How laser plastic welding ensures a leak proof device, while meeting tight tolerances and reducing cycle times.

1. LASER WELDING ■
The balloon is inflated in the vasocon-
striction at 8–12 bar and must remain
leak-tight (photo: eucatech)
Medical Technology. Balloon dilation catheters used to expand the coronary ves-
sels not only must be leak-proof but are also subject to tight tolerances. A CO2 laser
integrated into a welding system ensures the requirements are implemented in se-
ries production, while making for a robust process that offers short cycle times.
Leak-Proof All Round
FRANK BRUNNECKER dredths of a millimeter must also be guar- calized and kept to a minimum. What is
anteed. more, there is no contamination of the
he term “percutaneous transluminal Candidate joining methods were part.
T coronary angioplasty” (PTCA)
refers to the technique of widening
a constricted coronary vessel from the in-
bonding, and laser, hot air and hot-plate
welding. Due to its greatly inferior process
reliability and the additional footprint ne-
Material Bonding with Lasers
side – without open surgery. A PTCA is cessitated of the aforementioned module, There are several ways to laser-weld plas-
performed as a planned intervention for bonding could not be used for the bal- tics. The standard industry method is
chronic coronary heart disease and life- loon. There were numerous advantages through-transmission laser welding. It
saving emergency surgery in acute my- in favor of laser-assisted welding as op- joins one material which transmits the
ocardial infarction. It involves pushing a posed to the alternatives of hot-plate and radiation (wavelengths usually between
balloon dilation catheter bearing a bal- hot-air welding. Aside from much short- 808 nm and 1,064 nm) to one which ab-
loon at the end which expands in the er cycle times, it is characterized above all sorbs it. The beam is focused through the
vasoconstriction at 8 to 12 bar (Title pic- by good controllability and high process laser-transparent part directly onto the
ture). The constriction is expanded to re- reliability and stability. Laser welding absorbing adherend, as a result of which
store the blood. The technique primarily demonstrably enhances product quality. the surface melts. The transparent part
exploits the elasticity of the vessels. Scrap due to excessively high energy in- also becomes plastic due to heat con-
put is reduced because energy input is lo- duction. The two parts are pressed to-
The Correct Method for Joining? gether under a defined force to yield a
reliable material bond. This method pre-
eucatech AG, Rheinfelden, Germany, pro- ! Company Profile supposes, however, that one of the two
duces these PTCA balloon dilation joined adherends absorbs laser light, usu-
catheters for expanding coronary vessels LPKF Laser & Electronics AG, Garbsen, ally via an additive. For the present ap-
(Fig. 1). The central element of the Germany, produces machines and laser plication, therefore, a different solution
catheter is the sophisticated balloon. Its systems for use in electronics manufactur- had to be pursued.
intricate structure imposes special de- ing, the automotive industry and the man- Two undyed plastics can be joined to-
mands on the welding process. Not only ufacture of solar cells. The company cur- gether by lasers which employ longer
must the balloon be leak-tight, but parts rently employs some 370 employees, of wavelenghts of radiation. This approach
tolerances in the range of less than hun- which approximately 20 % work in re- exploits the optical property of thermo-
search and development. In fiscal year plastic polymers: the uncolored plastic
2008, LPKF boosted its sales by 7.6 % to progressively absorbs radiation from a
Translated from Kunststoffe 9/2009, pp. 78–80 EUR 45.4 million. wavelength (λ) of about 1.3 µm, absorb-
Article as PDF-File at www.kunststoffe- www.laserquipment.de ing it almost completey from around
international.com; Document Number: PE110046 2.7 µm. One common method for weld- V
Kunststoffe international 9/2009 51

2. ■ LASER WELDING
welding system uses standard modules ward the catheter. This is achieved with a
supplied by this manufacturer of welding custom-made mirror funnel. It deflects
equipment (Fig. 2). All components, such the beam, which emanates from the scan-
as lasers, coolers, and control unit, are in- ner parallel to the catheter, into the pro-
tegrated into the system housing, yield- cessing zone. The technology for deflect-
ing a compact design. The welding sys- ing the beam close to the processing zone
tem is loaded by hand on account of the is very simple and elegant. It requires a
manufacturing logistics. clean environment, but most manufac-
turing facilities for medical applications
Fig. 1. The balloon dilation catheter expands Precise Positioning would have this anyway.
the coronary arteries to allow blood flow freely Another indispensable production
(photo: LPKF) The core element of the system is the CO2 module is the unit for positioning the
laser with downstream beam shaping and balloon catheter. Since two welds are
ing two transparent polymers, for exam- made at each catheter and the compo-
ple, employs a laser with λ = 1.5 µm. Thin nents can vary in line with normal pro-
materials, such as PTCA catheters, how- duction tolerances, a precision axle with
ever, can also be welded with a low-cost clamping facility is required. The axle
CO2 laser system (λ = 10.6 µm). A laser employed can hold the part in position
beam of this wavelength is absorbed di- not only at the two welding spots, but al-
rectly in the upper film. Melting and so allows incremental positioning via
welding to the lower film proceed solely camera and tilting. User-friendly, fast op-
via heat conduction. After a thorough eration of the system in every day pro-
evaluation of the alternative methods, duction is assured by the human-ma-
CO2 laser welding was deemed to be the chine interface. The system boasts Pro-
best as regards quality and economics. SeT programming software for increased
flexibility. This enables the to quickly
Comparison of Component program the data for welding contour,
and Method feed rate and laser power.
On account of the medical and mechan- Summary
ical requirements, a medically approved
specialty polyamide blend was selected. Altogether positive experiences have been
All the components to be joined are used gained in mass production, both with the
undyed and without addition of additives laser through-transmission welding of
that would change absorption. The Fig. 2. In the laser-beam plastic welding system, plastics and with the welding equipment.
catheter design was modified to suit the the LQ-Individual System, all components, such The robust process guarantees high pro-
requirements of the method, with al- as lasers, coolers, and control unit, are inte- ductivity under the given fluctuations in
lowance for the functional and produc- grated into the system housing (photo: LPKF) material and component geometry. The
tion-specific constraints. Of particular system itself is marked by high availabil-
importance is a joining zone that is read- guidance section. The beam is directed by ity and low downstream costs. This is due
ily accessible to the laser beam, and the a special optics construction into a dy- in part to the low-maintenance laser and
possibility of immobilizing the very del- namic mirror system (x-y scanner). reliable mechanical and electrical com-
icate components in a fixture. Downstream of the scanner is an F-Theta ponents. ■
A system for producing the part was optics system, which focuses the beam in-
then developed in collaboration with the to the processing plane. Since the cir- THE AUTHOR
Plastics Welding Division of LPKF Laser cumference of the balloon catheter has to DIPL.-ING. FRANK BRUNNECKER, born in 1977, is
& Electronics AG, Erlangen, Germany. be radially welded without being moved, head of the Plastics Welding Division of LPKF in Er-
The customized laser-beam polymer the laser beam needs to be deflected to- langen, Germany.
52 © Carl Hanser Verlag, Munich Kunststoffe international 9/2009