Let’s review reaction injection molding (RIM) and compare that to other manufacturing processes used to manufacture products from a polymer material (plastic), some of which are fully automated and others that are very labor-intensive.
Another factor to consider is the level of complexity that can be achieved with the different processes and what degree of detail can be produced. One other major factor is the cost of both the tooling and the final part. All these factors, when combined, will determine what is the best process to be used for the production of a production part.
What is RIM?
Reaction Injection Molding (RIM) uses two-part thermoset liquid polymers which are lightweight and cost-effective. These thermoset polymers start as a liquid pumped into a mixing head which then injects the mixed liquid polymers into the tool cavity.
As liquid polymers require less heat and pressure to fill the cavity, tooling can be manufactured from lower-cost ‘softer’ materials such as aluminum rather than hardened steel.
The liquid polymer cures inside the tool at low pressures and a tool temperature of around 80 Degrees Celsius.
The term reaction injection molding comes from the fact that the polymer is a two-part liquid that has a chemical reaction when mixed which is then injected into the mold tool.
What are the Benefits of Reaction Injection Molding?
The benefits of reaction injection molding are as follows:
- Large lightweight parts can be produced
- Parts can be produced with variable wall thicknesses
- Low-cost tooling due to low injection pressure and low tool temperature requirements
- A variety of inserts can be placed in the mold prior to injection
- Dimensional stability over a large dimension
- High complexity and detail achievable
- Semi-automated process giving a low to medium cost production part
Comparison of RIM Against Other Molding Processes
The following table shows a comparison of the different manufacturing processes for polymers and the following attributes:
- capital requirements and labor intensity,
- tooling costs,
- piece part costs,
- part complexity based upon geometry
A similar comparison where you can see the suitability of each molding process for either mass production or small volumes and complex parts can be seen in this chart (based on a publication from https://romeorim.com/):
👉 Learn even more about the plastic injection molding production process in this collection of resources.
Production part examples
Reaction Injection Molding has been used extensively in the automotive industry for decades to produce bumpers and fenders, internal trim, and other decorative trim.
Another industry sector to utilize reaction injection molding as a manufacturing process is the healthcare industry. Parts include housings for medical devices such as DNA analyzers, analysis machines, and sides for medical beds.
Image source: https://goformold.com/th-reaction-injection-molding/
Conclusion
RIM as a process is ideal for the production of large lightweight complex parts manufactured from a thermoset polymer. The process is semi-automated, therefore, part costs are not as low cost as fully automated injection mold processes, however, the tooling cost will be a lot lower than those harder injection mold tools due to the lower temperature requirements and lower pressure during the production process.
