I looked at making 3D-printed keys for my own locks, just for show (think yellow key, green key, etc).

I found two issues when researching its feasibility: printing accuracy and temperature range of the plastic. My results were that the lower-cost 3D printers didn't have the required precision, and more importantly, the printed plastic would simply melt if it sat in a hot car during the summer.

My research is probably out of date now, so I wonder what kind of plastic is being used these days.