Matthew C. Frank

Rapid planning for CNC milling—A new approach for rapid prototyping

This paper presents a description of how CNC milling can be used to rapidly machine a variety of parts with minimal human intervention for process planning. The methodology presented uses a layer-based approach (like traditional rapid prototyping) for the rapid, semi-automatic machining of common manufactured part geometries in a variety of materials. Parts are machined using a plurality of 21/2-D toolpaths from orientations about a rotary axis. Process parameters such as the number of orientations, tool containment boundaries, and tool geometry are derived from CAD slice data. In addition, automated fixturing is accomplished through the use of sacrificial support structures added to the CAD geometry. The paper begins by describing the machining methodology and then presents a number of critical issues needed to make the process automatic and efficient. Example parts machined using this methodology are then presented and discussed.

Determining Setup Orientations From the Visibility of Slice Geometry for Rapid Computer Numerically Controlled Machining

oped in an effort to automatically create functional prototypes and parts in a wide array of materials. The method uses a plurality of simple two-and-a-half-dimensional (2 1 2 -D) toolpaths from various orientations about an axis of rotation in order to machine the entire surface of a part without refixturing. It is our goal to automatically create these toolpaths for machining and eliminate the complex planning traditionally associated with CNC machining. In this paper, we consider a problem that arises in automating this process—visibility to the surface of a model that is rotated about a fourth axis. Our approach involves slicing the computer-aided design (CAD) model orthogonal to the axis of rotation. The slice geometry is used to calculate two-dimensional visibility maps for the set of polygons on each slice plane. The visibility data provides critical information for determining the minimum number and orientation of 2 1 -D toolpaths required to machine the entire surface of a part. DOI: 10.1115/1.2039100

A computational/experimental platform for investigating three-dimensional puzzle solving of comminuted articular fractures.

Reconstructing highly comminuted articular fractures poses a difficult surgical challenge, akin to solving a complicated three-dimensional (3D) puzzle. Preoperative planning using computed tomography (CT) is critically important, given the desirability of less invasive surgical approaches. The goal of this work is to advance 3D puzzle-solving methods towards use as a preoperative tool for reconstructing these complex fractures. A methodology for generating typical fragmentation/dispersal patterns was developed. Five identical replicas of human distal tibia anatomy were machined from blocks of high-density polyetherurethane foam (bone fragmentation surrogate), and were fractured using an instrumented drop tower. Pre- and post-fracture geometries were obtained using laser scans and CT. A semi-automatic virtual reconstruction computer program aligned fragment native (non-fracture) surfaces to a pre-fracture template. The tibiae were precisely reconstructed with alignment accuracies ranging from 0.03 to 0.4 mm. This novel technology has the potential to significantly enhance surgical techniques for reconstructing comminuted intra-articular fractures, as illustrated for a representative clinical case.

Computing non-visibility of convex polygonal facets on the surface of a polyhedral CAD model

Visibility has found wide applications in manufacturing operations planning and computer vision and graphics. The motivation of this paper is to accurately calculate visibility for objects whose surface is represented by polygonal facets. In this paper, the authors focus on determining non-visibility cones, which are the complementary sets of visibility. This is accomplished by determining sliding planes that comprise the boundaries of a non-visibility cone. The approach presented in this paper directly evaluates the boundaries of the non-visibility cone of an arbitrary convex planar polygon due to the visibility blocked by obstacle polygons. The method is capable of calculating visibility for convex polygons with any number of sides, not limited to triangular facetted models. Implementation is demonstrated in this paper for three to six sided polygonal models.

RAPID PROTOTYPING AS AN INTEGRATED PRODUCT/PROCESS DEVELOPMENT TOOL AN OVERVIEW OF ISSUES AND ECONOMICS

ABSTRACT An overview of issues concerning current methods of rapid prototyping (RP)processes is presented. This paper establishes a basis for categorizing the models developed by both commercial RP systems and conventional means, in particular, CNC machining. Model accuracy in both representation and testing capability is described based on a set of three defining levels, Form, Fit, and Function. This classification system divides models into distinct categories based mainly on dimensional control and the build material used for model construction. The implication is that the accuracy of the model will determine its viability for a specific application. The current popular RP systems and CNC machining are reviewed with respect to these categories. Furthermore, an economic overview provides a second basis for deciding on a particular system for prototype development.

