The driving methods of injection screw in fully hydraulic injection molding machine - hydraulic motor drive and reducer drive - were analyzed and compared. The reducer drive has the characteristics of smooth motion, high efficiency, and time-saving. It is concluded that using reducer drive for injection screw has more advantages.
This research analysis has certain significance for saving the operating cycle of injection molding machines, especially for injection molding machines with long pre molding time and short cooling and mold opening time. The research and analysis in this article will solve the conflict between pre molding measurement and cooling, mold opening, and ejection time. Pre molding measurement will be carried out simultaneously during cooling, mold opening, and ejection, thereby reducing the production cycle.
The hydraulic motor driven injection screw is widely used in injection molding machines. Its function is to convert hydraulic energy into mechanical energy, drive the screw connected to it to rotate, and thus achieve the function of rotating the screw to transport and shear materials. The reducer can also play the same role, and its movement is smoother, more efficient, and takes less time.
This article will study and analyze the driving method of the injection screw in a fully hydraulic injection molding machine, and compare the driving methods. It is concluded that using a reducer for driving is better. This method of using a reducer to drive the injection screw to rotate has significant value for promotion.
1. Introduction and analysis of the working process of a fully hydraulic injection molding machine
The working process of a fully hydraulic injection molding machine mainly consists of processes such as mold closing, advance of the injection seat, injection and pressure holding, pre molding measurement, cooling, mold opening, and product ejection by the ejection mechanism.
Due to being a fully hydraulic injection molding machine, when hydraulic pump oil function is required to execute actions, they must be executed in chronological order. After executing one action, another action is controlled to be executed, resulting in actions that could have been performed simultaneously having to be executed in chronological order, which is relatively inefficient.
Therefore, it is necessary to study and analyze the time conflicts between pre molding measurement and cooling, mold opening, ejection of products, etc., in order to reduce the production cycle.
2. Principle and structure of hydraulic motor-driven injection screw
A hydraulic motor is a hydraulic actuator that converts the hydraulic pressure energy provided by a hydraulic pump into the mechanical energy of its output shaft for rotational motion. Hydraulic motors have small volume, light weight, and simple structure, but low efficiency, small starting torque, and poor low-speed stability.
When using it to achieve rotational motion, it can replace reducers in situations where structural space and reliability requirements are not high. Therefore, it has been widely used in various mechanical hydraulic systems and has been widely applied in the pre molding part of injection molding machines in recent years, that is, driving screw rotation.
The function of the screw rotation motion in the injection machine is to transport the material forward, and to shear and mix the material during the transportation process, so that the material is continuously heated and melted before being transported forward.
The output shaft of the hydraulic motor is an internal spline shaft, which is connected to the external spline of the transmission shaft in the injection seat. The left end of the external spline transmission shaft is linked to the screw through a coupling, so that the hydraulic motor drives the screw to rotate together. At the same time as the screw rotates, the injection seat moves backward, and the material continuously enters the front of the material cylinder, waiting for the next step of material injection.
Figure 1 External structure of injection screw driven by hydraulic motor
3. Principle and structure of gearbox driven injection screw
Gearboxes play a role in matching speed and transmitting torque between the prime mover and the working machine or actuator, and are widely used in modern machinery. Gearboxes can be divided into two categories based on their usage: general-purpose gearboxes and specialized gearboxes, each with unique design, manufacturing, and usage characteristics.
Due to the periodic rotation of the injection screw in the injection molding machine, the reducer used must be specially designed to drive the rotation of the injection molding machine screw. Its external structure is shown in Figure 2, and its internal connection with the injection screw is the same as the connection between the hydraulic motor and the injection screw.
Figure 2 External structure of the drive screw of the reducer
Due to the use of a reducer for driving, a driving source needs to be set up at the input shaft of the reducer, which can be a hydraulic motor or an electric motor. In this article, the electric motor is selected. And the injection screw of the injection molding machine corresponds to different plastics, and its speed is also different. In order to obtain multiple different speeds, it is necessary to choose a servo motor to drive the reducer, and then drive the screw to rotate.
4. Analysis and Comparison of Hydraulic Motor Drive and Reducer Drive
Hydraulic motors are relatively expensive, and their transmission efficiency is also relatively low. According to usage testing, the driving efficiency is generally around 70%.
In addition, the load-bearing capacity of hydraulic motors is relatively low, and the service life of motors is relatively short. To achieve long-term service life, it is necessary to choose hydraulic motors with relatively high rated torque, which invisibly increases investment costs. Moreover, maintenance of hydraulic motors is difficult and the maintenance cost is relatively high.
Compared to hydraulic motors, reducers have higher driving efficiency, with a single-stage efficiency of up to 99%. The three-stage reducer used in this article has an efficiency of up to 97%, a large load-bearing capacity, simple maintenance, and relatively convenient repair. Installing a servo speed regulating motor at the input shaft can achieve multiple output speeds and torques of the reducer.
Fully hydraulic injection molding machine operation? Cycle is a process of controlling a hydraulic pump in chronological order to pump oil and complete various actions. Hydraulic motor drive requires the hydraulic pump to pump hydraulic oil into the motor to drive the injection screw. Therefore, while the hydraulic motor drives the injection screw to rotate, other parts that require the hydraulic pump as a power source will have to stop. After the screw rotates, software control is used to pump hydraulic oil into other parts that require hydraulic oil, which is time-consuming and costly to control.
After the injection pressure maintenance is completed, pre molding can be carried out while the parts are cooled. However, when opening the mold and ejecting the product after the cooling is completed, the injection screw cannot perform pre molding or must wait until pre molding is completed before opening the mold and ejecting the product, which wastes a period of time in between.
If a reducer is used for driving, the input shaft of the reducer is connected to a servo speed control motor, which uses electronic control. The use and control of the motor are also very convenient, not affected by hydraulic pumps. During mold opening, cooling, and product ejection, the injection screw can continuously perform pre molding, continuously melting the raw materials of the product, and fully mixing them. This not only reduces the total pre molding time, but also lowers the operating cycle of the injection molding machine, improving its efficiency.
5. Conclusion
Through the above research analysis and comparison, using a reducer equipped with a servo motor to drive the injection screw can not only greatly increase the efficiency of the injection screw in shearing and mixing raw materials, but also reduce the operating cycle of the injection molding machine, increase the output of products per unit time, and increase production efficiency. Therefore, using a reducer to drive injection screws can be promoted and used in the injection molding machine industry, especially in injection molding machines with long pre molding cycles and short cooling, mold opening, and ejection times, which are more worthy of promotion and can greatly improve production efficiency.
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