Laser-based powder bed fusion of Ti-6Al-4V structures with different surface-area-to-volume ratios in oxygen-reduced and oxygen-free environment

Titanium alloys, such as Ti-6Al-4V, are particularly susceptible to oxidation, which is why their processing in the laser-based powder bed fusion process is carried out conventionally in a protective gas atmosphere. However, this atmosphere still contains critical residual oxygen levels, which are to be eliminated as part of a new approach. This approach envisages doping the argon protective gas atmosphere with small amounts of the highly reactive gas silane (ratio < 1:1000). The residual oxygen content is particularly critical in filigree and thin-walled structures that have a high surface-area-to-volume ratio and are a typical field of application for this additive manufacturing process. Therefore, this work focuses on the manufacturing of Ti-6Al-4V structures with different surface-area-to-volume ratios in conventional argon (< 200 ppm residual oxygen) and argon-silane atmospheres (< 10-14 ppm residual oxygen) on an innovative laboratory machine. After processing, the specimens are analyzed for surface topography, microstructure, and Vickers hardness. In addition, energy-dispersive X-ray spectroscopy and X-ray diffraction measurements are carried out to further investigate the chemical composition and present phases in the as-built specimens. The influence of the different atmospheres and their residual oxygen content, the surface-to-volume ratio, and possible interactions between them are discussed

Robot based remote laser cutting of three-dimensional automotive composite parts with thicknesses up to 5mm

With the intention to develop a robot based laser cutting process for automotive 3D parts with varying thickness consisting of carbon fibre reinforced plastics (CFRP), strategies of 2D investigations were adapted. The used setup consist of a fibre guided nanosecond pulsed laser with an average power of P L = 1.5 kW, a 6-axis robot and a 3D programmable focusing optic (I-PFO). In a first instance strategies for the remote cutting of material with a thickness of d = 5 mm were developed and optimized concerning cutting efficiency and quality. In a second step the results were transferred to a robot based 3D cutting process. Main challenges are the consideration of the correct angle of incidence, the geometric constancy and the accessibility of the cutting geometry by the I-PFO for complex shaped 3D parts. Therewith, “cutting-on-the-fly” strategies were realized for automated trimming and drilling of large automotive structures

Functional coatings of sol-gel on glass substrate using CO2 laser irradiation

Often Glass products achieve their component functionality only by a specific surface finishing, such as coating or patterning. Compared to vacuum based CVD and PVD coating techniques, the equipment for wet-chemical deposition of sol-gels is less expensive. Heat is needed for a chemical reaction to cure gels and form solid functional layers. In this study, sols with titanium and zirconium were applied on glass substrates by dip coating. The investigated layer thicknesses were in the range between 320 nm and 650 nm. The gel layers were annealed with CO2 laser radiation. Different scanning speeds and laser powers were investigated. Microscope images were used to compare the laser-annealed layers with oven-annealed layers. To conclude, the oven-process can be substituted by laser annealing and additionally enables local patterning. This allows gradient coating solutions for architecture applications

Thermoforming of planar polymer optical waveguides for integrated optics in smart packaging materials

The innovations in smart packaging will open up a wide range of opportunities in the future. This work describes the processing of additive manufactured and planar integrated polymer optical waveguides for use in smart packaging products. The previously published combination of flexographic and Aerosol Jet printing is complemented by thermoforming and thus creates three-dimensional integrated multimode waveguides with optical attenuation of 1.9 dB/cm ± 0.1 dB/cm @ 638 nm. These properties will be the basis to develop smart applications in packaging materials

Juxtaposition of Spin Freezing and Long Range Order in a Series of Geometrically Frustrated Antiferromagnetic Gadolinium Garnets

Specific heat measurements in zero magnetic field are presented on a homologous series of geometrically frustrated, antiferromagnetic, Heisenberg garnet systems. Measurements of Gd3Ga5O12, grown with isotopically pure Gd, agree well with previous results on samples with naturally abundant Gd, showing no ordering features. In contrast, samples of Gd3Te2Li3O12 and Gd3Al5O12 are found to exhibit clear ordering transitions at 243 mK and 175 mK respectively. The effects of low level disorder are studied through dilution of Gd3+ with non-magnetic Y3+ in Gd3Te2Li3O12. A thorough structural characterization, using X-ray diffraction, is performed on all of the samples studied. We discuss possible explanations for such diverse behavior in very similar systems.Comment: Accepted for publication in Physical Review

Influence of Silane-doped Argon Processing Atmosphere on Powder Recycling and Part Properties in L-PBF of Ti-6Al-4V

