An injection device is a device that injects a resin material into a mold after it is heated and melted. The resin is squeezed into the barrel from the material head as shown, and the melt is transported to the front end of the barrel by the rotation of the screw. In that process, the heater under the action of heating the resin material inside the cylinder heating, the shear stress of the screw under the action of the resin into a molten state, will be equivalent to the molded product and the mainstream road, the flow of molten resin is stranded in the front of the barrel (called metering), the screw continuously forward the material into the mold cavity. When the molten resin flow in the mold, the Screw movement speed (injection speed) must be controlled, and the resin filled with a cavity after the pressure (pressure) to control. When the screw position, the injection pressure reaches a certain value, we can switch the speed control to the pressure control.