Better Hearing Thanks To
Laser Welding
Phonak
Hearing Aid
The
development of hearing aids has been facilitated by the
incorporation of laser welding using the mask welding
concept. It is necessary to provide protection in the area
of the sound outlet in order to guarantee reliable
functioning of hearing aids that are getting ever smaller
and which are worn within the ear. In the novel «SmartGuard»
cerumen protection concept by Phonak, a highly elastic,
extremely thin diaphragm is welded onto a small carrier
ring. The mask welding process, developed and patented by
Leister Technologies, enables this high-precision joining
process providing protection from contamination.
Difficulty of
hearing and reduced hearing capability is widespread. In
many cases these conditions can be alleviated to a large
degree using modern hearing aids.
Continuous
development of hearing aids also leads to miniaturisation,
with the aim of providing the user with smaller, more
comfortable and virtually invisible hearing aids. There
are different types of hearing aids which differ in their
shape: so-called BTE (behind the ear) hearing aids and the
considerably smaller ITE (in the ear) hearing aids. In
addition to the technical differences, the ITE hearing
aids primarily have the optical advantage that, depending
upon the shape, they are virtually invisible from the
outside.
A big problem
with all hearing aids is the contamination of the sound
outlet by ear wax in the auditory channel, the so-called
cerumen. The loudspeaker – also called the earpiece – is
located deep within the ear channel, particularly in the
case of the ITE hearing aids. In order to ensure long term
functioning, this must be effectively protected from
contamination and moisture. The demands on such protection
are high. In addition to the acoustic properties,
strength, durability and media resistance as well as
consistent high quality of sound play a significant role.
The Swiss
hearing aid specialist Phonak has a turnover of more than
a billion Swiss Francs and a global market share of 16 to
17% and is thus one of the leading hearing aid
manufacturers in the world. Phonak is constantly making
new innovations that make a considerable contribution to
the society.
Leister
collaborated with Phonak to Laser weld cerumen
protectors on Phonak hearing aids.
The
improvement in quality of life of people with hearing
damage is beyond imagination. One of these innovations is
the new cerumen protector «SmartGuard». This uses a 15 µm
(micron) thick polymer diaphragm to protect the sound
outlet from cerumen and moisture, without having any
significant deleterious effect on the acoustic properties.
The diaphragm is mounted on a thermoplastic carrier ring.
The strength of the connection to the carrier ring is
high, despite the small area of the joint. Any deposits on
the diaphragm can be removed by regular wiping with a soft
cloth. This does not damage the diaphragm or the
connection to the carrier ring, thus ensuring a long
working life for the cerumen protector.
Laser welding
also means that the necessary media resistance of the
joint is achieved. The recommended period of use of two
months exceeds the period of use of the existing
fabric-based protection systems. After this period of use,
the cerumen protection can easily be replaced using a
special tool.
Mask
Welding
The mask
welding process – developed and patented by the Swiss
laser system manufacturer Leister Process Technologies and
operating on the principle of laser transmission welding –
is used for joining the diaphragm to the carrier ring.
This involves connecting a joining partner that is
transparent to laser radiation with an absorbing joining
partner.
In the case
of the cerumen protection, the diaphragm is transparent to
laser radiation. The carrier ring, on the other hand, is
made from a thermoplastic material which has a fixed
shape. It is black in colour and thus absorbs the laser
radiation. In the mask welding process used here, a mask
is inserted between the laser source (diode laser) and the
component. A linear, well collimated – in other words,
parallel – laser beam is moved over the parts to be
joined.
The laser
radiation only impinges on the parts to be joined that are
not blocked off by the mask. The use of the mask makes it
possible to illustrate the finest of structures. This
means that mask welding can achieve high levels of
precision. This welding concept allows fulfilling a
further requirement, namely the need to keep the area for
welding to a minimum. This means that there is more area
available for the acoustically active diaphragm surface.
It is only with the mask welding process that the
necessary strength can be achieved with the smallest of
welding areas. A further significant advantage is the
minimal weld pool depth. The formation of a weld bead can
be virtually eliminated. This, in turn, has advantages
with regard to dimensional reproducibility and acoustics.
Phonak
evaluated various joining processes for this demanding
application. The requirements for welding consisted, in
general, of the resistance to mechanical and chemical
activity. Laser welding had the following advantages when
compared with the other processes: No pre-treatment of the
surfaces, such as plasma irradiation or priming (chemical
activation of the surfaces) is required. These would have
a negative effect on the foil. Joining processes which
produce melting would not be acceptable because of space
restrictions.
The high
level of reproducibility associated with mask welding has
proven to be an advantage over joining processes involving
the application of additional materials.
In addition
to the process-technological reasons, mask welding also
has economic advantages. The consumption of supplies is
regarded to be low, when compared with other processes.
Batch processing processes, which are carried out
semi-automatically and which can be run on plants such as
the NOVOLAS WS allow volumes of several millions to be
produced in a year. Not least is the advantage that the
joining process is even more economical because of the
lack of additional material consumption.
Prospects
Because of
the properties already referred to, the mask welding
process is particularly suited to applications in medical
technology. In this way foils can be welded onto micro
well plates without the melt flowing into the apertures.
Mask welding is also recommended for fluidics in general –
and for micro fluidic components in particular. This
precise and cost-effective process finds applications in
products for the entertainment electronics and computer
peripherals.
Another
process developed by Leister is radial welding. In this
process, rotationally-symmetrical parts are welded
together without having to move with respect to the laser.
In medical technology this process is used for welding
catheter attachments. Radial welding also finds
applications in sensor technology, fluidics and in the
automotive engineering.
The GLOBO
welding process, patented by Leister, also finds
applications in medical technology. It allows dynamic
pressing together of the joining parts, and, for example,
it allows two transparent foils to be welded together. The
heat energy is transferred to the foils by an absorbent
black substrate [which has a melting point which is higher
than that of the parts to be joined together]. This
concept can be used to join large area components and
endless applications.
Success
Story, No 2/08 / ENG © Copyright by Leister India
Headquarters : Leister Technologies India Pvt Ltd No.
4/27B, Kambar Street, Alandur, Chennai 600016 phone: +91
44 45583436,
info@leister.in Leister Technologies AG is an ISO 9001
certified enterprise.
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