So, used to be the answer was no, or at least, not really. The whole thing about Glocks being able to pass through metal detectors was a myth. The slide and frame are high impact polymers, but barrel and most of the internals are still metal.
But, now we have the Defense Distributed Liberator. This was the 3d printed pistol that made a lot of headlines a couple years ago. Technically the pistol itself should be able to pass through a metal detector without setting it off, and that was one of the major concerns regarding the Liberator.
The problems are, it still needs bullets which will set off a detector, and, well, it’s crap. The Liberator is highly inaccurate and lacks actual sights, meaning you kind of have to guess where the bullet’s going to go. It’s a single shot weapon. Meaning, you have to reload after every shot. So, you either get extremely lucky with the first round or you go scrambling for a replacement assuming the gun survived. Finally, durability is still a huge issue for the Liberator. Defense Distributed got the weapon so it could reliably fire a couple times, but it will still explode after prolonged usage.
It’s worth pointing out, even by their own admission, the Liberator is more of a political statement than a practical weapon. It was supposed to illustrate the futility of gun control laws in an era when firearms could easily be printed on demand. I’m not convinced it has any more value than your run of the mill zip gun, but, anyway, moving on.
Another company, Solid Concepts does actual industrial grade 3d printing, and made a 3d printed M1911 .45 as a proof of concept piece, but that was mostly printed from stainless steel. (The springs weren’t printed, and the grips were, I think, produced by a polymer printer.) Regardless, they’re aiming at producing custom replacement components for rare firearms rather than full firearms.
As a single shot weapon, it’s certainly possible to design a firearm today that won’t set off detectors, but it wouldn’t be much use beyond a very close range assassination tool. At that point, a high impact polymer knife would probably serve your character better.
That said, hiding a gun when you’re being frisked, especially by someone who’s actually been properly trained, is a lot harder than just shoving it down your pants.
That’s today. Polymers have advanced a long way, even from the stuff used in the H&K VP70. It’s entirely possible that we’ll see polymers that you can feed through a commercial printer and will hold up under multiple gunshots by the time the 3d printer technology becomes commonplace. So, if you’re setting your story in the future, it’s distinctly possible you’re looking at firearms that could slip through a modern metal detector. It’s also more likely that whatever detector system they’re using then will pick up heavy chunks of plastics, like a 3d printed gun. That’s sci-fi… but, we’re already living in a cyberpunk novel from the late 70s… so… what the hell, right?