Modeling milling of thin-walled parts considering dynamic structure-process interactions

Official URL: https://risc01.sabanciuniv.edu/record=b2771069_(Table of contents)

Thin-walled parts are frequently used in industry and many engineering applications. These parts are commonly found especially in the field of aerospace, as they provide a high strength-to-weight ratio due to their inherent geometry. Some examples of thin-walled structures are turbine and compressor blades used in aero-engines, and frame structures used in aircraft. In addition to these, pin-finned structures are commonly utilized in the energy industry as heat exchangers. Machining of these parts is challenging due to their low dynamic rigidity. Therefore, stability analysis by modeling in-process workpiece dynamics is required to predict process stability condition. In this study, finish milling process stability of thin-walled geometries was investigated in detail. In modeling the workpiece dynamics, the effect of the material removal and cutter location at each cutting step on the workpiece dynamics and process stability was considered. In addition, the effect of variable pitch tools and crest-cut tools on thin-wall milling stability was investigated and compared with a standard end mill. In this thesis, the thin-walled workpiece was modeled as a 3D cantilever beam using the finite element method (FEM) and the increase in stiffness from free-end to fixed-end was considered in stability analysis. Moreover, the dominant bending and torsional modes of the workpiece were ii taken into account. In machining processes, the dynamic interaction between the cutting edge and the vibration wave left on the surface generates process damping effect, which occurs from process itself in addition to structural damping. Process damping provides deeper stability limits at low cutting speeds. In the stability analysis, process damping was investigated for the flexible part finish milling by selecting optimal parameters such as cutting edge geometry, semi-finish stock thickness and maximum allowable vibration amplitude according to the situation results. Furthermore, the effects of stability, marginal stability, and chatter conditions on the surface finish of the parts were investigated.