Plastics Processing
Image courtesy of Dilas
Breaking
the mould
Lasers produce strong welds in
plastics and are an effective tool for
joining two polymer layers together.
procedure opens up narrowed arteries by Two flat sheets can either be joined by
Greg Blackman looks at
embedding a stent into the artery walls. The overlapping or by butting them side by side.
stent itself is metal, but the delivery device is a Direct laser welding, which heats the polymer
how lasers are used to weld plastic catheter with a balloon laser-welded to from the outer surface, typically using a CO
2
and mark plastics
the end. The stent is loaded onto the deflated laser (10.6µm), is suitable for butt welding, as
balloon and fed through the vascular system to most plastics will absorb at 10.6µm. CO lasers
2
the artery. The balloon is inflated, embedding can provide high-speed welds, but as the depth
L
aser welding of thermoplastics was first the stent in the artery wall; then deflated and of penetration of the beam is limited to a few
demonstrated in the 1970s, but the the catheter removed. millimetres, the use of this laser technology for
technology has only recently begun to welding overlapping seams is restricted to
be used heavily in industrial applications. Factors to consider joining thin films.
Automotive and medical are two markets where Not all plastics are suitable for laser processing. A much more common technique for joining
lasers have been widely adopted for plastics In general, thermoplastics, which return to a two plastic sheets with an overlapping seam is
welding, with plastic components involved in molten state when heated, can be laser welded, transmission welding. Here, absorption occurs
fuel delivery, i.e. from the fuel tank along the but thermosets and elastomers cannot as they at the interface of the two layers and requires
fuel line, as well as plastic syringes and catheters simply degrade when heated. Furthermore the an upper layer transparent to the wavelength of
on the medical side, all commonly laser two parts must be compatible in that they must the laser (typically 0.8-1.1µm) and an absorptive
welded. have a similar melt point to be welded effectively. lower plastic layer. The lower layer absorbs the
Medical device manufacturers are subject to Plastics that have very different melting points, laser energy, which heats the plastic and
various approvals from regulatory bodies, and such as polyamide (nylons) and PEEK materials, generates the weld. The lower layer can be
therefore the high level of control afforded by cannot be laser welded because polyamide will engineered to absorb through incorporating
lasers allows them to qualify and document the degrade before the PEEK material begins to certain chemical additives – or, alternatively, if
process to gain these approvals. In addition, melt. In these instances, the manufacturer will both layers are transparent to laser light, an
biocompatibility of a device must be considered use glue. infrared absorber can be applied between the
if it is to be used on a patient and the A second consideration, according to Gary two sheets. Diode, Nd:YAG or fibre lasers are
manufacturing method must not introduce any Broadhead, sales director at UK-based supplier typically used as these emit suitable
foreign materials or contaminants, such as glue. of lasers and laser accessories Laser Lines, is wavelengths.
Balloon angioplasty is one example of a medical how the two parts fit together – ‘is the joint Other factors, such as wavelength and spot
procedure using laser-welded equipment. The design optimised for laser welding?’ he asks. size, must be taken into account for laser
10 laser sYsteMs eUroPe • issue 5 www.lasersystemseurope.com
LSEwin09 pp10-13 Plastics.indd 10 2/12/09 15:42:11
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