David Brereton advises the things to consider when plating a plastic part for vehicles.
David Brereton, Sales Director at Borough, a UK-based plastic injection moulder and chrome platers of plastic, looks at the use of chrome in vehicles and advises on what designers and manufacturers should consider when choosing to plate a part.
Over the years, car design has changed to incorporate advances in technology, changes in legislation and trends in fashion, but the use of bright chrome is one aspect of design that has remained consistent, across models and brands.
In the past the bright chrome plating was typically produced by electroplating a thin layer of chromium onto a metal substrate, providing corrosion resistance and increased hardness in addition to the decorative appearance.
Plating plastic components
The same results now can be achieved by metallising plastic components, which remain tough and durable, but have the added advantage of being much lighter. To increase surface durability for automotive applications, the metal must be integrated with the plastic surface.
Metal layers are applied to the surface through electrolytic deposition, which requires the plastic component to be made electrically conductive. First a layer of nickel is deposited in a chemical dipping process, applied over a catalytic palladium layer, which must become integral with the surface of the material for the bonding to be effective; one of the restrictions of plating plastic.
It is essential that automotive designers understand the effect this plating has, which effectively bonds a skin of very hard and inflexible chromium to the surface of the plastic. Plating ABS makes it brittle and best practice dictates, if the component has to bend, it should not be plated.
When designing long thin sections to be moulded and plated, rather than created in metal, they will need to be over-engineered, with thicker sections and strengthening webs to compensate for the reduced strength of plated plastic. And to guarantee the high quality finish of plated plastic components, the design must allow for gently curved convex surfaces and radiused angles, whilst minimising protrusions.
Satin where it’s seen
Fortunately, most of these requirements can be easily addressed when designing assemblies and components for the interior of modern cars. It is here that designers are reflecting changing consumer tastes, or perhaps influencing them, by including more components with a satin chrome finish than the more traditional bright chrome.
Products and components with a bright chrome finish, from kettles to car bumpers, have always been less tactile, with fear of leaving finger prints on the highly polished surface enough to make most people avoid contact. This aversion is something of a problem for automotive interiors, where components are included for function, rather than form – touch is essential.
Behind the chrome
Changing the deposited nickel layer from bright to satin nickel in the electroplating process is the first step in achieving the satin finish. The colour and finish of this nickel layer is affected by the organics used in the dipping process, which requires greater control and maintenance than a conventional bright nickel system.
Careful adjustment of the organic material used in the dipping solution allows the colour to be varied according to customers’ requirements, with a large shade range possible, resulting in the more tactile look and feel wanted for cabin interior switches and trim.
The satin nickel components still have a chrome surface layer applied for durability and although chrome isn’t really transparent, it is relatively thin at only 0.3 micron so the satin effect underneath shows through.
Consumer tastes are difficult to predict, but whilst the degree of shine inside the car may have been reduced, partly for practical reasons, partly for fashion, there seems little public appetite for a return to the chrome-less cars of the eighties.
Solving the necessary technical and quality issues associated with the different finishes and shades of satin chrome required by automotive manufacturers has ensured the future of chrome is bright, satin and also perhaps coloured?