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Deformation Prediction of Porthole Dies After Multiple Extrusion Cycles

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Deformation Prediction of Porthole Dies After Multiple Extrusion Cycles

Barbara Reggiani,,Lorenzo Donati, and Luca Tomesani
University of Bologna, Department of Mechanical Engineering, Bologna, Italy

Track: EXTRUSION/DIE THEORETICAL - Modeling, Microstructure and Simulation

ABSTRACT—Extrusion dies work under the combination of cyclic loads and high temperatures.
Accounting also for the billet-die contact time during each single extrusion, the die deflecting
mechanism is placed in the creep-fatigue interaction. In order to analyze the die deformation, a
physical experiment reproducing the thermo-mechanical conditions of an extrusion die was performed
on a Gleeble simulator. The specimens were made of AISI H11. The design of the experiment
consisted of four levels of temperature, three levels of stress, and three types of load (creep, fatigue,
and creep-fatigue with a dwell-time). It was found that creep is the mechanism that greatly affects die
deformation, and that the time-displacement histories of the specimens showed a marked primary
softening phase for each tested condition. Thus, a modified version of the time-hardening creep law
was chosen to estimate the die deformation. Coefficients of the law were optimized on the basis of
experimental data, starting from values found in the literature. Novel equations were formulated to
express the dependency of the coefficients on the stress-temperature state, as well as on the dwell-time
after multiple cycles. The presented procedure was validated against additional experimental data,
performed with different specimen geometries and on an industrial extrusion die. A good average
agreement was found between experimental and numerical results. Keywords: extrusion die, creepfatigue, deformation mechanism, multiple extrusion cycles, AISI H11.

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