Johannes Rauch

Assessment Of Mold-Design Dependent Textures In CIM-Components By Polarized Light Optical Texture Analysis (PLOTA)

By thermoplastic ceramic injection moulding (CIM) ceramic components of high complexity can be produced in a large number of items at low dimensional tolerances. The cost advantage by the high degree of automation leads to an economical mass‐production. The structure of injection‐moulded components is determined by the form filling behaviour and viscosity of the feedstock, the machine parameters, the design of the mold and the gate design. With an adapted mold‐ and gate‐design CIM‐components without textures are possible. The “Polarized Light Optical Texture analysis” (PLOTA) makes it possible to inspect the components and detect and quantify the textures produced by a new mold. Based on the work of R. Fischer (2004) the PLOTA procedure was improved by including the possibility to measure the inclination angle and thus describe the orientation of the grains in three dimensions. Sampled thin sections of ceramic components are analysed under the polarization microscope and are brought in diagonal position. ...

Polarization Light Optical Texture Analysis for the Structural Characterization of CIM Components

The mechanical properties of ceramic injection molded (CIM) components are largely influenced by microstructural inhomogeneities that result from the interaction of rheological properties of the thermoplastic feedstock with machine parameters and the design of mold and injection gate. These inhomogeneities (e. g. texture, turbulences, joints, and density gradients) can form weak spots in the material or lead to anisotropy of the material properties. Additionally, they can influence the local sinter shrinkage behavior and thereby lead to the formation of residual stresses in the component. For this reason, it is of great importance to analyze these inhomogeneities in order to improve CIM processes and CIM components. A method has been developed for the investigation of preferred crystal orientation and microstructural defects, applying polarization microscopy of ceramic thin sections and colorimetry. Polarization microscopy is used in order to visualize the crystal orientation of the single grains. Different orientations of the optical axes will result in different colors of interference for optically uniaxial materials. The polarization micrographs themselves are already suitable for the analysis of the microstructure of CIM components regarding texture, separation planes, etc. Colorimetry is used in order to measure and describe the colors in a standardized color system. By means of color/orientation calibration curves that are measured with single crystal references, a quantitative description of the orientation of single grains as well as texturized areas can be obtained.