The injection molding machine is made up of four major components: the injection unit, the clamping and ejecting unit, and the electric and hydraulic control unit. An injection unit's purpose is to melt the plastic and transmit or force it into the mold. It does this by either injecting hot liquid plastic into the mold cavity or injecting pellets of plastic material that have been heated in a heater bed. A clamping and ejecting unit's purpose is to open and close the mold while the injection unit is shooting plastic into it. This unit also removes the molded part from the mold and ejects it into a container for removal from the factory. The third component of an injection molding machine is the electric and hydraulic control unit. It controls the timing of events during each cycle of the machine so that the correct amount of plastic is injected into the mold at the right time. An injection molding machine requires very precise control of timing and temperature because any variation between these parameters can result in a defective part. For example, if the plastic melts too quickly it will leak out of the nozzle before it has time to fill the mold cavity, resulting in a blank piece. If it takes too long for the plastic to melt, then you will run out of material before you have time to fill the mold, which would be undesirable. The fourth component of an injection molding machine is the drive system.