Andy Toms, director at TLM Laser, discusses the benefits that pulsed lasers bring to welding and joining applications within medical device manufacturing.

When it comes to welding and joining metal components, lasers offer distinct advantages over other more traditional processes such as TIG (tungsten inert gas) or micro TIG welding, however those considering laser technology have yet another choice to make, a decision between a CW (continuous wave) laser or a pulsed laser.

Manufacturing processes continue to evolve year on year and as a result, we generally see the introduction of a new technology or process being adopted by forward thinking manufacturing sectors, before the technology becomes mainstream as others realise the benefits it can bring.

This scenario is certainly true of the original transition from conventional TIG and Micro TIG welding to that of laser by medical device manufacturers. Laser welding offered a wide range of benefits including greater precision, and by comparison, a much-reduced heat affected zone, and the fact that the process could be performed with more consistency with less skilled operatives.

Today manufacturers have another choice, that of adopting the latest generation Nd:YAG or pulsed fibre lasers as opposed to using CW lasers. Lasers are able to achieve greater penetration in CW mode than when pulsed welding because they are emitting light continuously. However whilst this might be a valuable attribute in some applications, within medical device manufacturing many components are delicate, and welding in CW mode may still generate too much heat and therefore a larger heat affected zone.

As the name suggests, pulsed lasers produce a series of short pulses at a certain width and frequency. A pulsed laser is capable of producing a peak power that is significantly greater than its average power due to the laser energy being stored prior to release. The pulsed welding process can take just a fraction of a millisecond to complete; and a pulsed laser is capable of producing several pulses per second.  

When deciding whether to purchase pulsed laser technology, either an Nd:YAG laser or a fibre laser, there are also several factors which potential users may wish to consider. Currently Nd:YAG lasers produce higher levels of peak pulse power when compared to fibre lasers. As an example a 200W Nd:YAG laser from Alpha Laser will generate a peak pulse power of 9kW, by comparison a 300W fibre laser from the same manufacturer produces just 3kW of peak pulsed power.

Fibre lasers do offer a number of benefits. The prime advantage is the greater process consistency which the technology offers, together with the fact that there is no loss of quality in the beam over time, a characteristic common with Nd;YAG lasers as the lamps deteriorate. Fibre lasers also deliver better wall plug efficiency and can also easily switch between Pulsed mode and CW mode, if the latter is required for greater levels of penetration when welding.

Due to the very short duration of the pulse from either technology, typically just a few milliseconds in duration, heat entering the part is kept to a minimum, making pulsed laser welding the ideal solution for heat sensitive components or very thin-walled materials.

Pulsed laser welding also tends to work well with reflective metals due to the high amounts of energy being delivered at the onset of the pulse. This intense power at the beginning of the pulse cycle only lasts for a fraction of the total pulse duration. However, it is powerful enough to penetrate the reflective surface of materials such as aluminium and copper, whilst keeping the average power low and in turn reducing heat input. By comparison, a laser operating in CW mode would have to deliver a lot of energy to break through the reflective metal, with the resultant heat potentially causing damage to the part, or in the case of very thin walled items, even destroying the part.

Pulsed laser welding is also the perfect solution for applications where sensitive components, such as electronics are either in close proximity to or encapsulated within a metal enclosure. The very small heat affected zone produced during the pulsed welding process keeps these delicate parts safe.

TLM Laser is the UK distributor for Alpha Laser, manufacturer of both Nd:YAG and fibre laser systems for metalworking applications.

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