It’s time to make the switch – From 2D to 3D

Alistar Dean, Mechanical CAD Reviewer at Cadd, CADdesk and MicroStation User Europe magazines takes a look at migrating from a 2D to a 3D CAD system

The benefits of computer-aided design in 2D have long been accepted by the mainstream engineering industry. Electronic draughting has provided many benefits over traditional paper-based methods. Now the industry is gearing up for a move to 3D solid modelling.

Although it is very powerful, there are clear limitations to what can be achieved using only 2D drawing software. It’s at the point the 2D `envelope’ closes that solid modelling begins to excel. Over the past decade, an amazing progression in software development has been reflected in a widespread adoption of 3D modelling. Whereas 2D draughting allows you to create, and edit, lines, circles and arcs, solid modelling provides brand new opportunities, which simply are not conceivable in a 2D world.

The overall aim of 3D solids is to provide the engineer with a complete virtual representation of a part or assembly. While 2D CAD offers a series of snapshots of a part made up of lines, circles and arcs, a solid model removes any possible ambiguity and represents the whole part in a singular form. Everything from the part’s dimensions to volumes, masses and centre of gravity can be extracted from a single file.

A solid model of a part is a 3D representation of its form, not just the boundary of a part as you would find in many modelling packages, but also the information regarding the material within the outer skin. This fundamental is further enhanced with the use of feature-based and parametric modelling techniques.

For many manufacturers, a critical issue is how to deal with legacy data. This generic term is used to describe the back catalogue of engineering information that many companies have: whether in paper or electronic form. Both forms of archive pose different problems.

One question is how easily can a paper-based archive of engineering data be integrated into your new working practices? That is easily answered but not easily carried out. With 2D CAD, this was a question of scanning the paper drawings into electronic format and converting to a vector format. With 3D solid modelling, the task is not so straightforward. The only real choices are to convert the drawings into vector format and use these as building blocks from which to create 3D models, or to use the drawings as reference and rebuild the models from scratch. Whichever route is chosen, there could be a great deal of work required.

Drawings or models from previous systems can also be converted to your new application’s format. This is a problem area that the CAD industry has failed to solve. There are several independently maintained data formats, which have been developed to be universally read, but very rarely are. One of the earliest was the Initial Graphics Exchange Specification or IGES format, developed by the ANSI committee. This was closely followed in 1983 by the Standard for the Exchange of Product Model Data or STEP initiative, developed by various technical committees and organisations around the globe. The disadvantages with these formats are twofold: first, the data is usually brought in as a dumb lump of geometry, in that it retains no intelligence from the original system. Second, there are very few systems which can accurately read or write IGES files without problems such as untrimmed surfaces.

NATURAL UPGRADE PATHS

If you are currently using a 2D package, then there may well be a solid modelling solution that has native links with your present system. For example, the natural progression from CoCreate’s ME10 is to upgrade to SolidDesigner, also developed by CoCreate, so the translation of your data from one to the other should be relatively trouble free. Another example is the upgrading from AutoCAD to Mechanical Desktop, both of which are developed by Autodesk and share links via their native DWG format.

Once you’ve decided to go down the solid modelling route, you’ll need to investigate all the available options. Vendor research is a critical stage of the upgrade process and must not be short cut. First, you’ll need to make an evaluation of your exact requirements in terms of modelling functionality. The majority of systems provide all-round modelling capability but if you are working in a very narrow field of engineering, it may be best to evaluate more specialist systems. Examples would include Radan’s Radbend product, which provides specific CAD tools for those in the sheet metal industry.

When sourcing your CAD system, do not just rely on published benchmarks, but devise some that cater specifically to your requirements. These could include reading customer/client data for integration with your models – another area in which data translation plays a major role. Another good option is to devise your own specific modelling tasks that relate to your organisation’s activities.

THIRD PARTY GOODIES

Other aspects to look for in a CAD package are its third-party applications. Most CAD developers don’t have the expertise to accommodate every single genre of designer in their applications. This is left to smaller companies who specialise in a specific niche industry or application areas such as Cosmos, which develops third-party Finite Element Analysis tools for many mainstream systems including SolidWorks, Mechanical Desktop and Solid Edge, to name but a few. Do not disregard a system purely for a lack of special features, because these may be available from a separate source.

Although there’s always going to be the need for the all-singing, all-dancing high-end CAD solution, typically priced at £20k a seat, the gap between the high- and medium-price range (around £3-6,000) is rapidly closing. This lower price bracket now contains the kind of modelling functionality that you would have paid around four times as much for only five years ago. At present there are three or four major vendors in this range: Autodesk with Mechanical Desktop (with around 100,000 installed seats), Dassault with SolidWorks (around 22,000 seats) and Unigraphics Solutions with Solid Edge (some 21,000 seats). Recent changes in its pricing strategy has brought PTC’s Pro/Engineer (around 200,000 seats) into this same mid-price band. The company has another card up its sleeve, too, with Pro/Desktop (formerly known as DesignWave) which provides excellent functionality at a low cost of £2,750. Other notables include Delcam with its Power range and Varimetrix with the forthcoming VX Vision.

