The way it should be

Dave Wilson spoke to Paul Pankhurst at PDD to find out which features he would like to find in a CAD package but can’t get.

Design engineers make extensive use of CAD systems in new product development, but often, the features of the CAD systems are dictated by the package vendors. Frequently, no single CAD package meets all their needs, so they end up using numerous packages – often with radically different interfaces – to get the design through to completion.

Starting with a free form surfacing package the designer experiments with the form and shape of the product. The data thus created is exported to an engineering package for more complex mechanical design. Component performance predictions are performed using, for example, FEA (finite element analysis) techniques. Finally, the data is transferred to yet another package so the designer can visualise CNC tool paths, visually assess the design, verify assembly features and confirm performance predictions.

Even this scenario is simplistic, and often still more dedicated packages may be called into play.

The primary problem is that the designer needs to understand numerous packages to expedite a particular design. Usually, it means that a team of individuals with expertise in disparate areas is needed to tackle a design.

One solution is to integrate existing packages. This has merits, but it fails to tackle the underlying problem, and that is that most CAD packages fail to reflect the way that engineers work, and constrains them into an unnatural methodology.

The real answer, according to Paul Pankhurst and his team at PDD, is to go back to basics and to develop a CAD package that reflects the way that designers go about their job.

To make his point, Pankhurst’s engineers have built a non-functional – but potentially very useful – demo of a CAD system that takes the designer from conception, through design and engineering all the way to production. PDD’s demo shows how the hypothetical CAD package could be used to design a computer mouse.

The first module in the package deals with the creative side of design. Figure 1 shows how the designer sketches out the part, defining parameters such as mouse size and PCB area. ‘The length and width of the PCB, for example, can be adjusted to fit the product while maintaining the same board area,’ says Pankhurst. ‘In design terms, the user is simply telling the computer that the PCB area is fixed, and asking the computer to fit it within the size envelope.’

Next, the designer might go into the model shop, and consider which material to build a model prototype from. The ideal software gives the designer the same options that he would expect if he were to perform the process manually in the workshop – as shown in Figure 2. ‘At this stage in the manual process, designers tend to ignore the dimensional aspect of the design in favour of form and appearance. So the ideal CAD package takes away the dimensional constraints to allow the designer to work free form.’

Once the shape is defined, the designer can move into the design environment. The first consideration here is the manufacturing process: the designer can choose whether the part is injection moulded, fabricated or die cast. Each option leads to further options for materials, surface finish (Fig.3), etc. The designer can then make use of the Internet to obtain the details of moulding companies, downloading their capabilities into the CAD system, and keeping model files updated. The other advantage of hooking up to a moulders’ databases is that costings can be obtained based on materials, and performance comparisons made. No more faxing around for quotes.

Figure 4 moves into the actual moulding of the part, and shows how the ideal software flags up problems such as a sink mark. ‘Why show a horrible complex map when you could actually see the sink mark as it will be?’ asks Pankhurst. ‘What’s more, this sort of thing should be sorted out during the design phase, not when the part enters production.’ Most products use mundane items such as screws and other components that have to be incorporated into the design. Rather than model them himself, the designer should be able to go to the Internet, and import the data directly into the model file.

Understanding how materials behave has always been a difficult problem for CAD packages to handle. Figure 5 considers the selection of a rubber grommet. ‘We want to understand the flexibility of the rubber at the design stage, so that when it comes to assembly we can be sure of a perfect fit,’ says Pankhurst.

Finally, when all the components have been designed and specified, the assembly can be simulated, including the rubber tube, which must be bent before entering through a hole in the moulding.

The product design is finished, all within one CAD package.

Before you get too excited, PDD don’t intend to develop the software. However, a number of software firms who were impressed by the logical approach have shown an interest. It may not happen this year, or in the next five years, but maybe one day, a vendor will develop package for real using these principles.

In the simulated model shop, the designer is given the same options he would expect in a real workshop. In this case, the designer has chosen to carve in clay, and is presented with the appropriate set of tools: cheesewires, knives, scrapers and so on. These are used as you would if you were holding a real tool.

PDD. Tel: London (0181) 735111.