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Several Additive Manufacturing (AM) processes are based on the deposition of a powder to form a powder-bed layer-by-layer which typically has a low packing density (35-50%) and consequently hinders the ability of sintering ceramic parts to full density.
The layerwise slurry deposition (LSD) is an innovative process for the deposition of layers in AM. In the LSD, a slurry with no or small organic content is repetitively spread as thin layers on each other by means of a doctor blade. During the deposition, the ceramic particles settle to form thin layers with a high packing density (55-60%). When coupled with a printing head or with a laser, the LSD enables novel AM technologies inspired to the 3D printing or selective laser sintering, but taking advantage of having a highly dense powder-bed. This approach has been successfully applied to silicate ceramics, but implementing technical ceramic slurries is more challenging, because the water is drained too quickly from the suspension into the pores of the previous porous layer forming a cast.
In this presentation, the variables involved in the LSD will be analyzed and the latest improvements in the deposition setup will be described. The application of the LSD to technical ceramics has the potential of generating additive manufacturing parts which in the green state are comparable to those produced by slip casting.
The layerwise slurry deposition (LSD) is an innovative process for the deposition of layers in AM. In the LSD, a slurry with no or low organic content is repetitively spread as thin layers on each other by means of a doctor blade. During the deposition, the ceramic particles settle to form thin layers with a high packing density (55-60%). The LSD therefore shares aspects both of tape casting and slip casting. The LSD differentiates from the classical powder-based AM layer deposition, which typically are able to achieve only a low packing density (35-50%), consequently hindering the ability of sintering ceramic parts to full density. The LSD is coupled with the principles of selective laser sintering (SLS) or binder printing, to generate novel processes which take advantage of the possibility of achieving a highly dense powder-bed.
This presentation will describe the most recent developments in the application of the LSD to technical ceramics, in particular Al2O3 and SiC, discussing potential and issues connected to the layer deposition and the selective laser sintering of such layers.
Kunststoffverarbeitende 3D-Drucker (FDM-Drucker) werden im Hobbybereich und in der beruflichen Ausbilldung immer beliebter und sind mittlerweile weit verbreitet. Es wird häufig noch nicht ausreichend beachtet, dass von diesen Geräten im Betrieb in erheblichen Mengen Gase und Partikel in die Umgebung emittiert werden. Der Vortrag berichtet über einen Vergleich des Emissions-verhaltens verschiedener Materialien für 3D-Drucker und stellt diese in Zusammenhang mit anderen Innenraum-Emissionsquellen.
Laser metal deposition is described with its applications for additive manufacturing. The necessary process chain is discussed, with regard to weld bead dimensions and 3D build-up strategy. Metallurgical cross sections, x-ray and tensile tests are conducted. As demonstrative components, a gas turbine burner and a turbine blade are shown
With ongoing innovation in process technology, the challenges of concrete technology are more and more focused on the rheological optimisation for these processes, since improper mixture stability or poor compaction ability negatively affect the concrete homogeneity and quality. However, along with the increasing complexity of today’s concrete mixture compositions, concrete becomes more prone to failure regarding the casting process. Variable properties of the raw materials typically cause changing workability. The reasons can be found among others in scattering water contents, physical or chemical properties of the cement or varying environmental temperatures. Robustness in the delicately adjusted rheology, however, is of utmost importance for modern and future process technology, from sprayed concrete over pumpable concrete towards 3D-printing, with regard to the long-term strength, the function and the durability. Typically, material induced changes cannot be identified easily due to the complex interactions of concrete constituents. Therefore, a precise and prompt counteraction is impossible. However, it is known that the yield stress can be controlled by addition of supplementary superplasticizer or stabilising agent. In combination with computerized process observation tools that can rapidly interpret and react on changes in the rheology, it is therefore thinkable, that only these two admixture types can adjust the rheology steadily and permanently, regardless of the actual root cause for observed macroscopic rheology change. The presentation will firstly give a comprehensive overview of effects at the interface between pore solution, particles and hydrates, which affect the rheology of fresh concrete. Secondly, ways are recommended how the rheology can be actively manipulated before eventually computerized methods are demonstrated that help to actively and rapidly assess and counteract performance scatter during steady casting processes.
In the present study, Ti-6Al-4V bridge-like specimens were manufactured additively by selective laser melting (SLM) under different laser scanning speed conditions in order to compare the effect of process energy density on the residual stress state. Subsurface residual stress analysis was conducted by means of synchrotron diffraction in energy dispersive mode for three conditions: as-built on base plate, released from base plate, and after heat treatment on the base plate. The quantitative residual stress characterization shows a correlation with the qualitative bridge curvature method. Computed tomography (CT) was carried out to ensure that no stress relief took place owing to the presence of porosity. CT allows obtaining spatial and size pores distribution which helps in optimization of the SLM process.
