Effect of chip thickness, sub-critical bifurcations and process parameters in high-speed milling
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] The main focus of the current research is to experimentally and numerically investigate of subcritical bifurcations in milling accounting for actual motion of the tool. In this work, a new approach for predicting the behavior dynamic model of a milling process is developed. Modeling of the discontinuous cutting forces takes into account the actual motion of the cutting tool. The chip thickness is determined by using a search algorithm at each simulation step that determines when the tool cutting edge is in contact with the work piece and how far below the surface the cutting edge is. This new model has lead to a new, more precise, understanding of the stability of the dynamic milling system. In this research, the author conducts a series of experiments to explore the dynamic behavior predicted by numerical simulation results for milling. Experimental cutting tests were performed on a relatively long aluminum work piece. The atypical length of the work piece was used so that the depth of cut may be slowly increased or decreased during the cutting process. This provides visual evidence of hysteresis in the bifurcation diagram and the existence of multiple stable periodic solutions. Furthermore, in an effort to improve productivity, another experimental study was conducted which combine the effects of system dynamics and process parameters on surface finish and dimensional accuracy. The importance of this exploratory experimental effort is that there are significant effects in the quality characteristics that may affect the process. An important outcome from this research was, (1) a small perturbation in the desirable stable solution near the borders of the stability diagram could result in a jump to the unstable cutting condition, and (2) the dynamic behavior in the cutting process affects the quality characteristics of the product, which must be closely monitored.
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