Byoung Kyu Choi

Automatic recognition of machined surfaces from a 3D solid model

Abstract It has been proposed that a direct link between CAD and CAM be provided through a computer-automated process planning system. Described in this paper are algorithmic procedures to identify machined surfaces (ie, machining requirements) for a workpiece directly from its 3D geometric description. A machined surface is a portion of workpiece that can be generated by a certain mode of metal removal operation. Machined surfaces are algorithmically recognized from a 3D boundary file, and then their 2(built|1/2)D descriptions are obtained in a data structure (format) suitable for an automated process planning system. A simplified boundary file data structure is introduced in order to explain the machined surface recognition procedures. A machined surface type is defined as a pattern of faces, and a syntactic pattern recognition method is used to find the machined surface from the boundary file.

Ball-end cutter interference avoidance in NC machining of sculptured surfaces

Abstract Cutter interference (or part surface gouging) is one of the most critical problems in NC machining of sculptured surfaces. Presented in this paper is an algorithmic procedure that converts CC data (cutter contact points data) into interference-free CL data (cutter location data). The algorithm automatically identifies ‘concave interferences’ as well as ‘convex interferences’ and then removes them. The undercut volumes left over by the removal of interfering CC data can also be machined subsequently by using a smaller ball-endmill. The time complexity of the algorithm is O(N) when the number of CC points N is increased by increasing the surface area (without increasing the density of CC points), and it becomes O(N) 2 if N is increased by increasing the density of CC points (with surface area fixed).

Compound surface modelling and machining

Abstract A method is presented for modelling and machining ‘compound surfaces’ commonly found in die cavities and punches. A collection of topologically unrelated surface elements specified in a domain of interest is termed as a compound surface. A constructive solid geometry scheme is employed to model compound surfaces that consist of planar surface elements, general quadratic surface elements, and composite parametric surfaces. Implementation strategies as well as computational details are presented. A prototype modelling system has been implemented on an IBM PC AT. It took less than five minutes to generate cutter location data for a compound surface of realistic complexity.

C-space approach to tool-path generation for die and mould machining

Presented in the paper is a new approach to 3-axis NC tool-path generation for sculptured surface machining. In the proposed C-space approach, the geometric data describing the design-surface and stock-surface are transformed into C-space elements, and then, all the tool-path generation decisions are made in the configuration space (C-space). The C-space approach provides a number of distinctive features suitable for high speed machining of dies and moulds, including: (1) gouge-free and collision-free tool-paths; (2) balanced cutting-loads; (3) smooth cutter movements; and (4) verification mechanisms. It is suggested, with some supportive results, that the Z-map model might be a suitable representation scheme for implementing the C-space method. Also discussed are other implementation as well as future research directions.

Tool-path planning for direction-parallel area milling

Abstract Presented in the paper is a tool-path planning algorithm for direction-parallel area milling consisting of three modules: (1) finding the optimal inclination; (2) calculating and storing tool-path elements; and (3) tool-path linking. For the optimal inclination, we suggest an algorithm that selects an inclination by reflecting the shape of the machining area as well as the tool-path interval. We make use of the concept of a monotone chain and the plane-sweep paradigm to calculate the tool-path elements. The concept of a monotone chain brings clarity and tight-time complexity to the proposed algorithm. The tool-path linking problem is modeled as a TPE-Net (tool-path element net) traversing problem. For the two direction-parallel milling topologies, one-way and zigzag, tool-path linking algorithms are proposed. Empirical tests show that the proposed algorithm fulfils its requirements.

A pair-wise offset algorithm for 2D point-sequence curve

Abstract Presented in the paper is an efficient pair-wise offset algorithm for closed 2D point-sequence curves (PS-curve). A key feature of the proposed algorithm is that all local invalid loops are removed from the input PS-curve before constructing a raw offset-curve, by invoking a pair-wise interference-detection (PWID) test. In the PWID test, each pair of elementary offset segments is tested for interference and then interfering segments are successively removed. The proposed algorithm has been implemented and tested with various PS-curves. Empirical tests show that the proposed PS-curve offsetting method is very fast and robust with a near O(n) time-complexity, where n is the number of points in a PS-curve.

Modeling the surface swept by a generalized cutter for NC verification

Presented in this article is a procedure for representing the cutter-swept surface (CSS) of a generalized cutter in a single-valued form, z = f(x, y). The key idea is that the z-value of the CSS at a 2D point (x, y) is expressed as the sum of 1) the z-value at a point on the silhouette curve of the cutter bottom surface and 2) the incremental z-value along the cutter movement direction. Thus, the main part of the modeling method is to obtain the silhouette curve equations, which becomes a root finding problem for a quartic polynomial (when the cutter bottom surface contains a toroidal surface). The proposed method not only renders a single-valued representation for the CSS of a generalized cutter (which was not possible with the existing methods) including rounded endmill but also results in a computational scheme that is faster than the existing schemes for ball- and flat endmills.

Die-cavity pocketing via cutting simulation

Abstract For die-cavity pocketing, the cavity volume is sliced into a number of cutting-layers by horizontal cutting-planes, and each layer is pocket-machined using the contour-parallel offset method in which the tool-paths are obtained by repeatedly offsetting the boundary-pocketing curve. The major challenges in die-cavity pocketing include: 1) finding a method for obtaining the boundary-pocketing curve, 2) generating evenly spaced contour-parallel offset toolpaths, 3) detecting and removing uncut-regions, and 4) estimating chip-loads for an adaptive feed control. No systematic solution for these problems has been offered in the literature, except the curve offsetting methods for computing contour-parallel offset curves. Presented in the article is a straightforward approach to die-cavity pocketing, in which all the four challenges are handled successfully by using the existing cutting-simulation methods.

Machining efficiency comparison direction-parallel tool path with contour-parallel tool path

Abstract In molds and dies manufacturing, estimation of the machining time of tool paths is a pre-requisite for planning the machining processes and balancing them. The machining time is computed by dividing the distance of the tool path by its feed-rate. This theoretical machining time always underestimates the actual time, because it does not take into account the effects of the acceleration and deceleration of the CNC machines. This paper proposes a machining time model that considers the acceleration and deceleration of the CNC machines. Using the proposed model, we compare the machining efficiency of the tool paths currently employed in molds and dies manufacturing—three types of direction-parallel tool paths (one-way path, pure-zig-zag path, and smooth-zig-zag path) and contour-parallel tool path. The results of the comparison simulation reveal that the smooth-zig-zag path is the most efficient regardless of feed-rates and path intervals and that the effects of acceleration and deceleration are notably revealed at higher feed-rates.

Constant-radius blending in surface modelling

Abstract A method for blending (rounding / filleting) parametrically defined surfaces is proposed. Any rectangular parametric surface patches can be blended as long as their offset surfaces (with offset distance equal to the blending radius) are smooth so that intersections between offset surfaces can be well defined. Rolling-ball (edge) blends are constructed mathematically by sweeping rational quadratic (conic section) curves. Corner blends where three surfaces meet are represented by a convex combination of linear Taylor interpolants. The fullness of edge blends (and of corner blends) can easily be controlled.