Mechanics and dynamics of multi-axis machining operations
Öztürk, Erdem (2010) Mechanics and dynamics of multi-axis machining operations. [Thesis]
Official URL: http://192.168.1.20/record=b1304383 (Table of Contents)
Machining process with a single cutting tool is called multi-axis machining if more than 3-axis are involved in the operation. On the other hand, parallel machining processes where more than one cutting tool simultaneously cut a workpiece is also called multi-axis machining. 5-axis ball-end milling where a single cutting tool is employed, parallel turning and parallel milling processes with two cutting tools are in the scope of the thesis. Moreover, face-milling process with inserted tools is also modeled. 5-axis ball-end milling operations are common in several industries such as aerospace, automotive and die/mold for machining of complex sculptured surfaces. Additional two degree of freedoms, namely, lead and tilt angles make it possible to machine complex parts by providing extra flexibility in cutting tool orientation. However, they also complicate the geometry of the process. In these operations, productivity, dimensional tolerance integrity and surface quality are of utmost importance. Part and tool deflections under high cutting forces may result in unacceptable part quality, whereas using conservative cutting parameters results in decreased material removal rate. Process models can be used to determine the proper or optimal milling parameters for required quality with higher productivity. The majority of the existing milling models are for 3-axis operations, even the ones for ball-end mills. In the thesis, geometry, force and stability models are presented for 5-axis ball-end milling operations. The effect of lead and tilt angles on the process geometry, cutter and workpiece engagement limits, scallop height, and milling forces are analyzed in detail. In addition, tool deflections/form errors and stability limits are also formulated for 5-axis ball-end milling. The use of the model for selection of the process parameters such as lead and tilt angles which result in minimum cutting forces or maximum stability limits are demonstrated. The model predictions for cutting forces, form error and stability limits are compared and verified by experimental results. Parallel machining operations are advantageous in terms of productivity since there are more than one cutting tools in operation. Due to the increased number of cutting tools, they have the potential for considerable increase in productivity as a result of higher material removal rate (MRR). However, the dynamic interaction between these parallel tools may create additional stability problems and the advantage of parallel machining may not be utilized to full extent. For that reason, dynamics and stability of parallel machining processes need to be modeled. In the thesis, dynamics of parallel turning and parallel milling operations where two cutting tools cut a common workpiece are modeled. The predicted stability limits for parallel turning are also compared with experimental results where good agreement is demonstrated. Die manufacturing is a very critical part of the overall production chain in many industries. Depending on shape and size of a die, machining time can be very time consuming. Furthermore, since usually one die is manufactured, the chance for testing is very limited. Machining processes in die manufacturing can be limited by many factors. Process models can be used in order to select process conditions which will yield the required quality in the shortest possible time. In this study, force and chatter models are developed for face milling processes with inserted cutters. Using the developed models, process parameters are modified and their effects on productivity are demonstrated.
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