Electroplated PC/ABS parts are widely used in automobiles, home appliances and IT industries due to their beautiful metallic appearance. Material formulation design and electroplating process are usually considered to be main factors affecting electroplating performance of PC/ABS. However, few people pay attention to impact of injection molding process on electroplating performance.

Under circumstance that material will not crack, higher injection temperature can get better electroplating performance.
At lower injection temperatures, fluidity of PC/ABS materials is poor, and injection molded products have greater internal stress. Stress is released during roughening process, resulting in uneven etching on the surface of product, which in turn leads to poor appearance of electroplated product and poor electroplating bonding force.
Higher injection temperature can reduce residual internal stress of product, thereby improving electroplating performance of material. Relevant studies have shown that compared with product with an injection temperature of 230℃, when temperature is increased to 260℃-270℃, adhesion of coating is increased by about 50%, and surface appearance defect rate is also greatly reduced.
However, injection temperature should not be too high. If pyrolysis temperature of material is exceeded, appearance of injection product surface will be poor, which will affect its electroplating performance.

 

Lower injection pressure and proper injection speed are beneficial to improve electroplating performance of PC/ABS.
Excessive injection pressure will cause excessive squeezing of internal molecules of product, resulting in higher internal stress of product, resulting in uneven product coarsening and poor electroplating bonding force;
Properly increasing injection speed can increase shear at gate position, leading to an increase in fluid temperature, which in turn will increase fluidity of entire material, which is conducive to filling of product and reduces internal stress of product; but too much shearing will cause cracking of material, resulting in air marks, peeling, burrs and other problems.

Too high holding pressure and late holding pressure switching position can easily lead to over-filling of product, stress concentration at gate position, and higher residual stress inside product. Therefore, it is necessary to set holding pressure and holding pressure switching point in combination with actual product filling state.

High mold temperature is beneficial to improve electroplating performance of material.
In the state of low mold temperature, material has poor fluidity. Due to extrusion and stretching between molecules during filling process of product, molecular chain orientation of material after product is cooled down is serious, internal stress of product is large, and electroplating performance is poor; On the contrary, in the state of high mold temperature, material has good fluidity, which is conducive to filling, molecular chain is in a natural curl state, internal stress of product is small, electroplating performance is greatly improved.
Actual mold temperature setting needs to be set according to requirements of mold waterway, heating method and molding cycle. Without affecting other properties, mold temperature should be increased as much as possible; while controlling mold temperature, it is also necessary to maintain a uniform distribution of mold temperature. Uneven mold temperature distribution will cause uneven shrinkage internal stress and affect plating performance.

Lower screw speed is beneficial to improve electroplating performance of material.
Setting of screw speed is to control measuring time of plastic, that is, time for plastic to enter barrel and receive screw mixing, then deliver it to nozzle.
Screw speed also affects uniformity of plasticization. Too fast screw speed will increase shear of material in screw, melt temperature will rise sharply. Moreover, the faster screw speed, the worse mixing effect of plastic, the greater difference in melting temperature, difference in filling flow and cooling, which is one of main reasons for formation of internal stress in product.
Therefore, in general, under premise of ensuring melting of material, screw speed is set to make metering time slightly shorter than cooling time.

In injection molding process, injection temperature, injection speed and pressure, mold temperature, holding pressure, screw speed, etc. will all affect electroplating performance of PC/ABS.
The most direct adverse effect is excessively high internal stress of product. Excessive internal stress will affect uniformity of etching in electroplating coarsening stage, then affect electroplating bonding force of final product.
In short, it is necessary to combine product structure, mold status and molding machine status, and try to reduce internal stress of material by setting appropriate injection process, which can significantly improve electroplating performance of PC/ABS materials.