Análise de consumo enerxético do sistema hidráulico dunha máquina de moldeo por inxección e análise de simulación do aforro enerxético despois da presión de reforzo

Introdución

Injection molding machine is an important production equipment in the plastics industry. Its hydraulic power and energy loss have an important impact on the manufacturing cost and operating cost of the system. High energy consumption of injection molding machines will not only lead to waste of electrical power resources, but also increase the production cost of injection molding machines. [1] China’s injection molding machine manufacturing number and annual output are among the forefront of the world, and injection molding products accounted for about 30% of the total plastic products, high electricity costs have become one of the important factors restricting the production efficiency of the injection molding industry. In order to improve the market competitiveness of injection molding machines, injection molding machine students

In response to the national call for energy conservation and emission reduction, production enterprises have continuously carried out energy-saving transformation of the existing energy consumption system of injection molding machines, improved energy efficiency of injection molding machines, and reduced production costs. [2] 。

Injection molding machine according to the type of power source can be divided into 3 categories, fully hydraulic, fully electric and electro-hydraulic hybrid. All-electric injection molding machine cost is high, and the scope of application is limited, the current hydraulic injection molding machine is still the mainstream product in the industry. The general hydraulic injection molding machine adopts constant pump and proportional flow pressure valve valve control system, the hydraulic pump output fixed flow in the entire injection molding process, when the system demand flow is low, the motor speed is unchanged, excess flow overflow back to the tank, resulting in greater energy loss. [3] Load sensitive hydraulic system uses variable displacement pump as system hydraulic pressure.

The proportional flow control valve is arranged on the variable pump, the output power is matched with the load change, the overflow loss and the throttling loss of the system are reduced to a great extent, and the energy saving effect is remarkable. Using electrical signals to realize various compensations can improve the control performance of the system, and it is suitable for the injection molding machine system with flow control, but it needs a set of more complex variable displacement control mechanism, and the displacement change is limited by the angle of the swash plate, and the range of speed regulation is limited. [4] Compared with the traditional volume control technology, the variable frequency hydraulic technology adopts the control form of frequency converter + motor + quantitative pump, which has the characteristics of wide speed range, low noise and high system efficiency. With the development of servo control technology, it has better control accuracy, response speed and overload ability than frequency control technology, and has become the mainstream hydraulic control system of injection molding machine.

Peng Yonggang [10] The servo motor directly drives the fixed quantity pump as the driving source of the precision injection molding machine, and the fuzzy synovium control strategy is proposed to realize the accurate control of the system pressure and speed in the injection molding process, and the energy saving is good. Liu et al. [11-12] compared the energy efficiency of five kinds of electro-hydraulic control schemes on the injection molding machine, and the results showed that the dynamic performance of the system is good, the control precision is high and the energy saving effect is the best. Xiao Wang et al [13] The simulation model of injection part of high speed injection molding machine is established by AMESim. The control strategy and implementation method of electro-hydraulic position-velocity servo system are presented. The two-variable control of injection position and velocity is realized. Wang Jianwait [14] The energy consumption of the clamping system of the internal circulation two-plate injection molding machine is simulated and analyzed. The energy consumption of the system can be reduced by reducing the valve control components, adopting the appropriate hydraulic cylinder diameter and adding the accumulator. Xiong Wennan and others [15] The energy consumption of injection molding machine during clamping, opening and ejecting is analyzed in three kinds of hydraulic systems. The results show that the energy consumption of fixed quantity pump + proportional pressure flow valve system is high, the energy saving effect of proportional variable quantity pump system varies with the product technology, and the energy saving of fixed quantity pump + servo motor system is good. Gao Junwei [16] Aiming at the problem of overflow loss in hydraulic system of injection molding machine, a scheme of double gear pump driven by asynchronous motor is presented. In order to meet the instantaneous large flow demand of injection molding machine, the pressure flow closed-loop control is adopted to improve the control accuracy and energy saving effect of the system, and the traditional hydraulic system of injection molding machine is reformed, which has a good energy saving effect.

Hydraulic control one-way valve flow distribution hydraulic motor can achieve higher working pressure, so that the injection molding machine into a high pressure can be [17]. Neste documento, high pressure hydraulic components are used in the hydraulic system of injection molding machine.

