How to optimize the injection molding process and improve the electroplating performance of PC/ABS?

How to optimize the injection molding process and improve the electroplating performance of PC/ABS?

Electroplated PC/ABS parts, with their stunning metallic appearance, are widely used in the automotive, home appliance, and IT industries. Material formulation and plating process are generally considered the primary factors affecting PC/ABS plating performance, but less attention is paid to the impact of injection molding on plating performance.

Injection Molding Temperature

While ensuring material cracking, higher injection molding temperatures can achieve better plating performance. At lower injection molding temperatures, PC/ABS material has poor fluidity, resulting in high internal stress in the molded part. This stress release during the roughening process leads to uneven etching on the surface, resulting in poor appearance and poor plating adhesion.

Higher injection molding temperatures, on the other hand, can reduce residual internal stress, thereby improving the material's plating performance. Research has shown that compared to products molded at 230°C, increasing the temperature to 260-270°C increases the plating adhesion by approximately 50%, while significantly reducing the surface appearance defect rate. However, the injection molding temperature cannot be too high. If it exceeds the cracking temperature of the material, it will lead to poor appearance of the surface of the injection molded product and affect its electroplating performance.

Injection Speed ​​and Pressure
Lower injection pressure and appropriate injection speed can improve the electroplating performance of PC/ABS.
Excessive injection pressure can lead to excessive molecular compression within the part, resulting in high internal stress, uneven part coarsening, and poor electroplating adhesion.
Increasing the injection speed appropriately can increase shear at the gate, raising the fluid temperature and improving the overall material flow, facilitating part filling and reducing internal stress. However, excessive shear can cause material cracking, resulting in air marks, peeling, and burrs.

Holding Pressure and Holding Switch Point
Excessive holding pressure and a late holding switch point can easily lead to overfilling, stress concentration at the gate, and high residual stress within the part. Therefore, the holding pressure and holding switch point should be set based on the actual filling conditions of the part.

Mold Temperature
High mold temperature can improve the material's electroplating performance. At low mold temperatures, the material has poor fluidity. Molecular compression and stretching during the filling process can lead to severe molecular chain orientation after cooling, resulting in high internal stress in the molded part and poor electroplating performance. Conversely, at high mold temperatures, the material has good fluidity, facilitating filling. The molecular chains are naturally curled, reducing internal stress in the part and significantly improving electroplating

performance.

The actual mold temperature setting should be considered in conjunction with the mold's cooling system, heating method, and molding cycle requirements. The mold temperature should be raised as high as possible without affecting other performance characteristics. While controlling the mold temperature, it is also important to maintain a uniform temperature distribution. Uneven mold temperature distribution can lead to uneven shrinkage stress, which in turn affects electroplating performance.

Screw Speed

A lower screw speed improves the material's electroplating performance.

The screw speed setting controls the plastic metering time—the time it takes for the plastic to enter the barrel, be kneaded by the screw, and be conveyed to the nozzle. Screw speed also affects plasticization uniformity. Excessively fast screw speeds increase material shear within the screw, leading to a sharp increase in melt temperature. Furthermore, faster screw speeds impair plastic mixing, increasing melt temperature variations and causing variability in filling, flow, and cooling. This is one of the main causes of internal stress in the product.

Thus, generally speaking, while ensuring material melting, the screw speed should be set so that the metering time is slightly shorter than the cooling time.

Summary:

Injection temperature, injection speed and pressure, mold temperature, holding pressure, and screw speed all affect the electroplating performance of PC/ABS during the injection molding process.

The most direct negative impact is excessive internal stress in the product. Excessive internal stress can affect the uniformity of etching during the electroplating roughening stage, further impacting the electroplating adhesion of the final product.
In short, by considering the product structure, mold conditions, and molding machine conditions, and by optimizing the injection molding process to reduce internal stress in the material, the electroplating performance of PC/ABS can be significantly improved.