日期：2017/08/07 發佈者: 流覽次數：321
Designing car bodies in practice is an expensive and time-consuming process involving designers (we used to call them “stylists”), clay modelers, feasibility engineers, ‘Body-in-White’ (BIW) engineers and manufacturing engineers. The objective is to create an attractive shape that fulfills the aesthetic and functional requirements of the car company – but creating that shape is not easy. Subtleties of how light interacts with the shape are crucial and so significant expertise and much time and money are invested in the process.
Since the early 90’s we have had CAD systems to help us and now the ‘master’ shapes are no longer locked into the physical tooling models (‘master models’) but are stored in CAD systems in the form of numerical surfaces. From this data, the engineering of dependent parts (body, chassis and trim) can be progressed. Ultimately, all forms of tooling (press tools, injection moulding tools, RIM tools etc.) can be manufactured from the CAD data. Capturing the crucial surface shape has evolved from spline based systems requiring a lot of care and time to more powerful systems available today.
Traditional methods ‘engineer’ the surfaces by laying out curves and then sweeping and lofting. Blends and fills can then be added. SOLIDWORKS can do this pretty well, but it can be time consuming and results in very long feature trees.
But there is an alternative – using the SOLIDWORKS Power Surfacing partner product. This is a tool that allows creation and manipulation of surfaces with ‘push and pull’ techniques. It is intuitive, easy to use and very fast – much faster for free-form work than with the conventional ‘multiple sketch and feature’ approach.
The underlying technology is called ‘SubD’ modelling meaning ‘Sub Division Modelling’. The method is based on a mathematical approach where a polygon is sub divided recursively to progressively form a smooth surface. The more sub divisions that are made, the smoother the surface. Typically, 3 – 6 sub divisions are sufficient to obtain very smooth shapes. There are several methods of doing this, but the ‘Catmull-Clark’ method is commonly used.
What’s the benefit of this? The answer is that the method creates surfaces that are automatically matched across all boundaries in tangency (‘C1’ continuity) AND curvature (‘C2’ continuity). Car bodies require C2 continuity (except for deliberate creases and styling lines) so tools that inherently create C2 continuous surfaces are hugely beneficial.
To demonstrate how Power Surfacing can be used to build automotive surfaces, I have recorded a Webcast series entitled ‘Power surfacing for Automotive Applications’ covering:
Below is an animation of an E Type Jaguar that I built from images in a couple of hours.