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Resin models - 25 Sep, 2012

Resin models


Many collectors have been asking why AUTOArt does not produce models made out of resin.  As a matter of fact, AUTOArt has done a few special projects in resin, but only models in large scales such as 1/8 and 1/5 which sell directly to car makers.  Because the quantity requirement is so small and the scale is so large, it is not commercially viable to tool up to make the models in die-cast metal, simply because the mold investment would be too high.  



Special project of scale 1/5 resin model produced by Autoart.  Only a few pieces have been produced.


Regardless of the materials used, a model car requires a mold in which to be cast.  To cast a zinc metal die-cast model requires the use of a steel mold. However, a resin model is cast in a silicon rubber mold.


Tooling a full set of die-cast steel molds for one model is expensive. The tooling investment for a 1/18-scale model car can be in the region of US$100,000 to $200,000, depending on the complexity of the model and the number of components.  It requires, at minimum, several months of engineering work to produce a complete set of steel molds. Once the mold is made, the product is cast in a split-second by injecting the molten metal into the mold cavity with a high-pressure casting machine. Hence, large quantities of products can be manufactured continuously and precisely, and the life of a mold tooled in high-grade steel can be as much as one million “shots,” or die-castings. It is therefore the most economical way to manufacture model cars in a large quantity, and all mass-market, toy-grade die-cast model cars are manufactured in such steel molds in order to make the product as cheaply as possible. 



The steel mold of a scale 1/18 car body.  It weights half a ton.


However, if the intended selling quantity is only a few thousand pieces, then a steel mold is also the most expensive way to manufacture the product because the investment in the tooling is amortized over a smaller quantity. Divided by only a few thousand pieces, tooling costs can get as high as US$40 per model car.


Resin models are cast in a silicon-rubber mold, and a set of such molds costs a fraction of that for steel molds—in fact, only hundreds of dollars to maybe a few thousand dollars. When the development of the model is completed, it takes only a few days to produce the silicon-rubber molds, versus months for the steel molds.  Resin is thus the ideal material for manufacturing a small quantity of model cars, in any scale, especially ones that require the shortest possible lead time for launch into the market.



A large silicon rubber mold half for casting large resin object.  There are intricate lines and contour in the rubber mold which would not be found in steel mould due to the draft angle.


We often see that a resin model of a newly launched car is always the first to appear in the market. It can be so quick that within weeks after the real car is officially unveiled to the public, the resin model is already available in stores.  In contrast, a die-cast model car in 1/18-scale requires at least nine months of development and mold making.



A small silicon rubber mold to cast small resin object


Lead time to market is one of the biggest advantages to resin models.  Because a silicon-rubber mold is elastic, the mold design can be simpler, and draft angle is not a major concern. That means complicated shapes can be cast easily. Also, producing a silicon-rubber mold is relatively simple and involves the mixing of the chemical compounds that form its material, and then pouring it into a small chamber containing the pattern.  Within hours, the silicon is cured.  In contrast, a steel mold is made of very hard material, and the cavities of the model’s pattern are formed by careful and time-consuming hand grinding and trimming, with electrical discharging and manual polishing as final steps. That’s why it can take months to complete a set. The upside is that steel tooling lasts for hundreds of thousands of “shots,” or molten-metal injections, whereas a silicon-rubber mold, in most cases, cannot survive more than a hundred injections. Hence, the smaller runs of resin models.



High detailed scale 1/18 resin model launched into the market within two or three months time after the debut of the real car.


Resin has another advantage: it is much softer than zinc metal. Hence, the labor-intensive trimming and polishing of a resin model requires less time than one rendered in metal.  Fine details are easier to cast in resin, and the model can be well presented with many intricate parts attached.



Fine detailed interior made of resin in scale 1/8


However, there are major shortcomings to resin models, mainly in the nature of the resin material itself. It is much weaker structurally than die-cast zinc-metal, and it may deform after some years as it ages. Working doors and bonnets cannot be made accurately, with a fine air gap around them, because a doorframe cast in resin is not rigid enough, especially in the area of A- and B-pillars.  Moreover, the fixing of the hinges is also very fragile, and they can easily break if not handled carefully.  Therefore, to avoid such problems, most resin models are made without any working doors or bonnets.



A high-detailed scale 1/43 resin model with workable doors and bonnets.  The model is retailed for over US$200.


