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

Answer 1

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.

I. Injection temperature

In the case of ensuring the material will not crack, a higher injection melt temperature can get better plating performance.

At lower injection temperatures, PC/ABS material has poor flowability, and the injection molded product has large uneven shrinkage internal stress, which will be released during the roughing process and lead 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 bond 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 in turn will affect their plating performance.

2. Injection speed and pressure

Lower injection pressure and proper injection speed can improve the plating performance of PC/ABS.

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

Increasing the injection speed can increase the shear at the gate position and lead to the increase of fluid temperature, which will improve the fluidity of the whole material and facilitate the filling of the product and reduce the excessive internal stress of the product; however, too much shear will lead to the cracking of the material and produce gas marks, peeling and burrs.

3. Holding pressure and holding pressure switching point

Too high holding pressure and late switching position of holding pressure will easily lead to overfilling of the product and stress concentration at the gate position and high residual stress inside the product.

Therefore, the actual product filling state should be combined to set the holding pressure and holding pressure switching point.

4. 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 the molecules in the filling process lead to the serious orientation of the molecular chain of the product after cooling down, and the internal stress of the product is large, and the plating performance is poor.

On the contrary, in the high mold temperature, the material fluidity is good, which is conducive to the filling, the molecular chain is in the natural curl state, the large internal stress of the product is small, and the plating performance is greatly improved.

The actual mold temperature setting needs to be combined with the mold water circuit, heating method, and plastic injection molding cycle requirements to set, without affecting other performance, 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.

5. Screw speed

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

The screw speed setting is to control the plastic metering time, that is, the plastic into the tube to accept the screw mixing and delivery time 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.