Sonova additive manufacturing for production progress

The Virto B-Titanium hearing aid (image credit: Sonova)

3D printing and hearing aids have been a good match for a long time; indeed, it has been more than a decade since additive processes were first used as the production tool of choice for hearing aid cases.

One of the earliest brands to adopt additive manufacturing (AM) for this production application was Phonak, which is owned by Sonova, the Swiss hearing solutions technology company that is among five of the world’s largest hearing aid companies.

Patrizia Richner, who works for Sonova, recently presented the latest AM developments at the company, highlighting that the evolution with AM continues within the hearing aid sector, while simultaneously demonstrating the progress of the AM industry itself over the last decade or more. The company has transitioned from using AM for high-volume production with plastic to metal.

After explaining how Sonova has been serially producing millions of polymer hearing aid shells a year since 2007 using EnvisionTEC platforms, Richner went on to outline the challenges and importance of the product itself.

It is a very personal product that enables people with varying degrees of hearing loss to lead normal lives. However, Richner said one of the greatest challenges of hearing aid use is discretion—a high proportion of people would rather struggle with their disability than be seen to be wearing a hearing aid.

Thus, the aim is for invisible, in-ear hearing aids. Not an easy design and manufacturing feat when one considers that all of the necessary tech components—battery, speaker, microphone, etc.—have to fit within a shell that fits within the confines of the ear canal.

Add on the fact that the ear canal of every individual has a complex shape and is as unique as a fingerprint and the design and manufacturing conundrum multiplies. Standard shell shapes just aren’t good enough, they are uncomfortable and irritating; again, resulting in non-use by patients.

Over time, therefore, Richner revealed how Phonak developed an end-to-end solution for customized hearing aids based on a digital manufacturing process. The process starts and finishes with the customer—gaining an accurate impression of their ear through 3D scanning, converting the scan data into a digital design, custom manufacture, assembly and final fitting of the ear piece.

While polymer 3D printing solved many of the traditional challenges of producing hearing aids—and improved both the outcome for patients and the manufacturing process and workflow—it is not a perfect solution. Richner cited two particular issues that remain with 3D printed acrylic hearing aids, namely wall thickness and durability.

The DLP process was able to achieve a minimum wall thickness of 0.6 mm for the hearing aid cases while maintaining the necessary functional stability. Thinner walls, however, allow for deeper (invisible) placement in the ear canal, meeting the priority demand of clients as well as accommodating the technical components of the earpiece more easily and improving overall functionality.

Moreover, hearing aids, according to Richner, should last ‘for five years with no trouble’, but the acrylic shells can prove less durable, particularly under environmental stresses such as UV rays, cosmetics (typically sunscreen), cleaning products and sweat, not to mention the physical handling and dropping involved with day-to-day wear.

Primarily for these reasons, Sonova has been conducting R&D into metal AM manufacturing processes for the last four years. This was not a light undertaking, as the nature of the product demands rigorous qualification of any new material and/or process. The results are now in the public domain, however, as Sonova has introduced its first metal, customized hearing aid product—the Virto B-Titanium. 

As well as allowing for the desired thinner wall thicknesses (0.2 mm) and improving durability, the transition to this medical grade, hypoallergenic metal material using the laser melting process has brought additional benefits, including the ability to ‘produce the right shell for the right patient 100 percent of the time,’ all with full traceability built in. The process allows for a unique four-digit ID number to be printed on the inside of the shell during production, allowing for easy identification at any future date.

Richner stated that this new generation of metal hearing aids has been worn by patients for the last 3-4 months and customer feedback is very positive, particularly on invisibility and durability. To illustrate the latter, Richner mentioned that one of the hearing aids had been driven over by a car and survived unharmed, remaining fully functional. She was quick to add that this was not recommended, but it goes a long way to illustrate the strength increases Sonova has achieved with the transition to metal.

The company is currently producing hundreds of the Virto B-Titanium hearing aids each day, but expects this number to rise.

So, once again the hearing aid sector is a beacon across the AM landscape of realistic process improvements and true progress.

About Rachel Park

Rachel is a passionate advocate of additive manufacturing/3D printing technologies and the industry that has sprung up around it. However, as the hype and hyperbole has gathered momentum, her aim is always to offer a reasoned voice in the midst of inflated expectations and to cut through the noise in order to provide a realistic outlook of how things are.