Abstract: This article briefly introduces the basic process of injection molding machines, analyzes the energy-saving principle and effect of frequency conversion retrofit, discusses the traditional and economical retrofit schemes of frequency conversion energy-saving speed regulation devices in the injection molding machine industry, and explains the main characteristics of the Transmission Star injection molding-specific frequency conversion energy-saving speed regulation device in application. Keywords: Frequency conversion energy-saving injection molding machine I. Overview With the widespread application of injection molding machines, electricity consumption is a major part of the production cost for the plastic products industry. Injection molding machines are one of the main energy-consuming equipment in plastic products factories. Therefore, reducing the energy consumption of injection molding machines has become an effective way for the injection molding industry to reduce costs and improve product competitiveness. Among various energy-saving measures, electricity saving has the highest efficiency. Using frequency conversion energy-saving speed regulation devices to adjust the speed of the motor (oil pump) to meet the pressure and flow requirements in real time is both economical and practical. Therefore, adopting frequency conversion energy-saving speed regulation devices for energy-saving retrofitting of injection molding machines has become the most effective way for the injection molding industry to reduce the energy consumption cost of injection molding machines and improve product competitiveness. II. Variable Frequency Energy Saving Principle The power consumption of an injection molding machine mainly manifests in the following aspects: ① Power consumption of the hydraulic system oil pump, ② Power consumption of the heater, ③ Power consumption of the circulating cooling water pump. The hydraulic oil pump accounts for more than 80% of the total power consumption of the injection molding machine, so reducing its power consumption is key to energy saving. The pressure and flow required by the injection molding machine change during mold closing, mold locking, injection, and cooling stages. When the oil demand of the injection molding machine changes, the overflow valve located at the oil pump outlet adjusts the load pressure and flow, while the motor's output power remains unchanged, resulting in energy waste. The variable frequency speed control device consists of a rectifier circuit, a filter circuit, an inverter circuit, and a control circuit. Its function is to rectify and filter AC power into DC power through the rectifier circuit, and then convert it into AC power of different frequencies through the inverter circuit to output to the motor. This allows the injection molding machine's oil pump motor to operate at different speeds. Furthermore, according to the theory of oil pumps, the formula for calculating the output flow rate Q of an oil pump is: Q = 2[π(R² - r²) - (Rr)S × Z/COSθ]B × N¹⁰ - 6] Where: R - radius of the blade; r - short radius of the stator; S - thickness of the blade; B - axial width of the rotor; Z - number of blades; θ - angle of inclination of the blade relative to the radius. From the above formula, it can be concluded that changing the rotational speed N of the oil pump motor also changes the output flow rate Q, that is, the oil flow rate of the oil pump is directly proportional to the rotational speed of the oil pump motor. Changing the rotational speed N of the oil pump motor is achieved by automatically controlling the output frequency of the variable frequency energy-saving speed regulation device through the synchronous signal of the injection molding machine computer. The power consumption of the oil pump motor is approximately cubic to its rotational speed, that is, the power consumption P of the oil pump motor is P = P'(N'/N)³. If the rated power of the injection molding machine's oil pump motor is 55KW, then when the speed drops to 4/5 of the original speed, its power consumption is 28.16KW, saving 48.8% of electricity; when the speed drops to 1/2 of the original speed, its power consumption is only 6.875KW, saving 87.5% of electricity, thus achieving a significant energy-saving effect on the oil pump load (where: P'=55KW, N'/N=4/5 and N'/N=1/2). II. Working Principle of Injection Molding Machine Plastic injection molding utilizes three states (solid-liquid-solid) to form the desired plastic products using an injection molding machine and mold. Although all injection molding machines are slightly different, their basic workflow is the same. As shown in Figure 1, the process can be roughly divided into seven steps: mold clamping, injection, pressure holding, melting and plasticizing, cooling, mold opening, and ejector pins (ejector pin in, ejector pin out, injection seat out). Each step requires different working pressures and flow rates. Except for high-pressure mold clamping, injection, and melting and plasticizing, which require higher pressures, the other steps operate under very low pressures. The pressure and flow rate are regulated by pressure proportional valves and flow proportional valves. The pressure and flow rate are controlled by adjusting the opening degree of the pressure proportional valves and flow proportional valves. III. Injection Molding Machine Variable Frequency Energy-Saving Retrofit Scheme 1. Traditional Injection Molding Machine Variable Frequency Energy-Saving Retrofit Scheme 1.1 Scheme Principle Diagram As shown in Figure 2: Since the beginning of the 21st century, the technology of using variable frequency speed regulation to retrofit injection molding machines for energy saving has been widely applied. Traditional variable frequency speed regulation mainly uses the conversion of the flow valve signal or pressure valve signal from the injection molding machine's main controller into a '0-10V' or '4-24mA' signal received by the variable frequency energy-saving speed regulation device to control the variable frequency energy-saving speed regulation device, so as to achieve the purpose of adjusting the oil pressure according to the process requirements. When an injection molding machine operates under conditions of high pressure and low flow (high flow and low pressure), the parameter points become too low, the motor speed is too low, and the pressure is insufficient, resulting in products that do not meet production requirements and impacting production. When adjusting a particular operating state, the overall machine speed must be increased, which significantly reduces the energy-saving effect. Although some energy-saving effects are achieved, several negative impacts exist, and traditional frequency conversion energy-saving retrofit solutions are insufficient to solve the existing problems. 