CAD Surface Research Articles

Computer Graphics in Rapid Prototyping Technology [Guest Editor's Introduction

Rapid prototyping has been called "real virtuality" to emphasize its transformation of virtual objects from cyberspace into real objects. It also goes by "3D printing" to highlight the direct realization of a 3D object from an abstract graphics design, in contrast to the more usual 2D plotting of views. "Free-form fabrication" and "tool-less manufacturing" are commonly used descriptive terms. "Desktop manufacturing" and "3D hard copy" are seen in the lay press. Other variants include RPM for "rapid prototyping in manufacturing" and LMT for "layered manufacturing technologies." Whatever the name, the evolving use of RP technologies like stereolithography and selective laser sintering to quickly produce parts directly from a CAD surface or solid model is an innovative application area for computer graphics. From a designer's abstract computer model, these technologies now make it routinely possible to fabricate a 3D solid part in a matter of hours or days, rather than the weeks or months conventional production methods can take.

Improved simulation of thin-sheet metalforming using LS-DyNA3D on parallel computers

Finite-element programs based on explicit time integration have proven to be currently among the most versatile instruments for the simulation of thin-sheet metalforming. This advantage is particularly evident if finite-element meshes with large numbers of unknowns and contact surfaces are used. Recent developments of the explicit program LS-DYNA3D have been concerned with contact search and contact treatment, focusing on the accuracy and efficiency of these algorithms. The introduction of general CAD surfaces for the surface description of rigid tools has improved the modeling capabilities and the results considerably compared to the faceted representation of contact surfaces, which is the standard in current FE technology. The latter algorithms are parallelized for shared memory and MIMD computers, resulting in a large overall increase in speed for the analysis. The present contribution presents an overview over the algorithms developed and of the most recent enchancements of LS-DYNA3D for sheet metalforming concerning materials and new shell elements. The efficiency of the parallel algorithms is demonstrated with some numerical and practical examples.

Rigid contact modelled by CAD surface

The present paper deals with the problem of large displacement frictionless contact between a rigid obstacle and an elastic body. In Klarbring a formulation of this problem which makes use of a distance function G is given, and in Bjorkman the related computational scheme is presented. We give in this introduction a summary of these works, which shows the central position in the computational scheme of the function G, its gradient ΔG and its Hessian Δ2G. In the next section we present a particular distance function that is useful when, in the computational realization, the rigid obstacle is a CAD surface with continuous curvature. As an example of such a surface, we briefly present the conceptual ideas of Ferguson bicubic spline surfaces. Then a search algorithm needed for determination of the value of G during iterations is given. Finally, we present some test examples.

GC 1 continuity conditions between adjacent rectangular and triangular Bézier surface patches

Necessary and sufficient conditions for geometric C 1 continuity (GC 1) that cover all the four combinations between rectangular and triangular Bézier surface patches are presented. Further, some more practical sufficient conditions are developed. The GC 1 conditions is several special cases might be useful for CAD surface modelling.

Optical measurement of surface form using computer-generated referencing

The topography of a complex surface can be measured by projecting a light pattern onto it and examining the moire fringes which are obtained when the image of the object is compared with a reference grid. It is possible to measure the difference in form of nominally identical objects by adding or subtracting the observed grids on the two components. The form of CAD generated objects is being measured in this way by comparing the grid obtained on the surface with a grid which is generated using the CAD surface data.

A method of interactive visualization of CAD surface models on a color video display

To introduce rendered surface display technology into the production design environment, many CAD operations envision a single color video display device for download processing of selected model pictures. Creation of a single image from a typical industrial CAD model involving a large number of higher order curved surfaces will normally require a minimum of several minutes' delay for data acquisition and visible surface computation. This paper describes a method that extends the visible surface operation to give the designer an interactive tool with which he can more effectively comprehend model composition. Instead of defining data for a single image, an intermediate three-dimensional structured file is created. A tailored display program manipulates the structured data file allowing a user to interactively create surface rendered images. Program capabilities include: • Section and cutaway viewing • Selected surface color, transparency, or translucency • Shadows projected from desired light-source locations Changing or combining any of these facilities requires only seconds for a new image to be created.