Machinability Analysis for 3-Axis Flat End Milling

This paper presents a method for geometric machinability analysis. The implementation of the strategy determines the machinability of a part being processed using a plurality of 3-axis machining operations about a single axis of rotation for setup orientations. Slice file geometry from a stereolithography model is used to map machinable ranges to each of the line segments comprising the polygonal chains of each slice. The slices are taken orthogonal to the axis of rotation, hence, both two- and three-dimensional (2D and 3D) machinability analysis is calculated for perpendicular and oblique tool orientations, respectively. This machinability approach expands upon earlier work on 2D visibility analysis for the rapid manufacturing and prototyping of components using CNC machining.

Implementation of response surface methodology using variance reduction techniques in semiconductor manufacturing

Semiconductor manufacturing is generally considered a cyclic industry. As such, individual producers able to react quickly and appropriately to market conditions will have a competitive advantage. Manufacturers who maintain low work in process inventory, ensure that specialized equipment is in good repair, and produce quality products at least possible cost will have the best opportunities to effectively compete and excel in these challenging venues. To support this nimble business model, our current efforts are directed toward creating efficient, accurate metamodels of the impact of maintenance policies on production efficiency. These validated polynomial approximations facilitate rapid exploration of the design region, compared with the original simulation models. The experiment design used for metamodel construction employed variance reduction techniques. When compared to a similar experiment design using independent streams, the variance reduction approach provided a decrease in standard error of the regression coefficients and smaller average error when validated against the simulation response.

Advanced Process Planning for Subtractive Rapid Prototyping

Purpose – Subtractive rapid prototyping (SRP) uses layer‐based removal from a plurality of orientations in order to create geometry in a highly automated manner. However, unlike additive means, the method can be inefficient due to redundant cutting operations on previously machined regions. The purpose of this paper is to present process planning methods for SRP, specifically dealing with stock material management in multiple setup operations.Design/methodology/approach – Analysis of remaining stock material was performed by considering slices of respective stereolithography (STL) models. Further, an initial approximation was made of accessibility to enable iterative visibility analysis. The combination of these approaches led to efficient and fast algorithms. After analysis, the slices could be converted back to useful STL models through polyhedral reconstruction.Findings – This method of approximation yields results similar to exact geometry. Using remaining stock data from this approach leads to a sign...

Polygon subdivision for pocket machining process planning

This paper presents a new approach to improve tool selection for arbitrary shaped pockets based on an approximate polygon subdivision technique. The pocket is subdivided into smaller sub-polygons and tools are selected separately for each sub-polygon. A set of tools for the entire pocket is obtained based on both machining time and the number of tools used. In addition, the sub-polygons are sequenced to eliminate the requirement of multiple plunging operations. In process planning for pocket machining, selection of tool sizes and minimizing the number of plunging operations can be very important factors. The approach presented in this paper is an improvement over previous work in its use of a polygon subdivision strategy to improve the machining time as well as reducing the number of plunges. The implementation of this technique suggests that using a subdivision approach can reduce machining time when compared to solving for the entire polygonal region.

Automated fixture design for a rapid machining process

Purpose – The purpose of this paper is to present a methodology for the automated design of a fixturing system for a rapid machining process.Design/methodology/approach – The method proposed is the use of sacrificial fixturing, similar to the support structures in existing rapid prototyping (RP) processes. During the machining process, sacrificial supports emerge incrementally and, at the end of the process, are the only entities connecting the part to the remaining stock material.Findings – The support design methods have been shown to be extremely flexible in securing a variety of complex parts with relatively tight part tolerances using a rapid machining process.Research limitations/implications – The automated design of support structures is currently relegated to use in a CNC rapid prototyping process that uses a fourth axis for rotary setups.Practical implications – The methods used here make rapid machining feasible, as it solves the daunting problem of automated fixturing.Originality/value – The p...