This paper investigates the microstructural and mechanical behaviour of overlap micro-joints produced by a blue laser system with a wavelength of ~450 nm. AISI 316L stainless steel was used to produce assemblies of 20 layers of 25 µm micro-foil welded to a single 200 µm foil. The welding speed was varied from 6.5 m/min to 9.5 m/min in incremental steps of 1.0 m/min whilst the power was kept at a maximum output level of 500 W. The joints were analysed for fusion zone microstructure, crystallographic grain structure, microhardness distribution and lap shear and T-peel strengths. Interface width and penetration depth were used as key quality indicators to characterise the fusion zone microstructure. The welding speed modulation indicated that the penetration depth can be easily controlled during blue laser welding. The mechanical strength was evaluated by performing lap shear and T-peel tests. The results indicated that the blue laser welding can have a considerable impact on weld geometry and joint strength as it can reduce discontinuities in welded regions and generate good mechanical properties. This study demonstrated for the first time that the blue laser can be successfully implemented for multiple stack-up joining of stainless steel.

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Blue laser welding of multi-layered AISI 316L stainless steel micro-foils

In-depth evaluation of laser-welded similar and dissimilar material tab-to-busbar electrical interconnects for electric vehicle battery pack

The qualification of production systems that enable reliable and stable production processes is a major challenge in manufacturing large-format lithium-ion batteries. During cell assembly, the electrode sheets of the anode and the cathode are stacked, and are electrically contacted by a welding process. It was shown that laser beam welding employing a beam source in the green wavelength range is a promising joining approach in terms of high productivity. Therefore, the influence of the process parameters, such as the laser power, the welding speed, the pulse frequency, and the pulse duration, on the weld seam quality was investigated. Particular emphasis was placed on the mechanical strength of the weld seam. Statistically planned experiments were used to determine feasible parameter sets for welding the most common current collectors of lithium-ion battery electrodes, copper (Cu), and aluminum (Al). The influence of the individual process parameters on the tensile shear force was evaluated. Stacks of 40 metal foils were welded with a thin metal sheet in lap joint configuration. Based on an analysis of the requirements for minimum mechanical seam strengths, this study confirms that laser beam welding using a green high-power disk source is an auspicious process for the internal contacting of lithium-ion batteries.

/pdf/laser-welding-of-current-collector-foil-stacks-in-battery-33c9zzlju0.pdf

Laser welding of current collector foil stacks in battery production–mechanical properties of joints welded with a green high-power disk laser

High-energy density beam processes for welding, including laser beam welding and electron beam welding, are essential processes in many industries and provide unique characteristics that are not available with other processes used for welding. More recently, these high-energy density beams have been used to great advantage for additive manufacturing. This review of the literature serves to provide an overview of the evolution of the laser and electron beam processes including the fundamental nature of the beam itself and how such a high-energy density beam has been applied for welding. The unique nature of each process regarding weld bead formation and penetration, and metallurgical considerations are covered in detail. In addition, the evolution of monitoring systems for both characterization and control of these beam processes is reviewed. Over 500 references have been cited in this comprehensive review that will allow the reader to both understand the current state-of-the-art and explore in more detail the fundamental concepts and practical applications of these processes.

A review of high energy density beam processes for welding and additive manufacturing applications

Effects of power modulation on behaviours of molten pool and keyhole during laser–arc hybrid welding of pure copper

Welding copper to itself and other metals is challenging using conventional welding techniques. The process window for welding copper with an infrared (IR) laser, resistance welder, or an ultrasonic welder is very narrow. In the case of the infrared laser, the high reflectivity at these wavelengths makes it difficult to couple the power into the material and control the temperature of the weld puddle. In the case of ultrasonic and resistive welding, the high thermal conductivity of the material and the tendency to create particles cause less than ideal welds. These fundamental problems can be overcome by using a laser with a wavelength that is highly absorbed by these materials. This paper will present recent welding results using a fiber coupled 500-W blue laser system coupled to a welding head to deliver a 215 μm spot size and an average power density of 1.6 MW/cm2. These results will be compared with the authors’ previous results from a free space delivered laser system that was the prototype for the 500-W fiber coupled laser. The fiber coupled laser system performance exceeded the free space performance because of two factors: (1) the welding was able to be performed at normal incidence (90°) to the surface allowing for greater power coupling into the copper and (2) a smaller spot size with a higher power density was used (1.6 MW/cm2 vs 398 kW/cm2). Tests on welding battery components, including stacks of foils, buss bars, hairpins (for motors), and other components, with no porosity and no spatter will be covered. Both copper and mixed metals welding results will be presented. Tests have also been performed with 1 kW of laser power from a processing head with a 400 μm spot size and an average power density of 800 kW/cm2. Both systems have enough power density to initiate the keyhole welding process in copper, stainless steel, and aluminum. The difference in welding speeds for these two systems will be compared in this paper.

Laser welding components for electric vehicles with a high-power blue laser system

This paper will report on the first full penetration bead on plate tests of a 1 mm thick copper plate with a 600-W blue laser with nominal spatter remaining on the surface. The 600-W continuous wave laser is focused to a spot size of approximately 200 μm, resulting in an average intensity at the surface of the part of 2.1 MW/cm2. This intensity is well above the power density required to initiate and sustain the keyhole in the part. During the welding process, the keyhole is observed to form rapidly, and once full penetration is achieved, the molten puddle exhibits a very stable surface indicating low turbulence in the weld puddle as the weld progresses. The stable welding process is observed over a wide range of welding speeds and with an Ar-CO2 cover gas for suppressing the surface oxidation during the welding process. This ability to create a stable keyhole weld can be attributed to the high absorptivity of copper in the blue [E. Spisz, A. Weigand, R. Bowman, and J. Jack, “Solar absorptances and spectral reflectance's of 12 metals from temperature ranging from 300 to 500 K,” NASA TN D5353 (1969)]. The blue laser light is uniformly absorbed by the walls of the keyhole during the welding process; however, when instabilities in the keyhole arise due to the turbulence in the melt puddle, the heat input is maintained, and the keyhole remains stable.This paper will report on the first full penetration bead on plate tests of a 1 mm thick copper plate with a 600-W blue laser with nominal spatter remaining on the surface. The 600-W continuous wave laser is focused to a spot size of approximately 200 μm, resulting in an average intensity at the surface of the part of 2.1 MW/cm2. This intensity is well above the power density required to initiate and sustain the keyhole in the part. During the welding process, the keyhole is observed to form rapidly, and once full penetration is achieved, the molten puddle exhibits a very stable surface indicating low turbulence in the weld puddle as the weld progresses. The stable welding process is observed over a wide range of welding speeds and with an Ar-CO2 cover gas for suppressing the surface oxidation during the welding process. This ability to create a stable keyhole weld can be attributed to the high absorptivity of copper in the blue [E. Spisz, A. Weigand, R. Bowman, and J. Jack, “Solar absorptances and spectr...

M. S. Zediker

Papers

Laser welding components for electric vehicles with a high-power blue laser system

Stable keyhole welding of 1 mm thick copper with a 600 W blue laser system