Seven car designs in seven days!

14 June, 2007

The Italian automotive vehicle design and contract manufacturing company, Bertone, is known for a timeless sense of style expressed over nearly a century in cars – from Alpha Romeo and Aston Martin to Volkswagen and Volvo. The company prides itself on being able to take a car design from original conception to the production line.

Bertone recently bolstered its international reputation with a new claim to fame: the ability to deliver a greater number of customised design alternatives to customers in much less time.

At the centre of this new flexibility and speed is a technology known as digital shape sampling and processing (DSSP), enabled by Geomagic Studio software. In a recent project, Bertone used this to present seven car design alternatives to a customer in seven days.

So what is DSSP?

DSSP is a category name that encompasses the convergence of multiple technology advances. It describes the ability to use scanning hardware and processing software to digitally capture physical objects and automatically create accurate 3D models with associated structural properties for design, engineering, inspection and custom manufacturing. What digital signal processing (DSP) is to audio, DSSP is to 3D geometry.

DSSP has evolved as a result of several technology areas that have matured over the last decade, including optical 3D scanning, reverse engineering, computer-aided inspection, and geometry processing. The demands within these areas have led naturally to integrated DSSP solution offerings.

It has faced some misunderstandings in relation to CAD/CAM. Far from being an overlapping or competing discipline, DSSP complements CAD/CAM and is an essential part of the digital design and manufacturing life cycle. It enables designers to capture physical entities such as prototypes and production parts and transform them into 3D digital models residing on the computer.

From sketch to clay model

The styling process at Bertone begins as it has for nearly a century – a sketch is drawn, revised and then finalised. After customer approval, the sketches are digitally photographed and the resulting JPEGs are imported into styling software where the designers use them as their reference in creating an initial surface model of the 3D envelope, or external shape, of the car. This design file is transferred to a CAM system used by major automakers for tool, die and mould manufacturing, which automatically generates the numerical control (NC) tool-path program required to mill a clay or foam model.

“We use clay or foam for scale models because these materials are easy to modify,” says Gianni Lucco, CAM manager for Bertone. “When changes are requested by the customer or result from an internal design review, we manually reshape the model.”

Bertone seeks to create as much realism as possible, typically producing prototypes in 2.5:1 and even 1:1 scale. This gives customers the luxury of being able to review a prototype that is more representative of the final product and eliminates the need for largescale data extrapolation once the prototype is scanned.

The designers add or remove material to change key body design attributes, such as curvature, thickness and features such as headlights. Once the client is satisfied with the clay or foam model, it is ready to be duplicated in digital form for further iterations.

Into the digital realm

The first step in the digital process is scanning the clay or foam prototype with a GOM ATOS scanner and TRITOP photogrammetry camera. The scanner projects patterns onto the surface of the prototype using a white-light projection unit. The pattern is captured with two integrated cameras at either side of the sensor head. The ATOS software can calculate the precise 3D coordinates of up to four million object points in seconds. TRITOP is used in conjunction with the ATOS scanner to accurately measure discrete object points and features.

The ATOS and TRITOP results are merged into a common object coordinate system and saved as an STL file. This is imported into Geomagic Studio DSSP software. This software is used by automotive manufacturers worldwide for automated reconstruction of CAD models from scanned physical parts and to produce the most accurate digital surface models possible for downstream CFD, FEA and other analyses.

For Bertone, Geomagic Studio is the tool around which much of its new styling process revolves, making it possible to quickly turn around design modifications and present new largescale physical prototypes to customers.

“In very little time and without the need for engineering experts, we can use Geomagic Studio to recreate an entire digitised object, capturing features such as the points at which a windshield is affixed,” says Lucco. “Even if a curve is irregular, it can be easily optimised within Geomagic Studio for smooth transfer to a CAD system. Geomagic Studio accelerates the design iteration process tremendously.”

Bertone relies on Geomagic software because traditional CAD systems are not designed to easily convert physical objects into accurate digital models, says Valerio Vezzari, account executive at Microsystem, the Geomagic distributor in Italy that supports Bertone.

“Traditional CAD systems have a couple of major problems with tasks that are critical to Bertone,” says Vezzari. “They cannot easily process the massive amount of data that comes from a highresolution scanner and they cannot accurately model the free-form surfaces that are a characteristic of today’s vehicle designs.” This situation arises from the fundamental differences between CAD/CAM software and DSSP software.

With its roots in drawing, CAD/CAM software is limited to prescriptive modelling methods. In other words, predefined geometry must be prescribed by an expert to a software tool for the purpose of modelling. CAD/CAM starts in the virtual world with a goal to produce better products in the real world.

As a drawing-based technology, CAD starts with a blank screen, requiring that the user input dimensions, shapes, curves and surfaces that will define an object. It is great for modelling new products, particularly those with simple facets and standard geometric shapes. It is limited, however, when it is faced with describing or representing the complexity of the existing world.

With its roots in imaging, DSSP offers descriptive modelling methods. The software extracts geometry and topology from measurement data and describes them to users for archiving and reuse for multiple purposes. DSSP starts in the real world with a goal to produce high-quality digital models in the virtual world that can be used by CAD/CAM/CAE applications.

So, Bertone uses Geomagic Studio to automatically generate an accurate polygon model from the scan data, fixing imperfections and patching holes in places the scanner cannot capture. Once the digital model is completed, it is saved as an STL file, brought into the CAM software to create a new clay or foam prototype, and the process of customer review and revisions is repeated until the design meets the customer’s satisfaction. With the final design decided, Bertone can engage in an abbreviated form of mass customisation, tweaking the look of the car within the software to offer customers a wide range of variations based on the approved design elements.

Added engineering value

By uniting the physical and digital worlds, Geomagic Studio delivers another key benefit: more accurate engineering analysis. Automakers worldwide use Geomagic surface models for engineering analysis because they provide an exact duplicate of an as-built part, assembly or prototype. This is a major improvement over conducting analysis with a CAD model, which often does not reflect design changes made to accommodate tooling and other manufacturing processes.

Bertone uses Geomagic Studio to automatically transform the polygon model into an accurate NURBS surface model that can then be used by customers for structural analysis, interference checks, CFD analysis, volume studies and other virtual testing. The ability to do accurate computer simulations saves time and money by reducing the number of physical prototypes and improving the credibility of results.

“Our customers are interested in the value of the design,” says Lucco. “Geomagic Studio provides that. It is possible, in just a few days, to create a complete surface model of the car and analyse all parts of the design.”

Lucco estimates that the combination of the GOM scanner and Geomagic Studio software has reduced scanning and processing time by 60% over the previous method, which involved a coordinate measuring machine (CMM) and a scanning head capturing data and feeding it into a CAD system.

Because of the time savings, Bertone can create more design iterations to present to the customer who can, in turn, request changes and have them turned around quickly by Bertone without significant delays in the design cycle.

“Now that customers see how easy it is to make changes, there might be too many changes,” laughs Lucco. “But the process gives customers much greater freedom of choice, leading to a design that perfectly fits their aesthetic and functional needs.”