Differences Between Vacuum Forming and Injection Moulding

The applications for various plastic parts are endless and almost every industry relies on plastic in some way – and for good reason. Plastics are both incredibly strong and very versatile and as such are used in the manufacture of various parts that can be used in everything from the automotive industry to the medical sector.

There is a plethora of methods that can be utilised when manufacturing plastic parts, however, two of the most popular are; vacuum forming and injection moulding. Both processes offer unique benefits and drawbacks and ultimately depend on the specific plastic part that needs to be manufactured.

Many businesses, however, do not know the difference between the two processes and often chose the wrong manufacturing technique for their plastic parts.

What is vacuum forming?

Vacuum forming, also referred to as thermoforming, is the process of forming heated plastic sheets to the surface of a specifically designed mould.

Each plastic sheet is loaded into the vacuum forming machine and heated until it is sufficiently malleable. A vacuum of air is then applied against the sheet in order to stretch the sheet over the mould which then creates the specific shape or design.

The newly moulded plastic is then cooled and ejected from the mould ready for any trimming or to then be carried out.

Benefits of vacuum forming

Vacuum forming has its own unique benefits which, in most cases, can make it more of a viable option as opposed to other types of plastic forming, including injection moulding. Some of the benefits of vacuum forming include:

• Fast prototyping and production times
• Ability to create large parts
• Lower start-up costs, associated to cheaper, less complicated tooling than injection moulding.
• Easily adaptable
• Various texture options
• Ideal for repeat jobs – as the moulds and castings made can last for years
• Cost effective pricing on small to medium batches of parts

Drawbacks of vacuum forming

However, as with most plastic forming services, vacuum forming does have its drawbacks which can, in a few cases, make other plastic forming methods more suitable. The drawbacks of vacuum forming include:

• More intricate designs can be difficult
• The price of manufacture begins to increase in larger batches (more than 3000 parts)
• The process only controls one surface

What is injection moulding?

Injection moulding is a more complex manufacturing technique than vacuum forming and can require high levels of engineering expertise.

The process begins by heating polymers into molten form. This liquid polymer is then ‘injected’ into a mould – usually made of steel or aluminium – and held in place. After the plastic has cooled the mould is then opened and the finished parts are removed.

Benefits of injection moulding

Similar to vacuum forming, injection moulding does have its unique benefits some of which include:

• Low levels of waste
• Ability to be fully automated
• Suitable for larger batches
• Can provide an appealing ‘finished’ look

Drawbacks of injection moulding

However, injection moulding does have its drawbacks which can make vacuum forming the favoured process especially where low cost and short lead times are imperative. The drawbacks of injection moulding include:

• Higher start up and tooling costs
• Longer lead times as mould needs to be specifically manufactured

The main drawback of injection moulding, however, is that it is heavily reliant on the correct design and manufacture of the mould itself. This means that any discrepancies in the mould could result in an incorrect or faulty product being manufactured.

Choosing the best manufacturing process for your plastic parts

It is apparent that both methods have their strengths and weaknesses and knowing these is the first step in deciding which manufacturing technique will be best for your plastic parts and, ultimately, the method in which you choose will depend on the part you need.

In order to determine which method is best it is imperative that you consider the following questions:

• What is the production quantity?
• What are the specific design requirements?
• What is my budget?
• When do I need these products?

Based on these questions it is likely that vacuum forming will be the best and most viable option as it has lower set-up costs, shorter lead times and is able to produce fairly large quantities of products.

In addition vacuum forming is more flexible than injection moulding and whilst extra finishing may be required to get the right colours or texture vacuum forming is often seen as a better alternative to injection moulding.

Vacuum Forming Services at Ansini

Here at Ansini offer an extensive and professional vacuum forming service suitable for making plastic parts for a variety of sectors. Please feel free to get in touch with our team for more information about our vacuum forming services.