The following seven parameters must be noted when setting up the
injection molding process:
1. Injection speed:
The injection speed is slow, the plastic is carried out in the cavity, there will be more heat loss, the flow viscosity increases, and the use pressure loss increases;
Higher rate of fire can often achieve higher precision, less deformed molded products, only through the thin and thick flesh, intense changes, corners and other areas, easy to appear poor appearance, and easy to produce poor exhaust, approval, and pressure Switching incorrectly and other issues.
2. Pressure switching:
Switching too early, the finished product size is easy to be insufficient, even short shots, and the surface is sunken, otherwise the over-compression is formed, the small size is too large, the flashing edge, whitening, deformation, and the large mold is damaged;
The switching of the holding pressure usually has a control method such as an injection stroke (position) and time.
3. Pressure holding size setting:
If the holding pressure is too high, excessive filling will occur, which will cause the plastic that has entered the cavity to flow backwards;
The correct and proper pressure holding setting should be based on the principle that the screw can continue to advance to the lower pressure of the target point after passing the pressure maintaining switching point;
During the holding phase, the internal pressure of the cavity gradually decreases due to the cooling of the plastic, so the holding pressure should be appropriately adjusted downward, otherwise it is easy to form high stress residual.
4. Setting of pressure holding time:
The holding time should be maintained until the gate condenses. It is meaningless for too long, but if the time is too short, it is easy to reverse flow, so that the position of the near gate is easy to be recessed and the size is insufficient;
Whether the retention time is appropriate or not should usually be judged by the stability of weight;
The gate is small, the mold temperature is low, and the dwell time should be set short. If the situation is reversed, the time is set.
5. Cooling time setting:
The plastic is cooled in the cavity, most of which starts at the end of the pressure holding switch, and the theoretical cooling time = dwell time + post-cooling time;
The theoretical time required should be based on the principle that the product can be smoothly ejected (not deformed), and its length varies depending on the thickness of the molded product, the material, and the cooling rate of the mold;
The gate thickness and mold temperature will affect the dwell time (the cooling time set by the machine, that is, the post-cooling time). If the gate is large and the mold temperature is high, the appropriate dwell time will be lengthened. Otherwise, the dwell time should be appropriately reduced.
6. Modal temperature setting:
If the mold temperature is set too low, the melt flows in the cavity, the temperature drops faster, and the material flow resistance increases, so the pressure loss increases, the internal stress increases, and the internal pressure of the cavity is increased.
7. High mode temperature setting:
Increase the crystallinity and uniform structure of the molded product, reduce the internal stress residual, deformation and increase the strength, reduce the flow resistance of the material during filling, reduce the pressure loss, and make the product look good, but it is prone to burrs and increase the near gate area. The depression of the far gate portion is reduced, the bonding line is made smaller, and the cooling time is increased.
