Discussion on Servo Energy Saving Transformation of Injection Molding Machine

Abstract: 

With the continuous development of the injection molding industry, more requirements are put forward for the energy-saving transformation of the injection molding machine servo. At present, the energy-saving transformation of injection molding machine servo has gradually become an important means for enterprises to improve economic efficiency and also meets the requirements of energy conservation and emission reduction currently advocated by the state. This paper mainly analyzes the current situation of traditional injection molding machines, the comparison of transformation methods, the necessity of servo energy-saving transformation, and the energy-saving principle and advantages of electro-hydraulic servo systems.

 

In recent years, the number of enterprises engaged in the production of plastic toys has gradually increased. Taking Chenghai District, Shantou City, Guangdong Province, China as an example, it has always been in the leading position in China in terms of plastic toys, plastic crafts, plastic daily necessities, and plastic building materials. It is known as the “Plastic City”. However, the injection molding machines used in the production process are still dominated by quantitative pump systems that consume energy and electricity, which is not conducive to the overall development of the enterprise itself and society. Therefore, the energy-saving transformation of injection molding machine servo will become an important part of the future development of the plastics industry.

 

Current status of traditional injection molding machine:

An injection molding machine is a molding equipment that uses plastic molding molds to make thermoplastic or thermosetting materials into plastic products of various shapes. The traditional injection molding machine is a three-phase asynchronous motor-driven vane pump. The oil pump usually outputs a constant flow at a fixed rotation speed, which is mainly adjusted through the flow valve. The excess hydraulic oil will be discharged into the oil tank through the overflow valve. This process causes A large loss of energy, wasting too much electric energy. Assume that if all or most of the enterprises in the Chenghai District of Shantou City use quantitative pump systems, the waste of electric energy will be extremely serious.

 

Comparison of transformation methods of quantitative pump injection molding machine:

The transformation of a quantitative pump injection molding machine can generally adopt three kinds of silicon-controlled rectifier voltage regulation, frequency conversion, and servo. Among them, the cost of thyristor voltage regulation is relatively low, and the renovation facilities are relatively simple, but the proportion of energy saving is too small, and the payback period is too long. The cost of frequency conversion regulation is relatively moderate, but the product cycle is longer, especially when changing molds, the parameters of the frequency converter need to be readjusted, which increases the difficulty of operation. Another servo transformation method is costly, but the energy-saving efficiency is extremely high and has no impact on the product cycle, which is of great help in improving product accuracy and prolonging the service life of the equipment. It can be seen that the servo energy-saving transformation should be the best choice for the energy-saving transformation of injection molding machines.

 

The necessity of servo energy-saving transformation:

The energy consumption system of the injection molding machine mainly includes the drive hydraulic system and the electric heating system, among which the drive hydraulic system accounts for a large proportion of power consumption. In terms of process, it is mainly divided into stages such as mold locking, glue injection, sol, pressure holding, cooling, shaping, and mold opening. Each stage has different requirements for pressure and flow. As mentioned above, in the traditional quantitative pump hydraulic system, the oil pump provides a constant flow rate at a fixed speed, and the excess hydraulic oil will be discharged into the oil tank through the overflow valve, and the energy loss generated in this process is as high as 36%-68%.

In addition, the traditional injection molding machine has the characteristics of excessive noise, excessive hydraulic oil leakage, high oil temperature, high electricity cost, and cumbersome maintenance. Lots of faults in the pump. Moreover, today’s society puts forward strict requirements on environmental protection, such as energy saving, noise reduction, and many other aspects. Traditional injection molding machines cannot meet the requirements of market economic development. Therefore, regardless of the energy consumption system of the injection molding machine and the drawbacks in the use of the quantitative pump, or from the perspective of social environmental protection, the traditional injection molding machine cannot meet the current development needs, and the practical application of servo energy-saving transformation must be strengthened.

 

Analysis of the energy-saving principle of the servo system:

Since the energy consumption of the injection molding machine is mainly reflected in the hydraulic part, the transformation work mainly focuses on this energy consumption point. At present, the energy-saving scheme mainly replaces the quantitative pump system with the electro-hydraulic servo system. The composition of the electro-hydraulic servo control system mainly refers to the replacement of asynchronous motors with servo motors, the replacement of vane pumps with screw pumps or gear pumps, and the addition of servo drives. In addition, the electro-hydraulic servo control system also eliminates the traditional PQ valve control, and the flow and pressure in production are mainly controlled by closed-loop control. During the use of the electro-hydraulic servo system, the servo motor and the servo driver will form a closed-loop control of the pressure model of the injection molding machine, and use the characteristics of the servo motor to start and stop quickly, and the start and stop can be performed within 30 milliseconds, so when maintaining pressure or The cooling phase generates almost no power consumption. Because the servo energy-saving system adopts a closed-loop control method for pressure and flow, the pressure repeatability is also guaranteed, and it can work normally even if the pressure is very low. In addition, the servo energy-saving system uses digital signals to control the output flow, which has good linearity and low-speed controllability and improves the repeatability of flow. Therefore, analyzing the principle of energy saving of the servo system plays an important role in energy saving and consumption reduction.

 

Analysis of the advantages of the servo system: 

Based on the data analysis of previous scholars’ research theory and practical application process, its advantages are mainly manifested in-

  • The energy-saving rate is high, and high-pressure throttling can be completely eliminated. Compared with the variable pump, it can save energy by 10%- 30%, 30%-60% energy saving compared to quantitative pumps.
  • The response speed is faster, the 0-100% pressure change can reach 30ms, and the 0-100% speed up and down time can be controlled within 0.1 seconds, so The production efficiency is greatly improved.
  • The control is precise. Since the PID of the system flow and pressure is adjusted under the PQ control card, its anti-disturbance ability is extremely strong, and the system repeatability is controlled within 0.3%, so that the product quality and product quality accuracy is guaranteed.
  • The high overload capacity is strong, and it can be found from previous research that the servo torque overload multiple can reach more than 200%.
  •  The state conversion of the servo system is relatively flexible, and it can be flexibly switched in terms of speed and torque control.
  • The extension of equipment life and the use of servo systems greatly reduce the impact of mold opening and clamping, which is beneficial to prolong the service life of molds, machinery, and hydraulic oil pumps.
  • The temperature of hydraulic oil is reduced, and the use of a servo system can Reduce the amount of cooling water to more than 30%, and even not need water cooling on many occasions.
  • The improvement of the working environment and the application of the servo system has greatly reduced the noise in the working environment, and the sound during operation is generally lower than 68db. Taking Guangdong Aofei Animation Culture Co., Ltd. as a typical representative, after a series of experiments on the transformation of the injection molding machine, compared with the traditional injection molding machine, the operation of the transformed equipment is more reliable, the laying of the main and control lines, terminals, oil pipes and The cleanliness of the box is good. In addition, it has also been recognized in terms of energy saving and power saving. Therefore, the advantages of the servo system determine that its application range will become wider and wider.

 

Conclusion:

The servo energy-saving transformation of injection molding machines has obvious advantages in terms of its necessity, principle analysis, advantages analysis, and comparison with other transformation methods. Its high energy-saving and power-saving rate can help enterprises achieve significant economic and social benefits Improvement while responding to the country’s call for environmental protection, conform to the market development trend. Therefore, power supply enterprises should pay attention to the use of new technologies and new equipment, apply and practice energy conservation and emission reduction work, and improve the comprehensive strength of enterprises.

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