are the ants reinfecting my plant with aphids?

Yes. Ants are accomplished ranchers. A systemic insecticide like Orthenex will
take care of the problem. Some people say not to use Orthenex on maples, but I
haven't noticed any problem.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)