Balls are headed so they are roughly round. They are then subjected to several hours of grinding in a batch. The grinding operation continuously makes then rounder, and rounder. It takes many hundred hours of grinding to completely finish a batch. The size of the batch is a function of the size of the balls.
They put the molten steel into a mold that shapes it. If they want to do another one, they use the same mold.
check out National Geographic channel or discovery channel in your area. Got a progran called How it's made. Shows 4 different things each time it's aired and it airs couple times a day. I know for a fact they had ball bearings on there once. Done with a machine. May be on one of their websites too.
High speed, cold heading machines take a wire or rod feed, chop it to length and cold forge a ball to fairly close limits of size and sphericity. Basically this is done by taking a cut slug of the right volume and bonking it between two hemispherical dies. Then there are grinding and lapping machines, and the final balls are selected for matching sizes.
