Peter Unseld

Recent Developments within Semi-Solid Forming at the Institute for Metal Forming Technology

This paper illustrates several research activities being carried out within the Center of Competence for Casting and Thixoforging Stuttgart (CCT `NOVUS´). A new method for manufacturing Metal Matrix Composites out of the semi-solid state has been developed at the Institute for Metal Forming Technology, Universitaet Stuttgart, and applied for patent pending. Within this new manufacturing method for the production of fibre and particle reinforced composites now disadvantages of liquid-phase-techniques can be reduced in combination with decreased manufacturing costs compared to conventional MMC-production technologies due to short cycle times and the ability of near-net-shape forming. It is obvious that manufacturing process in the fabrication of metal matrix composite materials will influence in some extent the performance of these materials. A current research project at the Institute for Metal Forming Technology (IFU), contributes implementing specific boundary condition of the manufacturing process to numerical analysis. Such boundary conditions exert direct influence on product quality. For manufacturing of metal matrix composites limiting factors are e.g. temperature, pressure, deformation, etc. Detecting input-parameter for numerical analysis basic rheological parameters, such as static and dynamic yield points, hysteresis and shear rate jump tests, detection of the differential structural parameter, evolution of apparent viscosity of different castalloys are topics of current research project at the Institue for Metal Forming Technology. For reheating-process of semi-solid alloys new technologies have been developed and applied for patent pending by the Institute for Control Engineering of Machine Tools and Manufacturing Units (ISW). The two main advantages of this technique as compared with other induction heating techniques are the direct online determination of liquid-, solid fraction and heating-homogeneity as well as robustness against variations of prematerial (chemical composition, billet-diameter, etc.).

FSI-Analysis of the MMC-Thixoforging Process Regarding the Rheology of the Aluminiumcast-alloy AlSi7Mg0,3

This paper illustrates investigations regarding the infiltration process of the thixotropic cast-alloy AlSi7Mg0,3 into laminated fibre woven fabrics by Fluid-Structure Interaction Analysis (FSI). As results of such FSI-Analysis on the one hand the kinematical behaviour of the reinforcement due to the infiltration process on the macroscopic and microscopic level on the other hand fluiddynamical effects of the regarded alloy are achieved. Thus in the run-up to timeconsuming and cost-intensive experiments, informative bases like fluidic optimizing of the cavity or the configuration and insertion of the reinforcement component can be numerically developed. Furthermore a reliable prediction of transient permeability of the fibre fabric is possible, which effects the infiltration process significantly. Numerical input data such as rheological parameters characterizing the behaviour of partial solidified alloys have been conducted. Therefor basic rheological tests of the aluminium cast-alloy AlSi7Mg0,3, like `HYSTERESIS TESTS´, `SHEAR RATE JUMP TESTS´ and detection of `STATIC´ and `DYNAMIC YIELD POINTS´ and the `DIFFERENTIAL STRUCTURAL PARAMETER´ have been conducted. Furthermore `EVOLUTION OF VISCOSITY´ has been correlated with thermodynamical calculations using ThermoCalc®. Finally the infiltration of a textile semi-finished part (carbon fibre fabric / canvas bonding) by A356 is discussed as an example to demonstrate the feasibility of FSI-Analysis, taking into account a two-way coupling between the interacting CSM- and CFD-Codes.

Fiber Reinforced Light Metal Composites by Thixoforging of Thermally Sprayed Prepregs

New manufacturing methods for metal matrix composites (MMC) are developed. Thermally sprayed metal coatings on reinforcement-fabrics are used as preforms (prepregs) for an advanced thixoforging process. The semi-solid forming and simultaneous infiltration in short cycle times offer the possibility to realize complex near net-shape geometries and reduces fiber damage to a minimum.

Fluid-Structural Interaction Analysis of the MMC-Thixoforging Process

High mechanical properties in combination with low density are key features for lightweight constructions in automotive and aerospace applications. The combination between the innovative thixoforging process and the potential of fibre or particle strengthened composites with metallic matrices (MMCs) provides an efficient manufacturing process of structural components with continuous or gradient reinforcements. The scope of the Center of Competence for Casting and Thixoforging Stuttgart (CCT) contains new semi-solid manufacturing methods for metal matrix composites which have been developed and applied for patent pending. While previous research projects were focussed on fabrication of continuous fibre reinforced metal matrix composites, the local reinforcement insertion, located in the center of high force and torsion load zones, is going to be the next evolution step of the CCT research team. Therefore it is essential to verify, to simulate and to reproduce the process during infiltration of the semi-sold matrix metal into the textile layer experimentally. This paper illustrates investigations regarding the infiltration process of the thixotropic cast-alloys AlSi7Mg0.3 (A365) into laminated fibre woven fabrics by computational fluid dynamics and fluid-structure interaction analysis, taking account into specific manufacturing technology, the rheological behaviour of the alloy with special focus on infiltration behavior.