UBC Theses and Dissertations
Virtual milling Bélanger, Isabelle
Milling is used to manufacture a wide variety of metal parts, from simple to complex geometries, in small or large volumes. The requirements for these parts usually necessitate that the milling operation is accurate, but also the production rate must be as high as possible. These two requirements, which appear conflicting as first, are met if the milling operation is well planned. While NC programming is still based in many industries on past experience and practical knowledge, research in the areas of cutting mechanics, modelling and simulation are gradually changing the manufacturing practices. This thesis investigates Virtual Milling, which is the integration of milling simulation and CAD/CAM capabilities. Available milling simulation systems can simulate the process for one set of cutting conditions. The objective with Virtual Milling is to not only simulate the milling operation for the whole NC program, but also to integrate features such as feedrate scheduling. A milling simulation for the whole part was developed based on the analytical closed-loop milling model presented by Spence. The input to the simulation is the cutter-workpiece intersections along the tool path. The simulation results include force, torque and power, and deflection along the tool path. The second part of this thesis is the implementation of a Virtual Milling framework. The first step is the selection of cutting conditions which is done during the NC programming. CAD/CAM software do not provide tools to select appropriate cutting conditions, therefore we established the requirements for such a tool using stability lobe theory. An interface was implemented in a commercial CAD/CAM software to demonstrate this. The milling simulation is then used to identify critical locations along the tool path, and it is also used to perform feedrate scheduling. Two offline approaches for feedrate scheduling were implemented, constraint-based feedrate scheduling and off-line adaptive force control, and evaluated to see if their use would lead to improved machining accuracy, better control of cutting forces, and improved machining time. Cutting tests were conducted and these approaches were also compared to an existing online adaptive force control.
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