An alternative to Reaction Injection Moulding (RIM)
Reaction Injection Moulding as a technique for making housing components has been around for a long time. A good alternative can be found in thermoplastic foam casting (TFC), otherwise known as Structural Foam Moulding (SFM). Both have advantages and disadvantages. But when should you choose which technique?
When should you choose RIM?
RIM is an ideal technique when annual volumes are very low and product accuracy is less important. It should be noted that RIM product dimensional accuracy can be further improved in the finishing process (e.g. milling, drilling and sanding). RIM is obviously ideal when expected sales are uncertain and (mould) investments must be kept to a minimum.
Various thermo-hardened plastics, or so-called thermoset plastics, can be processed with RIM, the best known of which is polyurethane. However, these plastics cannot be remelted for reshaping into other products.
And when should you choose thermoplastic foam casting (TFC)?
Thermoplastic foam casting is a proven technique that has been used by many injection-moulding companies around the world for a long time. It is ideal for small to very large components in small to medium annual volumes. TFC components can be made from an enormous variety of plastics and high levels of accuracy can be achieved. These plastics can always be recycled and reused to produce new products.
TFC components can be given various fine and coarse surface textures and subjected to heavy mechanical loads if made with the right plastics.
TFC requires an investment in TFC moulds that is generally somewhat higher than that for RIM. On the other hand, a TFC product can be used or painted almost immediately. Removing webbing and filling air pockets on its surfaces is not necessary.
So when should you use RIM and when should you use TFC?
Reaction Injection Moulding is ideal for:
- Small production batches (ranging from 1 to 100 units per year)
- Uncertainty about expected annual volumes (investment is lower)
- Products that must be made quickly
Conversely, TFC is ideal for:
- Larger production batches (from as few as 50 units to as many as 10,000 units)
- Products with a low unit price (it will still be cheaper than RIM in the long term even after having invested in a mould)
- Components requiring higher dimensional accuracy
- A multitude of plastics can be used
- End-of-life recyclability
Comparison of RIM and TFC
Density 1.07 – 1.40
Thermoplastic (with many options) with foaming agent
Density from 0.88
Recyclability not possible
Material properties impacted by
Material supplier and manufacturer
Resistance to creeping
DIN 16742-TG 4/5
DIN 16742-TG6/7 (more precise)
Substantial finishing required
Little to no finishing required