The relevant knowledge of
LCP injection molding is as follows:
1. Processing process of LCP material (liquid crystal polymer)
Key points: The LCP material should be dried before use. The temperature is about 150 °C and the time is about 4~6 hours. The residual moisture content of the LCP after dehumidification should be below 0.02%, and the dew point should be kept at -35 °C.
Note: It is recommended to use a vacuum dehumidifying dryer for the dryer. Do not use a general dryer. Because the vacuum dehumidification dryer can extract the moisture in the LCP material, the general dryer can not completely extract the moisture in the material, and it is difficult to achieve the required quality of the product.
2. LCP material injection molding process
Pay attention to the following issues when molding:
1 Proportional back pressure makes the feeding more precise and stable;
2 large products can use large back pressure, small product back pressure is small;
3 large products, if the back pressure is small, the density will be relatively small, and the surface gloss is poor;
4 High-sensitivity injection system and automatic VP (V injection pressure, P holding pressure) conversion function, so that the products are precise and stable. If necessary (such as the product is very precise), it is recommended to install a pressure sensor at the cavity gate. Make VP switching closer to reality;
6 The holding time of the beer flat product should not be too long, otherwise it will easily cause the product to warp and generate stress;
7 LCP material stays in the material tube for too long or too much residual amount, so that the LCP material is over-fired, there will be bubbles on the surface of the product. Generally, the mold is opened within 3 seconds after the end of the material melt, and the residual amount is guaranteed within 5mm;
8 If the machine is turned on again, the waste must be injected;
9 The molding cycle depends on the size, shape, thickness, mold structure and molding conditions of the product. The LCP material has good fluidity, so the filling time is relatively short, and the crystal forming speed is fast, so the molding cycle is relatively short.
3. Selection of special injection molding machine for LCP material
Must choose LCP material special injection molding machine;
The screw needs to be made of a material with better wear resistance;
The screw head uses a structure that prevents backflow;
Need a more precise temperature control system;
The nozzle part needs to be specially designed;
The feeding and injection system should be sensitive;
The capacity of the injection tube should be paid attention to the weight of the product, not too much or too little.
4. LCP material special mold process focus
1 The mold design of LCP products is very important. The glue inlet of the mold should use ordinary open mouth instead of hot nozzle. If the hot nozzle product is easy to foam, the temperature is too high and the product may overheat.
2 The general mold temperature is about 140 °C, the upper (front) mold temperature should be higher than the lower (rear) mold, because the upper (front) mold temperature is high, the meltability of the melt is not easy to cause cold glue, and the lower (rear) mold temperature is low. The product is easy to crystallize and the upper (front) bottom (back) mold temperature difference does not exceed 15 °C.
3 In terms of mold temperature selection, in order to shorten the molding cycle and prevent cloaking, a lower mold temperature should be selected; if the dimensional stability of the product is required to be high, and the occurrence of seams and insufficient filling are required, then a higher choice should be made. Mold temperature.
5. Pressure and speed
The most suitable pressure must depend on the material, the shape of the product, the mold design (especially sprues, runners, gates) and other molding conditions. However, LCP has no grade and its melt viscosity is very low, so the pressure is lower than that of ordinary thermoplastic resins.
It is a good method to use low pressure at the beginning of the molding and then slowly increase the pressure. The molded article can be molded under the pressure of 15 MPa to 45 MPa. In addition, the curing time of LCP is relatively fast, so it is easy to get good results when the speed is fast.
6. Molding cycle
The molding cycle depends on the size, shape, thickness, mold structure and molding conditions of the molded article. As mentioned above, LCP has good fluidity, so its filling time is short and the curing speed is faster, so we can get a shorter molding cycle. A representative molding cycle is from 10 seconds to 30 seconds.
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