Reaction Injection Molding is superior when creating large parts because of two unique characteristics: the low viscosity of the component chemicals and the innate strength of polyurethane. This allows a part to act as both a structural and an aesthetic component.
The low viscosity of RlM’s component chemicals allows large molds to be ﬁlled quickly and completely. This quality makes it possible to mold a part as a single piece, where other technologies require multiple parts to be molded and assembled. This ﬂow-ability also ensures that ﬁne details can be included in the mold and that the material will accurately and consistently ﬁll the details for each part. The low viscosity components also require lower mold pressures and generate less heat, allowing for lower cost molds to be used.
Large RIM parts are found in surprising applications. For instance, a farming combine currently on the market uses a one-piece rear shield, RIM molded out of rigid polyurethane. Measuring 6 feet by 6 feet, the ﬁnished part weighs only 56 pounds.
Exothermic has molded parts 10 feet long and other parts weighing 40 pounds.
Another unique property is the ability of a part to act as a structural member while still possessing enough aesthetic characteristics to serve as a ﬁnished surface. Because of the flow-ability of the polyurethane components, intricate ribbing can be designed and easily molded into the part, enabling it to act as its own support structure, even at large sizes.
From a tooling cost standpoint, the investment is more easily justified for larger scale parts when compared to other “closed mold” processes. RIM molds do not have to be built to withstand high pressures, therefore they are less expensive and faster to make with the associated shorter lead times.
To learn more download : “5 Reasons To Use RIM For Complex Parts“.