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. 

The weld depth divided by the weld width is known as the aspect ratio of the weld.  For example, conduction welds with shallow wide welds have aspect ratios < 1.  In contrast keyhole welding with deep penetration depths have aspect ratios >>1. 

Defined by the M2 "M-squared" number, this refers to the power distribution across the beam and how efficiently the laser can be focused.  Low M2 lasers can be focused to smaller diameters and tend to have higher intensities. 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.  

Assessing weld quality during the laser welding process. More recently the use of AI/ML learning algorithms are for G/NG 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.  

Laser is an anacronym that describes how it works, essentially a light creator and amplifier.  There are a number of lasers used in welding, including pulsed Nd:YAG, CW fiber, QCW fiber and laser diodes.  

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

Duration of the laser pulse.  

In many cases square pulses are used, however according to the material and application shaping the pulse can improve 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.