In one hand, Rick Fitzpatrick holds a pile of plastic pellets, in the other, a finished part. "How much energy do we need to convert this," he says, raising the hand with the pellets, "into that," he finishes, lifting the part. That essential question should be the only one injection molding technology answers, but to Fitzpatrick, many of the accepted material, machinery, and design norms taken as a given in injection molding, are old paradigms.
"We're taught that you generate shear heat in the screw barrel interface with pressure and that material will transfer heat to the full volume of plastic wrapped around the screw. " Fitzpatrick says, "but plastic is an insulator; it doesn't transfer heat well." To overcome this, Fitzpatrick says molders still must rely on excessive injection pressure and velocity to induce shearing during injection and generate heat at the nozzle, runner system and gate. In the end, "You use more energy to create the force than you would to electrically generate the heat than is needed to melt the volume of plastic required for the part."...