System and process development for functionalization of electrical components by laser-based gold micro deposition
Tobias Schmid M.Sc., Dr.-Ing. Dipl.Wirt.-Ing. Henning Janssen, Prof. Dr.-Ing. Christian Brecher

During the manufacture of electrical contact components, the contacts are coated with precious metals. Currently, energy- and resource-intensive electroplated coatings are used. A sustainable alternative is the local functionalization of sheet parts using small gold spots with the appropriate system technology for laser-based micro wire deposition. However, the necessary process reliability and required short cycle times represent a challenge for the technology. Within this paper, the system development of a stand-alone coating system is described. The approach presented is based on a laser beam deflection unit, fully automatic laser system control, a 5-axis wire head and a quality assurance system. An analysis of the deposition results was carried out, taking into account crucial process parameters. The resource efficiency study shows significantly reduced gold usage through local sustainable coating. Almost 100% material utilization is achieved, while gold spots geometry and position can be adjusted and replace the full surface electroplating coating.

Keywords: Laser-based gold coating; electrical contacts; gold wire deposition; laser micro deposition; environmentally friendly coating

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Effect of femtosecond laser shock peening on surface morphology and hardness of nickel titanium alloy
Hao Wanga, Evgeny L. Gurevich, Andreas Ostendorf

Nickel-titanium alloy (NiTi) has been widely used for the fabrication of microelectromechanical and body implants, so it is very important to enhance its surface mechanical property. Laser shock peening as a new and important surface treatment technique has been used to enhance the mechanical properties of different metal materials. Normally, the nanosecond laser with pulse-width between 5 ns and 20 ns is used to induce a high-pressure shock wave that can generate plastic deformation in the top layer of metals. In this paper, the surface morphology and hardness of NiTi alloy after femtosecond laser shock peening in the air are studied, which shows that the surface roughness and hardness increased after femtosecond laser treatment.

Keywords: nickel titanium alloy; laser shock peening; femtosecond laser; surface morphology; hardness

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Interaction between laser radiation and antifouling coating underwater
Stanislav Zimbelmann, Benjamin Emde, Jörg Hermsdorf, Tim Heusinger von Waldegge, Dorothea Stübing, Markus Baumann, Stefan Kaierle

Biofouling on a ship´s hull has an enormous economic impact on its operation. Increasing biofouling leads to the introduction and spread of invasive species, an elevated frictional drag in the water, an increased fuel consumption and thus an additional emission of greenhouse gases. In this context, the prevention or removal of biofouling is essential. Conventional, mechanical in-water-cleaning methods have several ecological and regulatory disadvantages. In the context of a laser-based underwater ship cleaning, which is currently under development, we investigated the interaction between laser radiation and a self-polishing copolymer antifouling coating. Important process parameters were investigated to determine the laser power damage threshold of the SPC coating. This includes the measurement of the reflection- and the surface properties of the SPC coating.

Keywords: laser; water; ship hull; biofouling; cleaning; ecofriendly

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Influence of multi-pass laser hardening on residual stress and distortion
Yang Lu, Heiner Meyer, Tim Radel

Laser hardening is used to harden the surface layer with minimal distortion and to induce residual compressive stresses. Within the literature, the approach of increasing the hardness and hardening depth by multi-pass laser hardening based on accumulation effects is shown. In this study, the effect of this approach is investigated on the residual stresses and distortion of normalized AISI 4140. The multi-pass laser hardening is carried out using a continuous wave laser with a rectangular beam shape using different process velocities and number of passes without heat accumulation between each pass. The results show that the compressive residual stresses at the surface slightly decrease with number of passes. Meanwhile the compressive residual stresses in the depth of the hardened zone increase with number of passes, along with an increase of the width (FWHM) of the diffraction peak in XRD spectrum. Nevertheless, for a comparable hardening depth, there is less distortion at one-cycle phase transformation with low scanning speed compared to the multi-cycle phase transformation with higher scanning speed. These findings indicate that multi-pass laser hardening could be beneficial for industrial application due to a larger phase-transformed zone with higher compressive residual stresses in depth and larger hardening depth, if the increased distortion is acceptable.

Keywords: Laser hardening; Multi-pass hardening, Phase transformation, Residual stress, Distortion

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Laser cleaning as a productive surface post-treatment method for L-PBF parts
Markus Hofele, Johannes Neuer, Malena Lindenberger-Ullrich, Jochen Schanz, David K. Harrison, Anjali K. M. De Silva, Harald Riegel

The additive manufacturing technique Laser Powder Bed Fusion (L-PBF) offers the opportunity to directly build solid metal parts with less geometric restrictions, low porosity and good mechanical properties. However, the surface of the parts exhibits a rough surface with massive adherent powder combined with an oxide layer on it. Laser cleaning provides the possibility of a contact-free and full-automatable surface treatment with high area rates.
This work deals with the investigation on laser cleaning of L-PBF surfaces made of Aluminium AlSi10Mg. The laser cleaning is investigated with a nanosecond pulsed fibre laser by variation of the pulse energy and single pulse fluency. The ablation efficiency is analysed by means of SEM, WLI and microscopic images. Dust and oxide layers can be effectively removed. Adherent powder particles can be partly removed. Fluencies more than 13.2 mJ/mm² are causing surface remelting and beyond 30.8 mJ/mm² surface structuring occurs.

Keywords: Additive Manufacturing; Laser Powder Bed Fusion (L-PBF); Post-Processing; Laser Cleaning; Surface-Treatment