In the additive manufacturing of metal powders, the residual oxygen in the processing atmosphere plays a crucial role, especially in highly reactive materials like titanium alloys. Besides oxidation of the built parts, it leads to oxygen pick-up into the unmolten powder. Since oxidized particles cannot be removed during recycling, the powder properties deteriorate after multiple uses. In this work, Ti-6Al-4V powder was processed under conventional argon atmosphere (residual oxygen content < 0.01 vol%) as well as silane-doped argon atmosphere (< 0.001 vol% silane in argon). The silane-doping leads to a residual oxygen content of < 10-20 vol%. The powder was sieved and used 5 times for each atmosphere. The powder properties morphology, chemical composition and flowability were analyzed for virgin as well as reused powder. Furthermore, the roughness and relative density of the built parts were evaluated. It was hypothesized that oxygen-free production improves recyclability and thus resource efficiency.Mechanical Engineerin

PROCESS-INTEGRATED ALLOY ADJUSTMENT IN LASER DEPOSITION WELDING WITH TWO WIRES

For Direct Energy Deposition (DED) with wire as filler material, the material selection is mostly limited to commercially available welding wires. This limits the achievable material properties for cladding and Additive Manufacturing purposes. Using a coaxial deposition welding head, in which two different wires can be fed and controlled individually, the alloy composition can be adjusted in the common process zone in-situ. In this study, the two wire materials AISI 316L and ER 70S-6 are used in different mixing ratios to fabricate single weld seams. The different mixing ratios are achieved by varying the wire feed rates. The material content in the weld is varied between 0% and 100% in 20% steps. The weld seams are examined with regard to the distribution of alloying elements, hardness and microstructure. Homogeneous mixing of the two materials was achieved at all mixing ratios. At a content of 40% or more of ER 70S-6 in the weld seam, there was a drastic change in the microstructure and a significant increase in hardness. The microstructure changed from austenitic to ferritic-pearlitic, which was accompanied by an increase in hardness from 170 HV0.1 to 428 HV0.1.Mechanical Engineerin

Additive Manufacturing Under Lunar Gravity and Microgravity

Mankind is setting to colonize space, for which the manufacturing of habitats, tools, spare parts and other infrastructure is required. Commercial manufacturing processes are already well engineered under standard conditions on Earth, which means under Earth’s gravity and atmosphere. Based on the literature review, additive manufacturing under lunar and other space gravitational conditions have only been researched to a very limited extent. Especially, additive manufacturing offers many advantages, as it can produce complex structures while saving resources. The materials used do not have to be taken along on the mission, they can even be mined and processed on-site. The Einstein-Elevator offers a unique test environment for experiments under different gravitational conditions. Laser experiments on selectively melting regolith simulant are successfully conducted under lunar gravity and microgravity. The created samples are characterized in terms of their geometry, mass and porosity. These experiments are the first additive manufacturing tests under lunar gravity worldwide

Combination of Cladding Processes with Subsequent Hot Forming as a New Approach for the Production of Hybrid Components

A new process chain for the manufacturing of load-adapted hybrid components is presented. The "Tailored Forming” process chain consists of a deposition welding process, hot forming, machining and an optional heat treatment. This paper focuses on the combination of laser hot-wire cladding with subsequent hot forming to produce hybrid components. The applicability is investigated for different material combinations and component geometries, e.g. a shaft with a bearing seat or a bevel gear. Austenitic stainless steel AISI 316L and martensitic valve steel AISI HNV3 are used as cladding materials, mild steel AISI 1022M and case hardening steel AISI 5120 are used as base materials. The resulting component properties after laser hot-wire cladding and hot forming such as hardness, microstructure and residual stress state are presented. In the cladding and the heat-affected zone, the hot forming process causes a transformation from a welding microstructure to a fine-grained forming microstructure. Hot forming significantly affects the residual stress state in the cladding the resulting residual stress state depends on the material combination.Mechanical Engineerin

All-fiber, single-mode spectral beam combining of high power Tm-doped fiber lasers

Signal beam combining of Tm-doped fiber lasers can increase the laser output power while simultaneously maintaining the single mode beam quality. We demonstrate an all-fiber integrated dual-wavelength Tm-doped fiber laser with an output power of 36 W by using the spectral beam combining method. The constituent lasers are operating at the wavelengths 1949 and 1996 nm and an in-house-made WDM is used for combination of these two different wavelengths. All-fiber truly single mode power combining is demonstrated for the first time in this wavelength region. © OSA 2015