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What is Reaction Injection Moulding (RIM)?

Reaction injection moulding is a cold casting process that involves mixing two liquids, polyol and isocyanate, to create strong yet lightweight plastic mouldings.

Despite only being developed in 1969, reaction injection moulding (RIM) has become a leading plastic moulding process thanks to its versatility and scalability in producing high quality polyurethane thermoset plastic parts.

Initial tooling investment in RIM is very cost effective compared to other moulding processes. Once initial designs and mouldtools have been made, it becomes incredibly efficient in time and costs to produce a large number of parts and scale production as necessary. Some tooling systems are specialised for prototyping, such as our FASTrim system, which makes it easy to modify and produce low volume parts.

What Industries is Reaction Injection Moulding Used in?

Reaction injection moulding is most commonly used to supply the automotive and medical industries, but can also be used in a wide range of other industries. It is particularly suited to manufacturing large, precise, multi part assemblies, ideal for making housings and enclosures for scientific, analytical, medical and research instruments.

How Does RIM Work?

Low-pressure meter mix equipment is used to separately pump the two liquids into the mixing head. Once they meet in the mixing head, the chemical reaction begins where the operator has a short period of time, what is often referred to as the ‘material pot life’, to fill the mould tool.

The materials used for the tooling vary depending on the application, including the size and geometry of the part and production volume. For example, composite materials and metal inserts are preferable for long-term projects with complex features, whereas polyurethane tooling boards offer great stability suitable for rapid machining and low volume projects or prototyping.

Is Reaction Injection Moulding Sustainable?

Unfortunately, due to the permanent chemical bonds that are formed through the moulding process, reaction injection moulding tooling and equipment cannot be easily recycled. Midas MRIM Tooling can be broken down so that the steel content is fully recycled and the composite element is shredded and ground into inert bulk filler. Midas PuR mouldings can also be shredded and used as bulk filler.

We remain committed to an environmentally friendly, zero-carbon economy. This includes our partnership with The Forest of Marston Vale and becoming a carbon neutral certified company in January 2021. Midas is certificated to PAS 2060 – Scope 1,2 & 3. We are carbon negative to Scope 1 & 2 and we offset a small amount of Scope 3, thus meaning we are Carbon Neutral certificated.

Additionally, all Midas Polyurethane RIM Mouldings can be returned at any time for refurbishment, repair, and modification, allowing you to get the most value from your mouldings and reduce downstream waste whilst saving you money.

As noted, we grind down polyurethane mouldings at the end of their life into an inert bulk filler for construction and composite industries. This keeps your unwanted mouldings environmentally safe for generations to come, helping support our vision of a circular economy.

Learn about the Midas Green Initiative for more information on how we are dedicated to sustainable development on a global and local level.

About Midas Pattern

We have been manufacturing in the UK for over 33 years and have grown into a leading moulding and toolmaking business. We are proud to have built a business that carries out all engineering and manufacturing processes in-house so you can be certain your products are of the highest quality.

All our processes are carried out to BS EN ISO 9001:2015 standards and we are audited by NQA as part of our accreditation. Additionally, we are accredited with ISO 14001:2015 and PAS 2060 (Scope 1,2 & 3). We also support companies working to ISO 13485:2015

Learn more about Midas pattern here or contact us today to discuss how we can work with you.


Do you process any other materials except for Polyurethane?

Although Reaction Injection Moulding can be used to process other materials, we only offer polyurethane mouldings (PU Moulding).  If you would like to understand more about the materials we use, we can discuss this in more detail and provide you with relevant data sheets and even material examples where appropriate. 

Where are you based?

We are located in Bedford, centrally placed between the M1 and A1 and ideally located between the London, Cambridge, and Oxford triangle. You can find directions to our factory on our contact us page.

How much does reaction injection moulding cost compared to other processes?

This is a tricky question to answer as it really will depend on each individual project but as a rule of thumb, on large panels which have a reasonable amount of 'B' surface complexity we would expect our MRIM production tooling to be 1/10th the cost of a comparable metal injection mould tool. 

RIM moulding provides a low-cost solution to enable you to get to market with stylish and very functional covers.  For example, you can have moulded in brass inserts or hinge pins, ribbing for support or mounting surfaces and edge details for gaskets.  Low cost also means low risk which can be beneficial when launching a new innovation or as a Start Up company where every penny counts.


For more answers to other questions including how you can get a projected quoted, how designs work, and the maximum and minimum size of projects, visit our FAQ page.

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What is Reaction Injection Moulding (RIM)?