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Manufacturing Processes - Reaction Injection Moulding (RIM)

Updated on January 2, 2012

RIM Fundamentals of Reaction Injection Molding

Reaction Injection Moulding Process (RIM)

This is a permanent mould process that fits in the general category of casting as a manufacturing process and is sometimes abbreviated to the RIM Process.

The general mode of operation of this process is to combine two feeds of preheated, low molecular mass reactants in a mixing head and inject them at high speed into a split die. The mixing head opens to allow the mixed reactants into the die and closes again when it is full. The end result is a high molecular mass casting which can be removed from the mould once set using an ejector arrangement.

As with all casting processes, 3D shapes can be produced and if a low modulus material is used, slight re-entrant angles can be included in the design. This process is used mainly for the production of polyurethane, polyamide and composite components, with a wide range of chemically reactive systems being possible.


  1. Can produce strong flexible lightweight parts
  2. Relatively quick cycle times (limited by the reaction time of the polymer) as compared to vacuum cast materials
  3. Has a lower viscosity than thermoplastic polymers
  4. Lower pressure means lower clamping forces
  5. No waste material 100% utilization (providing there is no scrap which cannot be recycled)


  1. Cycle times are slower than standard injection moulding for RIM
  2. Raw materials are expensive
  3. Process is difficult to set up
  4. Surface textures are variable
  5. Can suffer flaws as a result of premature reaction

The process is generally likened to injection moulding with the obvious difference in respect to the materials used and it can be used for the production of large, lightweight and thin components. The automotive industry have adopted this process for the production of rigid foam automotive panels.

The use of composites to strengthen components through the introduction into the process of glass fibre or mica is also an attractive option for the production of automobile panels and other large sheet like components. When this is done the process is known as Reinforced Reaction Injection Moulding or RRIM.

R.I.M. Reaction Injection Moulding

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