Papers by Author: Simon Muenstermann

Abstract: Isothermal semi-solid extrusion experiments using steel grade X210CrW12 as work material were performed on an industrial forging machine. An improved and up-scaled tool design was applied, based on the concept of self-heating ceramic dies tested in previous laboratory-scale studies and allowing for die preheating temperatures of up to 1400°C. Steel rods of complex cross sectional geometry were formed at low extrusion forces. Shape accuracy of as-formed rods is accurate and metallurgical examination yields no evidence of liquid phase separation. With a view on the intended industrial implementation construction of ceramic tools has to be improved in order to avoid rupture of ceramic parts due to thermo-mechanically induced stresses and to benefit from the advantages inherent to ceramics in metal forming.

Abstract: A novel ceramic tool concept allows near-isothermal steel thixoextrusion experiments. Thermal shock impacts are successfully eliminated from the load profile of conventional semi-solid processing technologies of high melting point alloys. Thus, the application of thermal shock sensitive oxide ceramics exhibiting excellent corrosion resistance as forming dies is feasible. Extruded steel parts show high shape accuracy at very low extrusion forces.

Abstract: The design and performance of silicon nitride (Si3N4) dies for the semi-solid processing of steels is studied by the example of a punch and a lower swage in upset forging. The observed failure mechanisms and degradation effects are related to short-term effects resulting from mechanical and thermal loads and long-term effects owing to chemical and tribological attack. Results show that well-defined process conditions (cycle time, solidification time in the die) and a ceramic-suitable design are a pre-requisite for reliability and sufficient service life of ceramic dies.