Main process parameter categories
The important conditions of the injection molding process include temperature, pressure and the corresponding action time of each parameter, which affect the plasticizing flow and cooling.
It can be said that to ensure qualified and stable quality of plastic parts, the necessary conditions are accurate and stable process parameters.
In principle, when adjusting the process parameters, the process parameters should be adjusted according to the following criteria When adjusting the process parameters, in principle, according to the order of pressure - time - temperature to adjust the machine, should not change at the same time
Two or more parameters should not be changed at the same time in order to prevent the process conditions from flocculating and causing unstable quality of plastic parts.
The main process parameters of injection molding are as follows.
(1) Barrel temperature
The melt temperature is very important and the injection cylinder temperature used is only a guideline. The melt temperature can be measured at the injection nozzle
or by using the air injection method. The temperature setting of the injection cylinder depends on the melt temperature, screw speed, back pressure, injection volume and injection cycle.
back pressure, injection volume and injection cycle. If you have no experience in processing a particular grade of plastic, you should start with the lowest setting.
Start with the lowest setting. The injection cylinders are divided into zones for ease of control, but not all are set to the same temperature. If operating
If operating for long periods of time or at high temperatures, the temperature of the first zone should be set to a lower value, as this will prevent premature melting and diversion of the plastic.
This will prevent premature melting and shunting of the plastic. Make sure the hydraulic fluid, hopper closers, molds and injection cylinders are at the correct temperature before injection begins.
before injection begins. The barrel temperature is generally increased gradually from back to front to allow for uniform plasticization.
(2) Melt temperature
Melt temperature plays a major role in the fluidity of the melt, plastic does not have a specific melting point, the so-called melting point is
A molten state of the temperature band, the structure and composition of the plastic molecular chain is different, and thus the impact on its liquidity
Also different, rigid molecular chain by the temperature is more obvious, such as PC, PPS, etc., while the flexible molecular chain such as PA, PP, PE
The fluidity is not obvious by changing the temperature, so the reasonable injection temperature should be adjusted according to the different materials.
(3) Mold temperature
Some plastic materials need higher mold temperature due to high crystallization temperature and slow crystallization speed, some need higher mold temperature due to control of size and deformation, or mold release.
Size and deformation, or the need for mold release, to a higher temperature or lower temperature, such as PC generally requires more than 60 ℃.
And PPS in order to achieve a better appearance and improve the flow, the mold temperature sometimes requires more than 160 ℃, and thus the mold temperature to improve the appearance of the product, deformation, and the product is not the same.
The temperature of the mold to improve the appearance of the product, deformation, size, mold and other aspects of the role can not be underestimated. In mold design and
In mold design and molding process, it is important not only to maintain the right temperature but also to distribute it evenly.
Uneven mold temperature distribution can lead to uneven shrinkage and internal stress, thus making the molded product susceptible to deformation and warpage.
warping.
The temperature of the mold affects the rate of hardening of the plastic in the mold cavity, too low will make filling more difficult as well as not properly
Too low will make filling difficult and harden without proper shrinkage (or recrystallization), making the molded products have more filling and residual thermal stress; too high will show burrs and require longer time.
If the temperature of the mold is too high, there will be burrs and longer cooling time. The mold temperature has a great influence on the intrinsic performance and performance quality of the molded parts.
For the plastic parts with high surface requirements, the mold temperature requirement is higher.
(4) Injection pressure
The resistance required for the melt to overcome the advancement directly affects the size, weight and deformation of the product.
Different plastic products require different injection pressure, for materials such as PA, PP, etc., increased pressure will make its liquidity significantly improved.
The injection pressure size determines the density of the product, i.e. the appearance of glossiness. It does not have a fixed value, and the more difficult it is to fill the mold, the more the injection pressure increases.
the more difficult it is, the injection pressure also increases. The injection pressure setting is mainly to control the oil pressure so that it is sufficient to push the screw to reach the set injection speed.
The injection pressure is set so that the oil pressure is sufficient to push the screw to the set injection speed. As the characteristics of each plastic are different, the degree of ease of flow is also different.
The melt temperature of the same material is different and the viscosity will also change, and different products, mold design and mold temperature will make the material
In order to maintain the same injection speed under different conditions, we have to change the injection pressure to overcome the resistance caused by the melt flow.
To maintain the same injection speed under different conditions, the injection pressure must be changed to overcome the resistance caused by the melt flow. Injection pressure differs from holding pressure in that the injection pressure mainly affects the filling phase, while the holding pressure is different.
is the filling phase, while the holding pressure affects the cooling phase.
For plastics with poor flowability, the injection pressure should be large, and for thin-walled rubber with high cavity resistance, the injection hardness
force should also take the maximum value.
(5) Injection speed
The injection speed is set to control the melt filling time and flow pattern, which is the most important condition in the flow process.
It is the most important condition in the flow process. The correct adjustment of the injection speed has an absolute influence on the quality of the product appearance.
The basic principle of injection speed setting is to match the flow of plastic in the mold cavity according to the size of the section formed by the flow.
The basic principle of injection speed setting is to match the size of the cross section formed by the flow of plastic in the mold cavity, and to follow the procedure of slow → fast → slow and as fast as possible (to confirm the appearance of defects).
The injection speed is achieved by adjusting the amount of oil supplied to the injection cylinder per unit of time, and generally speaking (without causing side effects) using as high as possible.
Generally speaking (without causing side effects), try to use high injection speed to ensure the fusion strength and apparent quality of the molded part, while the relatively low
The relatively low pressure also reduces the internal stress of the plastic part and improves the strength. The use of high pressure and low velocity feeding can make the flow rate smooth and
The shearing speed is small, the size of the plastic part is stable, and the shrinkage defect is avoided.
(6) Time parameters (molding cycle)
Injection time and cooling time are the basic components, and their length has a decisive influence on the quality of injection molded parts.
The mould filling time is generally not more than 10s. The holding time is longer and related to the wall thickness of the plastic part (wall thickness is taken for a long time) to ensure the minimum shrinkage.
The holding time is longer and is related to the wall thickness (wall thickness is taken as long time) to ensure the minimum shrinkage. The cooling time depends on the crystallinity of the plastic, the thickness of the product, the temperature of the mold and other factors, depending on the specific situation.
The cooling time depends on the crystallinity of the plastic, the thickness of the product, the temperature of the mold and other factors, depending on the specific situation.