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Nd:YAG versus fiber laser welding – What are your options?

Posted by Geoff Shannon on Wed, Nov 02, 2016 @ 12:30 PM

Are you looking to use lasers for micro welding? If so, you have four excellent options: pulsed neodymium-doped yttrium aluminum garnet (Nd:YAG) and three different fiber lasers: continuous wave (CW) fiber, quasi continuous wave (QCW) fiber, and nanosecond fiber. In today’s post, I am going to compare the pulsed Nd:YAG laser with the three fiber laser options, and give some general comments on why and when one might be chosen over the other. I’m going to follow that up with another post with more information on how to choose.

First up is Nd:YAG – this one has peak powers and pulse widths perfect for micro welding

The Nd:YAG laser uses neodymium as the active gain medium, doped into a host crystal of yttrium aluminum garnet. The laser’s simple optical design includes a power supply that drives and controls the flashlamp voltage and allows precise control of peak power and pulse width during the laser pulse using internal optical feedback.

The Nd:YAG laser also offers high peak powers in small laser sizes, which enables welding with large optical spot size. This translates to maximized part fit-up and laser to joint alignment accommodation. The pulsed Nd:YAG laser has been around for many decades and is a very popular option. I would say it is best suited to spot welding application under 0.02-inch penetration and seam welding heat-sensitive packages. See below for a few examples.

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Wire to ring spot weld

Electrical connections

Medical tool weld

Looking for fine focus with selectable beam quality? Go with a fiber laser

A fiber laser is generated within a flexible doped glass fiber that is typically 10 to 30 feet long and between 10 and 50 microns diameter. Ytterbium is usually used as the doping element. You do not have to align the medium to cavity mirrors, nor maintain optics and alignment. In fact, it’s such an efficient lasing process that this laser can be small, air-cooled, and provide high wall plug efficiencies. Fiber lasers offer great “focusability” and a range of beam qualities, which can be tuned for each welding application.

So which kind of fiber laser? Here are the options:

Continuous wave (CW)

With a CW laser, the laser output remains on until being turned off. For spot welding either a single weld or a seam, the laser output can be modulated – this means the laser is turned on and off rapidly. The CW laser’s peak power is the same as its maximum average power, so focused spot sizes are generally under 100 microns. CW fiber lasers are usually a good choice for general seam welding up to 0.06-inch depth for a 500W laser, high speed seam welding of same and dissimilar materials, and producing spot welds below 100 microns in diameter.

Quasi-continuous wave (QCW)

The QCW fiber laser’s peak power and pulse width characteristics are similar to those of the Nd:YAG laser. The QCW lasers offer single mode to multi-mode options with spot sizes from 0.001-inch to 0.04-inch. These lasers also shine in small spot size applications and penetration applications, although they really can handle many micro welding applications. The figure below provides a few QCW fiber laser application examples.

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Cross section of 0.06” deep weld for thick aluminum package seam sealing

Guide wire weld

Sensor seam weld

Nanosecond

The nanosecond fiber laser is a relatively new addition to the family. Often used for laser marking applications, nanosecond fiber lasers actually make a very cost effective welding solution. The nanosecond laser provides multi-kilowatt peak power, but with pulse widths around 60-250 nanoseconds that can be delivered between 20-500 kHz. This high peak power enables welding of almost any metal, including steels, copper, and aluminum. The nanosecond fiber laser’s very short pulse widths means you can get very fine control for welding small parts. This one is also a good choice if you need to weld dissimilar materials. See below for examples.

 

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Low volume battery tab welding

Top view of weld 0.0008” thick foil

Cross section of seam weld using the “wobble” function in 250 micron thick titanium

 

So stay tuned for more discussion on how to select the right one for your laser welding application. Spoiler alert: In some cases, several options may work; in that case, cost of ownership and serviceability can tip the scales.


 

Topics: fiber laser welding, laser welding

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