Software creates CAD models for custom vehicles

DSSP involves the use scanning hardware and processing software to digitally capture physical objects and automatically create accurate 3D digital models.

When a client wants a special-purpose vehicle based on a standard passenger vehicle, chances are that the company won't have access to any of the original design information relating to that vehicle.

In particular, the original CAD data will not be available.

So companies either have to generate the data themselves or revert to using traditional manual design methods.

Until recently, when MIRA was faced with this situation it had two options: either outsource the creation of the necessary data and live with the added cost and lack of control over the quality of the data, or turn down the job.

However, since the company implemented digital shape sampling and processing (DSSP) technology, everything can be done in-house, enabling MIRA to undertake more projects and to have control over data quality.

DSSP involves the use scanning hardware and processing software to digitally capture physical objects and automatically create accurate 3D digital models with associated structural properties for downstream design, engineering, inspection and custom manufacturing.

DSSP requires two essential components: scanner hardware to capture point data and software to process point data into useful digital results.

MIRA has used touch probe co-ordinate measuring machines (CMMs) to collect discrete point measurements for some years, but these aren't suitable for the digital capture of complex geometric shapes or of products made from deformable materials, such as plastics.

So in 2006 the decision was made to use the latest DSSP technology.

At MIRA this technology takes the form of a Faro Laser ScanArm optical scanner and Geomagic Studio 3D modelling software.

The two main uses for DSSP at MIRA are benchmarking projects and design-led activities.

Benchmarking projects often involve testing vehicle components and assemblies for compliance with pedestrian and passenger safety regulations.

Design-led activities might involve developing a special-purpose vehicle from an existing production vehicle or producing Class A surfaces from styling models.

"The big benefit to us of using DSSP is that when there is no original design information available for us to work with, we are able to rapidly create our own accurate 3D digital model of the component or vehicle that will form the basis of our new design", explains Dave Wykes, Senior Engineer, Vehicle and Systems Engineering Group at MIRA.

"This gives us the information we need to take on into the design and/or analysis process and enables us to have confidence in the feasibility of our downstream design and engineering activities".

Much of the new design work, engineering analysis and benchmark testing that MIRA undertakes for its clients can only be performed effectively with the use of a 3D digital model.

So whether it's the testing and measurement of components under load, understanding the performance of a competing product or creating a datum for new design work, the starting point is to perform a digital scan.

The Faro Laser ScanArm 3D digitiser fully integrates a contact/noncontact measurement device and laser scanner and can capture more than 19,000 points per second.

The data is saved as a point cloud which represents, within an accuracy of 50 microns, the set of three-dimensional points that describes the outlines of the object being digitised.

Once captured, the point cloud is brought into Geomagic Studio software for processing.

Geomagic Studio is the critical component in the digital shape reconstruction process.

It extracts geometry and topology from measurement data and creates high-quality 3D digital surface models that can be used within other CAD, CAE and CAM applications for downstream functions such as detailed design, engineering analysis, simulation and machining.

Depending on the size of the point cloud, the first step in the process of creating a 3D digital model may be to reduce the data to a more manageable amount, without affecting its accuracy, using random, uniform and curvature-based point sampling.

It may also be necessary to eliminate 'noise' generated during the scanning process.

Once this has been done, the next step is to create a polygon model from the point cloud data.

In most cases, this is achieved automatically by using the Wrap feature in Geomagic Studio.

This mathematically wraps a polygon surface around the point cloud data with a few simple button presses.

Tools within Geomagic Studio then allow MIRA's engineers to refine the polygon model, by filling any holes that might have been left by the scanning process and by smoothing, fitting, trimming, projecting and extending boundary edges, where necessary, to polish the model.

The result is an accurate, 'water-tight' digital polygon model of the original physical object.

If the model is for a design-led project, then Geomagic Studio is used to convert the polygon model into a high-quality NURBS (nonuniform rational b-spline) surface model.

This is then exported into the Catia V5 CAD software suite used by MIRA for its detailed design engineering work.

The digital surface model can then be modified within Catia as required for incorporation into the digital 'master' model of a new or revised product.

However, if the model is required for a benchmarking or engineering analysis exercise, then the polygon model is saved as an STL file in Geomagic Studio for export to a CAE application, such as finite element analysis (FEA) or computational fluid dynamics (CFD) analysis.

These types of application require a polygon mesh model.

In design-led projects, the use of Geomagic Studio software and Catia CAD software in tandem with each other enables MIRA's engineers to take a project seamlessly from initial surface model creation, through design modification, engineering analysis, documentation and into prototype production.

A good example of this can be found in some of the work the company carries out for the motor-sport industry.

World Rally Car and European Touring Car Championship cars, for example, are based on standard passenger cars.

An essential component of these highly modified cars is the roll cage which ensures driver safety.

This is usually a bespoke design and must meet international standards to ensure that it will adequately protect the driver - and the navigator in the case of rallying - in the event of a high-speed crash or roll over.

The traditional way of testing a new roll cage design is to put it through a physical crash test - and in the process, of course, destroy it.

Unfortunately, more often than not this will be the only one in existence.

This fact, coupled with the increasing use of exotic materials such as high-strength steels in roll cages, means it becomes an expensive and time-consuming exercise.

MIRA's engineers are able to create an accurate 3D digital model of the roll cage using Geomagic Studio.

This model can then be exported to Catia for the design development process or to various CAE software products for use in engineering analysis.

Using this process, MIRA is the only organisation in the UK that is able to certify bespoke roll cage designs to international standards without the need to crash test and destroy expensive physical prototypes.

The company also uses a similar approach to the design of new vehicles, such as hybrid, emergency and mobility vehicles that are based on existing production vehicles.

Usually there is no original CAD data available.

So Geomagic Studio is used to create surface models of the appropriate parts of the donor vehicle.

These models are then used within Catia to enable the required changes to be made.

These might involve changes to the power-train and chassis in order to accommodate a hybrid power unit or in the case of a mobility vehicle, changes to the suspension and bodywork to provide wheelchair access.

Apart from giving MIRA the ability to design and engineer automotive parts as well as complete vehicles in less time and with greater accuracy and confidence in the end result, the combination of DSSP, CAD and CAE enables them to avoid the tendency to 'over engineer' a product, as often happens in the traditional manual world in order to ensure it won't fail.

With a digital model everything can be digitally simulated and tested, saving tremendously on time and cost.

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