Service-oriented Energy Supplying Method of Hydraulic Forming Equipment for Efficiency

Author:Li Lei

Supervisor:liu zhi feng


Degree Year:2019





The forming process with advantages of high production efficiency,low material waste,and high quality,is widely employed in the manufacturing industry.As one of the main equipment to achieve forming,the hydraulic press is featured with large nominal pressure,high power to mass ratio and high degree of automation.However,the consequent problems are high energy consumption and low energy conversion efficiency during operation.In the background of fuel shortages,developing energy-saving control strategies for the hydraulic press is of great significance to achieve sustainable development of the country.The energy loss of hydraulic press during operation is caused by the mismatch between the output power of the drive system and power demand of the load.By analyzing the literature review on the problem,some obstacles that are still not being overcome are found and listed as follows: 1)The drive system is designed to meet the maximum power demand,and the power matching can be achieved by adjusting the output power of the drive system.But the energy efficiency of the drive system will decrease with the working condition moving away from the optimal one.How to improve the energy efficiency of the drive system when adjusting its output power? 2)How to reduce the energy loss caused by pipelines and valves during auxiliary operations in the forming process? 3)The gravity potential energy of the slider can be recovered after being stored and reused during forming process.However,there is a secondary energy conversion efficiency in the process of storage and reuse.How to reduce the loss caused by the secondary efficiency in the energy recovery process?Focusing on the above-mentioned problems,by taking the advantage of digital hydraulics,a service-oriented energy supplying system was developed from the perspective of sharing hydraulic circuits and drive system.The configuration,control strategy and optimization of the system for energy saving were investigated.These works contribute to the hydraulic forming equipment for energy saving from a systematic level,which has great significance on practice.The dissertation is organized as follows:In Chapter 1,challenges on current research were summarized by reviewing a series of literatures.Then,the main contributions and organization of this dissertation were proposed.In Chapter 2,on the basis of analyzing the behavior of energy transferring and dissipation of hydraulic press during forming process,a service-oriented energy supplying system was proposed for efficient manufacturing.Then,the energy flow of the units of the press in the working process was established.The energy consumption monitoring platform was built to obtain various state parameters during the operation,which lays a foundation for improving the energy efficiency of the equipment.In Chapter 3,the configurations of the service-oriented system for hydraulic press,including the drive system,valve matrix,and actuators were designed.The drive system composed of several motor-pumps,is partitioned into several sub drive systems according to load profiles.The system is used to supply power to several actuators with approximately same installed power.Each sub drive system is shared by grouped actuators in the same operation via valve matrix.Furthermore,a method for scheduling sub drive systems was presented to share sub drive system without conflict.The composition of each sub drive system is optimized to match the power demand of each operation to achieve the scheduling.The proposed energy-saving method was applied to a hydraulic press group in the case study to achieve service-oriented supplying strategy.In Chapter 4,based on the configuration of the hydraulic equipment equipped with service-oriented energy supplying system,a coordinate method was proposed to coordinate this multi-actuator system,where the operations related to the forming parameters are controlled by position of the slider,and the other operations are controlled by time.The forming operation in the hydraulic press begins with the end of the forming operation in the former hydraulic press.Coordinating time error between two successive presses is modified to improve the accuracy of each operation.A service-oriented energy supplying prototype system is built to validate the effectiveness of the control strategy and error adjustment scheme.Result shows orderly coordinate performance.In Chapter 5,to reduce the variation of the load in order to facilitate configuring the sharing drive system,a novel energy-efficient system with double-actuator was proposed for small-sized hydraulic press.In the proposed system,the chambers with rod of the two actuators are connected by pipes and valves to synchronize the falling procedure of one cylinder with the returning procedure of the other.One actuator remains at the top point to perform a procedure,while the other one remains at the bottom to perform the corresponding procedure.The energy-saving mechanisms during each working process with several procedures,have been analyzed using a built system energy consumption model,and improved energy efficiency and working efficiency were observed.Compared with the hydraulic press that currently undergoes services,the energy-saving effect of the developed system is obtained.Consequently,the load profile of the task is steadier.In Chapter 6,by applying the double-actuator system to large-sized hydraulic press,an energy-saving method by balancing the load of all operations during forming process was proposed.In the method,the motor-pumps in the drive system are shared in different time by a unit composed of two hydraulic presses,so that the energy loss caused by unloading operations can be reduced.Furthermore,these two presses are combined,and the excessive energy from one press can serve as the input energy to the other one during some operations to improve the energy efficiency of the drive system and the potential energy can be utilized directly.Meanwhile,operation durations of these combined presses are optimized for coordination of working processes.The method was applied to two hydraulic presses in a tandem line and the energy consumption was obtained by quantifying the characteristics of conversion components.The load balancing method applied to large hydraulic presses not only directly reuse the gravitational potential energy of the moving parts,but also reduces the energy loss during energy storage and recovery,and further improves the working stability of the task.In Chapter 7,an operation scheduling approach is proposed for a multi-actuator system to explore the potential on energy saving at system level for service-oriented energy supplying method.The scheduling formulation was developed based on power models of the forming process on individual actuator.Based on the built models of energy conversion units in Chapter 2,including asynchronous motors,piston pumps,hydraulic cylinders,valves and pipes,the energy consumption model and makespan at multiactuator level are obtained.In order to balance makespan and energy consumption,the duration of each operation is adjusted by optimizing the configuration of the drive and the schedule of operations.To demonstrate the applicability of the proposed approach,a case study on a four presses system is presented.Results show that this approach is effective in identifying schedules to reduce the makespan and total energy consumption during forming processes.Finally,a cyber-physical platform was established to serve the design and operation of service-oriented energy supplying system.In Chapter 8,the main works,innovations and contributions of this dissertation were summarized.Moreover,future potential research focusing on forming processes was proposed.