Plastics Processing
conventional welding, as high intensities can be
generated for a shorter time period.
The TWIST method is suited to plastic welding
applications requiring varying seam widths or also
in the field of microfluidics, which deals with the
manipulation of very small quantities of fluid and
has applications in inkjet printing and DNA
Image courtesy of SPI Lasers
microarrays. Microfluidic polymer chips will often
require a narrow channel system to be sealed.
TWIST can weld very close to channel edges
without overheating the workpiece, something that
would be difficult to achieve using standard
transmission welding due to extensive heat input.
Fraunhofer ILT has also developed a prototype
machine based on the TWIST process, called the
Twister, which contains a fibre laser, galvo head,
clamping device and control system for welding
small parts. It is currently being used to weld
micro-weld plates for medical diagnostics.
Laser-based plastics welding is still a growing
Car dashboard displays are often produced by selectively removing paint from a transparent plastic
market and laser technology is becoming more with a laser, so when backlit the marks are visible.
accessible, especially through low-cost, high-
efficiency diode lasers. Dilas has established its
Making a mark
Industrial Laser Systems business unit, based in
Mainz, Germany, which targets lower power (fewer Using lasers to indelibly mark plastics is ‘In the majority of cases, marking plastics
than 500W) markets, including plastics welding. relatively commonplace in many industries, involves breaking bonds within the polymer
Increasing laser power enables an increase in speed with applications ranging from marking without actually melting the matrix,’ explains
for plastics welding, but only up to a point. Plastics computer keyboards to inscribing company Gabzdyl. ‘Therefore, laser systems producing
welding involves a process called wetting, where logos onto promotional material. In the high peak power and short pulses are best
the first polymer begins to melt and transfers heat automotive sector, car dashboard displays are suited to marking plastics.’ A short, intense
to the second layer. This takes time and therefore often produced by selectively removing paint burst of radiation will create the mark without
limits the weld speed. Neukum, of Dilas, states: from a transparent plastic with a laser, so the melting the matrix, (melting the polymer
marks can be seen during the day and during reduces the mark’s contrast). SPI’s fibre lasers
The TWIST method is
the night by backlighting the display. As laser are well suited to these sorts of application, as
marking is indelible, there are also many the pulse length can be user-selected to
suited to plastic welding
anti-counterfeiting applications. provide maximum peak power. This is
applications requiring
Laser marking of plastics is usually a advantageous over other laser modules
chemical process that results in a colour containing Q-switches that release pulses of
varying seam widths
change. ‘Not all plastics can be marked using a energy at fixed times.
laser, as the material must be absorptive to the Typically, solid state or fibre lasers operating
‘There are not many applications in plastics wavelength of the laser,’ comments Dr Jack at around 1µm are used for laser marking
welding that require a laser of more than 1kW and Gabzdyl, product line manager at SPI Lasers. plastics. CO lasers operating at 10.6µm can
2
Dilas’ Industrial Laser Systems division has been However polymers, such as polypropylenes be used, but the spot size is larger than diode,
able to serve all enquiries to date with 500W power that are generally transmissive to light in the Nd:YAG or fibre lasers and therefore can’t
or less.’ 1µm wavelength range commonly used for produce fine detail. For more specialist
Leaving aside the more specialised applications, laser marking, can be optimised for laser applications, other laser wavelengths will be
such as microfluidics, plastics welding doesn’t processing through the use of additives. used; for example, Spectrum Technologies
require a high-quality beam that can be focused to Pharmaceutical and chemicals company supplies UV lasers to mark cabling used in the
a very small spot size, as the weld seam is often in Merck produces additives for plastics to aerospace industry. UV lasers have a very low
the order of several millimetres. ‘An expensive laser optimise laser marking. The reaction of laser thermal impact and allow material to be ‘cold’
is not needed for these types of application,’ light with the polymer results in a colour processed, causing no burning, no significant
remarks Broadhead of Laser Lines, ‘and the change either through carbonisation (causing material removal or change in the wire’s
improvements in diode laser technology, with darkening of the material) or foaming mechanical or electrical properties. The UV
lower costs and high efficiencies, has strengthened (resulting in lightening of the material). laser marking operates by rearranging the
the suitability for lasers used in plastics welding Certain additives will enhance the reaction to crystalline structure of TiO mixed into the
2
and I can only see the market growing at a faster produce high-contrast marks, while others sheathing material to create a permanent black
rate than some of the more well-established laser can produce a colour change. mark.
processes.’
12 laser sYsteMs eUroPe • issue 5 www.lasersystemseurope.com
LSEwin09 pp10-13 Plastics.indd 12 2/12/09 15:42:18
Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32