High tensile residual stresses were found at the lateral surface for samples in the as-built conditions. We observed that higher laser energy density during fabrication leads to lower residual stresses. Samples in released condition showed redistribution of the stresses due to distortion. A method for the calculation of the stress associated to distortion of the parts after cutting from base plate is proposed. The distortion measurements were used as input for FEM simulations.
The combination of tomographic, microstructural data with other experimental techniques and with modeling is paramount, if we want to extract the maximum amount of information on material and component properties. In particular, quantitative image analysis, statistical approaches, direct discretization of tomographic reconstructions represent concrete possibilities to extend the power of the tomographic 3D representation to insights into the material and component performance. This logic thread equally holds for industrial and academic research, and valorizes expensive experiments such as those carried out at synchrotron sources, which cannot be daily repeated.
I will show a few examples of possible use of X-ray tomographic data for quantitative assessment of damage evolution and microstructural properties, as well as for non-destructive testing. Examples of micro-structured inhomogeneous materials will be given, such as Composites, Ceramics, Concrete, and Additively manufactured parts. I will also show how X-ray refraction computed tomography (CT) can be highly complementary to classic absorption CT, being sensitive to internal interfaces.
Additionally, I will present a new technique in our portfolio, Neutron Diffraction, which is extremely well suited to the study of internal stresses, both residual and under external load.
Additive Manufacturing (AM) allows for the unique combination of building highly complex parts with integrated functional design. One particular design feature is known as lattice structures, which provide opportunities for innovative applications in the high-temperature regime of gas turbines. These structures require the development of reliable manufacturing methods to produce dependable structural integrity and geometrical accuracy. Consequently, the subsequent validation of these thin structures must also be examined in depth and differently than with current approaches.
In this study, a holistic assessment of Ni based high temperature lattice structures is pursued, utilizing a systematic design-follows-complexity approach. Single struts of different geometries and orientations are investigated first, then combined to a variety of unit cell types and finally multiplied to complex lattice structures.
Initial test trials with these thin structures proved a dependency of geometrical accuracy, microstructure and structural properties to the AM process setup. The trials underlined the need for design guidelines and a distinction between bulk and thin structures, as they showed differences in microstructural and mechanical behaviour. By application of high resolution, non destructive characterization methods such as computer tomography (CT and µCT), evaluation of defects and the thin structures’ metrology has been performed. First results revealed a number of defects compromising the structural integrity and therefore limiting the lifing behaviour. This was confirmed in destructive testing (e.g. tensile and compression). Furthermore, it was proven that the distribution, the number, the size and the type of defects are also dependent on the AM process setup.
While there are large potentials for use of lattice structures in gas turbine applications, the experiments indicate the strong need for an increased understanding of manufacturing and design for these complex structures and that this gap needs to be bridged.
Laser metal deposition (LMD) has been applied as coating technology for many years. Today, the technologies capacity to produce 3D depositions leads to a new field of application as additive manufacturing method. In this paper, 3D laser metal deposition of titanium alloy Ti-6Al-4V is studied with special regard to the demands of additive manufacturing. Therefore, only the powder nozzle is used to create the shielding gas atmosphere, which ensures high geometric flexibility. Furthermore, specimen with high aspect ratio and hundreds of layers are manufactured, which represent typical features in additive manufacturing.
Additive Manufacturing provides an important enabling technology for the digital transformation of the economy. As an emerging technology it has seen a remarkable development over the last three decades. Nevertheless, it is far from a broad adoption with several barriers to overcome yet. One of the major challenges is the lack of standards. The critical role of standardization for innovation is generally recognized, still the topic too often has been neglected in strategic roadmapping exercises for emerging technologies. Too little is known about the complex dynamics and interrelations of standardization and innovation. The anticipation of standardization needs and the timely and efficient implementation of standards is challenging. This paper aims at contributing to a better understanding of the role that standards play in the multi-dimensional system of innovation. It analyzes the trajectories of innovation in Additive Manufacturing in a systematic and holistic way, focusing on standardization activities with regard to coordination, stakeholders involved, the timing and types of standards developed. Putting standardization in context of the multi-dimensional innovation system of Additive Manufacturing the research shows where standards can support the diffusion of an emerging technology.