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

Plated PC/ABS parts are widely used in the automotive, home appliance, and IT industries for their beautiful metallic appearance. Material formulation design and plating process are usually considered to be the main factors affecting PC/ABS plating performance, however, little attention has been paid to the effect of the injection molding process on plating performance.

Injection Molding Temperature

A higher injection molding temperature gives better plating performance with the assurance that the material will not crack.

At a lower injection temperature, the PC/ABS material has poor flowability and the injection molded product has large internal stress, which is released during the roughing process and leads to uneven etching on the surface of the product, resulting in the poor appearance of the plated product and poor plating bonding.

A higher injection molding temperature can reduce the residual internal stress of the product and improve the plating performance of the material. Studies have shown that when the injection temperature is increased to 260°C-270°C, the plating bonding is increased by about 50% and the surface appearance is greatly reduced compared to the injection temperature of 230°C.

However, the injection molding temperature should not be too high. If the cracking temperature of the material is exceeded, it will lead to the poor surface appearance of the injection molded products, which will affect the plating performance.
 

Injection speed and pressure

Lower injection pressure and proper injection speed are beneficial to improve the plating performance of PC/ABS.

Excessive injection pressure will lead to excessive extrusion of molecules inside the product, resulting in higher internal product stress, which in turn will lead to uneven roughening and poor plating bonding.

Increase the injection speed to increase the shear at the gate position, which will increase the fluid temperature and improve the fluidity of the whole material, which will help to fill the product and reduce the internal stress; however, too much shear will lead to the cracking of the material and produce air marks, peeling and burrs. 

Pressure-holding pressure and pressure-holding switching point

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

Mold temperature

High mold temperature is beneficial to improve the plating performance of the material.

In the low mold temperature, the material fluidity is poor, and the extrusion and stretching between molecules during the filling process leads to the serious orientation of the molecular chain after the product cools down, which results in the high internal stress of the product and the poor plating performance.

The actual mold temperature setting needs to be combined with the mold water circuit, heating method, and molding cycle requirements to set, without affecting other performance, the mold temperature as high as possible; control the mold temperature, but also maintain a uniform distribution of mold temperature, uneven mold temperature distribution, will lead to uneven shrinkage of internal stress and thus affect the plating performance.

Screw speed

A lower screw speed is beneficial to improve the plating performance of the material.

The screw speed is set to control the dosing time of the plastic, i.e., the time it takes for the plastic to enter the tube, be mixed by the screw, and be delivered to the nozzle.

Screw speed also affects the uniformity of plasticization, too fast screw speed will make the material in the screw shear aggravated, the melt temperature rises sharply, and the faster the screw speed, the worse the mixing effect of plastic, forming the melt temperature difference increases, making the filling flow and cooling also cause differences, which is one of the main reasons for the formation of internal stress in the product.

Therefore, in general, under the premise of ensuring the melting of the material, the screw speed is set to make the metering time slightly shorter than the cooling time.

To sum up.

The injection molding process of injection temperature, injection speed and pressure, mold temperature, holding pressure, screw speed, etc. will have an effect on the plating performance of PC/ABS.

The most direct adverse effect is the high internal stress of the product, which will affect the uniformity of etching in the roughing stage of plating, and then affect the plating bond of the final product.

In conclusion, the plating performance of PC/ABS material can be significantly improved by setting the appropriate injection molding process and trying to reduce the internal stress of the material, taking into account the product structure, the state of the mold, and the state of the molding machine.