Papers by Author: Konstantin von Niessen

Abstract: Light-metal matrix composites with tailor-made fiber reinforcements offer a good balance between weight saving and high strength, a key feature for lightweight design in structural applications for the automotive and aerospace industry. Light-metal MMCs manufactured by thixoforging of thermally sprayed prepregs additionally exhibit superior mechanical properties of the matrix material as well as low fiber damage during infiltration of the reinforcement fabric. However, one of the difficulties during manufacturing of these materials is the difference in the thermal expansion coefficients (CTE) of matrix and fiber material. Different thermal expansions lead to the development of residual stresses during the cooling process that can deform the reinforcement fibers and hence, lead to a decrease of the mechanical properties of the reinforced component. Modeling by means of finite elements and numerical simulation is used in order to study parameter variations during the cooling procedure and to select an optimized process route. The modeling and simulation was performed in a collaborative work between the Institute for Manufacturing Technologies of Ceramic Components and Composites, University of Stuttgart, and the Polytechnic University of Cartagena.

Abstract: Processing of light-metals in semi-solid state offers some advantages regarding process temperatures, handling of the material, but also the resulting micro-structure of the final component. Reinforcement of light-metal components with fibers or particles can be applied in order to increase elastic modulus and yield strength of the material as well as its wear resistance. But, the manufacturing of metal matrix composites by thixoforging requires the supply of raw material that shows thixotropic behavior at processing temperature and that contains a definite volume fraction of well distributed reinforcement phase. In this work, an arc wire spray process is applied for the manufacturing of semi-finished parts by coating of long-fiber fabrics and by deposition of ceramic particle containing billets. The process technique is described and the suitability of thermally sprayed matrix material for semi-solid processing is verified.

Abstract: 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.

Abstract: Advanced continuous fiber reinforced light metal matrix composites (MMC) are manufactured using thermally sprayed prepregs and subsequent semi-solid forming. The prepregs consist of fiber woven fabrics, which will serve as reinforcement, and a thick metal alloy coating on top of the fabrics as the final matrix material. The coated fabrics are trimmed to the shape of the component and laminated in packages of 40 to 80 prepregs to form a component. The prepregs are reheated into the semi-solid state of the alloy and solidified to a dense, complex shaped MMC with no residual porosity by semi-solid forging (thixoforging). The deposited alloy infiltrates the fabrics with 40 % vol. to 60 % vol. liquid fraction. The fine-grained structure of the thermally sprayed metal coatings allows the required formation of globular grains during remelting and improves the impregnation behavior. The semi-solid forming and simultaneous infiltration in short cycle times offer the possibility to realize complex near net-shape geometries and make additional fiber coating not obligatory. A pilot plant was developed to provide the MMC production with prepregs consisting of various reinforcement fiber materials and a wide range of metal matrix alloys capable for thixoforging densification.