Using S7 - 200 PLC control system of injection molding machine hydraulic electric control -

1. Introduction

in recent years, automobile, construction, household appliances, food, pharmaceutical and other industries to the increasing demands of injection molding products, has promoted the development of the injection molding technology and improved. Which line is complex, relay action is slow, short service life, system control precision is poor, high failure rate of traditional injection molding machine is controlled by relay instead of PLC controller control system. PLC control system can well realize the injection molding machine of each action, improve the control precision and automation of the system.

2。 Injection molding machine hydraulic system working principle and requirements of

injection molding machine is through hopper into the propellers, the granular plastic screw rotation, the material is pushed forward, because is equipped with electric heater outside screw, material melt into mucus, prior to this, the mould clamping mechanism have closed, when the material in screw propeller front to form a certain pressure, injection agencies began mucus high-pressure rapid injection into the mold cavity, after a certain time of the pressure maintaining cavity after cooling, the molding plastic products out, a motion cycle is complete.

requirements for hydraulic system is: the clamping movement to smoothly, no impact when two pieces of mold closing; The closed mold, mold clamping mechanism should maintain closure pressure, in order to prevent the injection mold. After injection, injection of institutions shall keep the injection pressure, make plastic mould; Piasticising feeding, screw rotation, the material is pushed to screw the front screw back with injection of institutions, in order to screw the front plastic has a certain density, injection organization must have a certain backward resistance; System should be equipped with safety interlock device to ensure safety.

3。 Injection molding machine hydraulic system motion control process

a working process of injection molding machine to complete the mould clamping, slow and pressurized clamping, injection, injection, injection pressure, pressure relief vent, and pressurization, plastic material, injection mould opening seat back, fast, slow drive mode and unloading system. Hydraulic pressure original as shown in figure 1. Figure 1

action cycle of each components in the main rely on travel switch, time relay and pressure relay switch electromagnetic directional valve, the electromagnet work order in table 1.

4。 Traditional electrical control and PLC control

traditional electric control system mainly through the relay to control the gain and loss of electromagnet, control of the hydraulic system in oil flow direction, so as to realize the various working condition of the injection molding machine. Because the relay transmission system using a great deal of control relay, contact, and relay slow, life is short, so the existing in the working process of the poor control accuracy, high failure rate, poor reliability, complex wiring, shortcomings and so on is not convenient to maintenance. PLC controller as a kind of applied technology for industrial production, with CAD/CAM and NC technology and called the three pillars of modern industry, has been more and more people are familiar with and application. PLC specially designed for application in industry site, adopt the programmable memory, used in its internal storage to perform the logic operation, sequence control, timing/counting and arithmetic operations such as instruction, and through the digital or analog input and output interface to control the various types of machinery or production process. PLC is the microprocessor technology and the combination of the traditional relay contact control technology, it overcomes the relay contact control system of mechanical contact wiring complex, high reliability, low power consumption, versatility and flexibility poor shortcomings, and used to relay trapezoidal graph based simple instruction form, make the program image, intuitive, convenient and easy to learn to write, debug and error is very convenient.

5。 The design of electrical control system based on programmable logic controller (PLC controller)

PLC control of injection molding machine control system design includes hardware design and software design of two parts. The hardware design mainly PLC configuration, selection, wiring cables as well as the allocation of input and output ports; The software design is the preparation of the injection molding machine control program.

5。 Hardware system design of 1

according to the selected model of PLC and I/O ports, of the distribution of draw the PLC external wiring diagram 2.

5。 2 software design

sequential control design method of the system connected to a working cycle is divided into several order stage ( Step, Step) , with programming components ( For example, M) To represent each step.

at any step in the state of the output unchanged, the adjacent two step output in a state is different. Make the system by the current step into the next step signal called transition conditions. Sequential control design method with transition conditions control programming components of each step to change their status in a certain order, and then use on behalf of all the steps of programming components to control the output. Due to the injection molding machine is a step by step by step process to complete its work, so we use the sequential control design method, according to the requirements of the injection molding machine design, working principle and working steps, get the technological process of injection molding machine, designed the whole function of the order of the PLC control system in figure 3.

according to the sequence function diagram, by the aid of all PLC has a large number of relay, the bartender blackout road programming method, can get the corresponding ladder diagram, and the simulation validation. Program ladder diagram as shown in figure 4.

6。 Conclusion

using S7 - in this paper 200 design of PLC electrical control system for injection molding machine, use up security stop programming in the form of programming to control the plastic injection machine hydraulic system. Practice shows that the improved control system has high reliability, stable performance, convenient operation, greatly improve the quality of the injection molding products and production efficiency.

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