Abstract:The most successful additive manufacturing (AM) technologies are based on the layer-by-layer deposition of a flowable powder. Although considered as the third industrial revolution, one factor still limiting these processes to become completely autonomous is the often necessary build-up of support structures. Besides the prevention of lateral shifts of the part during the deposition of layers, the support assures quality and stability to the built process. The loose powder itself surrounding the built object, … Show more
“…This, in turn, explains why small particles do not pack well when freely settled.Figure (b) illustrates an alternative approach in which a gas flow is established throughout the powder bed. The effect of this gas flow is comparable to the slip casting process, and has shown its potential for the deposition of fine powders (<20 μm particle size) with appreciable packing densities which, however, still not exceed 45% TD when using commercial alumina powders ( d 50 = 17 μm) . Compared to slurry‐based technologies, the low mobility of individual particles in the dry‐state is hindering their free settling to a closed packed configuration in the recoating process, irrespective of the type of recoating unit used.Illustration of the forces acting on each individual particle during layer deposition in: (a) slurry‐based 3 DP and SLS , (b) gas flow assisted powder deposition.…”
Section: Feasibility Of Am Processing Of Monolithic Ceramicsmentioning
confidence: 99%
“…Furthermore, fine ceramic powders are prone to agglomeration and electrostatic charging and, thus, do not pack well. Packing densities of dry ceramic powders in a particle size range from 20 to 100 μm are generally below 50% of the theoretical density (typically between 25% and 45%) . The density also depends on the particular layer spreading technology used, that is, blade, roller etc.…”
Section: Feasibility Of Am Processing Of Monolithic Ceramicsmentioning
confidence: 99%
“…Packing densities of dry ceramic powders in a particle size range from 20 to 100 lm are generally below 50% of the theoretical density (typically between 25% and 45%). 140 The density also depends on the particular layer spreading technology used, that is, blade, roller etc. The use of ceramic suspensions or pastes, on the other hand, enables deposition of very thin layers, down to 10 lm thickness, and the use of finer particulates.…”
Section: Feasibility Of Am Processing Of Monolithic Ceramicsmentioning
Additive manufacturing (AM) is a technology which has the potential not only to change the way of conventional industrial manufacturing processes, adding material instead of subtracting, but also to create entirely new production and business strategies. Since about three decades, AM technologies have been used to fabricate prototypes or models mostly from polymeric or metallic materials. Recently, products have been introduced into the market that cannot be produced in another way than additively. Ceramic materials are, however, not easy to process by AM technologies, as their processing requirements (in terms of feedstock and/or sintering) are very challenging. On the other hand, it can be expected that AM technologies, once successful, will have an extraordinary impact on the industrial production of ceramic components and, moreover, will open for ceramics new uses and new markets.
“…This, in turn, explains why small particles do not pack well when freely settled.Figure (b) illustrates an alternative approach in which a gas flow is established throughout the powder bed. The effect of this gas flow is comparable to the slip casting process, and has shown its potential for the deposition of fine powders (<20 μm particle size) with appreciable packing densities which, however, still not exceed 45% TD when using commercial alumina powders ( d 50 = 17 μm) . Compared to slurry‐based technologies, the low mobility of individual particles in the dry‐state is hindering their free settling to a closed packed configuration in the recoating process, irrespective of the type of recoating unit used.Illustration of the forces acting on each individual particle during layer deposition in: (a) slurry‐based 3 DP and SLS , (b) gas flow assisted powder deposition.…”
Section: Feasibility Of Am Processing Of Monolithic Ceramicsmentioning
confidence: 99%
“…Furthermore, fine ceramic powders are prone to agglomeration and electrostatic charging and, thus, do not pack well. Packing densities of dry ceramic powders in a particle size range from 20 to 100 μm are generally below 50% of the theoretical density (typically between 25% and 45%) . The density also depends on the particular layer spreading technology used, that is, blade, roller etc.…”
Section: Feasibility Of Am Processing Of Monolithic Ceramicsmentioning
confidence: 99%
“…Packing densities of dry ceramic powders in a particle size range from 20 to 100 lm are generally below 50% of the theoretical density (typically between 25% and 45%). 140 The density also depends on the particular layer spreading technology used, that is, blade, roller etc. The use of ceramic suspensions or pastes, on the other hand, enables deposition of very thin layers, down to 10 lm thickness, and the use of finer particulates.…”
Section: Feasibility Of Am Processing Of Monolithic Ceramicsmentioning
Additive manufacturing (AM) is a technology which has the potential not only to change the way of conventional industrial manufacturing processes, adding material instead of subtracting, but also to create entirely new production and business strategies. Since about three decades, AM technologies have been used to fabricate prototypes or models mostly from polymeric or metallic materials. Recently, products have been introduced into the market that cannot be produced in another way than additively. Ceramic materials are, however, not easy to process by AM technologies, as their processing requirements (in terms of feedstock and/or sintering) are very challenging. On the other hand, it can be expected that AM technologies, once successful, will have an extraordinary impact on the industrial production of ceramic components and, moreover, will open for ceramics new uses and new markets.
“…Abdullah reports that powders with HR B 1.25 are considered as freely flowing and that cohesive and nonflowing powders show a HR [ 1.40. In the field of AM, Zocca [20] used HR as the flowability indicator for bulk ceramic powders. However, there are some drawbacks associated with HR, especially when compared to the situation in AM where thin powder layers are created and no compression or tapping is applied.…”
Key in powder-bed-based additive manufacturing is the use of appropriate powder materials that fit to the process conditions. There are many parameters affecting the build process and the corresponding quality of the parts being built. Therefore, an accurate assessment of the powders becomes important. Such an assessment involves, besides others, the powder flowability, which should be sufficient in order to create good-quality powder layers. The current study aims at the development of suitable parameters and values for the qualification of metal powders for selective laser melting (SLM) with regard to their flowability. The powder flowability is assessed by the statistical analysis of the measured powder avalanche angles and the powder surface fractal, which give valuable information about the significance of inter-particle forces. A set of 21 different Fe-and Ni-based powders has been analysed and good correlations between the powder avalanche angles, the surface fractal and the particle shape with the optically evaluated flowability could be derived. The method allows a quantitative powder flowability assessment, which correlates with the experiences for powders for powder-bed-based additive manufacturing, especially for SLM.
“…This approach is also used in AM methods relying on flowability. 28,29 A second important advantage is that contoured or cut tape is readily manipulated, permitting the use of multiple materials in a given layer. An illustration of one use of this is given in Figure 11.1, in which a fugitive tape is used to occupy space during the build which becomes an interior channel after firing.…”
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