Mikro frezelemenin mekaniği ve ısı modellemesi

Micro milling is widely used in high-tech industries such as biomedical, aerospace, optics, electronics and die-mold with the increasing demand for precisely manufactured miniature parts. In today's competitive industrial world, the manufacturing of high quality miniature parts having complex free form geometry with very tight tolerances is required. Therefore, surface and subsurface integrities, accuracy and repeatability of the micro machining process are critical. The main aim of this research thesis is to shed light on the mechanics and thermal aspects of micro milling in order to increase the efficiency and effectiveness of the process in industrial applications by understanding the micro milling physics. The contribution of this research is in the investigation of uncut chip thickness models and developing a cutting force model for micro milling. In this thesis, it is shown that based on the developed cutting force model, the cycle time of the process can be improved by scheduling the feedrate. Understanding and modeling the micro milling mechanics also helps to predict the micro tool deflection. Thermal modelling also allows predicting the temperature fields and machining induced micro thin part distortions. There are different chip thickness models derived from various kinematic analyzes for the micro milling in the literature. The most accurate chip thickness model for micro milling is selected by examining their direct effect on predictions of cutting forces. Using selected uncut chip thickness model and mechanistic cutting force coefficients a novel cutting force model is developed considering cutting forces formed due to shearing and ploughing dominant regimes. The geometry of the cutting flute is precisely modeled by scanning the tool using a laser sensor for determining the helix angle and using White Light Interferometer for determining edge radius. In order to validate the force model, the set of cutting experiments under different cutting conditions is performed. A new mathematical model for estimation of tool deflection in micro milling process using the FEM method is proposed. The tool is considered as a cantilever beam supported in the tool holder. The Timoshenko element beam is used for FEM analysis of the tool under distributed cutting force load. Specially designed setup with two laser displacement sensors is attached to the spindle of the machine to monitor the instantaneous tool deflection and to validate the mathematical model of tool deflection. In order to increase the productivity by decreasing the machining cycle time, an offline force based feedrate scheduling algorithm is proposed. This algorithm is tested on both flat and ball end mill for complex freeform geometries. Using the proposed model, the feedrate can be defined offline for each cutter location (CL) point accordingly. Prediction of the workpiece and tool temperature fields in micro milling of Titanium is important, due to the fact that not only the temperature in machining affects the tool wear, but also the temperature fields have direct influence on the residual stresses, the 3D distortions, dimensional and geometrical accuracy of micro parts. The cutting temperatures are predicted by new hybrid finite element model. Temperature simulations are validated by the thermocouple measurements in micro milling of Ti-6Al-4V. Finally, modeling micro milling induced distortions during thin wall machining is thoroughly investigated. A new strategy is proposed to estimate deflection of the thin wall. The novelty of the proposed strategy lies in combining thermal and mechanical effects during distortion modeling. The presented approach is validated experimentally through micro milling cutting experiments and White Light Interferometer measurements.