Yuan-Shin Lee

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

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.

Admissible tool orientation control of gouging avoidance for 5-axis complex surface machining

This paper presents a methodology and algorithms of admissible tool orientation control for gouging avoidance in 5-axis machining. A method is proposed to find the admissible tool orientation by considering both local and global surface shapes. A filleted endmill is used in this study for 5-axis machining. Based on the evaluation of local surface shape, a geometry analysis method is developed to first find a feasible tool orientation for gouging avoidance along two orthogonal cutting places. Adjacent geometry is then taken into consideration for detecting possible rear gouging. A localization algorithm is developed for filleted endmills to identify potential rear gouging area. Both the circular approximation, and the detailed gouging checking methods are proposed for rear gouging correction. The techniques presented in this paper can be used to eliminate errors of tool paths as they are generated. Unlike the traditional graphical verification and user-interactive correction of tool path generation, the proposed methodology can be used to automate the planning and programming of cutter path generation for 5-axis machining.

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

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.

Non-isoparametric tool path planning by machining strip evaluation for 5-axis sculptured surface machining

Abstract Presented in this paper is a new approach to 5-axis NC tool path generation for sculptured surface machining. Techniques of feasible machining strip evaluation are used for non-isoparametric 5-axis tool path generation. A searching algorithm is proposed to find the parameter increments of adjacent cutter locations along orthogonal path intervals for optimal non-isoparametric path generation. Compared to the use of the smallest path interval by the traditional constant parametric path planning, the proposed methodology can generate efficient tool paths for sculptured surface machining by reducing the redundant overlapping between adjacent tool paths. The proposed methodology includes three steps: (1) evaluating feasible machining strip, (2) solving parameter increments (Δu, Δv) along orthogonal path intervals, and (3) searching for adjacent non-isoparametric cutter locations. The techniques presented in this paper can be used to improve 5-axis machined surface quality and to automate the non-isoparametric cutter path generation for CAD/CAM systems.

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

Abstract 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.

Five-axis pencil-cut planning and virtual prototyping with 5-DOF haptic interface

Abstract In this paper, techniques of 5-axis pencil-cut machining planning with a 5-DOF (degree of freedom) output haptic interface are presented. Detailed techniques of haptic rendering and tool interference avoidance are discussed for haptic-aided 5-axis pencil-cut tool path generation. Five-axis tool path planning has attracted great attention in CAD/CAM and NC machining. For efficient machining of complex surfaces, pencil-cut uses relatively smaller tools to remove the remaining material at corners or highly curved regions that are inaccessible with larger tools. As a critical problem for 5-axis pencil-cut tool path planning, the tasks of tool orientation determination and tool collision avoidance are achieved with a developed 5-DOF haptic interface. A Two-phase rendering approach is proposed for haptic rendering and force-torque feedback calculation with haptic interface. A Dexel-based volume modeling method is developed for global tool interference avoidance with surrounding components in a 5-axis machining environment. Hardware and software implementation of the haptic pencil-cut system with practical examples are also presented in this paper. The presented technique can be used for CAD/CAM, 5-axis machining planning and virtual prototyping.

Non-uniform offsetting and hollowing objects by using biarcs fitting for rapid prototyping processes

This paper presents a new method of using non-uniform offsetting and biarcs fitting to hollow out solid objects or thick walls to speed up the part building processes on rapid prototyping (RP) systems. Building a hollowed prototype instead of a solid part can significantly reduce the material consumption and the build time. A rapid prototyped part with constant wall thickness is important for many different applications of rapid prototyping. To provide the correct offset wall thickness, we develop a non-uniform offsetting method and an averaged surface normals method to find the correct offset contours of the stereolithography (STL) models. Detailed algorithms are presented to eliminate self-intersections, loops and irregularities of the offsetting contours. Biarcs fitting is used to generate smooth cross-section boundaries and offset contours for RP processes. Implementation results show that the developed techniques can generate smoothed slicing contours with accuracy for rapid prototyping without suffering from handling the huge number of linear segments of the traditional methods.

Smoothing STL files by Max‐Fit biarc curves for rapid prototyping

Presents a method of Max‐Fit biarc curve fitting technique to improve the accuracy of STL files and to reduce the file size for rapid prototyping. STL file has been widely accepted as a de facto standard file format for the rapid prototyping industry. However, STL format is an approximated representation of a true solid/surface model, and a huge amount of STL data is needed to provide sufficient accuracy for rapid prototyping. Presents a Max‐Fit biarc curve fitting technique to reconstruct STL slicing data for rapid prototyping. The Max‐Fit algorithm progresses through the STL slicing intersection points to find the most efficient biarc curve fitting, while improving the accuracy. Our results show that the proposed biarc curve‐fitting technique can significantly improve the accuracy of poorly generated STL files by smoothing the intersection points for rapid prototyping. Therefore, less strict requirements (i.e. loose triangle tolerances) can be used while generating the STL files.

Dexel-based force-torque rendering and volume updating for 5-DOF haptic product prototyping and virtual sculpting

This paper presents new techniques of Dexel-based force-torque rendering and volume-updating for haptic virtual sculpting of complex surfaces with a developed 5-DOF (degree of freedom) haptic interface. In the proposed methodology, 5-axis tool motion and analytical tool swept volume are formulated for updating the virtual stock material, which is represented with the Dexel volume model. Based on the tool motion analysis, a Dexel-based collision detection method and a force-torque feedback algorithm are proposed for virtual sculpting. A lab-built 5-DOF force-torque output haptic interface system is developed for the proposed haptic sculpting system. With the proposed methodology, a user can virtually sculpt a volume stock to get an intuitive design by using the haptic interface. From the haptic sculpting system, both the corresponding tool motion of the creative process and the sculpted model can be recorded and output. The output STL models of the haptic sculpting system can be processed for machining planning. Based on the proposed techniques, hardware and software implementation of the haptic sculpting system as well as the illustrative examples are also presented in this paper.

Clean-up tool path generation by contraction tool method for machining complex polyhedral models

In high performance machining, multiple cutters of different sizes are used for roughing, finishing and clean-up cutting. In this paper, a contraction tool method is proposed to detect gouging and generate clean-up tool paths for machining complex polyhedral models. The proposed contraction tool method utilizes a series of intermediate virtual cutters to search for clean-up boundaries and construct the clean-up tool paths. The constructed clean-up tool paths consist of a set of clean-up CL-curves traced by the intermediate virtual cutters. The techniques presented in this paper can be used in CAD/CAM systems to automatically identify the clean-up regions of polyhedral models and to generate clean-up tool paths. Computer implementation and practical examples are also presented in this paper.