Introduction to RIM injection molding
The reaction injection molding (RIM) is an injection molding process that consists of intimately mixing under pressure several reactive components, possibly with added fillers, before introducing them 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 will be made in epoxy or silicone resin.
This mold will then be filled with polyurethane resin using a specific machine under low pressure.
The benefits of this production technology
RIM is an excellent alternative to injection molding for runs of 30 to 100 parts. The quality is equivalent, with a wide range of technical resins and colors.
Reaction injection molding can produce strong, flexible, lightweight parts that can be easily painted.
Cycle time is fast compared to vacuum cast materials.
The two-component mixture injected into the mold has a much lower viscosity than molten thermoplastic polymers, so large, lightweight, thin-walled articles can be successfully manufactured by RIM. This less viscous mixture also requires less clamping force, which leads to smaller equipment and reduced investment.
RIM Molding Materials and Finishes
At Axis we use mainly PP and a resin similar to ABS. Do not hesitate to contact us if you have a specific need.
We can take care of the different finishing touches if needed:
- Overmolding or installation of metal inserts;
- Realistic surface finish: glossy, satin, grained, obtained by paint finishing;
- EMC paint.
Deadlines and part design tips
For RIM molding, it will take 2 to 3 weeks to design the tools, with a production of 10 to 30 parts per week. This will depend on the size and complexity of your project.
The subassemblies are always made with your functionality in mind. We are at your disposal to evaluate your needs.
How it works?
- Step 1 : First of all, a master model must be created in
Stereolithography
.
- After receiving your 3D file, we process it to launch in production while applying to it or not a withdrawal according to the ordered material;
- The master model is launched into production using the Stereolithography process;
- It is cooked to be hardened;
- The 3D part is cleaned, sanded and blasted. The necessary finishing touches are provided by our prototypists, as the molding will have the appearance of its master (graining, transparency, …);
- Our mold makers stick a mark along the joint plane to facilitate the opening of the silicone mold.
- Step 2 : Making the mold
- The master in Stereolithography is installed in levitation in a wooden box with the help of a sprue (recycled feeder sprue, which will allow the material to circulate in the cavity of the mold) and vents (to evacuate air from the material);
- Once the part is installed, the silicone or resin is then poured into the box to take the impression;
- When the silicone has hardened, our molders open the wooden box along the parting line;
- After fully opening the silicone mold, the Stereo master is gently removed to avoid damaging the silicone.
- Step 3 : Realization of the duplication
- The casting operator in charge of the project carefully closes the mold manually, while avoiding any gap that could let the material soon to be injected into the mold escape;
- The two parts of the polymer are mixed, usually by injecting them under high pressure into an impact mixer. The mixture is then injected under a lower pressure into the mold. 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.
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