Injection liquid filling type mold clamping device
The injection molding liquid-filled clamping device is an advanced device that uses liquid pressure to assist in mold clamping. Its core principle is to inject high-pressure liquid into the clamping mechanism via a liquid-filling cylinder during the clamping process. Leveraging the liquid’s incompressibility, the clamping force is evenly transmitted to the mold, thereby achieving stable clamping. Compared to traditional mechanical clamping devices, it offers significant advantages such as high clamping force, uniform distribution, and fast response speed, making it particularly suitable for the molding of large or precision plastic parts. For example, when producing large plastic parts such as car bumpers, traditional mechanical clamping devices can cause flash or dimensional deviations due to uneven distribution of clamping force. Liquid-filled clamping devices, however, ensure consistent force distribution across all parts of the mold through the uniform transmission of liquid pressure, enabling the dimensional accuracy of plastic parts to be controlled within ±0.1mm, significantly improving product quality.
The structure of an injection molding liquid-filled mold clamping device is relatively complex, primarily consisting of key components such as the filling cylinder, master cylinder, mold shifting cylinder, and control system. The coordinated operation of these components is essential for ensuring the device’s performance. As a core component, the filling cylinder’s cylinder diameter and operating pressure directly determine the clamping force. Typically, the working pressure of the filling cylinder is between 10 and 30 MPa, and the cylinder diameter can be designed to be 300 to 800 mm depending on the required clamping force. The master cylinder is responsible for providing the primary power for mold clamping, working in conjunction with the filling cylinder to complete the clamping action. Its piston rod is connected to the mold’s movable platen, extending and retracting to drive the mold’s opening and closing. The mold shifting cylinder is used to drive the movable platen’s rapid movement, enabling rapid mold opening and closing, improving production efficiency. The mold shifting speed can generally reach 0.5 to 1 m/s. The control system uses a PLC or industrial computer, which can accurately control the filling volume, pressure and speed to ensure the stability and repeatability of the mold closing process. For example, in the initial stage of mold closing, the control system controls the mold shifting cylinder to quickly move the movable mold plate. When the mold is about to close, the filling cylinder starts working and gradually increases the pressure to the set value. The pressure fluctuation throughout the process can be controlled within ±0.5MPa.
The operating process of a liquid-filled mold clamping device for injection molding can be divided into rapid mold shifting, slow mold clamping, high-pressure clamping, pressure holding, and mold opening stages. The parameter settings for each stage are crucial to the mold clamping effect. During the rapid mold shifting stage, the mold shifting cylinder drives the movable platen toward the fixed mold at a high speed. During this stage, the liquid filling cylinder is inactive to reduce auxiliary time and improve production efficiency. This stage typically lasts 2-5 seconds. When the movable platen is 50-100 mm away from the fixed mold, the slow mold clamping stage begins. The mold shifting speed is reduced to 0.1-0.2 m/s to prevent damage from rapid mold collision. Simultaneously, the liquid filling cylinder begins pre-filling in preparation for high-pressure clamping. The high-pressure clamping stage is a critical step. The liquid filling cylinder injects high-pressure liquid into the system, rapidly increasing the clamping force to the set value. At this point, the piston rod of the main cylinder pushes the movable platen to lock the mold. The clamping time is determined by the size of the plastic part and the material properties, and is generally 5-15 seconds. During the holding phase, the clamping force is kept stable to prevent flash or sink marks caused by mold loosening during the cooling process. The holding pressure is typically 80%-90% of the clamping force. The mold opening phase is the opposite of the clamping phase. First, the pressure in the filling cylinder is released, and then the mold cylinder drives the movable platen to quickly retreat, completing the mold opening.
The performance advantages of liquid-filled mold clamping devices in injection molding have led to their widespread application in many fields, particularly in the production of large and precision plastic parts. In the production of large household appliance plastic parts, such as refrigerator doors and washing machine housings, which typically exceed 1000mm in size, a clamping force of 500-1000 tons is required. Liquid-filled mold clamping devices easily meet this requirement, providing uniform clamping force and ensuring a smooth surface without warping or deformation. In the production of precision optical plastic parts, such as light guide plates for liquid crystal displays, extremely high clamping accuracy is required. Liquid-filled mold clamping devices, through precise pressure control, can control mold parallelism errors to within 0.01mm/m, ensuring the optical performance of the plastic parts meets standards. Furthermore, in the production of small precision plastic parts in the aerospace industry, the rapid response of liquid-filled mold clamping devices can shorten molding cycles and improve production efficiency. For example, in the production of a plastic connector for aerospace applications, the use of liquid-filled mold clamping devices reduced molding cycles from 40 seconds to 25 seconds, increasing production efficiency by 60%.
Injection molding liquid-filled mold clamping units also require careful maintenance and care during use to ensure long-term stable operation. First, the seals of the filling cylinder and main cylinder should be regularly inspected. Aging or damage to seals can lead to fluid leakage, affecting clamping force and pressure stability. It is recommended to replace seals every 5,000 molds, and use high-pressure, wear-resistant fluororubber. Second, hydraulic oil cleanliness is crucial. Impurities in the oil can wear the cylinder and piston rod surfaces, causing leakage or sticking. The hydraulic oil should be filtered monthly and replaced every six months. Use anti-wear hydraulic oil with a high viscosity index. Furthermore, the control system’s sensors and solenoid valves require regular calibration to ensure accurate pressure and position detection. For example, pressure sensors should be calibrated quarterly, with an error control within ±1%. Through effective maintenance, a liquid-filled mold clamping unit can achieve a service life of over 10 years, significantly reducing equipment failure rates and production costs.
