Milling Tools, scrapers and clay in the oven: How modelers work in automotive Design

“Over the past decade, our design process has undergone a major digital transformation, allowing us to rapidly and efficiently explore various design directions for our future cars,” says Martin Bogner, Head of Design Modelling and Digitalization. “However, we also know that perfect design arises from combining the virtual world with physical reality. That’s why we still use physical design models to validate digital concepts, fine-tune details, and finalize designs at the board level. It’s this combination of digital tools and traditional craftsmanship that allows us to achieve top-level design quality,” Bogner adds.

Layer by layer

The preparation of physical models begins with a basic skeleton, built by the Technical Development department according to the Design team's specifications. Before modelling begins, the clay must be applied to this skeleton. “The structure has to be precisely built to accommodate the clay layer. Typically, we apply about a 4-cm layer of clay to the model, although this varies depending on the specific design and location,” explains Mick Allbutt, one of Škoda Design’s modelers. Altogether, about two tonnes of clay are used on a single model.

Mick Allbutt applies a layer of clay.

Before application, the clay needs to be softened by heating it in special ovens to 60°C. A full load takes about four to five hours to heat, and roughly four ovens' worth of clay is used per model. The clay is applied gradually, in layers—starting with a 10 mm layer to cover the foam of the skeleton.
 
“Six modelers apply this initial layer over about two hours,” says Allbutt. Because the polyurethane foam retains heat, it takes a while for the clay to cool and harden. When adding clay onto already cooled clay, the process is faster—about two hours for a new layer to set and cure. Still, modelers let the clay rest and cool overnight to ensure it is fully hardened before moving on.

Heating the modelling clay to 60 °C before application

Precision Work

Warm clay is soft and highly malleable, which makes it unsuitable for milling—the process that gives the model its first precise contours. The milling machine uses digital data prepared by digital modelers, and the initial milling stage can take a long time. “Milling half of the car can easily take 20 hours, which is why we often let the machine run overnight,” explains František Hladík.

A standard 10 mm ball-end mill is the primary tool used for shaping the surface with high accuracy and precision. “Tool positioning and angle matter, but we typically aim for a precision of within four tenths of a millimetre,” Hladík notes.

With a range of tools—including extended cutters for hard-to-reach areas like the lower diffuser—the milling machine handles about 95% of the model’s surface. However, some areas are inaccessible or there are areas where it leaves residual curves.

This is where modelers step in, refining surfaces the machine can’t reach and giving the model its finished look. They can also make manual shape changes, ranging from subtle tweaks to major adjustments. This flexibility is one of clay’s biggest advantages—it allows for easy and relatively fast modifications. “Altering a single design detail might only take a few hours,” says Andy Settle.

Modelers use traditional hand tools: smoothing paddles, rasps, scrapers, knives, and other sharpened implements. A special rasp (Clay plane) is used to shape surfaces from below; scrapers remove clay in 5 to 30 mm layers; and flexible steel paddles of various shapes help smooth and refine large areas.

Smoothing paddles, rasps, scrapers and knives are common tools in the model shop.

Knives help refine seams and emphasize edges, often first marked out with thin adhesive tape. “The tape helps us visualize and check shapes. But in the end, our most important tools are our eyes,” Andy Settle explains. Modelers’ hands and tools are incredibly precise—they can fine-tune surfaces by shaving off the thinnest flakes of clay.

Andy Settle controlling the lines.