Cha-Soo Jun

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.

Cutter-location data optimization in 5-axis surface machining

Abstract A method of generating ‘optimal’ cutter-location data for 5-axis NC contour milling from given cutter-contact data is presented in the paper. The cutter-location data-optimization problem is formulated as a 2D constrained minimization problem. The cutter orientation angles consisting of the tilt angle α and yaw angle β are used as decision variables. An analytic expression for approximate cusp heights is derived as a function of α, β (for a given path interval) to be used as a measure of optimality. The proposed optimization scheme has been successfully applied in the 5-axis face milling of large marine propellers.

A new curve-based approach to polyhedral machining

This paper presents a new approach to three-axis NC tool path generation for sculptured surfaces. In the proposed curve-based approach, the gouge-free tool paths are generated from a polyhedral model of the STL (stereolithography) format. The polyhedral model is offset by a local-offsetting scheme. Then, the offset elements such as triangular facets, trimmed cylinders, and trimmed spheres are sliced by a series of drive planes. The curve segments on a drive plane are sorted, trimmed and linked, while the concave gouge is removed during the trimming process. The method is implemented on a PC, and some illustrative examples are provided in this paper. The main advantage of the proposed method is that the tool path can be generated from a polyhedral model without any concave and convex gouge, especially on an NC machine that supports NURBS interpolation. Other advantages and disadvantages of the proposed model are also discussed.

Surface slicing algorithm based on topology transition

Abstract Presented in this paper is an algorithm to compute the intersections of a parametric regular surface with a set of parallel planes. Rather than using an ordinary surface-plane intersection algorithm repeatedly, we pre-process a surface to identify points, called topology transition points (TTPs), on the surface where the topologies of intersection curves change. It turns out that such points can be computed efficiently, exactly and robustly employing a normal surface, and they are categorized into seven distinct groups. Analyzing the properties of such characteristic points on the surface, the starting points to trace intersection curves can be found rather efficiently and robustly. Such intersection contours can be used in various applications including rapid prototyping, solid freeform fabrication, process planning, NC tool path generation for surfaces, etc.

MIMS : Web-based Micro Machining Service

Presented in this paper is a Micro Machining Service (MIMS) based on the World Wide Web (WWW) technologies. Taking advantage of the bi-directional communications of the WWW, the fabrication process of micro machining can be expedited and becomes more viable for students or researchers. In order to ensure an easy access to the service, web browsers are used as the user interface of MIMS. A three dimensional geometry generated from a commercial CAD system is uploaded as an STL (Stereo Lithography) file, and the process parameters for three-axis CNC micro milling are to be selected via the user interface. The communication architecture is based on the three-tier client-server model. Depending on the users knowledge on micro machining, novice or expert, controllable input parameters are differentiated, but at any case an STL-based process planner automatically provides NC codes. To achieve high precision, scanning toolpath and pencil-cut toolpath are created by a curve-based polyhedral machining method. The hardware system for micro machining was established, and a couple of sample parts were fabricated by micro endmills. The parts fabricated by scanning toolpath followed by pencil-cut toolpath resulted in less form error (within 1.5%) than the parts fabricated only by scanning toolpath. This service is available at http://fab.snu.ac.kr/cam.

Surface slicing algorithm for rapid prototyping and machining

This paper presents an algorithm to obtain the intersections of a free-form surface with a series of parallel planes. When sectioning the surface with parallel planes, the change of the topology of the intersection curves is caused by characteristic points of the surface. There are seven types of characteristic points: interior maximum, interior minimum, interior saddle, boundary maximum, boundary minimum, boundary max-saddle, and boundary min-saddle points. The starting points of the intersections are found efficiently and robustly using the characteristic points. The characteristic points as well as the intersection contours can be used to evaluate the machining information for process planning, to generate NC tool path for surfaces, and to generate slices for rapid prototyping.

Web‐based design and manufacturing systems for micromachining: Comparison of architecture and usability

In this paper, web‐based micromachining systems are compared with a commercial CAD/CAM system from the point of educational usability. The web‐based systems included in this study were MIcromachining System (MIMS) and SmartFab. In the MIMS architecture, a 3D model in STL format was read using the web browser, the file was sent to the web server where toolpath planner was located, and the NC code was reviewed by the designer through the web connection. In the SmartFab system, SolidWorks was used as the design interface with modified menus that support input parameters for micromachining. This additional function was available by SolidWorks API that provided links to the same toolpath planner as MIMS. In the commercial CAD/CAM case, without using any web connection, SolidWorks and CATIA were used for design, and PowerMill was used as a CAM tool. For each system, accessibility, user‐friendliness, toolpath‐reliability, and processing time were compared. Total of 91 students tested these systems in an undergraduate CAD class, and the users feedback showed better performance of the web‐based system in accessibility, user‐friendliness, and processing time. However, reliability of the web‐based system should be improved to be more useful design and manufacturing system.

Exact Polyhedral Machining

Presented in this paper is a new approach to three-axis NC tool path generation for sculptured surfaces. In the proposed curve-based approach, the gouge-free tool paths are generated from a polyhedral model of STL form. The polyhedral model is offset using local-offsetting scheme. Then, the offset elements such as triangular facets, trimmed cylinders, and trimmed spheres are sliced by a series of drive planes. The curve segments on a drive plane are sorted, trimmed and linked, while the concave gouge is removed during the trimming process. The method is implemented on a PC, and some illustrative examples are provided in this paper. The main advantage of the proposed method is that a polyhedral model can be machined without any concave and convex gouge, especially on a NC machine supporting NURBS interpolation.

Hole-Making on a Bent Thick Plate

A method for cutting non-circular holes on a bent thick plate is proposed. Generally, in order to cut holes on large plates, a special-purpose 5-axis machine is needed. However, such a machine is unavailable in most machine shops. This paper provides a description of a method that utilizes a general-purpose 5-axis water-jet machine in place of the special-purpose machine: First, the bent piece is transformed into a flat plate, where the shape of the holes is reconstructed by considering deformation during bending. Then, after 5-axis NC data is generated, the holes on the flat plate are cut using the 5-axis water-jet machine. In the final step, the desired shape of the piece is obtained by bending the plate with its newly-cut holes. Some illustrations are provided in order to show the validity of the proposed method.© 2005 ASME

Usability of Web-Based Design and Manufacturing Systems: Case Study of Micro Machining

In this paper, web-based design and manufacturing systems are compared with a commercial CAD/CAM system from the point of usability. The web-based systems included in this study were MIcro Machining System (MIMS) and SmartFab. In the MIMS architecture, a 3D model in STL format was read via a web browser, sent to the web server for toolpath planning, and NC codes were generated to be fed back to the designer through the web connection. In the SmartFab system, SolidWorks was used as the design interface with provided modified menus for micro machining. These additional menus were created by SolidWorks API that also provided web-based links to the toolpath planner. In the commercial CAD/CAM case, without using any web connection, SolidWorks or CATIA was used for design, and PowerMill was used as a CAM tool. For each design and manufacturing system, accessibility, user-friendliness, toolpath-reliability, and processing time were compared. Total 91 students tested these systems in undergraduate CAD class, and the feedback showed better performance of the web-based system in accessibility, user-friendliness, and processing time. However, reliability of the web-based system showed necessity of further improvement.Copyright