How many of the same artifact can be on the battlefield at once?
There is no limit. If you have more than one out, each one will trigger independently and give you a life.
The only three limits are:

Legendary permanents with the same name,
Planeswalker permanents sharing a subtype and
Enchantments with the World supertype.


704.5j If two or more planeswalkers that share a planeswalker type are on the battlefield, all are put into their owners’ graveyards. This is called the “planeswalker uniqueness rule.”
704.5k If two or more legendary permanents with the same name are on the battlefield, all are put into their owners’ graveyards. This is called the “legend rule.” If only one of those permanents is legendary, this rule doesn’t apply.
704.5m If two or more permanents have the supertype world, all except the one that has been a permanent with the world supertype on the battlefield for the shortest amount of time are put into their owners’ graveyards. In the event of a tie for the shortest amount of time, all are put into their owners’ graveyards. This is called the “world rule.”