Analytical and experimental investigation of orthogonal turn-milling processes

Official URL: http://risc01.sabanciuniv.edu/record=b1606659 (Table of Contents)

Machining of hard-to-cut materials is challenging due to their high strength resulting in reduced productivity and high manufacturing cost. Conventional machining processes are commonly used for production of these parts where cutting speed, and thus the material removal rate, is limited due to high tool wear rate. Because of the increasing market demands for higher quality, reduced lead times and cost, alternative techniques are required in order to increase productivity in machining of these materials. An increase in potential production capacity was observed in the recent years due to advancements in machine tools that offer high precision, increased flexibility and spindle speed. Multi-axis machining, which can be a remedy for these demands, have been continuing to spread rapidly in many industries particularly in aerospace and defense. These processes are generally performed on multi-tasking machines through simultaneous cutting operations on the same part or machining of more than one part simultaneously. Turn-milling, which is a promising multi-axis cutting process combining two conventional machining operations; turning and milling, can offer high productivity for difficult-to-cut materials such as Ti and Ni alloys as well as parts with large diameters which cannot be rotated at high speeds on conventional lathes. However, the work done on analysis and modeling of turn-milling operations is very limited. On the other hand, due to the high flexibility and capability of turn-milling operations, there are numerous process parameters which need to be selected properly to utilize the full potential offered by these processes. In order to achieve this, process models which consider all cutting parameters are required. In this thesis, analytical models for turn-milling process geometry, chip formation and cutting force including eccentricity effects are presented. Furthermore, circularity, cusp height and surface roughness are modeled and simulated. Model predictions are verified by experiments carried out on a multi-tasking machine tool under different process conditions. Tool wear tests for hard-to-machine materials are also performed on the same machine where effects of turn-milling process conditions on tool life are shown. Simulation and experimental results show that substantial increase in productivity can be achieved using turn-milling in machining of difficult-to-cut materials when process conditions are selected properly.