Is this actually a patent infringement if they aren't selling the patented design? If I get some parts, maybe for my car, 3D printed and give them away is that illegal?
That said, there is no reason to assume a product is covered by a patent unless it's marked with the specific patent number (a patent marking on it's packaging counts too). It might be, but most products aren't.
If you are an unknowing infringer (didn't know and had no reason to believe you infringed), your damages are limited (in the USA) to a "reasonable royalty." Basically, what a the parties would have hypothetically agreed to in a negotiation. That might be a few % of revenue or a small lump sum.
Counterfeiting in clothes is one thing, counterfeiting in hospital matherial, when even perfect products can be accidentally contaminated with biological matherial and create lots of problems (or even kill people)... Well, this plays in a very different league.
And cloning devices of course opens the door for other companies to crush the original maker flooding the market with cheaper products exactly when the maker rely on benefits to recover their money (after mass producing products). I assume [1] that there are laws also against this.
[1] I'm not a lawyer and could be wrong. Your mileage may vary.