Like most processes, making plastic parts look like metal can be done poorly or well, and can be appropriate or not. If you want to look at some really beautiful metal coated parts, check out some of the bathroom and kitchen fixtures at your local Home Depot, Lowe’s, etc. This requires specific material and design skill, but these parts are durable, wear reasonably well and look just like, particularly, chromed metal, in part because those items are chrome-plated.
In the past, Motorola used a method where the plastic parts were coated using an ink screen that was floated on top of water, then the plastic part came up thru the water and the ink/pattern/color was on the plastic part. The good aspect of the process was that it was not “painting” and would go over and around contours. The bad aspect, the process was not widely known about. The plastic parts that I saw usually were ABS, and the plant that did this was down in China.
If you want to see some stuff that is bright, shiny, very nice looking but whose surfaces don’t withstand much handling or abrasion, check out the figures on most trophies–many of those are vacuum plated or sputtered and then clear-coated. Because trophies typically don’t get much handling, that technique is quite sufficient.
Toys offer the lower end of the scale for coatings and molded-in metal colors. Check out virtually any model airplane kit to see the flow lines, etc.; check out any inexpensive model car kit for examples of the former in their “chrome” parts.
As with any project, the hard part is to define as closely as possible what it is you want: Does it have to “sort of look like metal,” does it have to look like a mirror, does it need to look like brushed stainless, etc., and how much abrasion, temperature resistance (e.g. will it sit on the top of a car dashboard where it could get to 180F), does the metal in the metallic look have to contribute anything other than aesthetics (e.g. conductivity)? The more time you spend closely defining the parameters, the better chance you have for success.
Another option depending on the level of polish you are looking for is compounded pearlescent grey. This results in a finish similar to metallic paint without the costs of paint and is being used extensively in the appliance industry. We have been developing an alternative utilizing a color technology that allows us to infuse organic dye into the surface of the polymer. We are using natural pearlescent pigments in clear resin which results in a translucent part. Our color is transparent resulting in a bright surface much closer to metallic than the compounded pearlescent with pigment.
There are multiple companies involved in the vacuum metallization (PVD) of plastics for decorative purposes. Volume will dictate whether it is practical or not practical. All metallization will retain the surface structure of the material being coated because the metallization process is only a few hundred to a few thousand Nm thick (typically less than 200 nanometers or 0.008 mils thick). Often they follow up with a polymer protective spray coating to prevent scratching the meal coating. The process of coating then spraying with the protective polymer is used on everything from faucets, to headlight reflectors, to most cosmetic metal-like bottles and lids.
And BTW: Remember that a metallic-looking surface will not lie: it will reproduce the SLIGHTEST imperfection in the underlying substrate and make it look like the Grand Canyon or Mt. Everest.
Once you know what your parameters are, a well-designed plastic part offers a world of possibilities.