TY - BOOK

T1 - A numerical modeling strategy for the damage-relevant evaluation of metrologically inaccessible thermo-mechanical milling tool loads

AU - Nemetz, Andreas

N1 - no embargo

PY - 2019

Y1 - 2019

N2 - The demand for components of difficult-to-machine materials, e.g. titanium alloys is increasing rapidly in technology areas such as aerospace. Due to the low degree of prefabrication of semi-finished products made of these materials, a large volume has to be removed. Hence, milling is the manufacturing method of choice to obtain the contour of the finished product. Tool failure is a main cost factor during manufacturing of expensive components. A prediction of premature critical wear, breakage or chipping of the cutting edge of milling tools reduces such costs and helps to fulfill the high quality requirements for the milled components. Great efforts are made in instrumentation of tools and application of sensors in machine tools. However, employing force- and temperature measurements only does not allow to directly deduce the damage mechanism in tools, especially at the cutting edge. On the one hand, temperature sensors cannot be placed arbitrarily close to the cutting edge. On the other hand, an in-situ investigation of the residual stress evolution in cyclically engaging milling tools is impossible. To circumvent these difficulties, newly developed thermo-mechanical simulations of the milling process were employed. As an important milestone towards the simulation of milling processes, a validated model of a dry milling process was gradually built up. The necessary development steps correlate with the four individual papers A, B, C and D, which have been combined for the present work. In paper A, a milling experiment documented in the literature was modeled to investigate the evolving residual tensile stress and thermally induced damage of a milling insert during the process time. Within the milling experiment, steel was machined and the evolving residual stresses at the rake face of the milling insert were documented after several milling cycles. The tool load was calculated using a thermo-mechanical 2D milling model. In a subsequent step, the obtained load was applied cyclically on a 3D model of the insert. In the simulation, tensile residual stresses were determined at the same position at the rake face and in the same order of magnitude as in the experiment. In the next development step, documented in paper B, the 2D modeling of the thermo-mechanical tool load was extended by a cyclic and iterative approach to simulate the heat-up of the tool in a more realistic way. Thus, the simulative approach was brought significantly closer to the real heat-up conditions during milling. In paper C, the newly developed approach to determinate the tool load situation was cyclically applied to the 3D model of the insert. It evaluated numerically the efficiency of various hard coating architectures during a high number of milling cycles. Within the last development step, documented in paper D, the transfer of the methods developed in papers A-C to the difficult-to-machine titanium alloy and a tool with complex geometry of the cutting edge was performed. The application of the methods developed in the predecessor models and their combination with the newly developed model of the cyclic heating of the workpiece yields a validated modeling strategy for the calculation of the thermal tool load, in particular at the cutting edge.

AB - The demand for components of difficult-to-machine materials, e.g. titanium alloys is increasing rapidly in technology areas such as aerospace. Due to the low degree of prefabrication of semi-finished products made of these materials, a large volume has to be removed. Hence, milling is the manufacturing method of choice to obtain the contour of the finished product. Tool failure is a main cost factor during manufacturing of expensive components. A prediction of premature critical wear, breakage or chipping of the cutting edge of milling tools reduces such costs and helps to fulfill the high quality requirements for the milled components. Great efforts are made in instrumentation of tools and application of sensors in machine tools. However, employing force- and temperature measurements only does not allow to directly deduce the damage mechanism in tools, especially at the cutting edge. On the one hand, temperature sensors cannot be placed arbitrarily close to the cutting edge. On the other hand, an in-situ investigation of the residual stress evolution in cyclically engaging milling tools is impossible. To circumvent these difficulties, newly developed thermo-mechanical simulations of the milling process were employed. As an important milestone towards the simulation of milling processes, a validated model of a dry milling process was gradually built up. The necessary development steps correlate with the four individual papers A, B, C and D, which have been combined for the present work. In paper A, a milling experiment documented in the literature was modeled to investigate the evolving residual tensile stress and thermally induced damage of a milling insert during the process time. Within the milling experiment, steel was machined and the evolving residual stresses at the rake face of the milling insert were documented after several milling cycles. The tool load was calculated using a thermo-mechanical 2D milling model. In a subsequent step, the obtained load was applied cyclically on a 3D model of the insert. In the simulation, tensile residual stresses were determined at the same position at the rake face and in the same order of magnitude as in the experiment. In the next development step, documented in paper B, the 2D modeling of the thermo-mechanical tool load was extended by a cyclic and iterative approach to simulate the heat-up of the tool in a more realistic way. Thus, the simulative approach was brought significantly closer to the real heat-up conditions during milling. In paper C, the newly developed approach to determinate the tool load situation was cyclically applied to the 3D model of the insert. It evaluated numerically the efficiency of various hard coating architectures during a high number of milling cycles. Within the last development step, documented in paper D, the transfer of the methods developed in papers A-C to the difficult-to-machine titanium alloy and a tool with complex geometry of the cutting edge was performed. The application of the methods developed in the predecessor models and their combination with the newly developed model of the cyclic heating of the workpiece yields a validated modeling strategy for the calculation of the thermal tool load, in particular at the cutting edge.

KW - Finite element model

KW - Arbitrary Lagrangian-Eulerian (ALE) model

KW - Metal cutting

KW - Instrumented Milling tools

KW - Hard coating

KW - Residual stress

KW - Comb crack

KW - Cutting edge temperature

KW - Heat transfer

M3 - Doctoral Thesis

ER -