1.2 Disadvantages of Traditional Frequency Conversion Energy-Saving Retrofit Solutions for Injection Molding Machines: 1. Insufficient dynamic response, prolonging the injection molding machine's working cycle and causing a decrease in output. 2. Inconsistent product quality and increased waste. 3. Insufficiently smooth working process with delays. 4. Electromagnetic interference to the injection molding machine's computer and electric heating circuits. 5. Poor technical applicability; the energy-saving rate after retrofitting some injection molding machine models is very small. 6. Insufficient exploitation of energy-saving potential, resulting in excess energy consumption. 2. The Most Economical and Practical Injection Molding Machine Variable Frequency Retrofit Solution 2.1 Solution Overview Considering the various shortcomings discussed in the previous three sections, and to resolve customer concerns while achieving a win-win situation of saving huge amounts of electricity costs without affecting production, our company's engineering and technical personnel, after in-depth research and analysis, believe that the root cause lies primarily in the control components. Improper retrofitting will result in the shortcomings described in Chapter 3 of this article. In response to the above situation, the Transmission Star SD series injection molding machine-specific variable frequency energy-saving speed control device adopts multi-terminal signal input control. Proportional pressure and flow signals are used as the main input signals, while several other unidirectional action signals serve as auxiliary input signals. When the working pressure of a certain action is insufficient, it can be adjusted independently without affecting other operating conditions. This ensures that the motor's energy consumption reaches the required minimum range across the entire varying load range, and guarantees stable and precise motor operation, thus ensuring product quality while saving energy, truly achieving economic practicality. It also employs technologies such as a dedicated variable frequency speed controller, current transmitter, and injection molding machine computer control. The schematic diagram of the scheme is shown in Figure 3. Based on the different oil pressure and flow rates required by the injection molding machine in each working stage and the energy-saving characteristics of the variable frequency speed control device, a 0-1A DC analog current signal is taken from the pressure or flow electromagnetic proportional valve of the injection molding machine. After processing by the current transmitter, it is converted into a 0-10VDC analog voltage signal to control the output frequency of the variable frequency speed control device, thereby changing the speed of the oil pump motor and thus changing the oil pump output flow rate Q. This satisfies the oil pressure and flow rate requirements of the injection molding machine in each working stage, transforming the traditional fixed-displacement pump into a variable-displacement pump, achieving an energy-saving efficiency of 20%-60%. 2.2 Advantages of the Scheme This changes the screw control method from the traditional proportional valve throttling speed regulation method to the motor variable frequency energy-saving speed regulation method, greatly improving the overall machine performance. The modified injection molding machine retains the original operation process unchanged, without requiring changes to the original circuit, making adjustment convenient and control precise. It truly realizes the perfect application of the most advanced variable frequency speed regulation technology to plastics industrial production. In the long run, the Transmission Star injection molding machine-specific frequency conversion energy-saving speed control device fundamentally simplifies the structure of the injection molding machine's hydraulic system and reduces the production costs for injection molding companies. Compared with traditional energy-saving measures such as variable pumps currently used, it is undoubtedly a revolutionary advancement and will inevitably become the future trend of injection molding companies. IV. Functions and Features of Transmission Star SD Series Frequency Conversion Energy-Saving Speed ​​Control Devices 1. Brief Description of SD Series Frequency Conversion Energy-Saving Speed ​​Control Devices Our company's SD series high-performance integrated frequency conversion energy-saving speed control device is a complete solution specifically designed for energy-saving retrofitting of injection molding machine users. The new generation of products boasts superior performance, more powerful functions, and a more refined appearance. The SD series integrated energy-saving device is widely applicable to energy-saving retrofitting of injection molding machines, constant pressure water supply, etc. It integrates frequency conversion energy-saving speed control devices, bypasses, cabinets, etc., facilitating user needs. The system design considers factors such as interference and heat dissipation of the frequency conversion energy-saving speed control device system. It is a user-end solution provided to distributors. Customization is also available according to customer requirements, avoiding adverse factors caused by differences in processes and installation during secondary integration by distributors. The basic wiring diagram of the Transmission Star SD series integrated frequency converter is shown in Figure 4. This series features a compact structure and attractive appearance; it has a keyboard locking function to prevent accidental operation; and it has both power frequency and frequency conversion operation loop designs. It also features automatic reset and power-off reset functions. 