Chloe Zhang
Plastic model kits are manufactured using injection moulding, a process that involves melting plastic pellets into a thick liquid, injecting them under pressure into a mould, and then allowing them to cool and harden. This process can be completed in under a minute, though the design process is often lengthy. Before injection moulding, a prototype is carved out of wood, coated with epoxy resin, and used to create a mould. This carving process can take over 1000 hours. The final product is polished, packaged, and shipped with instructions for hobbyists to assemble.
| Characteristics | Values |
|---|---|
| Manufacturing Process | Injection molding |
| Molding Time | About a minute or less |
| Molding Material | Plastic pellets |
| Molding Equipment | Hopper, Auger, Heater, Nozzle |
| Molding Steps | Melting, Injection, Cavity Formation |
| Prototype Creation | Carving, Coating, Curing, Molding |
| Prototype Size | 2-3 times bigger than the model |
| Prototype Accuracy | Fractions of a millimeter |
| Alternative Processes | Vacuum forming, Resin-casting |
| Kit Types | Quick Build, Build 'N' Play, Snap-Together |
| Kit Complexity | Beginner, Advanced |
| Kit Tools | Hobby knife, Sprue cutters |
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Injection moulding
The process begins with pattern-making, where expert carvers follow CAD drawings to carve a wooden prototype that is 2-3 times bigger than the intended model. This prototype is then coated and cured with epoxy resin, and a core mould of the resulting hollow space is made. The two halves of this mould come together to form a cavity mould.
Once the design is determined, plastic pellets are fed into the injection moulding machine via the hopper. An auger (or internal screw) rotates, moving the plastic pellets through the barrel and into the heater, where they melt into a thick liquid (molten state). This molten plastic is then injected through the nozzle via pressure. The nozzle moves into one half of the mould, and when the cycle begins, the two halves close, forming a hollow cavity.
The injection moulding process is completed in about a minute or less. The high pressure used to seal the mould when the plastic is injected can be extremely dangerous, as it is strong enough to flatten a coin or cause severe injury.
After the moulding process, the final piece is polished, and additional details are added. Instructions for hobbyists are drafted by reassembling the original pattern model, and artists work on the final touches for packaging illustrations, decals, and artist impressions.
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Master sculpture
The 'master' sculpture is the basis for the moulds used in plastic model kit manufacturing. It is the first step in the process and is usually created at a larger scale than the final product.
The master sculpture is initially designed using CAD (Computer-Aided Design) drawings, which are then used to guide the carving of a prototype from wood. This prototype is the first rough copy of the plastic model kit and is made larger than the intended scale model to allow for greater accuracy and the addition of fine details. Expert carvers work with incredible precision, ensuring accuracy to fractions of a millimetre.
Once the wooden prototype is carved, each piece is coated and cured with epoxy resin. After the resin hardens, the wooden pieces are removed, leaving behind a hollow space that traps the shape of the prototype. This hollow space is then used to create a core mould, which forms the cavity mould when its two halves are joined together.
The entire carving and epoxy process is extremely time-consuming, often taking over 1000 hours to complete. After this, a pantograph is used to copy the exact shape and design of each component of the scale model prototype on a smaller scale, resulting in the final product size.
The use of CAD technology has revolutionised the process of creating master sculptures, offering greater precision and detail than traditional methods.
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CAD drawings
The use of CAD drawings is an important step in the manufacturing process of plastic model kits. CAD, or Computer-Aided Design, is a modern method of creating highly detailed and accurate designs for a variety of products, including plastic models. This technology has largely replaced the older method of sculpting a large wooden master prototype and then scaling it down.
Once the CAD drawings are complete, they are used as a reference for the pattern-making phase. Expert carvers follow the CAD designs to create a prototype, typically made from wood. This prototype is usually larger than the intended scale of the final model, allowing for greater accuracy and the addition of fine details. The carvers carefully fit each piece of the prototype together, ensuring a precise match within fractions of a millimetre.
After the wooden prototype is complete, it undergoes a coating and curing process with epoxy resin. Once the resin has hardened, the wooden pieces are removed, leaving behind a hollow space that captures the shape of the prototype. This hollow space is then used to create a core mould, forming a cavity mould when the two halves are joined together. This mould will be used in the subsequent injection moulding process to create the plastic components of the model kit.
The use of CAD technology offers several advantages over traditional methods. It enables designers to create highly detailed and precise models, ensuring consistency across different parts. Additionally, CAD systems can be integrated with manufacturing processes, facilitating faster and more efficient production. While injection moulding remains the predominant manufacturing process for plastic models, alternative methods such as vacuum forming and resin casting are also employed, particularly for lower-yield productions or to achieve greater detail.
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Epoxy resin
Once the prototype is carved, each piece is coated and cured with epoxy resin. The resin hardens around the wooden pieces, capturing their shape within. The wooden pieces are then removed, leaving behind a hollow space. This space serves as a core mold, with its two halves coming together to form a cavity mold. The entire carving and epoxy process is intricate and time-consuming, often taking over 1000 hours to complete.
When working with epoxy resin, proper ventilation is essential due to the release of toxic fumes. Respiratory masks are recommended to reduce exposure to these fumes. Additionally, epoxy resin requires careful cleaning and smoothing using tools like hobby knives, sandpaper, or files. The use of standard polystyrene cement is not suitable for resin models, and instead, a two-part epoxy glue called epoxy cement is used to create a strong bond.
Overall, epoxy resin is an important material in the manufacturing process of plastic model kits, enabling the creation of highly detailed and durable models, but it comes with challenges in terms of cost, complexity, and safety considerations.
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Quality control
Prototype Inspection
The first step in quality control begins with the prototype. Expert carvers create a wooden prototype, carving it with extreme precision, sometimes to fractions of a millimetre. This prototype is then inspected to ensure it meets the design specifications.
Mould Creation
Once the prototype is approved, it is used to create a mould. In the past, this was done using a pantograph machine, but modern methods employ CAD/CAM designs and CNC technology to create steel moulds. The mould creation process is highly precise, as any imperfections in the mould will impact the final product.
Injection Moulding
The plastic injection moulding process is where plastic pellets are melted down and injected into the mould under high pressure. This step requires careful monitoring, as the pressure and temperature must be precisely controlled to ensure the plastic properly fills the mould.
Post-Moulding Inspection
After the plastic has cooled and solidified, the pieces are removed from the mould and inspected for any defects. This includes checking for inconsistencies, missing details, or imperfections in the plastic.
Assembly and Packaging
Before final assembly, each piece may undergo additional processes, such as shaving down parts to ensure a better fit or removing any excess plastic (flash). The assembly process is then tested to ensure the pieces fit together correctly. Finally, the assembled model is compared to the original design to ensure accuracy in scale and appearance. Once approved, the model is packaged, including instructions drafted by a separate team who assemble the prototype themselves.
The quality control procedures for plastic model kits are rigorous, ensuring that the final product meets the expectations of hobbyists and collectors alike.
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Frequently asked questions
The first step in the manufacturing process is pattern-making. Expert carvers follow CAD drawings to carve a wooden prototype that is 2-3 times bigger than the intended model. This prototype is then coated and cured with epoxy resin, and a core mould of the hollow space is made.
Plastic model kits are designed using CAD/CAM technology. The master sculpture, or prototype, is then CNC grown and a metal mould is cut. Plastic is then injected into the mould.
The carving and epoxy process can take over 1000 hours. However, once the design is determined, the injection moulding process is completed in about a minute or less.
