Explanation of terms related to injection molding (2)

1. Please take the horizontal screw injection machine as an example to describe the working process of the injection machine?

 (1) , heating and pre plasticization: driven by the transmission system, the screw will transport and compact the materials from the hopper forward. Under the shear and friction of the heater outside the barrel, the screw and the barrel, the materials will gradually melt, and a certain amount of molten plastic has accumulated at the head of the barrel. Under the pressure of the melt, the screw will slowly retreat. The backward distance depends on the amount required for one injection of the metering device. When the predetermined injection amount is reached, the screw stops rotating and backward.

 (2) Mold closing and locking: the mold locking mechanism pushes the mold and the mold moving part installed on the moving mold to close and lock the mold moving part on the moving mold to ensure that sufficient clamping force can be provided to lock the mold during molding.

(3) . forward movement of the injection device: when the mold closing is completed, the whole injection seat is pushed and moved forward to make the nozzle of the injection machine fully fit with the main sprue opening of the mold.

 (4) Injection and pressure maintaining: after the mold locking and nozzle are fully fitted with the mold, the injection pressure cylinder enters the high-pressure oil to push the screw forward relative to the barrel, inject the melt accumulated at the head of the barrel into the mold cavity with sufficient pressure, and shrink the plastic volume due to the decrease of temperature. In order to ensure the compactness, dimensional accuracy and mechanical properties of plastic parts, it is necessary to maintain a certain pressure on the melt in the mold cavity to supplement materials.

 (5) Pressure relief: when the melt at the gate of the die freezes, the pressure can be relieved.

 (6) Retreat of the injection device: Generally speaking, after the pressure relief is completed, the screw can rotate and retreat to complete the next feeding and pre plasticization process. After the pre plasticization is completed, the injection seat will withdraw from the main sprue gate of the mold.

 (7) , mold opening and ejection of plastic parts: after the plastic parts in the mold cavity are cooled and shaped, the mold locking mechanism opens the mold and pushes out the plastic parts in the mold.

2. How many stages is the injection molding process divided into?

The complete injection molding process includes feeding, heating plasticization, pressurized injection, pressure maintaining, cooling and shaping, demoulding and other processes.

3. What is the classification method of injection mold?

There are many classification methods of injection mold. 1. According to the form of the injection machine used, it is divided into vertical injection mold, horizontal injection mold and angular injection mold; 2. According to the molding materials, it is divided into thermoplastic injection mold and thermosetting plastic injection mold; 3. According to the number of cavities of the mold, it is divided into single cavity and multi cavity injection mold; 4. It is most common to classify according to the overall structural characteristics of injection mold. Generally, the injection mold can be divided into single parting surface injection mold, double parting surface injection mold, inclined guide column (bending pin, inclined guide groove, inclined slider) lateral parting and core pulling injection mold, injection mold with movable insert, fixed mold with ejector, automatic thread unloading injection mold, etc.

4. What structure does the injection mold consist of?

There are many kinds of injection mold, and its structure is related to many factors, such as the variety of plastic, the structure of plastic parts, the type of injection machine and so on. Generally, the injection mold is composed of molding parts, gating system, guiding parts, pushing mechanism, temperature regulating system, exhaust system and supporting parts. If the plastic parts have lateral holes or bosses, the injection mold also includes lateral parting and core pulling mechanism.

5. What is the common gating system of injection mold?

The common gating system of injection mold refers to the channel through which molten plastic enters the mold cavity from the nozzle of injection machine. It includes main flow channel, shunt channel, gate and cold material cavity.

6. What is the difference between single parting surface and double parting surface injection mold?

Single parting surface injection mold, also known as two plate injection mold, has only one parting surface; Double parting surface injection mold, also known as three plate injection mold, has two parting surfaces.

7. What is the need for lateral core pulling of injection mold with inclined guide column?

When there are through holes, pits or bosses on the side wall of the plastic part, the formed parts must be made into laterally movable parts, otherwise, the plastic part cannot be demoulded. The whole mechanism that drives the core slider to move laterally is called lateral parting and core pulling mechanism.

8. What are the advantages and disadvantages of injection molds with movable inserts?

The mold with movable insert structure not only saves the design and manufacture of complex structures such as inclined guide column and sliding block, reduces the appearance of the mold and greatly reduces the manufacturing cost of the mold, but also has the advantage that the movable insert form must be used in some occasions where the inclined sliding block and other structures cannot be arranged. The disadvantages of this method are poor safety and low production efficiency.

9. What is the function of the temperature regulation system?

In order to meet the requirements of injection process for mold temperature, a temperature regulating system is needed to regulate the temperature of the mold. The injection mold of general thermoplastic is mainly to design the cooling system of the mold.

10. What is the checking method of clamping force?

When the pressure of the injection cavity and the parting surface of the injection mold are equal to 4.4, it can ensure that the plastic overflow will occur on the parting surface of the injection mold.

The pressure in the mold cavity is about 80% of the injection pressure of the injection machine, usually 20 ~ 40MPa. The cavity pressure values selected for common plastic injection molding are listed in table 4.3. Table 4.3 cavity pressure MPa plastic varieties selected for common plastic injection high pressure polyethylene (PE) low pressure polyethylene (PE) PS as ABS POM PC cavity pressure 10 ~ 15 20 15 ~ 20 30 35 40

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