14-07-2012, 11:16 AM
Laser Welding Optical System
Laser Welder - Presentation 060117A.ppt (Size: 1.98 MB / Downloads: 135)
Choice of polymers
Generally all thermoplastics and thermoplastic elastomers can be welded to each other - and, moreover, many material combinations are also possible, provided the two melting temperature ranges overlap sufficiently and they are chemically compatible.
Unlike conventional techniques there are not yet any detailed and significant charts of laser welded material combinations. The current charts on ultrasonic laser welding may be taken as a first orientation guide. Weldability is determined by different factors of the component: tensile force, compression density, surface manipulation etc. as well as by the supplier of the polymer material.
Choice of suitable laser
For polymer welding using the transparent-absorbing overlap method diode lasers (808, 940 nm) and also cw Nd:YAG lasers (1064 nm ) are the most suitable lasers.
Diode lasers are designed with several optimal positioned single emitters as used in CD players. An appropriate optical refocussing allows these lasers to be focussed on the same welding spot. The technical design is very compact and costs are very attractive. Due to the simple scalability, laser sources with only few Watts up to several thousand Watts can be built. A wide range of different wavelengths is available, the standard wavelengths of 808 and 940 nm have the best availability at low costs. In comparison with conventional lasers with comparable power, such as Nd:YAG lasers, the beam quality, i. e. focussability of the laser beam, is less good. For many polymer welding applications, however, this is sufficient, so that diode lasers can be used for these applications.
Nd:YAG lasers are solid-state lasers which have been used in industry for more than three decades. For polymer welding, cw lasers in multi mode are used. The beam quality is considerably better even in power-optimized versions than in comparable diode lasers. Main applications are those with small focal diameters and scanner heads which require high focussability. Wavelength is here 1064 nm.
Laser Benefits
Laser technology features numerous process-related advantages in comparison to conventional joining techniques, such as glueing, ultrasonic-, vibration- or (heating element) hot stamp welding. Most important here are flexibility and consistent quality of welds.
The quality of a laser welding seam can usually compete with any conventional technology. Tensile shear force and pressure cycle tests show that a laser weld is at least as strong as a comparable ultrasonic welding seam.
Moreover, laser welding does not generate any micro particles. This is a significant advantage in particular for fluid reservoirs and medical components.
As the laser applies the melting energy tightly localized, very compact structures with welding seams extremely close to heat-sensitive components can be realized. Also, there is no melt ejection and therefore no distortion with laser welding. Another advantage is, that only as much as needs to be welded, is actually heated: ”Wywiwyw“: what you weld is what you want!
Lasers work without contact and do not show any wear. The quality of the weld remains consistent and the component shows the corresponding quality. Moreover, the components do not have to be preprocessed before welding - this fact also contributes to a constant welding quality. It has been proven that the reject rate with laser welding can be reduced to a very attractive minimum compared to conventional technologies.