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a)
E! NG TIM I N Y N A U DAYS RTUESDAY TO FRID 4 W O M N FRO
ULD O M E E TAV M FIT TH O T OME –C
E VISIT TH ING AREA D L U O M 21. International Exhibition for Metalworking Technologies Moulded perfectly for the future: The MOULDING AREA at METAV presents the full prototype to series potential of tool, model, and mould making. Here you’ll find the state of the art for process streams, manufacturing methods, and intertechnology solutions. Precision for pros!
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Powder Injection Moulding International
b)
Fig. 2 Fibre orientation profiles as determined by CT. Without subsequent overflow (a) and with overflow basin (b). Flow direction from left to right. Red/green/ blue = low/medium/high degree of orientation. (From paper: ‘Investigations on the processing behaviour of non-spherical particles’, by V Piotter, et al. Presented at the Euro PM2019 Congress, Maastricht, October 2019) tool, shown in Fig. 1, enabled a steady flow through a specimen geometry with small (bending bar geometry, not depicted by Fig. 1) or broad width. After passing the specimen geometry the feedstock flow reached an overflow basin which could be equipped with different inserts to vary the volume (see cut out in Fig. 1). As the feedstock fills the overflow basin the fluid stream is kept constant and cools down simultaneously due to the low tool temperature. The result of this procedure is a nearly full fibre orientation through the whole cross section of the moulded specimen. Fig. 2(a) shows the shear-induced fibre orientation profile inside the green CMC body without the overflow basin, i.e. without subsequent overflow. It can be seen that the apparent degree of fibre orientation is higher nearer the surface region than in the bulk. On the other hand, if the overflow basin was used, a nearly complete fibre orientation could be obtained throughout the whole cross section of the body, as can be seen in Fig. 2(b). CMC specimens produced without overflow reached theoretical densities of approx. 51%, whereas the higher-oriented specimen reached values of approx. 64%. Bending tests showed an influence of the sintering parameters as well. If sintering took place at 1100°C for 30 min a maximum bending strength of only 25 MPa was achieved. Once the sintering parameters were increased to 1250°C for 2 h the bending strength increased to approx. 44 MPa. However, such values are still quite low compared to the pure alumina material (up to 300 MPa) and can be attributed to the still relatively high porosity of more than 30% in the sintered powder injection moulded CMC. However, the authors emphasised that the intention of fibre filling is not to increase the infinite strength values of the alumina CMC but rather to improve the material’s breaking resistance capabilities. In this respect, all specimens with high fibre orientation showed increased elongation before brittle fracture, thus obtaining a certain strain reserve. Nevertheless, absolute strength values of the PIM alumina CMCs are still too low, mainly as a result of the high porosity in the sintered material and the researchers still have the intention to solve this issue. www.kit.edu
December 2019
© 2019 Inovar Communications Ltd
Vol. 13 No. 4