R. Pabst

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.

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.

Integration of a picosecond laser system into a machining centre

The application of fuel saving technologies like fuel-efficient engine oil or the implementation of an automated start-stop system into the engine management leads to increased loadson power train bearings. To improve the durability of these parts, the friction surfaces need to be modified. The optimization of already existing parts can be done by microstructuring of the surfacee.g. via laser ablation. This structuring leads to an improved tribological behavior due to an increased hydrodynamic pressure gain, thus disconnecting the friction partners even with oil of low viscosity.In order to reduce process time and improve the energy footprint of the process chain with an additional process, the aim of this work is to integrate the laser structuring into a multi process machine. In order to realize the laser ablation without surface damage which is caused by heat input and therefore leads to microstructural transformation, the laser system has to have a pulse duration smaller than 10 picoseconds. The use of such laser systems leads to challenges regarding the beam guidance which is not achievable by glasfibres because of the high pulse peak output exceeding the damage threshold. The guidance therefore has to be implemented by deflection mirrors and integrated into the machining centre.The application of fuel saving technologies like fuel-efficient engine oil or the implementation of an automated start-stop system into the engine management leads to increased loadson power train bearings. To improve the durability of these parts, the friction surfaces need to be modified. The optimization of already existing parts can be done by microstructuring of the surfacee.g. via laser ablation. This structuring leads to an improved tribological behavior due to an increased hydrodynamic pressure gain, thus disconnecting the friction partners even with oil of low viscosity.In order to reduce process time and improve the energy footprint of the process chain with an additional process, the aim of this work is to integrate the laser structuring into a multi process machine. In order to realize the laser ablation without surface damage which is caused by heat input and therefore leads to microstructural transformation, the laser system has to have a pulse duration smaller than 10 picoseconds. The use o...

Erhöhte Nachgiebigkeit steigert Standzeiten beim Fräsen

Kurzfassung Bei der Fräsbearbeitung, besonders von Werkstoffen mit hoher Härte oder solchen mit einer sprödharten Randschicht, treten durch die Verfahrenscharakteristik des unterbrochenen Schnitts hohe mechanische und thermische Wechselbeanspruchungen auf. Vergleichende Untersuchungen zur Dynamik des Antriebstrangs von Werkzeugmaschinen mit relativ steifen Motorspindeln und deutlich nachgiebigeren Riemenantrieben haben einen signifikanten Unterschied der erreichbaren Werkzeugstandzeiten belegt, da die Belastungsspitzen beim Schneideneintritt bei Systemen mit höherer Nachgiebigkeit weniger stark ausgeprägt sind [1]. Im Rahmen der hier beschriebenen Arbeiten wurde untersucht, inwieweit durch gezielte Nachgiebigkeitsvariation im Fräswerkzeug Standzeitsteigerungen erreicht werden können. Dazu wurden verschiedene metallische und polymere Werkstoffe in Form von austauschbaren Elementen im Fräswerkzeug integriert und deren Einflüsse auf die Werkzeugstandzeit durch Zerspanversuche ermittelt. Die Ergebnisse versprechen insbesondere für die verwendeten Kunststoffe als Nachgiebigkeitselement signifikante Standzeitvorteile.

Improving tool life by varying resilience and damping properties in close proximity of the cutting edge

During straight turning of workpieces with non-cylindrical geometry or during milling operations on workpieces with hard surfaces such as the scale layer on cast iron the cutting edge has to withstand high recurrent impact loads. These loads can destroy the cutting edge rather spontaneously than by continuous wear. Commonly used criterions such as a flank or crater wear are not suitable. As part of the research presented in this paper mechanical system properties such as resilience and damping are varied and the influence on tool life is presented. Variation was done passively by changing the material of a shim which was positioned directly under the cutting insert and actively by using a piezo actuator to change the pressure of an oil reservoir close to the cutting insert. The results of this research confirm the potential advantages of a properly adjusted resilience close to the cutting edge. However, a single set of optimal properties for different machining operations or workpiece/tool combinations cannot be derived.