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Laser Beam Melting (LBM) offers a high design flexibility and the possibility to create complex metal parts in small batch sizes efficiently. However, several questions regarding the mechanical properties are still not conclusively clarified. In general, the remaining degree of porosity is regarded as major indicator on the parts properties. Other properties such as the resulting residual stresses, the oxygen contents and possible contaminants of the powder or the influence of humidity are less often taken into consideration and difficult to measure. In this work, the mechanical properties for LBM generated specimens out of tool steel 1.2344 are investigated and compared to conventionally fabricated material. The quasi-static properties are comparable to conventionally fabricated materials, whereas a significant impact on the fatigue strength was observed together with a high oxygen content of 569 ppm, with significant oxygen peaks that can be allocated to the fractured area.

There is an increasing demand to enable high throughput experimentation to characterize and develop new materials in a very short time. The investigated hardness measurement method differs from conventional hardness measurements in how the force is applied. The new method is based on laser-induced shockwaves. A shockwave is created with a nanosecond pulsed TEA CO2 laser on top of an indenter. The pressure of the shockwave is used to push an indenter inside a workpiece. A quadratic laser focus area of 4 mm², having a diagonal larger than the indenter diameter, leads to interactions of the laser beam with the surrounding material, which affects the plasma formation and results in heating of the material underneath. Material heating decreases the yield point and accordingly the hardness. Therefore, influence of pulse energy and plasma formation on heating of material are investigated to understand the interaction between the high intensity laser beam, the indenter and the material underneath. It is shown that a 3 mm indenter diameter reduces the maximum estimated temperature of the workpiece (X5CrNi18-10) underneath down to 64°C. With an additional positioning unit in combination with indenter diameter of 3 mm or larger no significant heat input was obtained anymore in the workpiece underneath.

Laser shock forming is a new high speed forming process based on TEA-CO2-laser induced shock waves. In former publications laser shock forming was already presented as a process which can be used for deep drawing, stretch drawing and cutting of thin copper and aluminum sheets. The process utilizes an initiated plasma shock wave on the target surface, which leads to the sheets forming. Several pulses can be applied at one point in order to achieve a high forming degree without increasing the energy density beyond the ablation limit. During the process, pressure peaks in the range of some MPa can be achieved. In order to classify the process in the framework of high speed forming processes, the temporal varying deformation velocity due to different materials have been identified based on a stretch drawing process by using different pulse energies. Therefore a new high speed measurement system based on the shadowing effects is designed and its suitability is shown. The determined strain rate of 520 s-1 meets one of the criteria for the classification of laser shock stretch drawing as a high-speed forming process.

This work investigates the feasibility of a novel method to simultaneously alloy and reinforce a low alloyed Al alloy (i.e., Al6061) during selective laser melting (SLM) via in situ decomposition of zinc oxide (ZnO). Based on Gibbs free energy calculations, an Al6061+6wt%ZnO powder mixture is designed and prepared. The thermal decomposition of ZnO, resulting in the formation of Al oxide and free Zn, necessitates a completely different set of optimised SLM parameters compared to traditional Al alloys. After SLM, it is shown that this method can successfully reinforce the Al matrix with numerous nanometer sized oxide particles (typically ~ 50-120 nm). Despite this clear success to manufacture in situ reinforced Al composites by SLM, the applied method could not avoid partial Zn evaporation (limiting in situ alloying) and could not successfully suppress the cracking that also occurs after SLM of unreinforced Al6061. ispartof: pages:39-43 ispartof: Procedia CIRP vol:74 pages:39-43 ispartof: 10th CIRP Conference on Photonic Technologies [LANE 2018] location:Fürth, Germany date:3 Sep - 6 Sep 2018 status: published

This work investigates the influence of powder size/shape on selective laser sintering (SLS) of a thermoplastic polyurethane (TPU) elastomer. It examines a TPU powder which had been cryogenically milled in two different sizes; coarse powder (D50∼200μm) with rough surfaces in comparison with a fine powder (D50∼63μm) with extremely fine flow additives. It is found that the coarse powder coalesces at lower temperatures and excessively smokes during the SLS processing. In comparison, the fine powder with flow additives is better processable at significantly higher powder bed temperatures, allowing a lower optimum laser energy input which minimizes smoking and degradation of the polymer. In terms of mechanical properties, good coalescence of both powders lead to parts with acceptable shear-punch strengths compared to injection molded parts. However, porosity and degradation from the optimum SLS parameters of the coarse powder drastically reduce the tensile properties to about one-third of the parts made from the fine powders as well as those made by injection molding (IM). publisher: Elsevier articletitle: Effect of Powder Size and Shape on the SLS Processability and Mechanical Properties of a TPU Elastomer journaltitle: Physics Procedia articlelink: http://dx.doi.org/10.1016/j.phpro.2016.08.102 content_type: article copyright: © 2016 Published by Elsevier B.V. ispartof: pages:971-980 ispartof: Physics Procedia vol:83 pages:971-980 ispartof: Laser Assisted Net Shape Engineering 9 International Conference on Photonic Technologies - LANE 2016 location:Fürth, Germany date:19 Sep - 22 Sep 2016 status: published

The most recent developments in high power laser sources and handling optical systems create new options for optimizing the cutting process.However the selection of an optimal configuration is not evident since in laser cutting of metal sheets, the interaction between the laser and the material is geometrically complex. From an energetic point of view, parameters such as wavelength, polarization and beam shape can be optimized for different materials and thicknesses and, in theory, can significantly increase process efficiency. This paper offers an overview of possible techniques for such optimization and discusses their practical implications. ispartof: pages:714-718 ispartof: Procedia CIRP vol:74 pages:714-718 ispartof: 10th CIRP Conference on Photonic Technologies [LANE 2018] location:Furth date:3 Sep - 6 Sep 2018 status: published