Overview
Due to materially inefficient casting procedures, the team had an excess of thermal liners for 98mm motors. This lead to the idea to attempt a monolithic grain casting directly in the thermal liner.
Manufacturing
The motor is designed to utilize a 98mm thermal liner from RCS, a hot-wired foam core, 3D printed end caps, and 12.5 lbs of propellant. This load should be compatible with any appropriate case.
Making the Mandrels
The mandrels were designed in burnsim, and then CADed in Solidworks. The face of the grain was exported as a .dxf file from solidworks. The .dxf was run through this python script to generate a .dat file for the foam cutters. The foam cutter was run at .03 in/s at 20V to produce the mandrels. These values were determined by experimentation.
Making the Caps
The mandrel is held in place by 2 3D printed end caps. The aft mandrel fits over the casting tube and can be taped in place to seal that end. The foam mandrel is epoxied into the aft cap. The forward mandrel cap slides inside the liner tube and is designed to sit flush against the propellant. The mandrel slides through it. The forward cap contains captive nuts to allow it to be pulled out of place. Both of the caps were 3D printed from ABS plastic to allow them to be dissolved with Acetone should other extraction techniques fail. Both caps are designed to be an appropriate thickness so that the nozzle and seal disk can seat fully in the liner. Future improvements might include printing the aft cap to allow the propellant to match the taper of the nozzle converging section, or machining these from aluminum to make them more robust and extractable.
Cutting the Liner to Length
Simulations
Sam A designed a Burnsim file for the motor, uploaded here.
