Reaction Injection Moulding (RIM) is also known as low-pressure injection molding. It is a relatively newly developed process applied to the production of rapid prototypes and low-volume rapid injection moulding products.

It injects two polyurethane materials into the rapid mold at room temperature and low pressure. The products are formed through chemical and physical processes such as polymerization, cross-linking, and materials curing. 

Its advantages are high efficiency, a short production cycle, simplicity, and low production costs. In this case, rapid reaction injection moulding is an excellent choice for small-batch trial production during product development, short-run production of simple-structured coverings, and products with large and uneven wall thicknesses.

1. Molds for RIM

ABS molds (20-50 pcs), resin molds (50-500 pcs), aluminum alloy molds (500-5,000 pcs), and steel molds (10,000-50,000 pcs).

2. Materials for RIM

The material for RIM is called polyurethane, PU in short. It can be divided into three types.

  • Foamed PU. They can be soft foam and dense foam, which are used to make sound insulation covers, heat insulation layers, etc.
  • Micro-foaming PU. Its density is generally 0.6-0.7 kg/m³. They can be applied to thick-walled and high-strength products.
  • Non-foaming PU. The material performance is similar to PP or ABS with a density of about 1.1-1.2 kg/m³. They are suitable for various thin-walled shell products, with aging resistance, strong impact resistance, high cohesion, easy to load and unload, etc.

3. Injection pressure of RIM

The injection pressure is about 10MPa with a flow rate of 600g/s.

4. General working time of RIM

Each part takes 15-30 minutes to make. The demoulding temperature is usually controlled below 40℃, and after demoulding the parts are cured in an 80℃ environment for 2-4 hours for best performance. The materials and the sizes of the product determine the curing time.

5. Standard tolerances of RIM

According to its structure, the wall thicknesses of the product are different and their tolerances vary as well. The tolerance is usually within ±0.20mm/100mm. By designing the tooling, the part can be processed a second time to ensure tolerances of the position with particularly high precision requirements.

6. Thickness of the part injected

3mm or more.

7. Maximum size of the parts

Up to 30 kg of weight and up to 2500x1500x1000 mm in size.

8. The process of RIM

Initially, the monomer or prepolymer is mixed in a liquid state with a metering pump at a certain ratio into the mixing head. After the mixture is injected into the mold, it reacts rapidly and is cross-linked and cured in the mold. Then, after demolding, the part is complete. Finally, the RIM parts will be post-finished. Nearly all surface treatments are available, including painting, plating, screen printing, hand transfer printing, etc.

This process can be simplified as follows: storage → metering → mixing → mold filling → curing → demolding → post-treatment.

9. Applications of RIM

As one of the low-volume rapid injection moulding manufacturing methods, RIM is widely used for small-batch production of car models and accessories, medical equipment shells, toys, digital products, home electronics, fitness equipment, etc. If you need to make large-sized plastic products, but the quantity did not reach the MOQ of injection molding, you can turn to rapid reaction injection moulding.

rapid reaction injection moulding automotive parts

To better understand RIM’s applications, let's look at the top three most commonly applied industries. 

  • Medical device industry 

    The shell production of medical carts, CTs, ophthalmic treatment instruments, medical B ultrasound devices, color ultrasound devices, reagent instruments, hematology analyzers, cell analyzers, virus detection instruments, tumor detection instruments, laser treatment instruments, environmental detection instruments, gas chromatographs, liquid chromatographs, beauty instruments, etc.


  • Automotive industry

    The production of bumpers, car dashboards, car door panels, side trim panels, modified cars, etc.


  • AI industry

    The shell production of service robots, industrial robots, etc.

As a low-volume rapid injection moulding manufacturer, X Rapid Technologies provides a one-stop RIM service. Feel free to get in touch with us and discuss your requirements. You will get free quotes within 24 hours and kick-start your projects soon.