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Plastic Injection Mold Base Functions and Structure

SS Machinery

 

Definition Of Injection Mold

The plastic mold consists of a moving mold and a fixed mold. The moving mold is installed on the movable template of the injection molding machine, and the fixed mold is installed on the fixed template of the injection molding machine. During injection molding, the movable mold and the fixed mold are closed to form the gating system and the cavity, and the movable mold and the fixed mold are separated to take out the plastic product when the mold is opened.

Although the structure of plastic molds may vary due to the variety and performance of plastics, the shape and structure of plastic products, and the type of injection machine, the basic structure is the same.

 

Structure And Function Of Injection Mold

1. Formed parts

A molded component is a specified, moving part of the part that makes up the cavity. It is usually composed of a punch (or core), a die, an insert, etc. When the mold is closed, it forms a cavity for filling the plastic melt, which determines the shape and size of the plastic part, as shown in the mold shown in Figure 4-1 , the movable template 1 and the punch 7 form the internal shape of the plastic part, and the fixed template 2 forms the external shape of the plastic part.

2. Pouring system

The gating system is the channel through which the molten plastic enters the mold cavity from the nozzle of the injection molding machine. It consists of a main channel, a runner, a gate and a cold cavity.

3. Guiding mechanism

The guiding mechanism is divided into two types: the guiding mechanism between the movable mold and the fixed mold and the guiding mechanism of the ejector mechanism. The former is to ensure the accurate alignment of the movable mold and the fixed mold when the mold is closed, so as to ensure the accuracy of the shape and size of the plastic part, as shown in Figure 4-1. The guide post 8 and the guide sleeve 9: the latter is to avoid pushing out during the ejection process. The plate is arranged at an angle, such as the push plate guide post 16 and the push plate guide sleeve 17 as shown in Figure 4-1.

4. Demoulding mechanism

The device used to eject the plastic part from the mold when the mold is opened, also known as the ejection mechanism. There are many structural forms, and the common ones are ejector pin demoulding mechanism, push plate demoulding mechanism and push tube demoulding mechanism. In Fig. 4-1, the push rod 13, the push rod fixing plate 14, the pulling rod 15, the push rod 18 and the reset rod 19 form the push rod demoulding mechanism.

5. Lateral parting and core pulling mechanism

When there are concave-convex holes or bosses on the side of the plastic part, a lateral punch or core is required for molding. Before the mold is opened and the plastic part is pushed out, the lateral punch or the lateral core must be disengaged or extracted from the plastic part, so that the plastic part can be demoulded smoothly. The mechanism that moves the lateral punch or the lateral core is called the lateral core-pulling mechanism. Figure 4-2 is an injection mold with an inclined guide post driving the core slider to pull the core laterally. The lateral core pulling mechanism is the inclined guide post 10, the side core slider 11, the locking block 9 and the side core slider. The positioning device (block 5, slider rod 8, spring 7) and other components.

6. Heating and cooling system

In order to meet the mold temperature requirements of the injection molding process, the mold temperature must be controlled, so the mold is often equipped with a cooling system and heating elements are installed inside or around the mold. The cooling system usually has a cooling water channel on the mold (Figure 4-1 cooling water channel 3)

7. Exhaust system

In the injection molding process, in order to discharge the air in the cavity, it is often necessary to set up an exhaust system, usually by purposely setting up several grooves on the parting surface, or using the push rod of the mold or the gap between the core and the template. Exhaust through the fit gap between them. The exhaust volume of small plastic parts is not large, so the parting surface can be directly used to exhaust air without additional exhaust grooves

8. Other parts

Such as parts used to fix and support formed parts or play a role in positioning and limiting, etc.

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