Manufacturing Technology Portfolio

Leave-In Mandrels

Rotomolding

Rotational molding, or rotomolding, is an innovative process used in manufacturing composite solid rocket motors (SRMs) and other tank-like vessels. A rotomolding technique developed by CRG eliminates mandrel removal from the manufacturing process of SRMs. The process involves using unique leave-in mandrels rigid enough for filament winding and also suitable to remain in place and be used as insulation material in the SRM itself. Originally funded by the Missile Defense Agency (MDA), this SRM manufacturing is compatible with a variety of materials, resulting in low-cost, insulating, leave-in mandrels.

Leave-in Mandrels

Leave-in mandrels can be inserted into the traditional filament winding process used to manufacture SRMs. Conventional methods involve fabricating SRMs on multi-piece metal mandrels, a process that is both expensive and labor-intensive. In the conventional scenario, the mandrel is assembled, the insulation is applied, and the part is filament wound. The composite is then cured, and the metal mandrel is disassembled and removed.

CRG’s rotomolding technique uses the mandrel as the insulation. Since there is no need to remove the mandrel after fabrication, this novel process eliminates more than 50% of the manufacturing labor, with the added benefit of customizing insulation designs tailored to specific applications.

Benefits

Future tactical SRMs may have to operate at pressures nearly twice those of current designs for improved performance requirements. They will require greater maneuverability and longer burn times and will need the ability to withstand higher G-forces and carry additional propellant loading. CRG’s rotomolding process provides these properties with the capability of high specific strength composite parts made from high-temperature materials and high-performance insulation. This technology supports missile systems with enhanced multi-layer composite cases, providing improved performance with significantly reduced unit cost

Leave-in mandrels improve upon conventional rotational molding processes by using a new approach to mold design, dynamic loading, and heat transfer to accommodate a wider variety of component configurations, materials, and cure processes. CRG’s rotomolding is designed to allow for several processing variables including spin rate, angle of spin, and heating capability, resulting in leave-in mandrels with properties tailored to fit customers’ needs.

Additional details on leave-in mandrels can be found in the published article: Stahl, J., Pora, E., and Freeman, P. “Innovative Manufacturing for Solid Rocket Motors,” SAMPE Journal, Vol. 42. No. 6. November/December 2006. pp. 21-27.