Calibration is just calibration - either calibrated or not - so there's no need for a risk-based approach.
You only need to validate if the outputs aren't 100% verified so you could argue that the 3D printing process need not be validated. On the flip side of that, though, is that you're only verifying dimensional aspects, I expect. Are there any requirements that can't be verified like hardness, strength, etc?
You would still likely want to qualify the equipment to ensure it's properly installed, proper PM is defined, etc.
Risk, per 13485, "pertains to safety or performance requirements of the medical device or meeting applicable regulatory requirements" so your risk classifications would be (worst case) death then go down from there. So if a process could introduce something that would cause harm, that gets the higher levels of validation. Sterilization is a good example of a process that requires the most vigorous validation. A misprinted label may not result in harm (maybe!!) but would certainly be a regulatory nonconformity. You have to determine, based on the risk, where that failure would fall on the risk scale.