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Reaction injection molding RIM

Introduction to RIM reaction injection molding

Reaction injection molding (RIM) is an injection molding process in which several reactive components, possibly with added fillers, are intimately mixed under pressure before being introduced into the mold, where they react (polymerization, cross-linking) to form the finished object.

As with vacuum casting, we start with a master model created by Stereolithography, then a mold is made from epoxy or silicone resin.

This mold is then filled with polyurethane resin using a special low-pressure machine.

parc machines coulée sous vide RIM

The benefits of this production technology

  • RIM reaction injection molding is an excellent alternative to injection molding for production runs of 30 to 100 parts. Quality is equivalent, with a wide range of technical resins and colors.

    Reaction injection molding can produce strong, flexible, lightweight parts that can easily be painted.

    Cycle time is fast compared to vacuum-cast materials.

    The two-component mixture injected into the mold has a much lower viscosity than that of molten thermoplastic polymers, so large, lightweight, thin-walled articles can be manufactured successfully by RIM. This less viscous mixture also requires fewer clamping forces, leading to smaller equipment and reduced investment.

RIM molding materials and finishes

At Axis, we use mainly PP and a resin similar to ABS. Don’t hesitate to contact us if you have a specific need.

We can take care of the finishing touches if required:

  • Overmolding or installation of metal inserts;
  • Realistic surface finish: gloss, satin, grained, obtained by paint finishing;
  • EMC paint.

Lead times and part design advice

For RIM molding, it will take between 2 and 3 weeks to design the tooling, with production of 10 to 30 parts per week. It all depends on the size and complexity of your project.

The sub-assemblies are always designed according to your functional criteria. We’ll be happy to help you assess your needs.

How does it work?

There are several stages in the production of RIM parts:
  • Step 1: The first step is to create a master model in

    • Once we have received your 3D file, we process it for production, with or without shrinkage depending on the material ordered;
    • The master model goes into production using the Stereolithography process;
    • It is cooked to harden;
    • The 3D part is cleaned, sanded and blasted. The necessary finishing touches are provided by our prototypists, as the casting will have the same appearance as its master (graining, transparency, etc.);
    • Our moldmakers glue a marker along the parting line to make it easier to open the silicone mold.
  • Step 2: Making the mold
    • The Stereolithography master is levitated in a wooden box with the help of a sprue (a recycled feed sprue, which allows the material to circulate in the mold cavity) and vents (to evacuate air from the material);
    • Once the part has been installed, the silicone or resin is poured into the box to take the impression;
    • When the silicone has hardened, our moulders open the wooden box along the parting line;
    • Once the silicone mold has been completely opened, the stereo master is carefully removed to avoid damaging the silicone.
  • Step 3: Making the duplication
    • The casting operator in charge of the project carefully closes the mould by hand, avoiding any gaps that might allow the material to escape from the mould;
    • The two parts of the polymer are mixed, usually by injecting them under high pressure into an impact mixer. The mixture is then injected into the mold at a lower pressure. The mixture is left to rest in the mold long enough to expand and react;
    • Once the material is hard, the casting operator demolds the part.

To find out more about our other additive manufacturing production resources, please visit our our machines page.

Need a quote or information on rapid prototyping?

Ask us for a quick quote or call us on +33 (0)5 55 06 17 17