Injection pressure is provided by the hydraulic system of the injection molding system. The pressure of the hydraulic cylinder is transferred to the plastic melt through the screw of the injection molding machine. The plastic melt is pushed by the pressure, and through the nozzle of the injection molding machine, it enters the vertical passage of the mold. And through the gate into the mold cavity, this process is the injection molding process, or called the filling process. The existence of pressure is to overcome the resistance in the melt flow process, or conversely, the resistance in the flow process needs to be offset by the pressure of the injection molding machine to ensure the smooth progress of the filling process.