THE EVOLUTION OF LASER WELDING

Laser welding with pulsed Nd:YAG lasers is the technique of choice for applications requiring high precision, reduced heat affected zone, material purity and surface quality.

Typical applications include manufacturing of medical devices, prostheses and human implant devices, jewelry and watch manufacturing, opto-electronic device packaging, photonic components fabrication and microelectronic component production such as DVD/HD reader pick ups.

These applications have set new standards in the stability and beam quality requirements of laser spot welders due to typical joint width requirements of some tens of microns. Such applications hardly tolerate the limits of traditional flash-lamp pumped Nd:YAG laser welders.

Requested repeatable laser spot sizes of 0.1 mm or less represent a problem for traditional lamp pumped pulsed YAG lasers, since typical beam quality of such lasers is poor, as well as their pointing stability, which results in randomly fluctuating welding spot shape and position on the scale of tens of microns. Even if fiber optic delivery is used, such lasers can usually only be coupled into fibers with cores no smaller than 0.2 mm in diameter, which leads to distorted laser spots when focused at less than 0.1 mm.

Precision welding of fine mechanical parts can also require strict control of laser peak power and control of laser pulse shape in order to obtain consistent optimization of micro-welding spots.

Flash-lamped pumped lasers naturally show peak power fluctuations due to lamp flash statistics and lamp deterioration. Furthermore very few lamp power supplies allow the control of complex power profile of laser pulses, with the restriction that only slowly varying pulse shapes can be fully controlled.

Spot welding techniques based on pulsed lamp-pumped lasers continue to suffer from very low energy conversion efficiency which results in the necessity of noisy and cumbersome water cooling systems.

With the XELL, very small and consistent laser spots are created. Therefore the energy required to create a typical micro-weld is substantially lower than with the corresponding lamp pumped laser spot welder. For this reason, Heat Affected Zone (HAZ) is also greatly reduced. Current control of diode lasers through high precision power supplies requires lower currents at much lower voltages as compared to flash-lamps, thus a superior output power pulse profiles are possible, even in very fast transients. High conversion efficiency means small footprint and complete air cooling.

Perhaps best of all, with the XELL, expected diode lifetime is in the order of one billion shots and so the laser is essentially “set and forget”.

A monitor photodiode can be used to close a control loop allowing operation in "power mode" rather than "current mode" so that users can program an effective output power profile that will be performed by the laser, spot after spot, independently of diode age or other component degradation. In this case, laser power repeatability is better than 1% for the whole device lifetime.