When it comes to painting the model, there is also a big difference between resin and zinc. Paint requires baking time in an oven to cure properly, a step needed to ensure the paint achieves an accurate glossiness. Such oven curing can be done on metal, but not on resin, which will deform in the heat of an oven.  Thus, the paint used on a resin model cannot be oven baked; it requires extra clear coating to achieve the desired glossiness.  So while the color painted on metal will yield a similar effect to a real car, the paint finish on a resin model can appear very glossy, but only with clear coating, which somehow lacks the look and solid feel of single-step painting.


On resin models, colorful racing liveries are mostly done with water decals due to the small quantity of models being manufactured.  Pad printing or “tampon” printing yields a better result than using water decals, because the colors are printed directly onto the body rather than printed onto the decal membrane. But the pad printing process involves high setup costs, especially if the livery consists of many colors, and that’s only economically feasible if thousands of pieces will be manufactured.   Therefore, practically all the racing versions of resin models use water decals.   Water decals age and can become brittle and vulnerable to scratches after some years.  They also require great skill to apply precisely, and on the assembly line, maintaining a consistency of workmanship among the models becomes problematic.



The common problem of water decal: the transparent membrane between the words can turn yellowish after many years of storage.


The windscreens and side windows of resin models are made of clear acrylic sheet that is cut into shape and press-formed into the required contour.  Clear acrylic sheet can be so thin that it appears almost like real glass in miniature form, so that the interior is clearly visible without any distortion.  However, when the contour of the glass is curvy, it is a great challenge to form the correct shape from a flat sheet, and we can see many resin models in the market that are not well-made in the area of the windscreen and side windows.  On the other hand, injection-molded plastic, which is used for windows in die-cast zinc models, can be made in practically any contour using a mold that replicates the exact contour of the real thing.  Because injection plastic mold is expensive to make, it is seldom used in resin model due to the small quantity being produced.


Also, chrome plating, as on a bumper or headlight reflector, is something that cannot be done realistically on resin models. Putting the shiny-metal effect on resin material can only be achieved by vacuum metallization (or, vacuum plating). However, when done, the surface is not as brilliant as compared to a real car, for which “wet chrome plating” is used and in which the part is required to be dipped in acid compounds for pre-treatment. For a model, only injection-molded plastic and die-cast zinc metal can be plated using the same wet chrome plating technique as the real car to replicate the same finish. 


Thus, on resin models, metal trim tends to be rendered with thin, etched stainless steel plate, and that is expensive and labor intensive to apply. Such finely etched parts can appear very accurate and nice on a model car, but when it comes to components like the window frame around the windscreen and the side windows, such as that found on older cars, etched metal parts are flat and lack the soft edges of the real trim on the actual car. Moreover, the etched steel pieces are attached to the resin model purely by gluing. When the glue ages, the trim can start to separate and fall off.  Only injection-molded plastic can be replicated realistically to the accurate shape that duplicates the real thing, and by “wet chrome plating” these pieces, the same metal texture can be achieved. And the trims are securely bonded to the body with heat-deformable mounting pins rather than just the glue.


Another major issue with resin is breakage during transportation.  When the boxes are mishandled, resin models, in particular those with intricate parts that are long and thin, can break more easily.  This inevitably increases the product’s cost because a higher percentage of breakage must be factored in.  Customers are also not happy when the models they have bought arrive broken.


For all these reasons, resin models are normally sold at double- to triple-the-price of die-cast models built to the same scale. And that’s despite the fact that the resin piece typically has no opening of doors and bonnets.  As we’ve noted, the higher price starts with the development costs that must be amortized over the smaller number of models that can be produced on silicon-rubber tooling. Furthermore, the model is entirely handmade, which is costly to manufacture.  Resin mainly caters to a small number of collectors around the world who want the earliest batch of the new cars being released and who don’t want to wait for die-cast models that can only be launched at a much later time.  Otherwise, resin model cars are mostly of unique or rare subjects that will be sold only in quantities of dozens or hundreds of pieces for the small group of collectors around the world. Or, the model is in a scale so large that would not be feasible to make it in die-cast metal.


Other than special project, AUTOArt will not go into the production of resin models or make it part of our mainstream product program. We believe die-cast metal, along with injection-molded plastic, is the most ideal material to make an accurate and collectible model car to our standards of excellence.  Die-cast metal is harder and more challenging and costly to work with, but the model can be made with much finer detail overall and at a more affordable price.  It is structurally more rigid, and it will bring pleasure to its owner for much longer.