Setting of injection molding pressure parameters
During the injection action, in order to overcome the flow resistance of the molten rubber through the nozzle, sprue and mold cavity, etc., the injection screw must exert sufficient pressure on the molten rubber to complete the injection. The injection molding machine is mainly composed of injection and clamping. Pressure parameters such as injection pressure and clamping pressure (clamping force) are important technological parameters of injection molding. Injection molding pressure parameters include injection pressure, clamping pressure, holding pressure, back pressure, and other operating pressures. The specific pressure parameters are as follows:
- Injection pressure
Injection pressure, also known as injection pressure, is the most important injection molding pressure parameter. It has a decisive effect on the flow properties of the molten rubber and the filling of the mold cavity, and also has a direct impact on the dimensional accuracy and quality of the injection molded products. Injection pressure parameter settings are set according to different models.
Among the common models, there are generally one-level, two-level, and three-level injection pressure. In the specific production, the pressure parameters should be reasonably selected and set according to the plastic raw materials and the specific molding product structure.
- Setting of clamping pressure parameters
The clamping pressure is set from the low pressure clamping, through the high pressure clamping, until the clamping is terminated. The clamping action is divided into three stages. At the beginning of the clamping, the pressure parameters required for the rapid movement of the template are set to save cycle time and improve efficiency.
When the clamping action is about to end, in order to protect the mold, clear the inertia impact, and reduce the clamping pressure parameters. When the mold is completely closed, in order to achieve the preset clamping force, increase the setting value of the clamping pressure parameter.
- Setting of holding pressure
Holding pressure is to continue to compact the melted material in the horizontal cavity after the injection is completed, to fill and shrink the gaps formed by the cooling and molding shrinkage of the product in the cavity, and to densify the product. The holding pressure ensures that the cavity pressure is constant until the gate is solidified.
The holding time is often set to control the holding pressure. The holding pressure determines the parameter size of the feeding displacement, and determines the consistency, uniformity, compactness and other weight properties of the product quality, which is very important for improving product quality and production efficiency. significance. The general principle for setting the holding pressure parameters is that the holding pressure is slightly less than the filling force, and the gate holding time is longer than the curing time.
- Setting of back pressure parameters
The back pressure is generated during the plasticization and metering process of the plastic material in the barrel. At the top of the screw and the front end of the melt, the pressure on the molten rubber when the screw rotates and retreats is often called the plasticizing pressure. Back pressure negative force screw back too fast to ensure uniform and fine plasticizing process.
Appropriate setting of the back pressure parameter can increase the internal stress of the molten compound, improve the uniformity and mixing effect, and improve the plasticizing ability of injection molding.
Setting of injection molding flow parameters
Flow parameters include injection speed, melt speed, mold opening speed, mold clamping speed, etc.
1) Injection speed
The injection speed has a direct impact on the flow properties of the molten compound, the molecular arrangement direction and surface state in the plastic product. The injection speed promotes the flow of the molten rubber, which generates a uniform shear force between adjacent flow layers, and stably promotes the filling of the molten rubber, which has a significant impact on the quality and accuracy of injection molding products. The injection speed and injection pressure complement each other and are used together.
The setting of the injection speed generally starts from the first stage of glue injection, and goes through the second stage of glue injection ~~~~ until the end of the glue injection. The size setting of the injection speed is also determined by combining the characteristics of the plastic raw materials and the shape, size, precision and other comprehensive parameters of the design of the injection molding mold. The speed of the injection speed will affect the quality and quality of the molded product.
2) Mold clamping and mold opening speed
The parameter settings of mold clamping and mold opening speed are basically the same as the pressure parameter settings. For example, there are three stages of mold opening speed. In the first stage, in order to reduce mechanical vibration, in the initial stage of mold opening action, the moving template is required to move slowly. This is because the injection molded product is in the cavity. If the mold is opened quickly, there are The possibility of damaging the plastic parts, too fast mold opening can also produce huge noise;
In the second stage of mold opening, in order to shorten the cycle time, the moving platen moves quickly to improve the efficiency of the machine; in the third stage, when the moving platen is close to the end position of mold opening, in order to reduce the inertia impact, the mold opening speed is slowed down. Taking all factors into consideration, stability, speed and efficiency are the purpose of setting speed parameters.
Setting of injection molding temperature parameters
The injection molding temperature parameter is the core content of the injection molding process, which is directly related to the quality of the injection molded product, and affects the plasticizing flow and the setting of the time parameters of each process of the molded product. The general temperature parameters mainly include the heating temperature of the melt, the nozzle temperature, the mold temperature, the material temperature, etc.
- Melting barrel temperature setting
Injection molding is to heat the plastic, and uniformly plasticize the granular raw material into a molten rubber in the barrel to ensure that the molten rubber can be smoothly filled. The barrel temperature generally increases gradually from the hopper mouth to the nozzle. Because the plastic is gradually plasticized in the barrel.
The friction heat generated by the shearing action in the screw groove directly affects the temperature, so the temperature parameter setting is carried out in stages. Usually, the barrel is divided into front, middle and rear heating sections, and the required parameters are set respectively. The temperature of the molten compound is generally higher than the temperature at which the plastic flows and the melting point of the plastic, and lower than the decomposition temperature of the plastic.
In actual production, it is often determined by experience or according to the situation of injection molded products. If the temperature of engineering plastics is higher, the temperature of the barrel can be appropriately set higher to make the plastics fully plasticized.
- Nozzle temperature parameter setting
The nozzle is the hub connecting the mold cavity gate, runner and gate in the barrel. The nozzle temperature is set reasonably, the flow performance of the molten rubber is suitable, and it is easy to fill the mold. At the same time, the properties of plastic products such as welding strength and surface gloss can be improved.
If the temperature of the nozzle is too low, the nozzle will be blocked by the cold material or the gate and runner of the gating system will not be produced normally and smoothly, and the product will have cold material spots due to the cold material, which will affect the quality of the plastic product; If the nozzle temperature is too high, it will lead to the excessive decomposition of the molten rubber, resulting in the decline of the physical and mechanical properties of the plastic products. Nozzle temperature setting Generally, temperature setting is performed to fully maintain the nozzle temperature at a constant temperature.
- Setting of mold temperature parameters
The mold temperature generally refers to the temperature of the inner wall of the transverse cavity and the contact surface of the plastic product. Mold temperature has a great influence on the appearance quality and performance of plastic products processed by precision injection molding. The setting of mold temperature parameters is often determined by the size and structure of the plastic product, the characteristics of the plastic material, and the process conditions of the plastic product.
The setting of the mold temperature is all cooling for the molten rubber. Controlling the mold temperature can make the plastic molded products cool and form, providing conditions for smooth demoulding; The degree of heat dissipation of the products in the cavity is consistent, so as to avoid product performance degradation due to internal stress and ensure product quality.
- Material temperature
Plastic raw materials need to be processed before injection molding. Because the raw materials will absorb moisture in the atmosphere during storage and transportation.
Setting of injection molding time parameters
The injection molding time parameter is an important parameter to ensure normal production. It directly affects labor production efficiency and equipment utilization. Usually, the time required to complete an injection molding is called the molding cycle. The molding time includes injection time, cooling time, low-pressure mold clamping time, ejector pin time, cycle time, glue melting time, mold opening time, blowing time, etc.
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