How to chrome plastics

In the world of 3D printing, there is an increasing need to increase the manufacturing possibilities of all types of parts and finishes, to help the evolution of the industry. In this case you will find the chrome plating of parts made with a 3D FDM printer.

The appearance of new materials, such as PC-ABS has revolutionized 3D FDM printing and not only because it is a material with high mechanical properties and resistance to adverse environments, but also because it is one of the most used plastics when it comes to get excellent surface chrome. The chrome plating of plastic parts is used to make decorative or non-functional pieces, which show an identical finish to a chromed metal but much lighter and cheaper.

Image 1: Polymaker PC-ABS printed part. Source: Polymaker

Because of plastics are non-conductive materials of electricity, it is necessary to subject them to a series of operations of high toxicity and difficult control so that they are able to capture the layers of metal that are part of the chromium plating. In order to achieve an ideal, uniform and shiny finish, it is necessary to apply a layer of nickel to the plastic part for shine and a component that ensures the adhesion of copper.

Once the pre-chrome treatment has been carried out, the next step is to remove all types of dirt that may exist on the surface of the piece with organic solvents (ethanol), which also eliminates possible oxides. This step is performed in ultrasonic washers for 5 - 20 minutes to ensure that all areas of the part are completely free of debris. With the piece completely clean, it is placed in a container with chromic acid solution (20 - 30 %) at a temperature of 80 ºC. The contact of the ABS or PC-ABS with this solution causes the reaction of one of the components of these materials, resulting in micropores along the entire surface of the piece, microporesity necessary for the products of the following steps to adhere . The piece is washed again, but this time with distilled water, then it is immersed in a 1 % palladium solution at a temperature of 70 ºC and subsequently dried with hot air blowers, obtaining a conductive piece of electricity.

The next step is to attach the piece to a copper conductor (cathode), through which the current passes and submerge the whole assembly in a copper bath at a temperature of 70 °C. When introducing the activated plastic (conductor of electricity) with palladium, it leaves the microporous surface to allow the copper to enter, producing a thin layer of copper. Once copper is obtained on the surface, it is thickened with a conventional electrolytic bath to increase the resistance of the surface finish. The chromium layer is produced on the second copper layer by electrodeposition in a chromic acid bath. In this way, apart from chroming, nickel, silver, tan, etc., parts made with a 3D FDM printer and filaments containing ABS (ABS or PC-ABS) are achieved.

Image 2: Chrome PC-ABS part. Source: Metal Products Factory

If you need to get a chrome effect on other types of plastics that are not ABS or PC-ABS, or on these but more economically, there is some spray. With a chrome spray, a finish similar to that of the process explained above can be achieved, but with less brightness and a very low resistance to scratches and bumps.

To obtain the best possible surface result, the user must prepare the surface of the piece until a uniform and smooth finish is achieved, because on the contrary that in the painted finish, the chrome plating shows all the possible imperfections that the piece can have.

From the Filament2print team we recommend that users who wish to metallize (chrome, nickel, silver, etc.) their 3D printed parts, contact a company specialized in the chrome plating of plastic parts, since it is a complex process, tedious and with some danger.