What is the difference between injection moulding and casting plastic?

Mar 20, 2024

The success of your plastic product, both practically and financially, relies heavily on the production process that you opt for. If you are just starting out in the world of plastic production, you’ll likely come across both plastic injection moulding and plastic casting as options to explore. However, whilst they are similar in some ways, there’s significant difference in what they can achieve.

How do you know which process is right for you? In this article, we’ll look at the advantages and disadvantages of each method to support you in making an informed decision.

What is plastic injection moulding?

Plastic injection moulding is the process whereby granulated thermoplastic material that has been heated into liquid form is injected into a bespoke mould to produce the desired component. Once cooled, the component is ejected from the press and the cycle repeated to produce the number of components required.

What are the benefits of plastic injection moulding?

High accuracy – When the mould tool is considered, designed, and manufactured, the products it produces can be made to tight tolerances, with complex forms and fine detail.

Repeatable - A product can be made repeatedly from one mould, making it ideal for production of different volumes of products that all need to be identical.

Cost effective in high volumes - Once the initial moulding tool has been made, the cost-per-part for injection moulding is low when compared to other processing techniques, particularly for medium to high volume production runs.

Quick production runs – Rapid cycle times can be achieved from the plastic injection moulding process, meaning that products can be mass-produced quickly.

Low waste – Mould tooling can be designed to minimise the waste produced during the production process. Where waste does occur, it’s usually only in small amounts, and it can often be reground and reused.

Material options – Vast thermoplastic material options are available with the option of compounding and additives to help you achieve the quality of finished product that you require.

What are the disadvantages of plastic injection moulding?

High initial cost – The initial cost in product design and mould tool manufacture can be high. However, it’s worth weighing up the low cost-per-part once the mould is complete, and the speed at which products can be produced at this point too.

Specialist skill to be sought – Due to the specialist skills that are required for mould tool design, you will need to work with tooling experts to ensure the mould is designed and produced to a specification that is fit for purpose. Failure to do so could make for inefficient production runs, as well as inaccuracies or quality issues in the finished product.

Extended lead times - It’s true that production is swift when using plastic injection moulding, but there is a lot of preparation to be done beforehand in terms of designing the product, producing the mould, and trialling the parts. This can cause delay if you are looking to bring a product to market quickly.

What is plastic casting?

Casting is like injection moulding in that a cavity mould is used, but it relies on atmospheric pressure to fill the mould, rather than forcing the fill via an injection process. Polystyrene, Acrylic, Nylon 6, Polyester and Polyurethane are common materials for plastic casting. The material is poured into the mould and allowed to cool to form the finished product.

What are the benefits of plastic casting?

Cost effective - The cost of plastic casting moulds, equipment and tooling are low in comparison to plastic injection moulding, which is great news if you are on a budget.

A simple process - The plastic casting process is not complex, so it is easy to understand and does not involve too many components.

Little or no internal stress - This ensures a quality finish that fits product specifications.

What are the disadvantages of plastic casting?

A slower process - The output rate of a plastic casting process is slow, with long cycle times that make high production runs tricky.

Low dimensional tolerances - This makes it an unfavourable process for those looking to produce complex products.

Moisture and air bubbles - These can occur during the process, rendering the product a failure.

Should I choose plastic injection moulding or plastic casting?

Whether you choose plastic injection moulding or plastic casting will rely largely on the type of product that you are looking to produce and the size of the production runs that you require. If you are only producing a small number of products, or simply prototyping, then casting is an avenue to explore. If you are looking to mass produce products, particularly if they’re complex or have critical to quality dimensions then plastic injection moulding may be the preferred option.

Who should you call when you choose plastic injection moulding?

If you have decided on plastic injection moulding, we would be only too happy to help you bring your product to life. Our team will support you with the entire process, from mould design to production and postproduction activities. Simply give us a call to get initial conversations underway; the earlier you involve the experts, the smoother your production process will go.

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