Application of the pyrotechnic control computer an

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The application of industrial computer and PLC in low-pressure casting

1 introduction

casting is the earliest hot metal forming process mastered by human beings, which has a history of about 6000 years and is the basic process of modern machinery manufacturing industry. The casting process is a process in which the metal is melted into a liquid that meets certain requirements and poured into the mold. After cooling, solidification and cleaning, the castings (parts or blanks) with predetermined shape, size and performance are obtained. The cost of blank produced by casting is low, which can show its economy for parts with complex shapes, especially those with complex cavities; At the same time, it has wide adaptability and good comprehensive mechanical properties

low pressure casting is a method to make liquid metal fill the mold cavity under pressure to form castings. Because the pressure used is low, it is called low pressure casting. The technological process is as follows: dry compressed air is introduced into the sealed crucible (or electric furnace), the liquid metal rises along the riser under the action of gas pressure, enters the mold cavity (metal mold) smoothly through the gate, and maintains the gas pressure on the liquid level in the crucible (or electric furnace), and maintains the pressure for a period of time until the casting is completely solidified. Then release the gas pressure on the liquid level, so that the non solidified metal in the riser flows into the crucible (electric furnace), and then open the mold by the cylinder and push out the casting. The unique advantages of low-pressure casting are shown in the following aspects: liquid metal filling is relatively stable; The good formability of castings is conducive to the formation of castings with clear outline and smooth surface, which is more conducive to the formation of large thin-wall castings; The casting has dense structure and high mechanical properties. Low pressure casting is a filling casting method with low pressure, high strength and low speed. Compressed air is used as the filling power, and the filling of liquid metal is required to be stable; The main products that can be tested are: electronic and electrical products with good formability, clear outline and smooth casting surface; It is required that the mold has good cooling property, dense casting structure and high mechanical properties

2 low pressure casting automation system

2.1 system structure

system composition of industrial computer and PLC in low pressure casting in order to meet the requirements of low pressure casting, the industrial computer and PLC are combined into an organic system, as shown in Figure 1. The system adopts hierarchical control mode. The industrial computer completes the requirements of liquid level pressure control and mold temperature (cooling) controlled pressure casting

Figure 1 low pressure casting automation system

2.2 system principle

the principle of computer control system of pressure/temperature control system of low pressure casting machine is shown in Figure 2

Figure 2 system principle

(1) pressure control: the pneumatic principle of the pressure control system of the low-pressure casting machine is shown in Figure 3. The industrial computer and the liquid level pressure i/o template controlled by it control the digital combined valve island, realizing the pressure control of the low-pressure casting. The industrial computer system adopts sensitive pressure sensor and software PID controller. The set pressure curve and the actual control pressure curve of the casting process are displayed on the computer screen at the same time, and the superposition and comparison are carried out. The real-time temperature curves of four temperature measuring points are displayed in four colors on the computer screen. In addition, a graph is used to indicate the liquid level of aluminum in the holding furnace to remind the operator that when the liquid metal in the furnace is less than the minimum limit, the system will automatically stop pressurizing

Figure 3 pressure control system

y1 ~ Y9: regulating valve (normally closed)

y11: main inlet valve (normally closed)

y13: slow pressure relief of furnace (normally open)

y14: all pressure relief of the furnace (normally open)

yk1: pressure switch, monitoring the furnace pressure at "0" mbar. It is adjusted to about 50mbar when leaving the factory

yk2: pressure switch, which monitors the maximum pressure in the furnace and is adjusted to about 950mbar when leaving the factory

b1: pressure sensor, 0 ~ the technicians of our company will introduce the precautions for the purchase and measurement of pressure testing machine 1600mbar, 4 ~ 20mA. Detect the furnace pressure

b2: pressure sensor, 0 ~ 7000mbar, 4 ~ 20mA. Check the air supply pressure of the intake pipe

(2) cooling control: the industrial computer and the cooling control i/o template controlled by it control 12 (5-way air cooling, 7-way air cooling + water cooling) cooling channels, and you can choose several channels to work at will. Three working modes of "on", "off" and "auto" and two control modes of time control and temperature control are provided for each cooling channel. The man-machine interface has a cooling screen, and the on-off of the solenoid valve can be adjusted by any switch

2.3 hardware configuration

low voltage control system configuration is as follows:

rising will be the main melody

(1) panel870 panel industrial control computer: piii700 CPU, 40g hard disk, 128M memory, 12 "LCD, touch keyboard, with floppy drive and DVD drive, USB interface and RJ45 interface

(2) board card: a set of 813b a/d board, a set of 1751d

i/o board, a set of 7216 relay board (including odc5 or idc5b solid state relay), and a set of 785 relay board

(3) s series plc:

cpu module: a set of CPU314, a flash EPROM memory card (64K), a ps307 power supply 5a, sm321 input mode control keyboard and electronic counter Equipped with 3 sets of vacuum cleaner blocks (32 point 24V DC), 4 sets of sm322 output modules (16 point 24V DC), 3 40 pin terminals, 4 20 pin terminals, and 1 480mm guide rail

3 project evaluation

(1) the control system can effectively control the process parameters including pressure, temperature, time and position in the process of machine operation, hydraulic mechanical action, casting process, holding furnace heating and mold cooling. The system has the function of data saving, and can access, adjust and manage casting parameters

(2) high control accuracy, pressure deviation value in mold filling and pressure maintaining stage ≤ 3mbar, pressure deviation value in liquid rising stage ≤ 5mbar, and pressure deviation value in pressure rising stage ≤ 10mbar

(3) it has the ability of automatic pressure compensation, and the pressure in the holding furnace can be reproduced accurately and repeatedly according to the set curve, without being affected by the leakage of the holding furnace, the fluctuation of air pressure in the gas supply pipeline and the change of metal liquid level (except for the serious leakage of the holding furnace)

(4) up to eight pressure rise curves and one pressure maintaining curve can be set freely according to the process needs. For the furnace with furnace volume ≤ 800L, the maximum pressure rise speed can reach 100mbar/s

(5) it has a friendly man-machine interface and can easily input various process parameters

(6) it has the function of data saving and calling. The casting process parameters of each wheel mold can be input and saved automatically after confirmation, and can be called directly from the system in the future

(7) the low-pressure casting control system has the function of fault self-test, which is convenient for maintenance

4 Conclusion

China's industrial control automation technology is developing rapidly, especially the application of industrial control computer and PLC is more mature. After nearly three years of efforts, we have successfully applied industrial control computer and PLC to wheel hub low-pressure casting machine at the same time. (end)

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