Plastics Processing
welding and manufacturing companies will look that must be considered from the laser Advances in transmission welding
at cycle time and the ability to carry out the perspective – how well do the parts fit together Laser transmission welding is now a relatively
welds in a certain time period. and do they vary too much to give the laser a well-established method for joining two polymers
problem?’ he asks. together. In Issue 4 of this magazine (Autumn
Weighing the pros and cons A further advantage laser welding has over 2009), the technique was discussed as part of the
‘The benefits of laser welding are that it is a non- alternative polymer welding techniques is that ALTEX project led by TWI for the manufacture
contact, single stage process, which produces it can provide online process control. ‘Dilas’ of a waterproof jacket. Researchers at Fraunhofer
an aesthetically high quality join, free from galvo scanning system includes an integrated Institute for Laser Technology (ILT) in Aachen,
contamination,’ comments Broadhead. pyrometer, allowing the power levels to be Germany, have developed a new method for
Ultrasonics and friction welding, two established adjusted to maintain a constant welding transmission welding of plastics called TWIST
(Transmission Welding by an Incremental
A further advantage laser welding has over Scanning Technique).
alternative polymer techniques is that it can
Conventional laser transmission welding
using a diode laser creates a fixed intensity
provide online process control distribution on the workpiece; intensity is
highest in the middle of the beam. TWIST uses
techniques used to join polymers, both have temperature throughout the process,’ comments a laser beam that can be focused down to 10-
their uses. Jörg Neukum, director sales and Neukum. This sort of control is not really 20µm and moved very rapidly on a circular
marketing at diode laser specialist, Dilas, notes: possible with other welding techniques, such as path superimposed to the linear feed of the
‘Ultrasonic welding makes sense for high- ultrasonic. weld contour, thereby creating a screw line
volume production without the need for Without control over the power output, the effect. ‘The result,’ explains Dr Alexander
flexibility, such as the manufacture of car welding temperature could vary resulting in a Olowinsky, group leader microjoining at
headlight components, for instance.’ weaker seam. Neukum says that, through tests Fraunhofer ILT, ‘is that, compared to
Ultrasonic welding requires a tool adapted to carried out by Dilas, automotive plastic conventional transmission laser welding, the
the shape of the weld, which therefore lowers components produced using a diode laser with cross section of the heat affect zone (HAZ) is
its flexibility to handle a variety of weld contours. a galvo scanner and pyrometer exhibit up to 20 not lens-shaped, but is a shallow weld seam.’
In contrast, a laser system using a galvo scanner per cent higher burst pressures than those Conventional laser transmission welding
to position the beam provides a degree of welded using a laser with a fixed output power. generates a relatively deep and/or wide HAZ.
flexibility, as any weld contour can be generated In addition, on-line control enables medical and Therefore, the minimum weld seam width that
within the working field. Dilas’ Compact diode automotive manufacturers to document the can be achieved with a standard diode laser is
laser system series, with modules available welding process for components subject to approximately 200µm. With the TWIST
delivering 500W out of a 400µm fibre, 400W regulatory requirements. approach, the intensity distribution can be
from a 300µm fibre, and 300W from a 200µm Finnish company, Cencorp, also uses a tailored on the workpiece, because the beam
fibre, are suitable for plastic welding using a scanning system for its laser welding process for movement is faster than the heat conduction.
galvo scanner. plastics, providing flexibility, among other ‘The beam rotates and returns to its original
One of the disadvantages with using attributes, by allowing the seam width to be position faster than heat conduction and this
ultrasonics is that it’s not suited to welding parts changed easily. The laser welding system was enables seam widths as thin as 100µm to be
containing sensitive electronics, such as the used to provide high-quality joints on plastic welded,’ explains Olowinsky. TWIST can produce
casings for car key fobs. ‘The ultrasonic training computer components for heart rate welds between 100 and 500µm in width. In
transducer … puts a lot of energy into the part,’ training technology, manufactured by Polar. addition, weld speed is also higher than
explains Broadhead, adding that can damage
sensitive electronics close to the weld zone.
Laser welding, however, provides a low heat
input that won’t affect sensitive internal parts.
Laser welding also has advantages over friction
welding (where the two parts are abraded
together) and gluing, especially in medical device
manufacture, as both can pose the risk of
contamination – from dust when friction welding
and from the adhesive when gluing.
‘However, a laser is not the best tool to use if
there is a gap between the two parts,’ comments
Broadhead. Plastics welding is not analogous to
conventional metal welding, where a filler wire
is melted into the gap between the two metal
sheets. ‘If part tolerances are low, i.e. if parts vary
a lot – which can be the case, especially with
moulded plastic parts – then this is something The TWIST concept developed by Fraunhofer ILT can weld very thin seams, as used in microfluidics.
www.lasersystemseurope.com issue 5 • laser sYsteMs eUroPe 11
LSEwin09 pp10-13 Plastics.indd 11 2/12/09 15:42:14
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