LCP injection molding process guide:?
1. barrel temperature?
Usually the barrel temperature, nozzle temperature, material melting temperature as shown in Table 1.
If the life of the screw is considered, the temperature difference between the rear, center, and front can be reduced. To prevent nozzle drooling, the nozzle temperature can be 10°C lower than that shown in the table, and the temperature can be set 20°C higher than that shown in the table if flowability is to be improved, but care must be taken in the following cases.?
When lowering the barrel temperature: the retention time is too long, it will not cause aging of the pellets in the barrel, and will not produce corrosive gases, so the retention time is long generally does not produce any major problems. However, if the molding is interrupted for a long time, please reduce the barrel temperature, and when molding again, it is better to throw away a few molds.
Cylinder temperature for each grade of molding (℃)?
Fig. 1 Relationship between cylinder retention time and tensile strength retention rate
2. Mold temperature?
The mold temperature at which LCP can be molded is in the range of 30℃-150℃. But we generally set the mold temperature around 70℃-110℃. In order to shorten the molding cycle, to prevent flying edge and deformation, you should choose a low mold temperature; if you require the product dimensional stability (especially for products under high temperature conditions), to reduce the generation of fusion joints and to solve the problem of underfilling, etc., you should choose a high mold temperature.
Figure 2 Relationship between retention time in the cylinder and tensile retention rate
3. Plasticization?
The speed of the screw is normally 100 rpm. In the case of materials containing glass fibers or carbon glass fibers (e.g. A130, A230, etc.), we have to choose a lower speed in order to prevent the glass fibers from being broken. In addition, the back pressure is as low as possible ?
When the barrel temperature is set to 300°C, the effect of the material retention time in the barrel on the mechanical properties and color is shown in Figure 1 - Figure 2. The mechanical properties of the unfilled grade are slightly reduced when it is left in the barrel for 15 minutes. The mechanical properties of the GF grade remain basically unchanged when it is left in the cylinder for 60 minutes.
There is a slight change in color (?E) for either grade. The weight loss obtained by the thermal balance is shown in Fig. 4. The temperature at which decomposition gradually begins is about 460°C, much higher than the usual molding temperature.?
Fig. 3 Residence time and discoloration (?E) in the cylinder
4. Pressure and speed?
The optimum pressure must depend on the material, the shape of the product, the design of the mold (especially the gate, runners, gates) and other molding conditions. But LCP without any grade its melt viscosity is very low, so the pressure is lower than the general thermoplastic resin. It is better to use low pressure at the beginning of molding and then slowly increase the pressure. Most of the molded products can be molded under the pressure of 15MPa-45MPa. In addition, the curing time of LCP is relatively fast, so it is easy to get good results with fast speed.
? Fig. 4 Thermal decomposition curve
5. Molding cycle ?
The molding cycle depends on the size, shape, thickness, mold structure and molding conditions. As mentioned above LCP has good flowability, so it has shorter filling time and faster curing speed, so we can get shorter molding cycle. The representative molding cycle is 10 seconds-30 seconds.