Injection molding machine hydraulic system working pressure, to ensure that the output power of the same conditions, reduce the injection molding machine in the work cycle of the system flow demand, while reducing the hydraulic system hydraulic cylinder diameter size, reduce the system throttling loss and pipeline along the pressure loss program. Neste documento, the hydraulic injection molding machine with clamping force of 1 200 kN is used as the research object, and the hydraulic system of the plastic injection machine is modeled and simulated by the software AMESim. By reducing the cylinder diameter, the pressure drop of electromagnetically operated valve port, pipeline and system power consumption before and after the hydraulic cylinder reduced flow and increased pressure were compared to study the energy saving effect of the hydraulic system of injection molding machine.

Due to the high power demand of the injection molding machine in the actual working state, When the overflow pressure of the system is low, it is often necessary to input a large flow rate. In the large flow hydraulic system, the pressure drop of the valve port and the pressure loss along the pipe path are large, and the system temperature rise and noise are also accompanied by the problems, which cause the system energy loss.

The hydraulic system of injection molding machine consists of hydraulic pump, solenoid directional control valve, hydraulic cylinder and hydraulic motor. Agora mesmo, most of the hydraulic components have achieved high pressure, but also for the injection molding machine hydraulic system to improve the working pressure to create conditions. High pressure can achieve high power density and high power output of the hydraulic system, which is consistent with the requirements of the hydraulic system of the injection molding machine.

Theoretical analysis of energy consumption loss of hydraulic system of injection molding machine

2. 1 injection molding machine hydraulic system overflow flow loss Traditional injection molding machine hydraulic system adopts fixed pump output flow

The hydraulic system is simple and reliable, and the output flow of the hydraulic pump is constant during the injection molding process. In the stage of low flow demand of the system, the oil flows back to the tank through the overflow, and the overflow flow loss is serious. Agora mesmo, most of the hydraulic systems of injection molding machines use proportional variable pump control system or servo motor system, which can effectively adjust the output flow of hydraulic pump during injection molding process and reduce the loss of system overflow flow. In the working cycle of injection molding machine, high energy consumption and short working time, so the servo control system can save 30% ~ 60% energy consumption compared with the proportional flow control valve system. [2] .2 Hydraulic system of injection molding machine valve throttle pressure loss

During the working process of the injection molding machine, the hydraulic source passes through the electromagnetic control valve, In order to shorten the cycle time of injection molding, the flow rate of the system is usually high in the hydraulic pressure cylinder, and the output flow of the hydraulic pump flows through the electromagnetic control valve, which has a certain throttle pressure loss. Solenoid directional control valve after its opening is similar to the thin-walled orifice throttle, so the valve port throttle pressure drop can be calculated through the orifice flow-pressure drop formula, the formula is

Q1 = CdA rilodelta p ■ 2

Where: Q1 is the valve port flow; Cd is the flow coefficient of thin-walled orifice. A is the orifice area; The density of fluid; Delta p is the pressure difference before and after the valve port, so the throttling energy loss is

Through the throttle orifice flow-pressure drop formula, the throttle pressure

Drop delta p is proportional to valve port flow Q21, so throttling energy delta P is directly proportional to gate flow Q31. To reduce the injection molding machine hydraulic system

Each electromagnetically operated valve port throttling pressure drop energy loss, should give priority to reduce the system flow. In order to ensure that the output power of the hydraulic system of the injection molding machine is unchanged when the system flow is reduced, it is necessary to increase the working pressure of the hydraulic system to maintain the normal operation of the actuators.

2. In the hydraulic system of injection molding machine, the hydraulic source is connected to the solenoid directional control valve by pipeline, and then to the hydraulic actuator by pipeline. choose

The larger pipe diameter can reduce the average velocity, ensure the laminar flow state, reduce the resistance coefficient and reduce the pressure loss along the pipe, but it is difficult to arrange the pipe. If the pipe diameter is small, the average velocity of the pipe is large, which will easily lead to turbulence in the pipe and increase the energy loss along the pipe path. The calculation formula of pressure loss along the pipeline is

Deltap pipeline = λ l × ρv2d2

Where lambda is the resistance coefficient along the path; L is the length of the pipe; D is the diameter of the pipe; Density of hydraulic oil; V is the average velocity in the tube. The formula for calculating the flow velocity in the tube is

4Q2 v = π d2

The Reynolds number formula is

Re = vd = 4Q2π

Among them, upu is the kinematic viscosity of oil; Q2 is pipe flow. The resistance coefficient λ is related to the flow state in the tube and the formula is

λ=

64 Re

 -0.25 0.3164Re

，Re <2320 ，3000<Re <10

5

 0.308 ，105<R<108 ( 0. 842 – lgRe ) 2 e

In order to reduce the loss of hydraulic pipeline along the way, it is necessary to ensure that the flow state in the pipe is laminar flow, so the resistance coefficient along the road is λ = 64 / Re, and the formula of pressure loss along the route can be obtained.

