Ming-Chuan Leu

Progress in Additive Manufacturing and Rapid Prototyping

Abstract Rapid prototyping generally refers to techniques that produce shaped parts by gradual creation or addition of solid material, therein differing fundamentally from forming and material removal manufacturing techniques. This paper tries to summarise one decade of research and developments in rapid prototyping. The first part surveys some general economical and technological trends. The second part of the paper goes into some more details on a process-by-process basis.

The Sweep-Envelope Differential Equation Algorithm and Its Application to NC Machining Verification

Abstract A new method, called the sweep-envelope differential equation, for characterizing swept volume boundaries is introduced. This method is used as the theoretical foundation of an algorithm for computing swept volumes using the trajectories of the sweep-envelope differential equation which start at the initial grazing points of the moving object. The major advantages of this algorithm are: (1) the grazing point set need essentially only be computed at the initial position of the object—the remaining grazing points are generated by the flow of the sweep-envelope equation—so the computation complexity is drastically reduced; and (2) it provides automatic connectivity for computed boundary points that facilitates integration with standard algorithms and cad software for visual realization and Boolean operations. Examples are presented that illustrate successful integration of a prototype program (based on the algorithm) with commercial NC verification software.

Electroforming process and application to micro/macro manufacturing

Abstract Electroforming is the highly specialised use of electrodeposition for the manufacture of metal parts. This paper describes the process principles and mechanisms of electroforming, outlining its advantages and limitations. A review of modelling and simulation of electroforming and experimental analysis work is also presented. The metals that can be electroformed successfully are copper, nickel, iron or silver, thickness up to 16 mm, dimensional tolerances up to 1 μm, and surface finishes of 0.05 μm R a . The ability to manufacture complex parts to close tolerances and cost effectively has meant that electroforming has applications both in traditional/macro manufacturing and new micromanufacturing fields. These include tooling; mould making; fabrication of microelectromechanical systems (MEMS) and the combination of lithography, electroforming and plastic moulding in the LIGA process. Applications in micro-optics and medicine are included.

Design of optical triangulation devices

Abstract This paper presents the derivation of the precise relation between the displacement of a light spot on an objects surface and the displacement of its image on the detector in an optical triangulation device, along with applications of the design of triangulation devices. Based on this relation, improved designs of optical triangulation devices, including devices of adjustable configurations, are proposed and discussed.

Analysis of swept volume via Lie groups and differential equations

The development of useful mathematical techniques for an alyzing swept volumes, together with efficient means of im plementing these methods to produce serviceable models, has important applications to numerically controlled (NC) machin ing, robotics, and motion planning, as well as other areas of automation. In this article a novel approach to swept volumes is delineated—one that fully exploits the intrinsic geometric and group theoretical structure of Euclidean motions in or der to formulate the problem in the context of Lie groups and differential equations. Precise definitions of sweep and swept volume are given that lead naturally to an associated ordinary differential equation. This sweep differential equation is then shown to be related to the Lie group structure of Euclidean motions and to generate trajectories that completely determine the geometry of swept volumes. It is demonstrated that the notion of a sweep differential equation leads to criteria that provide useful insights concern ing the geometric and topologic features of swept volumes. Several new results characterizing swept volumes are obtained. For example, a number of simple properties that guarantee that the swept volume is a Cartesian product of elementary mani folds are identified. The criteria obtained may be readily tested with the aid of a computer.

Mathematical modeling and experimental verification of stationary waterjet cleaning process

The use of stationary waterjet for the removal of coating material from the substrate is investigated analytically and experimentally. In the analysis, the cleaning width as a function of standoff distance, water pressure, and nozzle radius is derived by considering the structure of waterjet and the cleaning mechanism. Also derived are the relations of the optimal cleaning standoff distance and maximum cleaning width to the critical cleaning standoff distance, and how the water pressure and nozzle radius affect this critical standoff distance. These derived analytical relations are verified with experimental results.

Fractal geometry model for wear prediction

Abstract Fractal characterization of surface topography is applied to the study of contact mechanics and wear processes. The structure function method is used to find the fractal dimension D and the topothesy L . We develop a fractal geometry model, which predicts the wear rate in terms of these two fractal parameters for wear prediction. Using this model we show that the wear rate V r and the true contact area A r have the relationship V r αA r m ( D ) , where m ( D ) is a function of D and has a value between 0.5 and 1. We next study the optimum ( i.e. the lowest wear rate) fractal dimension in a wear process. It is found that the optimum fractal dimension is affected by the contact area, material properties and scale amplitude. Experimental results of wear testing show good agreement with the predictions based on the model.

Experimental study on the ice pattern fabrication for the investment casting by rapid freeze prototyping (RFP)

The process of investment casting has come to occupy a key position in the range of modern metal casting techniques. Wax pattern is widely used in the investment casting. However, there exist some problems and technical difficulties in using it such as wax pattern expanding, ceramic shell cracking, etc. A new investment casting technology, named freeze cast process (FCP), has demonstrated the possibility and advantage of investment casting with ice patterns. But how to make ice patterns is really an important concern in the FCP process. RFP is a novel, environmentally conscious solid freeform fabrication process that can generate three-dimensional ice patterns by selectively depositing and rapidly freezing water layer by layer. With RFP it is possible to make ice patterns with better accuracy and more flexibility directly from CAD models in a short time, without the cost and other issues of mold making. In this paper, the current status of the experimental study of the RFP process was introduced. The effect of different processing parameters on the layer thickness and layer width was studied quantitatively and thoroughly. These parameters include: frequency of pulse signal, stagnation pressure, scanning velocity, distance between nozzle and building surface, duty cycle of pulse signal, layer offset (slant angle), environmental temperature, scanning trajectory, any depositing material. And further the effect of the processing parameters on the dimension accuracy and surface roughness were analyzed qualitatively. The optimal parameters were chosen and used to fabricate complex ice patterns based on these experiments and analyses. Finally, an example was given to demonstrate that an ice pattern can be used to make the metal prototype.The fabricated metal prototype has a very good appearance, although surface roughness and dimensional accuracy have not been measured. The experiment results showed that RFP provides an enabling way to quickly make ice patterns for the investment casting with better quality and more flexibility.

RAPID FREEZING PROTOTYPING WITH WATER

Abstract Rapid Freezing Prototyping (RFP) with water is a novel solid freeform fabrication technique that can generate three-dimensional ice objects by depositing and rapidly freezing water layer by layer. It provides a means to build a solid part (ice part) with the potential of better performance than other solid freeform fabrication techniques in many aspects. The support, where necessary, is made of brine whose freezing point is lower than pure water. After building the part, the support can be removed by utilizing the melting temperature difference between brine and water. Preliminary experiments have shown that the ice patterns can be used for design visualization and silicone molding. This paper will present the concept and some experimental results of the RFP process as well as its potential applications.

Geometric Representation of Translational Swept Volumes and its Applications

This paper presents a method for representing the geometries of translational swept volumes of three-dimensional objects which can be constructed by the union of three types of primitive objects: blocks, cylinders, and spheres. The representation method involves three major steps. First, the swept volume of each primitive object is modeled by a boundary representation. Second, based on ray-casting and scan-rendering methods, the boundary representation is converted into a ray in–out classification, which represents the rays entering and exiting from the primitive swept volume. Third, the ray in–out classifications for various primitive swept volumes are combined to represent the swept volume of an object constructed from the primitive objects. Examples are given to illustrate how swept-volume representations can be useful in the context of off-line NC and robot program verifications.