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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.
Simulations
Sam A designed a Burnsim file for the motor, uploaded here.
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.
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Cutting the Liner to Length
Simulations
Sam A designed a Burnsim file for the motor, uploaded here.
The liner was cut to 30 inches long for 28.75 in of propellant. The madrel caps are .6 inches thick. This should leave the propellant section slightly long to be trimmed back to the correct length. The inside of the liner was abraded with 150 grit sandpaper to improve adhesion of the propellant to the liner and avoid a debonding failure which could lead to the outside surface burning, and a rapid, unscheduled disassembly. The inside of the liner was then cleaned with Acetone to provide a good surface to bond the propellant to.
Casting
The liner was measured to be 29.75 inches long and weigh 707g. The ID of the liner was measured to be 3.384 inches. This will serve as the OD of the propellant slug. The foam mandrel was measure to have a cylinder diameter of .956 inches. There are six fins, each .2 inches thick, protruding .474 inches from the cylinder.
The foam core was expoxied into the aft casting cap with 5-minute epoxy. The 3D printed caps were coated