KEYWORDS: Copper, Cladding, Laser processing, Near infrared, Laser systems engineering, Fiber lasers, Absorption, High power lasers, Laser sources, Additive manufacturing
Today, high performance components rely on a controlled heat dissipation by copper layers, which can be applied by laser cladding with lasers in the near-infrared (NIR) wavelength. However, current cladding processes are restricted to copper alloys with reduced heat conduction in order to achieve a sufficient melting of the material. The challenge of pure copper is the high reflectivity in the NIR wavelength range and the variation of the heat dissipation during the melting of the copper material. This leads conventionally to an undefined energy coupling into the substrate and process instabilities, which can cause a variation in the melting depth and pores in the layers. With the application of a laser wavelength of 450nm, the laser absorption in pure copper is highly improved and similar to alloyed copper or even steel, which allows for a reproducible melting even of pure copper material. This processing opportunity is enabled for the first time with the development of a novel high power blue laser source with 1kW output power at 450 nm wavelength in continuous wave mode, which is applied for the cladding of pure copper powder. In this contribution we will demonstrate the performance of a high power blue laser cladding process of pure copper powder on steel and on copper substrate. The assessment of the resulting homogeneity and reproducibility of the resulting copper coatings give new perspectives for conventional applications such as heat pipes or heat dissipation layers but also for new applications such as pure copper components produced by additive manufacturing.
Spatial and spectral emission characteristics and efficiency of high-power diode laser (HPDL) based pump sources
enable and define the performance of the fundamental solid state laser concepts like disk, fiber and slab lasers.
HPDL are also established as a versatile tool for direct materials processing substituting other laser types like CO2 lasers
and lamp pumped solid state lasers and are starting to substitute even some of the diode pumped solid state lasers. Both,
pumping and direct applications will benefit from the further improvement of the brightness and control of the output
spectrum of HPDL.
While edge emitting diodes are already established, a new generation of vertical emitting diode lasers (VCSELs) made
significant progress and provides easy scalable output power in the kW range. Beneficial properties are simplified beam
shaping, flexible control of the temporal and spatial emission, compact design and low current operation. Other
characteristics like efficiency and brightness of VCSELs are still lagging behind the edge emitter performance.
Examples of direct applications like surface treatment, soldering, welding, additive manufacturing, cutting and their
requirements on the HPDL performance are presented. Furthermore, an overview on process requirements and available
as well as perspective performance of laser sources is derived.
Within the plastic industry laser transmission welding ranks among the most important joining techniques and opens up
new application areas continuously. So far, a big disadvantage of the process was the fact that the joining partners need
different optical properties. Since thermoplastics are transparent for the radiation of conventional beam sources (800-
1100 nm) the absorbance of one of the joining partners has to be enhanced by adding an infrared absorber (IR-absorber).
Until recently, welding of absorber-free parts has not been possible.
New diode lasers provide a broad variety of wavelengths which allows exploiting intrinsic absorption bands of
thermoplastics. The use of a proper wavelength in combination with special optics enables laser welding of two optically
identical polymer parts without absorbers which can be utilized in a large number of applications primarily in the
medical and food industry, where the use of absorbers usually entails costly and time-consuming authorization processes.
In this paper some aspects of the process are considered as the influence of the focal position, which is crucial when both
joining partners have equal optical properties. After a theoretical consideration, an evaluation is carried out based on
welding trials with polycarbonate (PC). Further aspects such as gap bridging capability and the influence of thickness of
the upper joining partner are investigated as well.
In this contribution we evaluate laser scanning approaches for the interconnection of the 31 electrical contacts of a MWT
back-contact solar cell. The selective energy deposition with a laser system allows the minimization of thermomechanical
stress in the wafer, but requires adapted scanning strategies to prevent damages in the solar cell top layer.
The laser scanning process of the MWT solar cell is conducted in combination with a composite foil as an interconnector
and a pre-dispensed solder paste. This approach is evaluated regarding the joining quality of the interconnection as a
function of the scanning strategy.
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