About injection molding, you don’t know the dead angle knowledge.
First, why should the plastic parts be designed in the form of rounded corners?
The sharp corners of the plastic parts will generate stress concentration during molding, and will be easily cracked when subjected to impact vibration. The plastic parts are designed to be rounded, which not only avoids stress concentration, but also improves the strength of the plastic parts and also facilitates the filling flow of the plastic parts. At the same time, the corresponding part of the mold cavity is also rounded, so that the mold does not crack due to stress concentration during quenching and use, which improves the firmness of the mold.
Second, which components are made up of plastic?
Plastic is composed of resin and additives. Resin is the main component of the plastic. He determines the type and basic properties of the plastic. The role of additives is to improve the molding process performance, improve the performance of plastic parts and reduce costs. Additives include fillers, plasticizers, colorants, lubricants, stabilizers, curing agents, and the like.
Third, what is the role of plasticizers?
When a plasticizer is added to the resin, the distance between the molecules is increased, and the force between the macromolecules is weakened, so that the resin molecules are easily slipped, so that the plastic has good plasticity and flexibility at a lower temperature. Although the addition of plasticizer can improve the processability and performance of the plastic, it also reduces some properties of the resin, such as hardness/tensile strength.
Fourth, describe the role and types of stabilizers
The addition of a stabilizer to the plastic prevents or inhibits degradation of the resin during processing or use. The so-called degradation is the reaction of the polymer under the influence of external factors, the macromolecular chain breaks or the molecular structure is harmfully changed. The degradation of the polymer greatly reduces the performance of the polymer, and it cannot be processed or even completely lost. According to the role played by the stabilizer, it can be divided into the following three types: 1. Heat stabilizer 2, light stabilizer 3, antioxidant
5. What are the three common physical states of thermoplastics after they are heated? What kind of molding can be done separately?
1. Glass state; in this state, it can be cut by car, milling, drilling, etc. It is not suitable for large deformation processing.
2. High-elastic state: In this state, vacuum forming, calendering, hollow molding, stamping, forging, etc. can be performed.
3. Viscous flow state: The deformation of plastic in this state has no reversible properties, and its shape is always maintained once formed and cooled. In this state, molding processing such as injection molding, blow molding, and the like can be performed.
What are the characteristics of compression molding?
The advantage of compression molding is that an ordinary hydraulic machine can be used; and the compression mold has a simple structure; the production process is also relatively simple; the internal structure of the compressed plastic part is less; the performance is uniform; the molding shrinkage rate of the plastic part is small. The characteristics of compression molding are: long molding cycle, low production efficiency, high labor intensity, and manual operation is not easy to achieve automatic production; plastic parts often have flashing edges, and the dimensional accuracy in the height direction is difficult to control; the mold is easy to wear, Therefore, the service life is short.
7. When designing the mold, the mold must be checked for the selected mold and the selected injection machine (from the process, the mold part parameters).
The maximum injection volume, injection pressure, clamping force of the injection machine should be checked, and the relevant dimensions of the mold part, the mold opening stroke, and the ejection device should be checked.
8. What is the role of the gating system? What are the components of the injection molding system?
A: The function of the gating system is that the plastic melt is filled into the cavity in a smooth and sequential manner, and the injection pressure is fully transmitted to various parts during the filling and solidification process to obtain a tightly structured and clearly shaped plastic part. The injection molding system consists of a main flow channel, a runner port, a gate, and a cold hole.
9. What problems should I pay attention to when designing the runner?
Answer: The design of the runner should be such that the flow direction of the plastic can be smoothly converted and the cavity can be refilled as quickly as possible. The temperature in the flow is reduced as low as possible, and the plastic melt should be evenly distributed to each cavity.
Should pay attention to the design
1. The cross-sectional dimensions of the runners depend on factors such as the size and wall thickness of the plastic part, plastics and variety, injection rate and length of the runner.
2. The surface of the runner should not be very smooth, and the surface roughness should be 1.6um, so that the flow velocity of the outer layer of the flow channel is low, and it is easy to cool to form a fixed skin layer, which is beneficial to the heat preservation of the runner.
10. What is the principle of gate selection?
A: The choice of gate location should pay attention to:
1. Avoid causing melt fracture
2. The location of the gate should be able to avoid the occurrence of weld lines. If it is unavoidable, they should not be in the functional area, load area, and appearance area.
3. Conducive to melt flow and feeding.
4. Conducive to gas discharge in the cavity.
5. Prevent the flow from deforming the core or insert.
6. Ensure that the flow ratio is within the allowable range.
11. What are the factors that affect the core pulling force?
Answer: The factors affecting the core pulling force are the core pulling resistance caused by the tightening force and the frictional force of the mechanical transmission. For the plastic parts of the casing without the through hole, the resistance caused by atmospheric pressure should also be taken into consideration when pulling the core. .
What is the difference between the single-faceted and double-fractal injection molds?
Answer: The single-split injection mold is also called two-plate injection mold. There is only one fractal surface. After the single-section mold is opened, the plastic parts together with the pouring system are left on the side of the movable mold and taken out from the same surface shape. . The double-split injection mold, also known as the three-plate injection mold, has two sub-surface shapes. Compared with the single-section shape, a flow path plate that can be moved at a fixed distance is added between the movable mold and the fixed mold. The cast aggregate is taken from two different facets.
13. What is the role of the temperature regulation system?
Answer: During the mold production process, the mold temperature will directly affect the filling of plastics, the shaping of plastic parts, the molding cycle and the quality of plastic parts. In the molding process, the plastic mold is a heat exchanger. To maintain the heat balance of the mold itself, the mold should generally be set to a temperature control system. In the mold design, the temperature of the mold should be adjusted in different ways according to different conditions such as plastic type and mold size.
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