Clamping system of injection molding machine

I. Main Functions

The primary function of the mold clamping system is to provide sufficient clamping force (locking force) to ensure a tight closure of the mold cavity, prevent the plastic melt from escaping during the injection process, and ensure the quality of the molded product.

II. Basic Components
The mold clamping system primarily consists of a movable platen, a fixed platen, tie rods, a clamping mechanism, a product ejection mechanism, and safety mechanisms. Large injection molding machines (e.g., those over 500 tons) often utilize hydraulic or hydraulic-mechanical clamping designs. These systems use tie rods as cylinder pistons. High-pressure cylinders are typically mounted on the fixed platen for clamping, while short-stroke clamping cylinders are used on the movable platen to rapidly establish clamping force and open the mold.

III. Technical Requirements
Clamping Force: Clamping force refers to the maximum clamping force that the clamping mechanism can exert on the mold. It must be greater than the average pressure of the melt within the mold cavity. The thinner the part wall, the higher the injection pressure, and the greater the required clamping force. The clamping force setting is typically determined by the product of the injection pressure and the projected area of ​​the part. Platen: The maximum opening and closing stroke of the platen determines the maximum thickness of the mold that can be installed in the injection molding machine. Therefore, the platen stroke should be adjustable. Furthermore, the platen must possess sufficient strength and rigidity to prevent deformation caused by frequent pressure during injection molding, which could affect the dimensional and shape accuracy of the molded product.
Motion Speed: The mold clamping system must provide reliable mold opening and closing motions and provide a cushioning effect during mold opening and closing. The moving platen's speed should vary from slow to fast to slow during mold closing and opening to prevent damage to the mold and product and avoid excessive vibration and noise from the machine, thereby ensuring safe operation and extending the life of the machine and mold.
IV. Types
Injection molding machine clamping systems are primarily categorized into the following types:

Fully hydraulic: Fully hydraulic clamping systems utilize liquid pressure in conjunction with auxiliary components to open, close, and lock the mold. Common types include pressurized, liquid-filled, liquid-filled pressurized, and secondary-action pressure-stabilized. Liquid-filled clamping devices can meet the requirements for both fast, low-pressure and slow, high-pressure locking in injection molding machines. Toggle-Lock Clamping: A toggle-lock clamping system utilizes a linkage or toggle support mechanism to generate internal stress in the clamping mechanism under the action of oil pressure, thereby locking the mold. This compact structure offers high clamping force, high mechanical rigidity, and self-locking properties. However, it is susceptible to wear, has numerous components, can significantly deform the mold plates, and complicates mold adjustment.

Tie-Bar-Less Clamping: A tie-bar-less clamping system is a relatively new type of clamping mechanism. It lacks the traditional tie-bar structure and instead uses other methods to secure and lock the mold.

Two-Platen Clamping: A two-platen clamping system has a relatively simple structure, consisting of two platens and a clamping mechanism. It is suitable for small and medium-sized injection molding machines.