The advances made in solid modelling have gone hand-in-hand with the leaps made in computer hardware technology. The industry-wide adoption of Windows NT as the favoured operating system has meant that many organisations have chosen to abandon their costly UNIX systems for a platform that can be more easily integrated with other IT systems. The benefits of Wintel-based solutions are that the hardware suppliers are plentiful so you’ve a lot of choice.

BACK TO BASICS

The most basic system requirements for many systems are along the lines of a Pentium II-based system, with as much RAM as possible to cope with complex parts and assemblies. It’s important to appreciate the increasing significance of graphics cards in the CAD industry. Where once the graphics featured in CAD applications consisted of lines, arcs and so on, the use of 3D graphics in today’s solutions is becoming increasingly sophisticated. As with the actual hardware box manufacturers, there is plenty of choice to suit all requirements. You’d be well advised to ensure the inclusion of OpenGL support in your graphics card choice.

Although many routine jobs could still be carried out in 2D CAD, there are few that wouldn’t benefit from the introduction of solid modelling into the design environment. With the benefits of 3D solids now widely accepted, the range of possible solutions is rapidly reaching a saturation point. Whichever specific industry you’re working in, there is bound to be an application to suit your working practices.

* A dedicated two-day Solid Modelling event takes place April 20 and 21 in Birmingham. Separate conference streams will address the needs of CEOs and managers as well as end users and system implementers. There is also an exhibition featuring the major solutions vendors. Details of Solid Modelling 99 on 0171 681 1000 or visit the exhibition web site: www.eda-expos.co.uk/SM/

FIGURE 01

dV/ProductView from Division allows individual users to get access to the information they need wherever it may be stored. So now from your standard web browser you can access and view all types of product information. The 3D geometry representation is compact, typically 1/20th the size of the original CAD part data so that it can be distributed even across slower wide area networks. The geometry is represented by the same topological entities as the source CAD data, so no precision is lost. dV/ProductView also provides fly-through of even the largest assemblies (>100,000 discrete components), so it’s now possible to load the whole product in seconds

NASA scientists rely on reaction wheels to manoeuvre observation satellites in space. Based on information gathered by sensors, four reaction wheels position the satellite to face constellations of interest. The reaction wheels must withstand rocket launch vibrations to operate effectively in orbit. Engineers at the NASA Goddard Space Flight Center, Greenbelt, Maryland, used random vibration stress analysis software from Algor to test the structural integrity of a redesigned reaction wheel that can position satellites more quickly. NASA simulated vibration forces during a rocket launch and analysed deflection in the reaction wheel’s outer housing structure. NASA then optimised the housing’s design on the computer to reduce deflection that would otherwise cause the reaction wheel to fail. The new reaction wheels were launched successfully on the Transition Region and Coronal Explorer (TRACE) in April 1998 – a satellite mission that is studying the sun’s coronal region – and are scheduled to be used on two upcoming space expeditions.

WHAT DOES THAT MEAN?

FEATURE-BASED MODELLING

Early solid modelling systems used geometric primitives from which you constructed your model. These usually took the form of cuboids, cylinders and spheres combined with extrusions, revolutions/lathes and lofts. Boolean operations were also common, allowing the geometric shapes to be combined or removed from each other to allow for more intricate forms. The modelling process became like using sophisticated building blocks to create the required forms.

What feature modelling has done is to take these mathematical processes and move them into the background to provide real world engineering terms that represent these operations. To create a hole in a part, you simply select the hole command rather than subtracting a cylinder. Another advantage is that as the hole is a separately-defined entity in the part, additional non-geometric information (or attributes) can be attached, such as threading details, tolerances and so on. This `non-model’ data can then be extracted into bills of materials and part lists etc.

PARAMETRIC MODELLING

Although 2D parametric draughting packages are commonplace, the use of parametric solid modelling provides a whole new toolkit for engineers. The ability to create a model’s basic form, apply dimensions and then vary those dimensions enables a part’s possibilities to be explored quickly. The ease with which changes can be made is enhanced by the use of design rules and design tables. These allow the engineer to enter formulae which constrain a part’s form according to relationships between dimensions. Using these techniques it is possible to drive entire families of parts, even entire assemblies, from a single model file.

ASSEMBLY MODELLING

One of the biggest advances in solid modelling in recent years is the use of assembly modelling. Previously restricted to high-end CAD systems, assembly modelling can now be found in the most average CAD application. The progression from designing single parts to entire assemblies with hundreds of parts gives the engineer the advantage of viewing and analysing a part or set of parts in-situ. Many systems provide interference-checking tools that identify areas in which parts collide and some even provide kinematic tools that analyse a mechanism in use. The benefits of this are self-evident: shop floor changes can be dramatically reduced as problems can be easily identified and dealt with at the design stage.