| As an energy-intensive process, in injection molding, energy cost is one of the major cost components. The energy expenditure during molding can be divided into two forms: thermal and mechanical energy, although both are initially transferred from electrical energy. The former is mainly the energy consumed for heating the barrel, while the latter can be further partitioned as energy related to mechanical motions such as injection and mold clamping, and thermal relevant mechanical energy such as plastication. The energy saving problem has been addressed by many researchers from the equipment modification angle, for example, improving pump and motor efficiency. Different from that, this dissertation, from a system operation viewpoint, attempts to develop an energy-efficient control system. Energy over-consumption is mainly related to the overheating of melt, therefore the thermal related variables, including barrel temperatures, screw rotation speed and back pressure, are major variables concerned in this design. Proper controls and settings of these machine variables is the key to energy-efficient operation. In the previous research, the control and setting of these variables are usually considered separately, despite strong interactions existing among them. In this thesis, the energy problem is analyzed systematically first, and then control methods for these variables are developed. Afterwards, melt temperature, a key process variable, is studied to develop a faster process stabilization control strategy. Finally, an integrated setting approach for these key variables is proposed leading to an energy-efficient operation of the process. |
