Raphael Holtermann

Modelling, simulation and experimental investigation of chip formation in internal traverse grinding

We present recent developments in modelling and simulation of internal traverse grinding, a high speed machining process which enables both a large material removal rate and high surface quality. We invoke a hybrid modelling framework, including a process scale model, simulations on a mesoscale capturing the proximity of a single cBN grain and an analysis framework to investigate the grinding wheel topography. Moreover, we perform experiments to verify our simulations. Focus in this context is the influence of the cutting speed variation on the grain specific heat generation.

Modelling and simulation of Internal Traverse Grinding: bridging meso- and macro-scale simulations

Abstract In this work, we focus on the computational bridging between the meso- and macro-scale in the context of the hybrid modelling of Internal Traverse Grinding with electro-plated cBN wheels. This grinding process satisfies the manufacturing industry demands for a high rate of material removal along with a high surface quality while minimising the number of manufacturing processes invoked. To overcome the major problem of the present machining process, namely a highly concentrated thermal load which can result in micro-structural damage and dimension errors of the workpiece, a hybrid simulation framework is currently under development. The latter consists of three components. First, a kinematic simulation that models the grinding wheel surface based on experimentally determined measurements is used to calculate the transient penetration history of every grain intersecting with the workpiece. Secondly, an h-adaptive, plane-strain finite element model incorporating elasto-plastic work hardening, thermal softening and ductile damage is used to simulate the proximity of one cBN grain during grinding and to capture the complex thermo-mechanical material response on a meso-scale. For the third component of the framework, the results from the preceding two simulation steps are combined into a macro-scale process model that shall in the future be used to improve manufacturing accuracy and to develop error compensation strategies accordingly. To achieve this objective, a regression analysis scheme is incorporated to approximate the influence of the several cutting mechanisms on the meso-scale and to transfer the homogenisation-based thermo-mechanical results to the macro-scale.

Evaluation of different approaches for modeling phase transformations in machining simulation

Presently, the main mechanism for phase transformations in machining of steels is not absolutely clear and is still subject to research. This paper presents, three different approaches for modeling phase transformations during heating in machining operations. However, the main focus lies on two methods which can be classified into a stress related method and a thermal activation related method for the description of austenitization temperature. Both approaches separately showed very good agreements in the simulations compared to the experimental validation but were never compared in a simulation. The third method is a pre-calculated phase landscape assigning the transformation results based on a micro-mechanically motivated constitutive model to the workpiece in dependence on the temperature and strain history. The paper describes all three models in detail, and the results are also presented and discussed.

Modelling and Simulation of Internal Traverse Grinding—From Micro-thermo-mechanical Mechanisms to Process Models

This contribution deals with the modelling and simulation of Internal Traverse Grinding (ITG) using electroplated cubic Boron Nitride (cBN) wheels. This abrasive process fulfils the industrial demands for an extensive rate of material removal along with a good surface quality while minimising the number of manufacturing processes. To overcome one drawback of ITG in terms of a highly concentrated thermal load on the workpiece surface, a multi-scale simulation framework that combines different modelling methods in a hybrid framework is presented. In this context, a geometric-kinematic simulation is combined with a finite element analysis which focuses on the thermo-mechanical response of a single cBN grain being in contact with a hardened workpiece. Via a special scale-bridging scheme, the results of both the former simulations are used to compute a thermo-mechanical load compound acting as a boundary condition in a process-scale finite element model. The latter is then used to capture thermally induced geometrical errors during ITG and to develop compensation strategies accordingly.