1. Please take the horizontal screw injection machine as an example to describe the working process of the injection machine?
(1) Heating and pre plasticizing: driven by the transmission system, the screw will transport and compact the materials from the hopper forward. Under the shear and friction mixing of the heater outside the barrel, the screw and the barrel, the materials will gradually melt. 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 retreating 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 retreating.
(2) . Mold closing and locking: the mold locking mechanism pushes the template and the mold moving part installed on the moving template and the mold moving part on the moving template to close and lock, so as to ensure that sufficient clamping force can be provided to lock the mold during molding.
(3) Move the injection device forward: after the mold closing is completed, the entire injection base is pushed forward, so that the nozzle of the injection machine can fully fit with the main runner of the mold.
(4) Injection and pressure maintaining: after the mold locking and nozzle are fully fitted to the mold, the injection pressure cylinder enters the high-pressure oil, which pushes the screw forward relative to the barrel, injecting the melt accumulated at the head of the barrel into the mold cavity with sufficient pressure. The plastic volume shrinks due to the temperature drop. In order to ensure the compactness, dimensional accuracy and mechanical properties of the 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 mold gate is frozen, the pressure can be relieved.
(6) . Injection device retreat: generally speaking, after the pressure relief is completed, the screw can rotate and retreat to complete the next feeding and pre plasticizing process. After the pre plasticization is completed, the injection base will be removed from the main runner of the mold.
(7) . Mold opening and ejecting 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 and plasticizing, pressurized injection, pressure maintaining, cooling and molding, demoulding and other processes.
3. What is the classification method of injection mold?
There are many ways to classify injection molds. 1. It can be divided into vertical injection mold, horizontal injection mold and angle injection mold according to the form of the injection machine used; 2. It can be divided into thermoplastic injection mold and thermosetting plastic injection mold according to molding materials; 3. It can be divided into single cavity and multi cavity injection molds according to the number of cavities; 4. The most common classification is based on the overall structural characteristics of the injection mold. Generally, the injection mold can be divided into single parting surface injection mold, double parting surface injection mold, oblique guide pillar (bent pin, oblique guide groove, oblique slider) lateral parting and core pulling injection mold, injection mold with movable inserts, injection mold with ejection device and automatic thread removal injection mold.
4. What structure does the injection mold consist of?
There are many kinds of injection molds, and their structures are related to many factors, such as the types of plastics, the structures of plastic parts, and the types of injection machines. In general, 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 part has lateral holes or bosses, the injection mold also includes lateral parting and core pulling mechanisms.
5. What does the common gating system of the injection mold refer to?
The common gating system of an injection mold refers to the channel through which molten plastic enters the mold cavity from the nozzle of the injection machine. It includes the main runner, the branch runner, the gate and the 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; The double parting surface injection mold, also known as the three plate injection mold, has two parting surfaces.
7. Under what circumstances does the side core pulling of the injection mold with an inclined guide pillar be required?
When the side wall of the plastic part has through holes, recesses or bosses, the molded 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 an injection mold with movable inserts?
The mold with movable insert structure has the advantages of not only omitting the design and manufacturing of complex structures such as inclined guide post and slide block, reducing the mold appearance and greatly reducing the manufacturing cost of the mold, but also using movable insert in some situations where the structure such as inclined slide block cannot be arranged. The disadvantage of this method is that it has 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 on mold temperature, a temperature regulating system is required to regulate the mold temperature. In general, the injection mold of thermoplastics mainly designs the cooling system of the mold.
10. What is the checking method of clamping force?
When the high pressure plastic melt fills the mold cavity, it will produce a force that causes the mold parting surface to expand. The force is equal to the sum of the projected areas of the plastic part and the gating system on the parting surface times the pressure of the mold cavity. It should be less than the mold locking force Fp of the injection machine to ensure that there is no overflow during injection, that is, (4.4) - the rising opening force of the molten plastic on the parting surface, N.
The pressure in the mold cavity is about 80% of the injection pressure of the injection machine, usually 20~40MPa. The cavity pressure values used in common plastic injection molding are listed in Table 4.3. Table 4.3 Cavity Pressure MPa for Common Plastics Injection High Pressure Polyethylene (PE) Low Pressure Polyethylene (PE) PS AS ABS POM PC Cavity Pressure 10~15 20 15~20 30 35 40