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Different Materials for Scale Modelling

Posted March 10, 2020

Different Materials for Model Kits

Nowadays model kits are made of different materials. The first models ever were made out of wood. Since wood is inflexible, most of the work was made by hand, with little to no automation. Because of that, the production was slow, limited, and expensive. After injection molding was found, it allowed mass production of kits which made them widespread and cheap. In turn, this hobby received the popularity it deserved.

To this day, when you think about model kits, the first thing that comes to mind is plastic kits. But apart from plastic, few more materials can be used for models. In this article, we’ll try to summarise the different materials used in the model kits industry, while going in a bit of detail about their characteristics. 

List of Materials Used in Model Kits 

  • Injection-molded polystyrene plastic

  • Cast polyurethane resin

  • Photo-etched metal frets

  • Metal gun barrels and ammunition

Injection Molded Polystyrene Plastic 

As we mentioned before, plastic is the most prevalent material in the industry. There are thousands of different molded plastic model kits attainable on all scales. Which many of them made out of only plastic since the 1950s. 


Production Method 

Large metal molds are used to melt the beads of polystyrene to form the sprues and parts while constantly applying pressure and heat to them. When the molds are fully loaded with liquid polystyrene and solidified, mold halves are detached from each other, releasing the sprues. Then they wait a couple of minutes for it to cool off and become completely rigid.

Attributes of Plastic


 

There are no color restrictions for manufacturing. Which means you can choose any color, including transparent, like windows. The kits used to come in the color of the finished product so that it wouldn't need painting. But today, although every manufacturer has a preference, the color of the base model is inconsequential because of all the priming, painting, and, weathering.

Even though injection-molded plastic is the most common model kit type in the world, the metal molds used in manufacturing are quite expensive. This means injection-molded kits can only be produced by big companies. They need to adhere to popular subjects in manufacturing to keep the sales high because of the price of the molds.

The disadvantage of this process is the detail. Having solid molds with two halves reduces the complexity of the item significantly. Since the molds only have two parts that can come apart, you can’t use undercuts. This means that you either break the complex part into pieces to manufacture each piece on its own or you give up on some detail to produce a simpler version of it. 

Although Dragon found a way around this situation by using molds with more than two halves, it came with a caveat. This granted them the power to create exceptionally detailed parts, but the technology they use is equally more expensive to how good it is. The already pricey molds got much more expensive since they strive for more detail.

Of course, the traditional injection mold techniques improved significantly over the years, achieving a level of detail that was impossible to think at the beginning.


Cast Polyurethane Resin

Resin is the niche version of molded plastic. It was created as aftermarket accessories to modify your plastic kits.

As indicated previously, due to the price of the molds, only the subjects that have wide appeal were manufactured by the injection mold method. But there was also a market for less popular subjects. So small companies started to produce conversion kits for modelers to change their plastic kits as they desire. As time goes by, people get used to handling resin and companies started manufacturing entire kits with resin.


Production Method 

They mix thermosetting resin with some kind of curing agent. The agent hardens the resin that was injected into the mold. Like metal molds, after the liquid hardens, they detach the molds to receive the part.

Unlike metal molds, resin casting molds are much cheaper and easier to make. They create the part that they design to produce. Then they cast the mold around it. Since it's cheaper, this method is more suitable for smaller companies. You can even do this at home since it's possible to obtain all the ingredients. 

The downside of resin casting is that the molds are nondurable and takes a lot of work to complete, which makes resin kits much higher priced than injection-molded kits. 


Attributes of Resin 

While the cast sets in, the resin reduces in size. While cooling off, sometimes the texture of the part can warp or can be subjected to excess flash. These are the things that always need to be taken into account. That's why the quality of the kits may differ massively. Be that as it may, resin kits have the potential to best everything on the market in terms of detail. The place where using resin shines the most is cloth textures, folds, and cockpits. 

You can find our detailed guide about how to work with resin here.


Photo Etching of Metal Parts 

Photo-etching(PE) is a method to create very small and thin metal pieces by using strong acids. When the essential parts are too tiny or fragile to be produced by resin casting or injection mold methods, we can create them using PE. First of these products, introduced to the market as after-market accessories to allow hobbyists to create very detailed models. Since they first showed up, PE kits became an essential part of this industry.

Lately, more and more companies introducing PE frets in their injection-mold product lines. Tamiya and Dragon, two of the biggest companies that manufacture injection mold kits, adopted this method for their own product line.


Production Method 

First of all, Using the CAD program, the components drawn on the computer first, then imprinted on a clear film. Then, the design exposed to light while on a photoresist plate. After it is placed upon the sheet of metal that will be etched, the unprotected part of the photoresist got dissolved, leaving only the design on the plate. Using strong acids, the metal is etched, leaving only the designed part. Even though it looks complex, this is a small scale manufacturing method that can even be performed at home.


Attributes of PE Metal

Since the PE parts are usually very small, it's very difficult to handle. They don't work well with polystyrene cement, so people often use cyano or epoxy, the same as resin. That's why some modelers hate PE parts. If you want to create custom shapes by folding the PE parts, you need various folding equipment, some of which are quite expensive.

Keep in mind that the aftermarket PE sets may have been made for different uses. Some are made for particular model kits, even indicating the serial number of the kit it is made for. Others made for a more comprehensive vision in mind. These can fit into a wide range of sets. Lastly, some may not indicate any particular model at all. These could be a selection of tools essential to many models like seat belts and buckles.


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