Mechanical and dynamical process model for general milling tools in multi-axis machining

Official URL: http://192.168.1.20/record=b1306356 (Table of Contents)

Multi-axis milling operations are widely used in many industries such as aerospace, automotive and die-mold for machining intricate sculptured surfaces. The most important aspects in machining operations are the dimensional integrity, surface quality and productivity. Process models are employed in order to predict feasible and proper process conditions without relying on empirical methods based on trial and error cutting and adaptation of previous experiences. However, previously developed process models are often case specific where the model can only be employed for some particular milling tools or they are not applicable for multi-axis operations. In many cases, custom tools with intricate profile geometries are compatible with the surface profile to be machined. On the other hand, for more robust and stable cutting operations, tools with wavy cutting edge profiles and varying geometric edge distributions are utilized. In this thesis, a complete numerical mechanic and dynamic process model is proposed where the tool is modeled as a point cloud in the cylindrical coordinates along the tool axis. The tool geometry is extracted from CAD data enabling to form a model for any custom tool. In addition, the variation in the cutting edge geometry, where serrated and variable helix/pitch cutting edges can be adapted for any milling tool is taken into account. The cutting engagement boundaries are identified numerically using a Boolean intersection scheme. Moreover, a Z-mapping algorithm is integrated in the proposed multi-axis mechanistic force model to predict cutting forces for a continuous process. As for the multi-axis milling dynamics, previous single-frequency stability models are extended to encompass all possible tool geometries taking the time delay variation introduced by irregular cutting edge geometries. The proposed model is experimentally verified with different tool geometries investigating cutting forces and also predicting the stable cutting conditions.