Circular milling operations are used to enlarge die and mold cavities, cylinder bores and machine airframe pockets. The tool attached to the rotating spindle follows a circular trajectory with a machining feed rate, while gradually moving forward in the direction of global axis with a step over feed. This paper presents the mathematical model of chip removal mechanism by predicting time varying cutter-part intersection as the cutter travels along the circular path. The vibration free cutting forces are predicted and experimentally verified. The dynamics of the process are modeled by considering vibrations of the end mill in two directions. The chatter stability of circular milling is modeled both in frequency domain and with a numerical model based on time finite element analysis which considers time varying immersion and directional factors. The resulting stability solutions are compared against experimental results.

Lubrication is one of the process variables that affect the quality of stamping sheet materials. Using a good lubricant can significantly reduce sciap rate and/or improve the quality of stamping. In this study, different types of lubricants were evaluated using strip draw test (SDT) and deep draw test (DDT) for stamping of galvannealed steel sheets. Einite element (EE) simulations were carried out to determine the coefficient of friction at tool-work piece interface during deep diawing under different lubrication conditions and blank holder forces. Elow stress data of materials under biaxial load which are used in EE simulations are obtained by viscous pressure bulge tests. SDT was used as a preliminary test to evaluate the relative performance of the lubricants. Lubricants that showed good performance in this test were tested using DDT. Dimensions of the formed strips and cups and the maximum applicable blank holder force to draw parts without fracturing were the criteria used for evaluation of lubricants in both tests. In general, it was possible to form cups with higher blank holder force when synthetic/water-based lubricants were applied to ¡he sheet. In conclusion, evaluated synthetic/water-based lubricants had better lubricity than petroleum-based lubricants.

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