64l π v 2 128π Q D p pipeline = Red × 2 = π d4

Under the condition that the pipeline diameter is not changed, the pressure loss along the pipeline is proportional to the pipeline flow, and the energy loss along the pipeline pressure drop is proportional to the square of the pipeline flow.

3 3. 1

AMESim Imitation Model of Hydraulic System of Plastic Injection Molding Machine

Simulation Parameters of Injection Molding Machine Hydraulic System

According to the hydraulic system schematic diagram of injection molding machine and the parameters of related hydraulic components, in order to analyze the power consumption of the hydraulic system of injection molding machine, The model is simplified, and the simulation model of injection molding machine hydraulic system is built as shown in Figure 2. The model uses step signal to simulate the servo motor to achieve variable speed control under different working conditions, so that the system basically does not produce overflow phenomenon. AMESim model simulation analysis parameters set as shown in Table 1. According to the injection process sequence, the electromagnetically operated valve is set as shown in Table 2.

Ó mesmo tempo, in order to simulate the effect of valve port throttling pressure drop, refer to Huade WE6 type O three-position four-way solenoid directional control valve, Because of its valve port structure, when the flow rate is 60 L / min, the valve port P flow to the valve mouth A / B pressure drop is 1.0MPa, and the pressure drop to the port T is 0.8MPa. In order to simplify the simulation model, the maximum flow of the three-position four-way electromagnetically operated valve is set to 60 L / min, and the pressure drop is 1 MPa.

After setting the simulation parameters of hydraulic system, the motion curve of hydraulic cylinder is set.

The line is shown in figure 4, and the die closing movement is completed in 0 ~ 2 s, and then the moving cylinder moves for 1 s with the injection device, aligns the nozzle of the screw cylinder with the injection nozzle and applies a certain contact force of the nozzle. In 3 ~ 4 s, o parafuso, driven by two injection cylinders, injects the molten material into the mold cavity at a very high pressure, and holds the pressure to cool for a certain period of time, in order to simplify the simulation process, omit the holding stage; then the premolding motor works and presses the injection cylinder back to prepare for the next injection; 9 ~ 10 s inner seat displacement cylinder retracts; and then retracts the mold cylinder to complete the mold opening movement. Under the action of ejection cylinder, the finished product is ejected into the mold, then the cylinder is retracted, and then the cylinder is retracted, thus completing an injection cycle.

3. 2

Analysis of Energy Consumption of Injection Molding Machine

Each hydraulic actuator in the working stage, the required flow is different, the load size is different, the system pressure also changes, in order to avoid the system overflow flow, so in the operation of the actuator stage, so that the hydraulic source to provide its required flow. When exploring the influence of hydraulic system pressure drop energy consumption, in order to eliminate the influence of throttling speed regulation, to ensure that the working pressure and flow of hydraulic cylinder are relatively constant, it is set in the hydraulic cylinder mass block model of large motion damping, so that the hydraulic cylinder working state to maintain a constant power.

In the case that the system does not produce overflow, the output flow rate and pressure of the liquid pressure pump in each movement stage are shown in Figure 5. In the clamping, pre-molding and injection stage, the input pressure and flow rate of the hydraulic system are large, and through the analysis of the energy loss of the hydraulic system of the injection molding machine, it can be seen that in the larger flow stage, the energy loss of the pressure drop is large. Ó mesmo tempo, in the simulation test, the length of the mold oil cylinder is larger. , running long, so its flow needs to be large, opening and closing die process, sobre 30% of the total flow of the system input, if the system can achieve boost, reduce the mold cylinder input flow, can effectively reduce the hydraulic system pressure drop energy consumption, improve the energy efficiency of the injection molding machine hydraulic system.

