Aluminum Laser Welding

As for any welding technology, aluminum and aluminum alloys present a challenge for laser welding. Generally, 1xxx, 2xxx and 3xxx are ok however beyond that care and suitable testing is needed, as crack sensitivity and porosity increase. Note for package sealing 4047 is used with 6061 to provide a weldable combination.   For macro welding applications > 1mm / 0.04” penetration beam mode shaping can be used to increase weldability. 

Defined by the M2 "M-squared" number, this refers to the power distribution across the beam and how efficiently the laser can be focused.  The M2 value is a ratio of the actual laser with the perfect laser that has an M2 of 1 with a purely Gaussian profile. Different processes require different M2 lasers. For example, precision laser cutting uses a low M2 laser whereas many welding applications use a high M2 laser 

Joint geometry in which two pieces of material are placed side by side and the weld is made at the interface between the two materials 

Refers to how the laser power is conducted as heat from the top surface into the material. Typically, conduction welding uses relatively low power densities for a laser, around 0.5 MW/cm2. As the weld is formed by heat conduction the weld nugget is shallow and wide, with an aspect ratio (depth/width) <1 

A laser that produces output that remains on continuously until turned off. 

 Copper has a high reflectivity to fiber and Nd:YAG 1 micron wavelength, noting that laser mirrors are made from copper! The challenge is to have sufficient power density to overcome the high reflectivity to start the welding process, but then not overpower the weld when the keyhole formation significantly reduces reflectivity.  Single mode fiber lasers can weld copper, which can be further enhanced by using scan heads or wobble heads to create required weld dimensions. To solve the reflectivity issue, blue and green wavelength lasers can be used, this wavelength shift from 1 micron significantly reduces reflectivity enabling even conduction mode welding of copper.  

A joint geometry in which the materials are placed one on top of another. The weld penetrates the top layer into the second layer, creating the weld.  

Contains lenses and mirrors that direct and focus the output from the laser delivery fiber onto the work piece.   There are 3 categories of focus head; fixed that simple collimate and focus the laser, scan heads that also can move the laser, and wobble heads that superimpose a small high frequency pattern onto the weld motion for single mode welding applications.   

Diameter of the laser spot on the work piece. Note that this is not the same as the weld width, which in many cases is larger than the focused spot size.  

Describes a laser with a flat power density distribution across the beam. Many micro welding laser have flat top modes, which can have M2 values > 50. 

A CW laser can also produce pulses of light output. The peak power does not exceed the laser’s rated average power and is known as gating or modulating the output.

Describes the power distribution in the laser cross section that has a maximum at the beam center which drops away similarly to a bell curve to the edges 

Assessing weld quality during the laser welding process. More recently the use of AIML learning algorithms are increasing G/NG accuracy and enabling fault diagnosis. 

When the laser power density is increased beyond 1-1.5MW/cm2 a narrow, vaporized element forms that acts like a conduit delivering laser power deep into the material. This is known as the keyhole or capillary. For seam welding the keyhole is maintained by the vaporization pressure that exceeds the surrounding liquid pressure of the molten metal. For spot welding it is maintained for the duration of the pulse. It should be noted that the keyhole is highly dynamic during the welding process even for stable welding conditions.  

Characterized by deep narrow welds with aspect ratios greater than 1.5. The weld depth can range from 0.5mm / 0.02" to beyond 1" depth. 

Joint geometry in which the parts are placed one on top of the other.  Offers the largest fit-up tolerances, with no requirement for joint following.  

There are a number of lasers used in micro welding, including pulsed Nd:YAG, CW fiber, QCW fiber and laser diodes.  For many legacy applications the pulsed Nd:YAG lasers has a massive install base.  However, for new applications and projects the QCW fiber laser is most commonly used.

Are lasers with M2 squared values typically > 2. The laser resonator and medium allow the amplification of modes beyond the Gaussian.  

The original pulsed micro welding laser, the medium is Yttrium Aluminum Garnet that is doped with Neodymium. 

The general term that covers all the optical elements in the focus head, and includes the collimator lens, dichroic mirror, focus lens and cover slide.  

Pulsed laser parameter that directly controls weld penetration that can be controlled and programmed on the laser. The units of peak power are watts (W).  

When a keyhole is formed, metal vapor is ejected above the melt pool. This acts to ionize the surrounding gas, which can be observed as a white plume above the weld.  

Trapped pores and gases in the weld are called porosity, commonly occur when welding with too much power or when welding aluminum alloys. 

The energy contained within a pulse. Product of peak power x pulse width 

Duration of the laser pulse.  

In many cases square pulses are used, however in some cases according to the material and application shaping the pulse improves the weld. Commonly, pulse upslope and downslope are used. 

Can operate in either CW, pulsed or modulated mode. This laser was developed to replace pulsed Nd:YAG lasers for welding and drilling. 

The weld is made along a length, produced by keeping the laser turned on in CW mode or by placing a series of spot welds on a part.  

Provides an inert atmosphere for the weld to minimize oxidation and the detrimental effects of the weld plume on the laser 

Refers to small core diameter fibers, between 10-20 microns, that restrict the laser to a single transverse mode that results in a power density cross section through the laser that has a high central maximum that falls off sharply.   Single mode lasers have the lowest M2 squared value, between 1.1-1.3.