Abstract: The present invention provides a method for sectionally controlling a cooling efficiency of a mold. The method comprises steps of: (a) configuring at least a cooling passage including a first section having a first heat-dissipating inner surface area and a second section having a second heat-dissipating inner surface area in the mold; and (b) adjusting the first and the second heat-dissipating inner surface areas unequally by using a heat-dissipating element.

Abstract: A method for forming an U-shaped metal frame includes a preparing means: bend forming a straight tube in a continuous curve shape to be a billet including a spaced section and a first and a second side segments twisted toward opposite directions individually; a forming means: placing the billet into a cavity of a forming mold, closing two ends of the billet, and feeding a high-pressure fluid into the billet; a cutting means: cutting the billet into the first and the second pipes, the first pipe including a first connecting portion formed in a first cut position thereof, the second pipe including a second connecting portion formed in a second cut position thereof; a connecting means: twisting the first side segment and the second side segment toward the same direction, and connecting the first connecting portion and the second connecting portion together to obtain the U-shaped metal frame.