Freeform surfaces, also called sculptured surfaces, have been widely used in various engineering applications. Freeform surfaces are primarily manufactured by CNC machining, especially 5-axis CNC machining. Various methodologies and computer tools have been developed in the past to improve efficiency and quality of freeform surface machining. This paper aims at providing a state-of-the-art review on recent research development in CNC machining of freeform surfaces. This review primarily focuses on three aspects in freeform surface machining: tool path generation, tool orientation identification, and tool geometry selection. For each aspect, first concepts, requirements and fundamental research methods are briefly introduced. The major research methodologies developed in the past decade in each aspect are presented with details. Problems and future research directions are also discussed.

Review: Recent development in CNC machining of freeform surfaces: A state-of-the-art review

This paper presents a methodology and algorithms of optimizing and smoothing the tool orientation control for 5-axis sculptured surface machining. A searching method in the machining configuration space (C-space) is proposed to find the optimal tool orientation by considering the local gouging, rear gouging and global tool collision in machining. Based on the machined surface error analysis, a boundary search method is developed first to find a set of feasible tool orientations in the C-space to eliminate gouging and collision. By using the minimum cusp height as the objective function, we first determine the locally optimal tool orientation in the C-space to minimize the machined surface error. Considering the adjacent part geometry and the alternative feasible tool orientations in the C-space, tool orientations are then globally optimized and smoothed to minimize the dramatic change of tool orientation during machining. The developed method can be used to automate the planning and programming of tool path generation for high performance 5-axis sculptured surface machining. Computer implementation and examples are also provided in the paper.

Optimizing tool orientations for 5-axis machining by configuration-space search method

Accurate measurements and degradation mechanisms of the channel mobility for MOSFETs with HfO/sub 2/ as the gate dielectric have been systematically studied in this paper. The error in mobility extraction caused by a high density of interface traps for a MOSFET with high-k gate dielectric has been analyzed, and a new method to correct this error has been proposed. Other sources of error in mobility extraction, including channel resistance, gate leakage current, and contact resistance for a MOSFET with ultrathin high-k dielectric have also been investigated and reported in this paper. Based on the accurately measured channel mobility, we have analyzed the degradation mechanisms of channel mobility for a MOSFET with HfO/sub 2/ as the gate dielectric. The mobility degradation due to Coulomb scattering arising from interface trapped charges, and that due to remote soft optical phonon scattering are discussed.

Mobility measurement and degradation mechanisms of MOSFETs made with ultrathin high-k dielectrics

This paper presents a machining potential field (MPF) method to generate tool paths for multi-axis sculptured surface machining. A machining potential field is constructed by considering both the part geometry and the cutter geometry to represent the machining-oriented information on the part surface for machining planning. The largest feasible machining strip width and the optimal cutting direction at a surface point can be found on the constructed machining potential field. The tool paths can be generated by following the optimal cutting direction. Compared to the traditional iso-parametric and iso-planar path generation methods, the generated MPF multi-axis tool paths can achieve better surface finish with shorter machining time. Feasible cutter sizes and cutter orientations can also be determined by using the MPF method. The developed techniques can be used to automate the multi-axis tool path generation and to improve the machining efficiency of sculptured surface machining.

A machining potential field approach to tool path generation for multi-axis sculptured surface machining

Five-axis machining has been used widely in manufacturing freeform surfaces. The traditional approach of using a homogeneous transformation matrix (HTM) relies on heavy symbolic manipulation of the matrix multiplication. In this work, a new approach - the matrix summation approach - is developed and implemented for modelling the geometric errors of five-axis machine tools. This approach breaks down the kinematic equation into six components, each of which has clear physical meaning. It reduces the computations substantially and makes the five-axis kinematic model manageable and understandable.

Modelling of Five-Axis Machine Tool Metrology Models Using the Matrix Summation Approach

In this paper, a new approach is presented to find the 3D shape-generating profiles of different types of cutters for constructing the G-buffer models for 5-axis machining. The G-buffer for 3-axis machining is natural because the tool has only three degrees of freedom (x,y,z) for the configuration space. Five-axis machining has five degrees of freedom, and two of them are non-Euclidean. The traditional G-buffer method cannot be directly used for 5-axis machining due to the complex tool motions. In this paper, the analytic 3D shape-generating profiles are formulated to construct the swept envelope in 5-axis tool motion. The enhanced G-buffer models are updated by the constructed 5-axis swept envelope. A generalized cutter geometry, which represents different types of endmills, is used in this study. The techniques presented in this paper can be used for 5-axis tool path generation and the machined surface error analysis. Computer implementation and illustrative examples are presented in this paper.

Chuang-Jang Chiou

Papers

A machining potential field approach to tool path generation for multi-axis sculptured surface machining

A shape-generating approach for multi-axis machining G-buffer models

Unfolded projection approach to machining non-coaxial parts on mill-turn machines