Fitting of constitutive material parameters for FE-based machining simulations for functionally graded steel components

Tiffe, M.1, a; Biermann, D.1, b; Zabel, A.1, c

1)
Institut für Spanende Fertigung, Technische Universität Dortmund, Baroper Str. 303, 44227 Dortmund

a) tiffe@isf.de; b) biermann@isf.de; c) zabel@isf.de

Kurzfassung

The composition of different materials and their specific properties like tensile strength and toughness is one way to achieve workpiece characteristics which are tailored to the later application. Another approach is the subsequent local heat treatment of workpieces made of homogeneous materials. However, both ways are costly and go along with several subsequent process steps. Therefore, mono-material workpieces which were manufactured by thermo-mechanical forming processes may provide such tailored properties in the form of functional gradations. Furthermore, the process chain is shortened by the combination of forming and heat treatment, but nevertheless machining processes are still needed for proper workpiece finish. This puts the challenge of varying process conditions due to hardness alterations within a single process step, e.g. turning. In addition to experimental investigations simulative analysis techniques are desired to evaluate mechanical as well as thermal loads on tool and workpiece. In the case of FE-based microscopic chip formation simulations proper material behaviour needs to be determined with respect to material hardness. This paper describes the approach of fitting Johnson-Cook material parameters as a function of workpiece material hardness. In order to achieve realistic stress states within the process zone, this approach considers the yield strength as a linear function of the hardness. It is shown how the hardness influences the cutting conditions and how the Johnson-Cook parameters are identified. Then these parameters are validated in three-dimensional simulations of exterior dry turning by comparison of simulated process forces and chip formation to experimentally achieved ones.

Schlüsselwörter

FEM, Johnson-Cook material model, functional gradation, hardness, turning

Veröffentlichung

Key Engineering Materials, 611-612 (2014), S. 1202-1209, doi: 10.4028/www.scientific.net/KEM.611-612.1202