J. Michna

Modeling the process-induced modifications of the microstructure of work piece surface zones in cutting processes

Cutting processes lead to mechanical and thermal loading of tool and work piece. This loading entails a direct influence of the cutting process on the surface layers of the manufactured work pieces. As a result, residual stresses and modifications of the micro-structure like white layers can occur in surface-near zones of the work piece. This paper presents the development of a FE-simulation model to predict phase transformations due to cutting processes. Therefore a 2D-FE-cutting simulation including a dynamic re-meshing is combined with a simulation routine to describe phase transformations that was primarily developed to simulate laser hardening. This paper illustrates the implemented mechanisms to determine phase transformations considering short time austenization and shows first experimental results revealing the influence of process parameters on the surfaces microstructure.

Influence of cutting parameters, tool coatings and friction on the process heat in cutting processes and phase transformations in workpiece surface layers∗

Abstract The surface states and thus the functionality of machined workpieces are influenced by parameters of the process and the cutting tool. Depending on these variables different mechanical and thermal loads lead to changing characteristics of components. This paper presents a 2D-FE-cutting simulation model predicting machining induced phase transformations of workpiece surface layers for the steel 42CrMo4 (AISI 4140) considering detailed friction modeling between tool and workpiece, based on tribological experiments. The cutting simulation model was developed using the commercial software ABAQUS. Friction and phase transformations are implemented using specific user subroutines. The model calculates the process of austenization and the transformed volume fraction of the phases ferrite/perlite, bainite and martensite. Additional thermo dynamical simulations of the heat transfer using the code INSFLA are performed. The simulated temperatures, cutting forces and phase transformations are compared to orthogonal cutting experiments.

Investigation of the Machining Behavior of Metal Matrix Composites (MMC) Using Chip Formation Simulation

The machining of metal matrix composites (MMC) induces cyclic loadings on tools, which creates new challenges for machining. In particular the distributed reinforcement, consisting of silicon carbide (SiC) or aluminum oxide (Al2O3), evokes especially high mechanical loads. The development of metal matrix composites is pointing towards higher fractions of reinforcements, which affects the resulting forces and temperatures. In this regard the influence of varying particle filling degrees, particle diameters, cutting velocities and tool geometries in terms of rake angle and cutting edge radius have been investigated by means of cutting simulation. For the process a self-designed continuous remeshing routine was used for which a dual phase material behavior has been implemented. The developed simulation model enables investigations of the machining behavior of metal matrix composites to the extent that ideal process strategies and tool geometries can be identified by multiple simulations.

Surface Layer States of Worn Uncoated and TiN-Coated WC/Co-Cemented Carbide Cutting Tools after Dry Plain Turning of Carbon Steel

Analyzing wear mechanisms and developments of surface layers in WC/Co-cemented carbide cutting inserts is of great importance for metal-cutting manufacturing. By knowing relevant processes within the surface layers of cutting tools during machining the choice of machining parameters can be influenced to get less wear and high tool life of the cutting tool. Tool wear obviously influences tool life and surface integrity of the workpiece (residual stresses, surface quality, work hardening, etc.), so the choice of optimised process parameters is of great relevance. Vapour-deposited coatings on WC/Co-cemented carbide cutting inserts are known to improve machining performance and tool life, but the mechanisms behind these improvements are not fully understood. The interaction between commercial TiN-coated and uncoated WC/Co-cemented carbide cutting inserts and a normalised SAE 1045 steel workpiece was investigated during a dry plain turning operation with constant material removal under varied machining parameters. Tool wear was assessed by light-optical microscopy, scanning electron microscopy (SEM), and EDX analysis. The state of surface layer was investigated by metallographic sectioning. Microstructural changes and material transfer due to tribological processes in the cutting zone were examined by SEM and EDX analyses.

Experimental and Simulative Modeling of Drilling Processes for the Compensation of Thermal Effects

This work focuses on the prediction of phase transformations and shape deviations for drilling of demonstrator workpieces. In a first step, a 2D chip formation simulation was developed with all physical effects. Based on this simulation a simplified workpiece geometry with only one drilling hole was 3D modeled and tested for its predictive capability of phase transformations and shape deviations. Therefore, the feed rate, the rotation of the drilling tool and the material removal were considered for the process kinematics. Using these results the modeling approach was optimized and transferred into a simulation model with a demonstrator workpiece to minimize shape deviations and control phase transformations using different compensation strategies. The simulations were validated by experiments.