrast with traditional processes, an end- of-the-line acoustic testing is possible just after assembly without any buffer.


26 DESIGN SOLUTIONS MAY 2023


Adhesives have contributed to high-end sound quality in the ‘Phantom II’ speaker


The flexible material properties of the acrylate- based DELO PHOTOBOND products are a key feature for the applications within a transducer, as it is perfectly adapted to acoustic constraints. It’s flexibility and peel strength enable large displacements of moving components, for example up to ±6.5mm of woofer excursion (the visible thumping at the center of the woofer). A very rigid adhesive was required for the full-


range transducer. Rigid adhesives are usually epoxy-based and reach their final strength after 24 hours at room temperature. To enable fast processes for this production step, and to enable a full testing of the bonded part at the end of the production line, the adhesive company developed a rigid tailor-made acrylate-based adhesive. It can be dispensed precisely and cures by light in a matter of seconds. The company’s light-curing adhesives are also


used for the accurate positioning of parts during assembly so that all the components of the transducer are perfectly coaxial.


MAGNET BONDING For magnet bonding, the requirements for process speed are even higher, but since all components are opaque they do not allow for a proper fast light curing. For this reason, Devialet uses special light-curing metal adhesives from DELO. Metal adhesives cure anaerobically (in the


absence of air) and by contact with metal ions, so are therefore ideal for a reliable curing in shadow areas. However, to comply with the short cycle time, the adhesive’s additional light fixation feature enables lighting and curing of the adhesive overflow just after assembly. The sub-assembly can then be fixed for further processing. Metal adhesives achieve very high strengths after only a few minutes. This allows the permanent magnet to be magnetized without slipping. Today, the entire transducer production takes place in cycles of seconds, enabling an efficient


ELO’s high-tech adhesives can be used wherever reliable, durable and fast connections are required. In fact the


Needing high reliability adhesives for the transducers used in its speakers, Devialet turned to DELO. Dr. Karl Bitzer, managing director and head of product management, explains why


and space-saving production. And, of additional benefit, both the acrylate- based and the metal adhesive have fluorescent properties. Because of this,


cameras can follow the entire bonding process and detect whether the defined adhesive quantity has been applied properly.


CLOSE COLLABORATION Devialet worked closely with DELO to find the very best adhesives and process solutions to produce its transducers, with over 50 tests being performed on original components and directly in production. “Our transducers and their manufacturing


make us proud. Our goal is to provide our customers with the very best quality and performance,” said Raphaël de Labarthe, industrial director of Devialet. “DELO has been an integral part of getting us to a fully automated process by providing us valuable technical advice on adhesive processes. They have a lot of experience in the transducer field and are just as meticulous as we are. It has been a cooperation at high level right from the start. The engineering teams from each company work well together, innovating and finding new solutions that benefit our products and their manufacturing.”


DELO www.delo-adhesives.com


Schematic illustration of a transducer with the basic elements coil membrane subassembly, speaker basket and magnet system. Bonding areas are marked in pink


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