Moulding is the process of manufacturing by shaping liquid or pliable material using a rigid frame called a mold or matrix.
When moulding plastics, a powder or liquid polymer such as polyethylene or polypropylene is placed into a hollow mold so the polymer can take its shape. Depending on the type of process used, various ranges of heat and pressure are used to create an end product.
Many different objects are made from plastic — thin sheets for wrapping food, long strips for curtain rails, hollow bottles and complicated toys. With such a huge range of items made of plastic it is not surprising that there are many different ways of moulding plastic.
The Types of Plastic Moulding
1. Rotational Moulding
Rotational Moulding, also called rotomoulding, is a manufacturing process for producing large hollow parts and products by placing a powder or liquid resin into a metal mould and rotating it in an oven until the resin coats the inside of the mould. The constant rotation of the mould creates centrifugal force forming even-walled products. Once the mould cools, the hardened plastic is removed from the mould.
Very little material is wasted during the process, and excess material is often re-used, making it economical and environmentally friendly.
Common Uses for Rotational Moulding
Rotational moulding is commonly used to make large hollow plastic products like bulk containers, storage tanks, car parts, marine buoys, pet houses, recycling bins, road cones, kayak hulls, and playground slides.
2. Injection Moulding
Injection moulding is the process of making custom plastic parts by injecting molten plastic material at high pressure into a metal mould. Just like other forms of plastic moulding, after the molten plastic is injected into the mold, the mould is cooled and opened to reveal a solid plastic part.
Commonuses for Injection Moulding
Injection moulding is commonly used for making very high volume custom plastic parts. Large injection moulding machines can mold car parts. Smaller machines can produce very precise plastic parts for surgical applications.
3. Blow Moulding
Blow moulding is a method of making hollow, thin-walled, custom plastic parts. It is primarily used for making products with a uniform wall thickness and where the shape is important. The process is based upon the same principle as glass blowing.
Blow moulding machines heat up plastic and inject air blowing up the hot plastic like a balloon. The plastic is blown into a mould and as it expands, it presses against the walls of the mould taking its shape. After the plastic “balloon” fills the mould, it is cooled and hardened, and the part is ejected. The whole process takes less than two minutes so an average 12 hour day can produce around 1440 pieces.
Common Uses for Blow Moulding
Blow moulding processes generate, in most cases, bottles, plastic drums, and fuel tanks.
4. Compression Moulding
Compression moulding is done exactly like the name suggests. A heated plastic material is placed into a heated mold and then pressed into a specific shape. Usually, the plastic comes in sheets, but can also be in bulk. Once the plastic is compressed into the right shape, the heating process ensures that the plastic retains maximum strength. The final steps in this process involve cooling, trimming, and then removing the plastic part from the mould.
Common Uses of Compression Moulding
The best use of compression moulding is the replacement of metal parts with plastic parts. It is mostly used for small parts and products in very high volume. The automotive industry uses compression moulding heavily because the final products are very strong and durable.
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