Modelling Developing a vehicle is an arduous process of design and evaluation, trial and error - constant improvement and adaptation. Initial design concepts go through a range of stages to bring them closer to realisation and modelling is a key to evaluating a design at each stage.modelling can take several forms. Traditionally, clay models have been used at various scales to help understand and resolve the form and proportions of a vehicle. To varying degrees, this has been supplemented, sometimes even replaced, by CAD modelling. Whilst clay is still a medium used to evaluate predominantly visual characteristics, CAD systems can additionally help evaluate other factors such as aerodynamics, impact scenarios and other physical considerations. Clay Modelling Clay modelling is one of the most established 3D visualisation techniques used in the automotive industry. This section looks in detail at clay modelling - the process, history, current practices. CAD Modelling Computers are now used to accelerate virtually every aspect of vehicle development. Computer aided design (CAD) modelling allows designers and engineers to resolve increasingly large amounts of a vehicle before even the first model is made. This section covers the principles and technology behind computer aided design. Additional Modelling Processes There are other processes involved in modelling, and sometimes entirely different approaches. We take a look at some of the more significant variants in
Clay Modelling Clay modelling is one of the oldest and most traditional methods used in car design. Studios are divided in their preferences relating to CAD or clay but many believe that it remains one of the best ways to visualise developing designs in three-dimensions. GM modellers use renderings, sketches and tape drawings as reference to create a 1/4 scale half model. Using a mirror in this way enables modellers to produce results more quickly. With full proportioned models, substantial time is spent balancing one side with the other. In this view it is possible to see the rig beneath the clay. In the rear wheel arch the base can be seen along with the core of light blue modelling foam. Clay has been used since the earliest stages of car design and emphasises the strong links between three-dimensional automotive styling and sculpture. Working on the form of a vehicle in clay is a very tight form of sculpture, reliant upon a expert eye and an advanced perception of form and proportion. Clay modellers work on the Holden FJ many decades ago. This practice is still common today. The modellers shown here are using, amongst other things, gauges to measure height and depth (to balance both sides) and profile guides to ensure the model corresponds to the design.
The Principles There are several stages to producing a clay model.first, the scale of the model is determined. Using a package drawing or profile sketch, the vehicles dimensions are worked out and the scaled dimensions calculated.using the core dimensions, a rig is built. A rig is designed to be a solid working base for the model as it is built and developed. In the case of small scale models - such as 1/4 scale - the rig will be designed to be mounted on a bench where modellers can stand to work on the model. It is often preferable to position a model to create the most lifelike perspective. In addition to providing a base for the model, the rig is also a means of reducing the amount of clay used on a model. Rather than using expensive and heavy styling clay all the way through, an inner core of foam is often used on which the clay is applied. Manual Method With the rig configured, clay is applied. Using a system of '10-lines', reference points are transferred from the drawings to the model. Clay is built up to match the profile from the drawings and is then added to fill out all the proportions. From here, designers can either rigidly follow their drawings, creating guides and templates to help develop the model from the package drawing, or they can begin to experiment and develop the form freely. The beauty of automotive styling clay is its ability to be reworked and continually adjusted. This freedom of form development is rarely matched by computer. Chevrolet designers work on a full scale Corvette model. Dynoc has been applied to give the impression of real glass and upper body paintwork. Real wheels add to the effect whilst designers make final adjustments to the surfaces.
Automated Method Instead of designers and modellers labouring over a clay for weeks, many car firms are now in the habit of sending a CAD model directly to a specialist milling machine. The machine can precisely mill out the form and proportions of the 3D computer design in a relatively short period of time, although humans may still be called in to finish the surfaces or make slight adjustments. Although most aspects of a design can be resolved on computer, especially with the aid of virtual reality evaluation, almost all companies will still produce a full size clay towards the end of the process. The cold light of day can produce suprises that manufacturers want to be aware of before a vehicle enters tooling and production phases. Once a vehicle is completed, one of several next steps may be taken. If the vehicle is to be shown as a concept, it might be painted and detailed but will more likely become the template for 'hard modellers' to use to create a production look-a-like with individual panels, real glass and details as well as an interior. If the vehicle is ready for production, it will usually be scanned using 3D digital equipment which will in turn create a new CAD wireframe model. This will be tweaked by CAD specialists to remove imperfections before being passed on to engineers who will begin the arduous process of creating panels, componentry, drivetrain and propulsion based on the design. Of course, if a vehicle was simply an in-house research project, as many are, it may never be seen by the public; in fact the clay may be reused in later projects. These Holden models give an idea of the processes involved and their purpose. Both vehicles are full-size clays that give an accurate representation of the proposed vehicles. Applying a neutral coloured paint and sitting the model outside in a typical working environment is about the most accurate way to assess a concept's visual impact without actually building it. The vehicle in the upper image appears to be in the later stages of development. Details such as light graphics, shut lines and Dynoc to imitate glass allow designers to quickly and effectively evaluate the model.
CAD - Computer Aided Design Computers have been used in the design of cars for many years. The automotive industry has been one of the leading forces for CAD development alongside aerospace and the military. In fact, some years ago, the British military research unit - DERA - and Ford initiated a joint development programme to investigate new computer design technologies. As with all the things in the world of computers, things started big and expensive and eventually became cheaper and smaller. Although design studios may now have large CAD walls to visualise developing vehicles, it is also possible to work on the design of a car from a single PC. There are a few, core systems and programmes used in the automotive industry. In this section, we look at the key features of each ranging from specifications to usage. Key CAD Programmes Alias AutoStudio Alias SurfaceStudio ICEM Surf ICEM Style CATIA Digital Scanning of Clay Models (3D Digitising) CMMs (Coordinate Measuring Machines)
Additional Modelling Processes A technician oversees the milling of this Hummer model. The image shows a full size model being milled from high-density foam by a machine that has been given three-dimensional data from previously completed CAD models.