posted 12-10-2003 04:20 PM              

the part must be "open" enough for the resins to move around and through the mold. any sub-assembly that you wanted to have inside the part would have to be securely fastened to the inside of the part so that it would withstand the "tumbling" action that is characteristic to the process.

since your sub-assembly would have to touch the inside surface of the mold, the plastic would be prevented from flowing there and would effectively form a hole in the part.

RM is primarily used to make hollow parts. think of the objects that you have seen manufactured by this process; dock floats, fuel and waste-holding tanks, etc.

at a company that i worked for we used to mold motorcycle saddlebags with this process. the parts shrank (like ALL plastic does) in a very unpredictable manner and the fit/interface with their metal components was a constant nightmare.

generally RM parts should not be thin and flat, nor, long and slender. the dimensional characteristics of the items made in this way are also not too stable, owing, in part, to the heating process not being tightly controlled (as in injection molding)and the fact that the "shot" of resin is usually dumped into the mold out of an old coffee can... we used to find cigarette butts on the inside of the molded parts, and once found a guy's wedding band.