Free-form surface

D CAD/modeler Free-form surfaces, parametric geometry, trim curves, surface/material properties, assembly information Tessellation (static dynamic), data reduction (LOD), siuface properties — > textures, materials, reflection mapping... 

Fraunhofer Institute for Production Systems and Design Technology, 218 Freedom (privacy service), 269 Free-form surfaces, modeling, 182, 1881 Free trade zones (FTZs), 1489-1490 Freight vehicles, 2063... 

Surface-oriented systems are able to generate objects, known as free-form surfaces, whose surfaces are made up of numerous curved and analytically indescribable surfaces. One feature visible in an internal computer representation of free-form surfaces is their interpolated or approximated nature. Therefore, various processes have been developed, such as the Bezier approximation, Coon s surfaces, the NURBS representations, and the B-spUne interpolation (see Section 4.1). 

As with aU other models, the computer internal representation of an object implies characteristic methods and techniques used in generating free-form surfaces. In general, basis points and boundary conditions are required for the surface description. Free-form surfaces, such as the one portrayed in Figure 2, can be generated using a variety of techniques. A few examples for the generation of freeform surfaces will be described later. 

Figure 2 Modeling Processes for Free-Form Surfaces. ...

Solid models with a number of free-form surfaces are realized using surface-oriented modeling techniques that correspond to the surface model presented. With one of these techniques, sweeping, one attains a 3D body through an intermediate step when creating a 2D contour. The 2D contour is expanded to three dimensions along a set curve. The desired contours are generated with known 2D CAD system functions and are called up as bases for sweep operations. 

The interface standard VDA-ES was developed by the German Automotive Industry Association for the transfer of CAD free-form surface data. VDA-FS is standardized and described in Standard DIN 66301 and has proven efiScient for use in many areas, but its efficiency has been demonstrated principaUy in the German automotive industry (Grabowski and Glatz 1986 Nowacki 1987 Scheder 1991). 

Often special application modules are required that cannot be integrated seamlessly into the CAD system. Therefore, various automobile manufacturers, such as Ford, General Motors, Nissan, VW, Audi, and Skoda, have implemented special surface modelers besides their standard CAD systems to enable free-form surface designs to be carried out. 

The diamond machining process most frequently employed for the generation of free-form surfaces is single-edge circumferential milling. 

There are two different kinematics applied in fly-cutting of free-form surfaces ... 

Such geometric characteristics can refer to absolute dimensions (e.g., diameter) and form (e.g., free-form surfaces), to tolerances of dimensions and form (e.g., flatness), as well as surface parameters (e.g., average surface roughness). 

An enhanced force model-based /eedrate scheduling (FFS) technique is used to optimize the feedrate for rough cutting of parts with complex free-form surfaces in 5-axis ball-end milling and micro end milling processes. 

In free-form surface machining, the distance and rotation angle between two CL points are relatively small therefore, the effect of rotational velocities of the tool is negligible. Considering this, the instantaneous chip thickness for a... 

Free form surfaces, as their name suggests, can have any shape. Variations of their shape are limited by the capabilities of model representation and manufacturing processes. Input information (Figure 3-38) defines their initial shape ... 

Free form surfaces are also called sculptured surfaces because the result is sometimes like a sculpture. These surfaces sometimes are created in a manner similar to making a sculpture. Curve set inputs suggest the third name for free form surfaces mesh surfaces. 

Most of the surfaces in part boundaries are created by one of the shape control rules. The shape is generated according to the selected rule. Control rules are often used to give an initial shape, and then some regions are modified as free form surface or by associative relations to other parts. 

A series of filleting operations may produce a complex set of analytic surfaces and curves. Advanced filleting methods can fit a single or several free form surfaces to replace a large number of analytical curves and surfaces. Fillets in advanced shape models are often created as free form surfaces instead of as simple analytic surface segments. However, continuity constraints do not allow too many variations of their shape. 

Creating Free Form Surfaces Using Ciouds of Points... 

The resulting surface can be improved by refined local redigitization of the physical object. Data sets can be improved by union and subtract combinations. In advanced modeling systems, dimensions can be defined as for dimension-driven free form surfaces within arbitrary points, in arbitrary directions. 

Another solution approach subdivides the CAD model that needs to be exchanged in two portions a confidential portion which has to be encoded, and a non-confidential portion which can be fully accessed by a partner without any restriction. The subdivision of the free form surface description in such a way can be realized with wavelets [44]. These functions are used to divide the data into hierarchically arranged coefficients. A crucial step is to localize confidential information in the coefficients of one or a few levels and encode these contributions only. The selection of the usable wavelets is an important choice, because it... 

Yuan, X. Zhenrong, X. Haibin, W. (2001). Research on integrated RE technology for forming sheet metal with a free form surface. Journal of Materials Processing Technology, Vol.112, pp. 153-156, ISSN 0924-0136... 

As already mentioned above, the calculation methods are strongly dependent on the data model. The geometries can be illustrated differently from point, to lines, to surface, to volume models and provide different advantages in the CAD program depending on the objectives (Figure 2.20). Thus, for example, free-form surfaces can be produced and modified on surface models. 

For simple components, constructive circle methods can be applied that are similar to the flow pattern method. However, in complex components with (for example) different rib depths and rib densities in combination with free-form surfaces, the limits of the methods are quickly exhausted, and a design with numerical methods is essential. 

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