1:18 AutoArt FORD SHELBY GR-1 CONCEPT - ALUMINIUM CASTING

1:18 AutoArt FORD SHELBY GR-1 CONCEPT - ALUMINIUM CASTING

AUTOart is striving to achieve a new standard by launching its first 1:18 die-cast model with a polished aluminum body in the form of the Ford Shelby GR-1 concept car. The goal is to achieve the same quality of finish as that on the actual concept car.

Die-cast model cars are usually cast using zinc alloy, a material that is user-friendly, has a low melting point and is easy to cast. The mold used to cast zinc alloy can easily survive a million shots. Aluminum alloy, on the other hand, has a higher melting point and the molten material will attack the mold during casting, thereby shortening the mold life by 20 to 50 times when compared with zinc alloy casting.

Very few model makers have tried to cast aluminum alloy and then manually polish to achieve a high gloss surface finish. Normally manufacturers would apply chrome-plating to the zinc cast body to simulate the finish. However, chrome-plated surfaces are too bright and do not accurately replicate the surface texture of a polished aluminum finish. To compensate for this some makers would polish the zinc cast body to achieve more or less the same glossy finish of polished aluminum. However, zinc is sensitive to air and humidity and surfaces easily oxidize, even in sheltered indoor conditions. Therefore, a clear coat must be applied to prevent this. When this is done the zinc polished surface is very clearly wrapped in a thick, clear layer that looks unreal compared to the actual finish of the real car. Moreover, the clear coating can become slightly yellowish under prolonged exposure to sunlight.

In order to replicate the polished aluminum finish of the real car, actual aluminum alloy must be used to cast the scale model body. The casting will then require more than 130 minutes of trained manual labor to polish the whole body-including the panels - until the desired glossy finish is achieved. The biggest challenge is to align the contours between the main body and the attached panels (bumper, bonnet, trunk and doors) after polishing. Even slight over-polishing of the bonnet and door edges will make the connecting surfaces of the main body uneven and such parts will need to be scrapped. Even with a trained workforce the scrap rate is well over 50%. With labor costs rising in China, the overall cost of producing a polished aluminum body is 5~6 times that of the usual painted body cast in zinc alloy.

The final polished aluminum body is deliberately not coated with a clear protective layer in order to simulate the bare aluminum texture of the concept car. As with the real car, the surfaces will oxidize at a very slow rate under indoor conditions and the gloss will decrease slightly after one or two years. However, the shiny finish can easily be restored by simple hand-buffing using metal polish compounds such as Brasso, Autosol, Pennibrite or mag-wheel polishing cream. Like any precious sterling silverware, the polished surfaces require occasional maintenance to retain their glossy texture.