The case for 2D design

If solid modelling is so effective why are 80 per cent of CAD users still sticking with AutoCAD? Charles Clarke reports.

If you’re a CAD user working anywhere in the manufacturing process and you’re still using 2D as your primary CAD tool you might just as well sit in the office and burn money, we are told.

3D is a far more effective way of working and if you need drawings, as long as the drafting process allows you to include the data you want, it can be the primary mechanism to produce absolutely correct drawings from ‘solid’ components.

Yet since the mid-1980s, despite dramatic changes in the power and affordability of hardware to support solid modelling operations, around 80 per cent of CAD users have continued using 2D.

The major reason people have stuck with 2D is that it’s difficult to get the kinds of drawings they need from 3D systems, and drawings are still the currency of design and manufacturing operations. Users need production-quality drawings to communicate their designs effectively to others. This should act as a wake-up call to many 3D developers who only pay lip service to drafting.

CAD is very ‘us and them’, fuelled by vendors’ marketing messages extolling the virtues or otherwise, of either 2D or 3D. In reality good engineering design needs a mixture of both 2D and 3D to function to its full potential. Just because contemporary hardware can cope and affordable new solid modelling systems are available, if 2D systems are serving you well and there are no compelling reasons to change, why bother?

2D systems are getting better and 3D functionality is creeping slowly but surely into 2D. For most people this is all the 3D functionality they will ever need, and AutoCAD is still cheaper than the mid-priced solid modellers. Plus very few will give up their 2D and take a leap in the dark.

Whether or not you go to 3D depends largely on where you sit in your supply chain. There is no point in going 3D if the rest of your process to manufacture is not tending that way. Where the OEM insists on sending native model files to the toolmaker, who in turn makes a drawing and cuts from that, the toolmaker will only keep the business if he buys compatible software. True, he would not need 70 per cent of the functions offered by the software, but he could take better advantage of these if he changed his manufacturing process. This, of course, could be costly.

Standalone 2D is important, as it is usually a crucial development step. There are dozens of instances in design development when you want a 2D approach and not 3D or a 3D model. These 2D steps rarely involve manufacture or prototype production. They are an aid to thinking about the problem.

It’s not fair to compare 2D or 3D definition of an object, as they both have important but different roles in the design process. While you can’t ‘rotate’ a 2D drawing, you can use it to check fits and assemblies before committing to 3D.

3D only makes sense if the design stages and the software are linked from concept to machined prototype or finished product. The main challenge is thinking about your process to decide where and whether 2D or 3D is relevant. It’s less a question of how to turn your drafters into modellers than how do you get your people to think about the whole process and choose the right discipline for each part.

To stay competitive and profitable companies have to bring higher-quality products to market in shorter time scales and at lower costs. Solid modelling, as the only true computer representation of the internal parts of a physical item, can assist in a number of ways, as documented over the years.

Even greater benefits are realised if solid modelling is seen as the heart of a product modelling environment, a common point of reference for the entire development team. Under this environment concurrent use of applications speeds design refinement, verification, manufacturing and documentation. Linked to these are the process instructions such as routeing and approval lists, engineering notes and test results.

This provides a route to exploit the benefits of simultaneous engineering and to maintain electronic control and distribution of all the design and manufacturing documents and drawings. Thus, as a project proceeds all the accumulated knowledge can be accessed and decisions made on the basis of fact and not guesswork.

It is possible to turn draughtsmen into modellers. Even if they don’t have an aptitude for 3D you can teach design discipline which is 90 per cent of the problem. Most importantly, people need to be encouraged to think about their process, and when and where to use 2D or 3D – or both.

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