Como se mostra na figura 6, in the entire injection cycle, the clamping stage, the injection stage and the premolding stage have large power consumption. In order to study the pressure drop of the electromagnetically operated valve and the pipeline loss along the way in the hydraulic system, we take the mold opening stage of the closed hydraulic cylinder as an example. The cylinder rodless cavity pressure, the electromagnetically operated valve port pressure of V1, and the pressure of valve port P in V1 as well as the output pressure of hydraulic pump line in Figure 2 are selected as the research nodes of the pressure drop in the inlet oil section of the clamping hydraulic cylinder. The pressure of each node is shown in Figure 7. Through the pressure difference of the above nodes, the valve port pressure drop is 0.456 MPa, and the pressure loss along the 1 m oil pipe is 0.067 MPa. The pressure drop of the simulated valve port is close to the actual one. The theoretical value of pressure drop along the pipeline is 0. 058 MPa, which is slightly larger than the theoretical one. Through the above comparison can be obtained, in the system flow larger stage, the valve orifice throttle pressure drop loss is greater than the pipeline along the loss, in the pipeline length is longer, along the pressure loss can not be ignored.

3. 3 Simulation analysis of injection molding machine hydraulic system pressure boosting formula of throttle-pressure drop through valve orifice and pressure drop along pipeline

It can be seen that the throttle pressure drop and pressure drop along the hydraulic system can be significantly reduced by reducing the system flow rate. In order to meet the load driving force and working speed of hydraulic cylinder, the effective area of sprinkler operation must be reduced and the working pressure must be increased when the system flow is reduced.

In order to verify the pressurization and energy saving scheme of the hydraulic system of the injection molding machine, the former cylinder diameter was changed from 70mm-35mm to 50mm-28mm, taking the clamping cylinder as an example. The effective action area of the hydraulic cylinder has been reduced to half of the original area of sprinkler operation. After calculating the mold flow into half of the original flow, work pressure doubled, so the relief valve relief pressure increased to 32MPa.

Figura 8 shows the pressure and flow curve of the system before and after changing the diameter of the clamping hydraulic cylinder, As can be seen from the figure, in the mold closing and mold opening stage, the system input flow is reduced, while the system pressure rises, and the mold closing process, the system flow is reduced by half, while the pressure rises to twice the original, consistent with the expected value. Non obstante, after the boost, the mold closing stage, the system working pressure is high, and it takes a certain time to build pressure, but it basically does not affect the mold closing effect.

Figura 9 shows the energy consumption of the system before and after the pressure boost of the clamping cylinder. In the clamping and opening stages, the system power is lower than that before the pressure boost, and the decrease is about 0.7kW, and the power is reduced by 7.5%. Figura 10 shows the pressure of each node in the oil inlet section of the clamping cylinder after boosting the pressure, From the figure, the pressure drop from the hydraulic source to the rodless chamber of the hydraulic cylinder is about 0.138 MPa, which is about 70% less than that before the pressure rise, and the system flow rate is reduced by half, so the pressure drop energy loss is only 15% of that before the pressure rise, and the energy consumption of the system is reduced by 85%. When the working pressure of a single clamping cylinder is raised, the energy consumption of the system can be saved by 3.7%. If the working pressure of the entire hydraulic system cylinder can be raised, the energy consumption of the system pressure drop will be greatly reduced and the energy efficiency of the system will be improved.

By comparing the pressure drop before and after the hydraulic cylinder is boosted, the diameter of the hydraulic cylinder is reduced under the condition that the reversing valve and the pipeline are unchanged. Ó mesmo tempo, to ensure that the load and running speed remain unchanged, the system pressure will rise, and the required flow rate of the system will be reduced, thereby reducing the pressure drop between the hydraulic pump and the hydraulic actuator, reducing the system pressure drop energy loss, and reducing the system oil temperature rise and noise.

4 Conclusión

1) The input flow of the hydraulic system of the injection molding machine changes in the cycle

Large, the use of servo control technology can solve the system overflow phenomenon, Non obstante, the system has a large number of directional valves and a long pipeline, and the working pressure of the system is low. In the high-power stage, the system has a large input flow demand, and there is pressure loss along the valve port and pipeline, which causes the system to reduce energy efficiency, noise and high temperature.

2) through the orifice pressure drop formula and the pipeline along the pressure loss formula, the valve port pressure drop energy loss is proportional to the flow through the 3rd square, the pipeline along the pressure drop energy loss is proportional to the flow through the square, and through the simulation test to verify the correlation.

3) In order to improve the energy efficiency of the hydraulic system of the injection molding machine, the system input flow can be reduced by increasing the working pressure of the hydraulic actuator, and the pressure drop along the valve port and pipeline can be reduced.

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