Advantages and disadvantages of plastic injection moulding

Thermoplastic Injection Moulding is a very commonly used process to manufacture identical parts that are required to be produced in large volumes. The Plastic Injection moulding process is injecting molten material into a closed mould. By using a variety of materials for a properly designed part and a mould to facilitate the moulding process, we can produce the required parts consistently and economically.
To understand the process of Plastic Injection Moulding, the granules of plastic material are loaded onto the machine using a hopper loader into the hopper, which is one of the simplest conveying systems. 

The plastic material then passes through a heated barrel (under controlled temperature) and is injected under high pressure through a runner system into the cavity of the mould. The cavity and core define the shape of the part that is to be moulded. Once the injection process is completed to fill the cavity, the part needs to be cooled before the mould opens and the part is ejected and removed from the mould. This process repeats, allowing each cycle to produce an identical part. The Plastic Injection Moulds are manufactured using Special tool steels and specialist equipment and tools.

Advantages of Injection Moulding

Fast production – Plastic Injection moulding process can produce more number of parts per hour, depending on how many cavities/impressions there are in the moulding tool. When a good moulding tool design is manufactured with an effective filing system, cooling circuit and ejection system, we can produce consistently good parts with reduced cycle time.

Significant strength enhancement -The plastic injection process offers a unique option within applications where parts need to be strong or durable. In plastic injection moulding, it is possible to use fillers with the moulding raw material which reduces the plastic materials density, while also adding greater strength to the moulded part.

Material, Texture and Colour Flexibility – the material and colour can be changed depending on the customers’ requirements. The texture and finish required can be produced on the part.
Reduced finishing operations – There is often very little post-production work required on these injection moulded parts, they usually have a good finished look upon ejection.

Ability to use multiple materials – Multiple plastic materials can be used simultaneously during the injection moulding process – over moulding, and also metal inserts ( usually for threaded applications) can be used as inserts to be kept in position in the mould before the moulding cycle starts. After the injection moulding process is completed, the moulded part along with the inserts is ejected from the mould.

Low Labour Costs – a well-designed automatic plastic injection mould can run without any interference by human labour, which means the required parts can be ready with little or no labour for production.

Design Flexibility – when you are able to design a part considering the design restrictions, we can integrate other parts of an assembly into a single plastic injection to reduce the cost and production time for these parts.

Scrap – A well-designed mould can produce parts without runners by using hot runner systems. Commonly most moulds produce runners for every part moulded. A majority of the moulders recycle these runners by grinding for reuse.

Disadvantages of Injection Moulding

High initial costs – the main disadvantage of plastic injection moulding is the plastic injection moulding tool, plastic injection moulding machine and its auxiliary equipment which are very high.

Lead time – from product conception to the final part, it can take months of design, reviews, testing and tool manufacturing. Once the tooling is done, as mentioned under the advantages, it takes very little time to produce the required parts, especially when you have a multi-cavity / impression moulding tool.

Not cost-effective – producing parts required in low volume is less cost-effective.

Design restrictions – unless an experienced design team works on the part required along with the mould manufacturer and the raw material suppliers, there may be few restrictions in the part for Plastic Injection Moulding.