Tien-Chien Chang

Protrusion-features handling in design and manufacturing planning

Abstract In a feature-based design system, a designer should be able to design with both protrusion and depression features. Since depression features loosely correspond to machining processes, they are easy to handle during process planning and NC cutter-path generation. However, the same cannot be said for protrusion features. Not only do the removal volumes surrounding the feature need to be extracted into depression features, but the original workpiece needs to increase in size so that there is enough material for the protruding features. A backward-growing methodology for handling protrusion features for process planning is discussed. Its implementation in an integrated design/ manufacturing system called QTC II is described.

Application of computational geometry in optimizing 2.5D and 3D NC surface machining

Abstract To machine a part from the CAD data, machining information has to be extracted from the design model. In the planning stage, the machining information such as the cutting area, removal volume, estimated machining time, etc., is important for the generation of a “good” process plan. This machining information is typically not readily available from the design. This paper discusses a methodology of applying computational geometry techniques to extract machining information of geometric constraints from a given complex surface design to support the process planning activity. The machining process is determined by part surface classification based on surface geometry interrogation. An application of convex hulls is also presented to improve the machining productivity by preprocessing the object geometry for machining. The proposed methodology can be applied in the automation of planning and manufacturing of complex surface parts. Some practical examples and testing results are presented to show the application in solving manufacturing problems.

CASCAM—An automated system for sculptured surface cavity machining

Abstract A systematic procedure that automatically generates machining processes for sculptured surface cavity machining is presented. The work proposed here includes the evaluation of machining information, decision for machining process strategy, automatic cutter selection, and cutter path generation. Machining information is first evaluated by considering the cavity geometric shape, removal volume, and constraints of machining. A decision on the process strategy is determined based on the machining information evaluated. Then the procedures of machining the cavity are decided. The cutter selection is automatically determined by considering geometric constraints, the maximum material removal rate in the roughing process and the minimum cutter movement with the required accuracy in the finishing process. The roughing process is approached by some arbitrary-shape pocketing procedures combined with islands on the cutting planes. Cutter movements and cutter selection are optimized by considering the global information of machining conditions on adjacent cutting planes. A system called cascam has been developed to prove the feasibility of the proposed concept.

Three-axis machining of compound surfaces using flat and filleted endmills

Abstract Flat and filleted endmills are less frequently used than ball-end cutters in 3-axis sculptured surface machining. However, they improve cutting efficiency to a great degree in some applications, such as machining smooth part surfaces or rough cutting. Presented in this paper is a method to generate cutter paths to make effective use of these cutter types. A part surface is first approximated into a triangular polyhedron. Cutter paths are then generated from the tessellated surface model. The robust method makes it possible to machine any compound sculptured surfaces regardless of their complexity. An efficient algorithm is used for calculating cutterlocation data.

Prospects for process selection using artificial intelligence

Abstract On problem facing modern industry is the lack of a skilled labor force to produce machined parts as has been done in the past. In the near future, this problem may become acute for a number of manufacturing tasks. One such task is process planning. Since process planning requires intelligent reasoning and considerable experiential knowledge, almost all existing computer aided process planning systems require a significant amount of supervision by an experienced human being. There is some prospect that “expert computer system” techniques from the field of Artificial Intelligence may be successfully used to automate (at least partially) several of the reasoning activities involved with process planning. This paper discusses some current prospects for automating a process planning task known as process selection. These ideas are currently being considered for use int he Automated Manufacturing Research Facility project at the U.S. National Bureau of Standards, and steps are being taken to implement them in an expert computer system.

Hierarchical representation of problem-solving knowledge in a frame-based process planning system

In most frame‐based reasoning systems, the information being manipulated is represetned using frames, but the problem‐solving knowledge that manipulates the frames is represented as production rules. One problem with this approach is that rules are not always a natrual way to represent knowledge; another is that systems containing lots of rules may suffer from problems with “exponetial blowup” in the amount of computation required. This paper describes a way to address these problems by organizing the problem‐solving knowledge not as rules, but in a particular kind of frame hierarchy. the approach described in this paper has been implemented in a problem‐solving system called SIPP (Semi‐Intelligent Process Planner), which produces plans of action for the manufacture of metal parts. the paper gives an overview of SIPP, compares its knowledge representation and problem solving methods to approaches used in other knowledge‐based systems, and describes goals for further research.

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.

Using virtual boundaries for the planning and machining of protrusion free-form features

Abstract Sculptured surfaces are frequently encountered in modern engineering designs. Sculptured surface machining is a time-consuming and error-prone process. It is critical that proper tools are selected and cutter paths generated. In this paper, a method called the virtual boundary approach is proposed to integrate a protrusion free-form surface feature with conventional polyhedron features in a feature-based design and manufacturing system. Using the proposed virtual boundary approach, a protrusion free-form feature can be converted into a virtual pocket with islands. The machining of a protrusion sculptured surface feature is transformed into a series of virtual pocketing processes. The proposed methodology transforms the union operation of a protrusion free-form feature into a difference operation of removal volumes. Techniques of automatic cutter selection and cutter path generation are presented. A complete operation plan and cutter path can be generated for machining using the proposed virtual boundary method. Practical examples and automatic cutter path generation for machining are also presented.

A collision-free sequencing algorithm for PWB assembly

The main task of printed wiring board (PWB) assembly is to mount electronic components on a PWB. The generation of efficient insertion and placement sequences will lead to significant time saving in assembly and thus save production cost. When generating insertion sequences, the first consideration is to avoid potential collision problems. This research is aimed at finding the minimum assembly time for each assembly machine through the generation of machine-head sequences and component sequences. Mathematical programming may be used to solve the sequence problem; however, the solution is computationally explosive and is impractical to implement. The proposed collision-free and closest-distance heuristic approach is based on the various characteristics of printed wiring assembly, such as insertion heads and component feeding types. This approach reduces the complexity of the problem and detects potential collisions before the generation of machine-head sequences and component sequences. Not only can the algorithm generate machine head sequence and component sequences effectively, it also guarantees no conflict between these two levels.

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.