Testing vehicle designs using CAE can be cheaper than building prototypes, but specialist training is needed to use the software
Computer aided engineering has become cheaper, faster and easier to use over the past few years, spreading from large to smaller manufacturing companies. But it is still not a tool for the untrained, and some observers warn about its effectiveness if improperly applied.
CAE is used to analyse 3D computer models of products or parts to determine whether they will perform reliably in real life the tasks for which they have been designed. It aims to be a cost-effective and less time consuming alternative to tests using physical prototypes.
The most commonly used CAE tool is finite element analysis, which is used to predict a structure’s behaviour under stress. It is available from specialist CAE software developers, such as MacNeal Schwendler and Ansys, as well as from CAD/CAM vendors such as SDRC and Parametric Technology (PTC), which sell it integrated with their CAD packages.
Finite element analysis software now runs on PCs and its cost can often be recovered in one project, claims Dr Paul Kurowski, a lecturer and the president and owner of Acom Consulting, a London, Ontario, consulting firm specialising in finite element analysis. `Building and testing a prototype can easily cost £10,000,’ he says. This is about the same cost as a single seat of PTC’s Mechanica finite element analysis software, or of Ansys’s DesignSpace (including hardware and a solid modelling package).
The software is much easier and faster to use now, being menu-driven rather than command-driven as in the past. But, crucially, it still requires a trained design engineer or a specialist CAE expert to build appropriate models for analysis and then interpret the results, which can add substantially to the cost of setting up a system.
Enhancing CAE Effectiveness, published early this year by US research and consulting firm DH Brown Associates, warns about the cost of developing in-house CAE expertise. It calculates that an organisation may have to spend up to $400,000 over five years to train an effective CAE expert.
The notion a few years ago was that CAE software could be made so user-friendly that designers could carry out an analysis on the CAD model they had created, accurately interpret the results and, by repeating the process, eventually produce an optimised design. While steps have been taken towards achieving this goal, a number of obstacles remain.
First, CAD models invariably have to be simplified before they can be analysed in a reasonable time, which takes skill. The finite element meshes that have to be created on the model before analysis should ideally be finer in areas of greater stress, which implies some knowledge about the expected stress patterns in the product before it is analysed. Although automatic meshers are available, they are not guaranteed to produce an appropriate mesh.
Once the model has been analysed, the results need careful interpretation. `It is very easy with this technology to talk about how fast models can be created and analyses run but, while these are important, what matters is whether or not you can get results of the accuracy you need,’ says Gary Carter, Ansys’s northern European sales director.
To further help designers understand the results of an analysis, SDRC has developed variational analysis, as part of the latest release of its I-Deas CAD/CAM/CAE software.
Variational analysis is based on finite element analysis but it is capable of presenting the results of an analysis in terms of geometry and shape, which a designer can understand more easily, rather than, say, stress plots. It is also capable of producing optimised results from only one analysis.
Karen Daggett, a senior engineer at SDRC, explains how the new technology might be applied: `If you have a design where there are ten dimensions you are allowed to change, variational analysis will show you the effect of changing those dimensions on mass or stiffness, and so on. The designer can then choose the dimensions to meet the required performance of the part.
`You can also go one step further and ask, for instance, for a minimum mass design and variational analysis that will give you that information and the design model.’
Having invested in analysis software and an expert to run it, Kurowski stresses the importance of implementation. CAE should be used in a concurrent engineering environment, he says, and the software used early in the product development cycle and continue through to design validation.
But DH Brown warns again about costs. CAE’s use at the front-end of a design will tend to increase product development costs and time for this stage of the process, it says. However, overall costs and time should be reduced, because CAE can achieve a better designed, more reliable product and reduce prototype testing.