2. Transmission Star SD Series Parameter Setting Reference: The following parameters must be set: FO-OOO=01: Select the inverter control mode; FO-OO1=10: Select injection molding machine specific parameters; F0-007=1.5-2.5: Select inverter acceleration time; FO-008=1.5-3.0: Select inverter deceleration time; F0-123=0: Output a valid signal when a fault occurs; F0-151=0: Select dual input control, connect the flow signal to INA and the pressure signal to INB; F0-153=1: The minimum control signal corresponding to the proportional flow is 1V; F0-154=5: The frequency corresponding to the minimum control signal of the proportional flow is usually the minimum operating frequency of the controlled motor; FO-155=10: The maximum control signal corresponding to the proportional flow is 10V; FO-156=55: The frequency corresponding to the maximum control signal of the proportional flow is generally slightly higher than 50.00Hz. F0-157=1: Minimum control signal of proportional pressure, 1V. FO-158=10: Frequency corresponding to the minimum control signal of proportional pressure. F0-159=10: Maximum control signal of proportional pressure, 10V. F0-160=55: Frequency corresponding to the maximum control signal of proportional pressure. Note: FO-153～160 (Please adjust according to actual working conditions; the above is for reference only). 3. Application effects of using Transmission Star SD series frequency converter retrofit: 1. Significantly reduced energy consumption: The SD series frequency converter energy-saving speed regulation device changes the traditional fixed displacement pump to a variable displacement pump, adopting a frequency conversion speed regulation method with dual input of flow and pressure signals, replacing the previous proportional valve speed regulation method, significantly reducing energy consumption. Under the premise of meeting process requirements, it achieves a significant energy saving effect of 20%-60% for the oil pump motor. 2. Improved Production Process and Extended Equipment Lifespan: The SD series variable frequency energy-saving speed control device adopts external extended synchronous control, allowing for arbitrary speed adjustment at any speed range. This easily meets the requirements of the injection molding process, achieving optimal values ​​and improving production efficiency compared to previous methods. It also reduces system oil temperature, extends the lifespan of sealing elements, and reduces equipment maintenance costs. 3. Convenient Control and Operation: The SD series variable frequency energy-saving speed control device uses advanced computer control methods. Utilizing the synchronous signal from the injection molding machine's computer, it automatically controls the oil pump motor according to the injection molding machine's process requirements. Operation is safe and reliable, and no adjustments to the device are required during production. Control and operation are convenient and simple. 4. No Throttling Energy Loss and Significantly Reduced Overflow Energy Loss: This reduces system noise by 3-5 decibels, reduces oil pipe heating, and lowers oil temperature. 5. Achieve true soft start: The SD series variable frequency energy-saving speed control device has a small starting current, which greatly reduces the vibration of the injection molding machine during startup, mold closing, and mold opening. It can significantly reduce the requirements for the power supply transformer capacity, improve the power grid quality, avoid the impact on the equipment itself, and extend the service life of the equipment and mold. 6. High reliability: The SD series variable frequency energy-saving speed control device can realize the conversion between power frequency and variable frequency. Even if the variable frequency fails, it can be switched to the power frequency. (Alternatively, according to customer requirements, the variable frequency energy-saving speed control device can be set to automatically switch to the power frequency after reporting a fault.) It will not affect the production progress. It has a large lifting torque and a fast dynamic response, which is suitable for the sudden speed increase of the injection molding machine. V. Matters to be noted in the modification of injection molding machines 1. Issues to be noted in the process of variable frequency modification of injection molding machines: (1) Only injection molding machines that must use fixed quantity pumps can be modified for variable frequency energy saving; (2) Variable quantity pumps do not need to be modified for variable frequency energy saving. Because variable quantity pumps themselves have a certain energy-saving effect, adding a variable frequency energy-saving speed control device will not reflect its advantages. (3) Under normal circumstances, injection molding machines controlled by relays also need to be carefully retrofitted for frequency conversion due to the special requirements for the response speed of frequency conversion energy-saving speed regulation devices. 2. Issues to be noted when installing frequency conversion energy-saving devices: (1) Generally, a dual-circuit system with power frequency and frequency conversion is adopted (the Transmission Star frequency conversion energy-saving speed regulation device has this function); (2) Consider the environmental conditions, grid voltage, and load size; (3) The power line and control line of the frequency conversion energy-saving speed regulation device should be routed separately as much as possible, and the control line should use shielded wire as much as possible; (4) Strengthen the anti-interference capability of the frequency conversion energy-saving speed regulation device (add magnetic rings, reactors, filters, etc.). VI. Conclusion The high performance and perfect functions of the Transmission Star SD series integrated frequency conversion energy-saving speed regulation device have led to its widespread application in various industries. With the continuous development of frequency conversion energy-saving retrofitting of injection molding machines, more users will understand the advantages of using frequency conversion energy-saving speed regulation devices in injection molding machines, and more and more enterprises and units will join the frequency conversion energy-saving industry. Therefore, promoting the application of AC frequency conversion speed regulation devices in injection molding machines is of great significance for reducing energy waste. References: Shenzhen Star Drive Technical Manual (www.stardrive.com.cn) Author Biography: Liu Jiachang, Male Engineer, currently working in the Engineering Department of Shenzhen Star Drive Electric Co., Ltd. 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