Analysis of The Chip Formation of Bainitic Steel in Drilling Processes

Continuously cooled bainitic steels have the potential to replace conventional quenched and tempered steels in automotive applications. Whereas the machining performance often decides about the cost effectiveness of a particular part, little general knowledge exists about the machinability of such novel steels. First practical experiences with drilling operations confirm the good machinability of bainitic steels as well as the potential for further optimization. Also from a scientific point of view a better understanding of chip formation in the drilling process is desirable. This includes the variation of forces over the drilling edge and the determination of corresponding shear angles. For generating real chip roots a quick stop device was developed. In addition to conventional metallographic micro sections, a non-destructive method namely computer tomography was used for characterization of chip formation based on chip roots.ISSN:2212-827

In-process measurement of friction coefficient in orthogonal cutting

ISSN:0007-8506ISSN:1660-277

Analysis of two parameter identification methods for original and modified Johnson-Cook fracture strains, including numerical comparison and validation of a new blue-brittle dependent fracture model for free-cutting Steel 50SiB8

A non-linear relation between fracture strain and temperature is observed in Split Hopkinson Tension Bar (SHTB) tests for free-cutting steel 50SiB8 at high strains and high temperatures, due to blue-brittleness. A fourth-degree polynomial function for the thermal parts of the original and modified Johnson-Cook (JC) fracture strain constitutive equation is suggested and the corresponding parameters are identified. Fracture modelling of 50SiB8 is not reported in literature. 50SiB8 is characterized under quasi-static, isothermal, high temperature and high strain rate conditions using smooth and notched tension specimens. For the calculation of the original and modified JC fracture parameters, two different parameter identification procedures, so-called forward and backward parameter identification methods are performed, compared with each other and explained in detail. For the stress triaxiality factor of the original and modified JC fracture model, the forward parameter identification method is suggested for the original JC fracture model, while backward parameter identification method is proposed for the modified JC fracture model. The effect of blue-brittleness in the temperature factor and the corresponding parameters are presented. Furthermore, FEM simulations of the original and the blue-brittleness including JC fracture model are compared with experiments. In the blue-brittle temperature range, the new adjusted JC model shows more accurate results, regarding fracture diameter and strain. Additionally, this work introduces a fracture model combining the Bai-Wierzbicki stress triaxiality dependent model, JC fracture models and the nonlinear temperature factor with blue-brittleness effect, while further experiments are required in order to determine its parameters