An Introduction To Plastic Manufacture

Since the explosion of its mass production in the early 1940s, plastic has grown to dominate an enormous range of industrial, commercial and domestic products. Its popularity is down to a number of its attributes including its low cost, durability and ease of manufacture. Today it has replaced a number of materials, such as wood, ceramic and glass, in many of their traditional applications. The UK alone consumes some 5 million tonnes of plastic each year.

With some 60 million tonnes produced in Europe every year it is clear that manufacturing of plastic is big business. It is estimated over 60,000 companies operate within the European plastic industry, which has a turnover of around 320 billion Euros. Over 1.45 million people are directly employed in the plastic industry within Europe alone, with 134,000 employed in the actual manufacturer of plastic.

The industry has not been without its challenges. In the past decade the developed world has strived to reduce the amount of plastic waste going to landfill. In Europe, international initiatives have managed to increase the amount of plastic recovery (that is, plastic that is diverted from landfill and instead is used in recycled products or the production of energy) to over 60%. That means 60% of the plastic we use is recycled rather than going to landfill.

There are a variety of different manufacturing processes, each suited to their respective products. Whilst some are geared up for large scale industrial production, others can be carried out at home. Some processes produce beautifully finished products, whilst others require post production and the removal of flash or defects. Here we take a look at some of the most popular.

Blow Moulding

Blow moulding is one of the most common methods used to form hollow plastic products. Plastic is melted down and formed into a tube like piece called a parison. This is then clamped into a mould before hot air is blown into it, forming the plastic into the shape of the mould. Once the plastic has cooled the part is rejected from the mould. As tooling costs are relatively high, this process is best suited to high volume, batch production. Minimal post-production finishing is required.

Casting

Perhaps the most simple of plastic manufacture procedures, casting simply involves pouring molten plastic into a mould and leaving it to set. The tooling costs are very low (involving only the costs of the mould and plastic melting device) as are typical production volumes. Post-casting, some finishing may be required as the process is prone to leaving air bubbles and rough finishes.

Compression Moulding

Compression moulding is used for moulding complicated shapes, such as casings, and products that require high tensile strengths. The plastic is heated, poured into a mould cavity and then compressed by a second mould into the desired shape. Once cooled, the second mould is removed and the part ejected. Whilst producing very strong plastic products, articles generally require post processing. Manufacturing firms often use industrial gas burners to remove flash and produce a smooth finish.

Extrusion

An interesting process used to form parts that require a uniform cross section, extrusion involves heating plastic pellets before driving them with a screw into a die. Once in place, the plastic is left to cool and then removed from the die. Again, tooling costs are high and the process lends itself well to mass production.

Injection Moulding

Plastic injection moulding is a process used to create precision parts and relatively complicated shapes in high volume and at very low cost. Plastic is injected at high temperatures into a mould where it is held to cool before being ejected into a tray for removal. Batch times can be as low as just a few seconds, making this process ideal for mass production. Whilst some post-production processing is required to remove the sprue, injection moulding generally produces high quality finished products.

Thermoforming

Finally, thermoforming is a process suitable for low volume production. Preformed plastic sheets are heated before being sucked or pushed into a mould to form shallow bowls, hulls and pots. As there is no application of great heat or pressure, tooling costs are very low. Moreover, cheap plastic can be used without sacrificing the quality of the final product.