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News Release from: Rofin-Baasel UK | Subject: Laser welding of polymers
Edited by the Engineeringtalk Editorial
Team on 23 December 2003
Laser welding of polymers
Current market research forecasts a steadily increasing significance for laser polymer welding technology.
Current market research forecasts a steadily increasing significance for laser polymer welding technology The reason for this is the production of components that are based on innovative joining techniques
This article was originally published on Engineeringtalk on 16 May 2003 at 8.00am (UK)
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For example, sensitive electronic components can be embedded free of dust and humidity, medical instruments with antiseptic surface qualities can be welded or even highly aesthetic sealed components in the telecommunications industry can be realised.
Additionally it can be noted, that the comparatively young diode-based laser technology keeps investment costs low and maintenance intervals negligible.
Rofin-Baasel has a complete laser family for polymer welding: lasers and laser systems with innovative scanning technology as well as compact diode lasers, which can be easily integrated into existing systems by fibre coupling.
The newly launched StarWeld diode laser family comprises diode lasers (SWD) and diode pumped Nd:YAG lasers (SWD-Y) for polymer welding.
Every laser is equipped with galvo deflection heads (scanner) as standard.
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All common laser wavelengths such as 808, 940 and 1064nm are available for polymer welding.
According to the application, users can choose between highly focused micro welding lasers (HQ series, welding spot diameters of 0.15mm and wider) and powerful high-speed lasers (HP series).
In the StarWeld diode, two galvanometer-driven rotary mirrors move the laser beam across the work piece.
Thanks to the high beam quality of the StarWeld diode laser sources it is possible to access comparatively large work pieces.
Typical applications are either quasi-simultaneous welding or contour welding of two-dimensional welding paths.
The centrepiece of the system is the laser module.
The diode modules for direct processing were developed by Rofin subsidiary Dilas: they use a patented principle of beam shaping, which guarantees the laser beam quality required for galvo head technology.
At the same time sufficient laser power can be provided for an economic welding process.
The diode-pumped solid-state laser is based on a Baasel Lasertech patent.
High efficiency and hence good focus ability can be achieved thanks to a special pump cavity for the laser crystal.
A very attractive benefit is that the diode modules can be exchanged in an extremely simple plug and play method - even if the laser power is subsequently upgraded.
PolyScan is the new turnkey laser system for polymer welding, into which any laser with a galvo head from the StarWeld Diode series can be integrated.
Choosing between diode and Nd:YAG lasers allows the flexibility to cater for different requirements.
Applications using contour welding and quasi-simultaneous welding are easily implemented.
The excellent beam quality of these lasers makes them particularly suitable for micro welds, for example in prototype and small batch production.
The system is also optimised as far as ergonomic aspects are concerned.
Loading and unloading as well as system programming is achieved in a comfortable seated position.
The extensive legroom and good access to all essential components guarantee fatigue-free working, even after a complete shift.
The system comprises all necessary modules such as the laser source with galvo head, control unit, power supply and cooling unit.
Via the integrated LCD monitor with a multiscreen function, the beam movements can be programmed and the status parameters can be viewed.
As an option an observation camera for the welding process can be integrated and the picture of the work piece together with the welding process can be displayed on the monitor.
The DLx laser series is based on the proven diode laser series produced by Dilas.
Due to the very compact design of the diode modules, they can easily be integrated into tight system solutions or onto robot arms.
The main application is polymer contour welding, usually with laser powers between 30 and 120W.
The diode lasers are offered with wavelengths of 808 and 940nm, providing significant advantages in particular for the welding of pigmented polymers.
As an option, camera viewing as well as a pyrometer can be used to control the welding seam temperature.
What is new is the additional fibre coupling for these modules, thus homogenising the beam.
This offers significant time saving and quality enhancements for two-dimensional welding.
For precision welding with powers of up to 30W, there is even a fibre with only 400um core diameter.
Thomas Merk, CEO of Baasel Lasertech says: "Our established access to markets of micro technologies has now provided us with very good contacts, for example in the medical device, electronics, automotive or tool and mould making industries".
Company founder and CEO Carl F Baasel adds: "Approximately half of the more than 7000 Baasel lasers and systems have been delivered with galvo heads.
Ideal technological preconditions for the laser polymer welding are opening up here for us".
Laser welding is a relatively new joining technology for thermoplastic polymers, with the following advantages compared with conventional methods: superior visual quality of the weld; nonporous surface; minimal surface contamination; minimal thermal or vibrational stress of the component; and high tear resistance of the weld.
Almost all industrial laser welds are realised according to the overlap principle - in that respect polymer welding differs from welding of metals, where butt-welding is equally significant.
In case of overlap welding of polymers, the upper cover layer is transparent to the laser beam and the lower layer is absorbing.
As the laser wavelength is outside the visible range (400-700nm), the lower and upper layer can be dyed according to functionality in case of many kinds of polymers with special pigments.
Present developments of different kinds of polymers are carrying on in order to weld any kind of coloured or even optically transparent bottom layers.
The advantage of overlap welding is, that the weld forms inside the material.
In case of optically nontransparent components the seam is therefore invisible.
An additional advantage is the localised heat input - it allows welding extremely close to sensitive electronic components.
Welding of two different polymers needs a sufficient overlap of the melting areas on the temperature scale.
As the characteristics of the joint strongly depend on the respective material parameters, it is in most cases difficult to validate a suitable laser solution just on paper.
It is always recommended to make samples in the application lab first.
There are four different processes for laser welding of polymers: contour welding, simultaneous welding, quasi-simultaneous welding and mask welding.
The most extensive market coverage is using contour and quasi-simultaneous welding.
Contour welding means that the laser moves via an axis system or a robot over the welding contour.
In this case, fundamentally, the compact design and fibre coupling of the diode lasers are major advantages.
With a pyrometer the welding temperature can be measured and controlled in many cases.
Using this technique, the acceleration phase of the motion system and possible production tolerances or nonhomogeneities of the workpiece can be compensated.
This technique allows welding of components of almost any size - however, the tolerances of the gap between the two parts, which are to be welded, have to be sufficiently tight.
Quasi-simultaneous welding means that the laser beam is moved quickly over the work piece several times.
Because of the low thermal conductivity of polymers, the welding path heats up gradually and approximately evenly, so that a quasi-simultaneous melting of the entire welding track occurs.
The laser beam is moved only via scanning mirrors to achieve the required speed, and therefore lasers must have correspondingly good beam qualities.
Due to the nature of simultaneous welding, the top part of the work piece moves slightly under pressure towards the bottom part and thus bridges small potential gaps.
It should be mentioned that this method shows very low thermal distortion.
The disadvantage of this technology is, that the complete heat energy for melting must be supplied in a very short time - that is why considerably more laser power is required in comparison to contour welding.
So quasi-simultaneous welding is best suited for smaller components with shorter welding paths. Request a free brochure from Rofin-Baasel UK ...
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