I have a problem I hope someone can help me with!

I have two cones. In the beginning they are more than 2r apart from eachother and the volume are just the volume of two cones. But as they are moved closer together some of the volume are overlapping and the total volume are less than two cones. In the end the total volume are the volume of one cone.

How do I find this total volume for when the cones are less than 2r apart?